Title:

Sheet beam-type testing apparatus

Document Type and Number:

United States Patent 7417236

Abstract:

An electron beam apparatus such as a sheet beam based testing apparatus has an electron-optical system for irradiating an object under testing with a primary electron beam from an electron beam source, and projecting an image of a secondary electron beam emitted by the irradiation of the primary electron beam, and a detector for detecting the secondary electron beam image projected by the electron-optical system; specifically, the electron beam apparatus comprises beam generating means 2004 for irradiating an electron beam having a particular width, a primary electron-optical system 2001 for leading the beam to reach the surface of a substrate 2006 under testing, a secondary electron-optical system 2002 for trapping secondary electrons generated from the substrate 2006 and introducing them into an image processing system 2015, a stage 2003 for transportably holding the substrate 2006 with a continuous degree of freedom equal to at least one, a testing chamber for the substrate 2006, a substrate transport mechanism for transporting the substrate 2006 into and out of the testing chamber, an image processing analyzer 2015 for detecting defects on the substrate 2006, a vibration isolating mechanism for the testing chamber, a vacuum system for holding the testing chamber at a vacuum, and a control system 2017 for displaying or storing positions of defects on the substrate 2006.

Inventors:

Nakasuji, Mamoru (Kanagawa, JP)
Noji, Nobuharu (Kanagawa, JP)
Satake, Tohru (Kanagawa, JP)
Kimba, Toshifumi (Kanagawa, JP)
Sobukawa, Hirosi (Kanagawa, JP)
Karimata, Tsutomu (Kanagawa, JP)
Oowada, Shin (Kanagawa, JP)
Yoshikawa, Shoji (Tokyo, JP)
Saito, Mutsumi (Kanagawa, JP)

Plaque It!

CROSS-REFERENCE TO RELATED APPLICATION

This application Continuation of U.S. application Ser. No. 09/891,612, filed Jun. 27, 2001, now U.S. Pat. No. 7,049,585.

Claims:

What is claimed is:

1. A method of sucking and holding a wafer having at least one surface coated with an insulating film, comprising the steps of: providing the wafer on an electrostatic chuck; applying a voltage to at least one surface of the wafer through a contact having a knife edge shaped metal portion by braking the insulating film, the contact being operable to contact with a side surface of the wafer; and chucking the wafer by applying a voltage to the contact, a first voltage to a first electrode and a second voltage to a second electrode, respectively, the first electrode and the second electrode being disposed below an insulating layer on which the wafer is disposed.

2. The method according to claim 1, wherein the step of applying the first voltage and the step of applying the second voltage are performed in sequence.

3. The method according to claim 1, wherein the first electrode has a central portion.

4. The method according to claim 3, wherein the second electrode has a peripheral portion.

5. The method according to claim 1, wherein the first voltage and the second voltage gradually reduce so that gradually reduced voltage is applied to the first electrode and the second electrode.

6. A method of evaluating a wafer having at least one surface thereof coated with an insulating film, comprising the steps of: providing the wafer on an electrostatic chuck; applying a voltage to at least one surface of the wafer through a contact having a knife edge shaped metal portion by braking the insulating film, the contact being operable to contact with a side surface of the wafer; and chucking the wafer by applying a voltage to the contact, a first voltage to a first electrode and a second voltage to a second electrode, respectively, the first electrode and the second electrode being disposed below an insulating layer on which the wafer is disposed; emitting an electron beam to the wafer; detecting a secondary electron beam to capture an image on the wafer; evaluating the wafer based on the image on the wafer; and reducing the voltage across the wafer to zero and removing the wafer from the electrostatic chuck.

7. An electrostatic chuck for sucking and holding a wafer having at least one surface coated with an insulating film, comprising: a first electrode plate disposed below the wafer for holding the wafer and applying a first voltage to the wafer; a second electrode plate disposed below the wafer for holding the wafer and applying a second voltage to the wafer; an insulating layer disposed between the wafer and said first and second electrode plates; a contact having a knife edge shaped metal portion and operable to contact with a side surface of the wafer for breaking the insulating film to make a conduction to the wafer; and a power supply connected to the contact, the first electrode plate and the second electrode plate through a resistor.

8. The electrostatic chuck according to claim 7, wherein the first electrode plate has a central portion.

9. The electrostatic chuck according to claim 7, wherein the second electrode plate has a peripheral portion.

10. The electrostatic chuck according to claim 7, wherein the first voltage and the second voltage are applied to the first electrode plate and the second electrode plate, respectively.

11. The electrostatic chuck according to claim 10, wherein the first voltage and the second voltage gradually reduce so that gradually reduced voltages are applied to the first electrode plate and the second electrode plate.

12. An electron beam apparatus, comprising: an electron beam source for emitting an electron beam to a wafer; a detector for detecting a secondary electron beam to capture an image on the wafer; and a carrier unit for carrying and placing, on a stage device, a wafer having at least one surface coated with an insulating film, wherein the stage device comprises: a first electrode plate disposed below the wafer for holding and applying a first voltage to the wafer; a second electrode plate disposed below the wafer for holding the wafer and applying a second voltage to the wafer; an insulating layer disposed between the wafer and said first and second electrode plates; a contact having a knife edge shaped metal portion and operable to contact with the surface of the wafer for breaking the insulating film and making a conduction to the wafer; and a power supply connected to the contact, the first electrode plate and the second electrode plate.

13. The electron beam apparatus according to claim 12, wherein the first electrode plate has a central portion.

14. The electron beam apparatus according to claim 12, wherein said second electrode plate has a peripheral portion.

15. The electron beam apparatus according to claim 12, wherein the first voltage and the second voltage are applied to the first electrode plate and the second electrode plate.

16. The electron beam apparatus according to claim 12, wherein the first voltage and the second voltage gradually reduce so that gradually reduced voltages are applied to the first electrode plate and the second electrode plate.

17. A beam testing apparatus, comprising: a testing chamber having a stage for holding an object under test, wherein the stage has an electrostatic chuck for sucking the object; a beam generator for generating a rectangular or elliptic electron beam as a primary electron beam; an electro-optical system for guiding the primary electron beam in one direction and for guiding a secondary electron beam generated from the object in the opposite direction, the stage being movable relative to the electro-optical system; an image processing system for displaying or storing information of the object; and a transport mechanism for transporting the object into and out of the testing chamber and comprising a mini-environment chamber for supplying a clean gas to the object to prevent dust from attaching to the object and a sensor provided within the mini-environment chamber for observing the cleanliness of the mini-environment chamber, wherein the pressure in the mini-environment chamber being equal to atmosphere pressure; wherein the electrostatic chuck comprises: a first electrode plate disposed below the object for holding the object and applying a first voltage to the object; a second electrode plate disposed below the object for holding the object and applying a second voltage to the object; an insulatiua layer disposed between the wafer and said first and second electrode plates; a contact having knife edge shaped metal portion and operable to contact with a side surface of the object for breaking the insulating film and making a conduction to the object; and a power supply connected to the contact, the first electrode plate and the second electrode plate through a resistor.

18. The beam testing apparatus according to claim 17, wherein the first voltage and the second voltage gradually reduce so that gradually reduced voltages are applied to the first electrode plate and the second electrode plate.

Description:

TECHNICAL FIELD

In semiconductor processes, design rules are now going to enter the era of 100 nm, and the production scheme is shifting from small-kind mass production represented by DRAM to a multi-kind small production such as SOC (silicon on chip). Associated with this shifting, the number of manufacturing steps has been increased, and an improved yield of each process is essential, so that testing for defects caused by the process becomes important. The present invention relates to a charged particle beam suitable for a sheet beam-type testing apparatus for testing a wafer after each of steps in a semiconductor process, and more particularly, to a sheet beam-type testing apparatus using a charged particle beam such as an electron beam, and a semiconductor device manufacturing method and an exposure method using the testing apparatus.

BACKGROUND ART

With the trend of increasingly higher integration of semiconductor devices and finer patterns, a need exists for high resolution, high throughput testing apparatuses. A resolution of 100 nm or less is required for examining defects on a wafer substrate of 100 nm design rule. Also, as the amount of testing is increased to cause an increase in manufacturing steps resulting from higher integration of devices, a higher throughput is required. Further, as devices are formed of an increased number of layers, testing apparatuses are required to have the ability to detect defective contacts (electric defect) of vias which connect wires between layers. While optical defect testing apparatuses are mainly used at present, it is anticipated that electron beam based defect testing apparatuses will substitute for optical defect testing apparatus as a dominant testing apparatus in the future from a viewpoint of the resolution and defective contact testing capabilities. However, the electron beam based defect testing apparatus also has a disadvantage in that it is inferior to the optical one in the throughput.

For this reason, a need exists for the development of a high resolution, high throughput testing apparatus which is capable of detecting electric defects. It is said that the resolution of an optical defect testing apparatus is limited to one half of the wavelength of used light, and the limit is approximately 0.2 μm in an example of practically used optical defect detecting apparatus which uses visible light. On the other hand, in electron beam based systems, scanning electron microscopes (SEM) have been commercially available. The scanning electron microscope has a resolution of 0.1 μm and takes a testing time of eight hours per 20 cm wafer. The electron beam based system also has a significant feature that it is capable of testing electric defects (broken wires, defective conduction, defective conduction of vias, and so on). However, it takes so long testing time that it is expected to develop a defect testing apparatus which can rapidly conduct a test.

Generally, a testing apparatus is expensive and low in throughput as compared with other process apparatuses, so that it is presently used after critical steps, such as after etching, deposition, CMP (chemical-mechanical polishing) planarization processing, and so on. Now, describing a testing apparatus in accordance with an electron beam based scanning (SEM) scheme, an SEM based testing apparatus narrows down an electron beam which is linearly irradiated to a sample for scanning. The diameter of the electron beam corresponds to the resolution. On the other hand, by moving a stage in a direction perpendicular to a direction in which the electron beam is scanned, a region under observation is tow-dimensionally irradiated with the electron beam. The width over which the electron beam is scanned generally extends over several hundred μm. A secondary electron beam generated from the sample by the irradiation of the narrowed electron beam (called the “primary electron beam”) is detected by a combination of a scintillator and a photomultiplier (photomultiplier tube) or a semiconductor based detector (using PIN diodes). The coordinates of irradiated positions and the amount of the secondary electron beam (signal strength) are combined to generate an image which is stored in a storage device or output on a CRT (Braun tube).

The foregoing is the principle of SEM (scanning electron microscope). From an image generated by this system, defects on a semiconductor (generally, Si) wafer is detected in the middle of a step. A scanning speed, corresponding to the throughput, is determined by the amount of primary electron beam (current value), diameter of the beam, and a response speed of a detector. Currently available maximum values are 0.1 μm for the beam diameter (which may be regarded as the same as the resolution), 100 nA for the current value, and 100 MHz for the response speed of the detector, in which case it is said that a testing speed is approximately eight hours per wafer of 20 cm diameter.

In the SEM based testing apparatus described above, the cited testing speed is considered substantially as a limit. Therefore, a new scheme is required for increasing the testing speed, i.e., the throughput.

DISCLOSURE OF THE INVENTION

The present invention relates to an electron beam apparatus suitable for a sheet beam based testing apparatus, and a semiconductor device manufacturing method and an exposure method using the apparatus.

A first embodiment of the present invention provides a map projection type electron beam apparatus. For this purpose, the first embodiment provides a substrate testing apparatus, a substrate testing method and a device manufacturing method using such a substrate testing apparatus, characterized by comprising:

beam generating means for irradiating an electron beam having a particular width;

a primary electron-optical system for leading the charged particle beam to reach the surface of a substrate under testing;

a secondary electron-optical system for trapping a secondary electron beam generated from the substrate and leading the same to an image processing system;

a stage having for transportably holding the substrate with a continuous degree of freedom equal to at least one;

a testing chamber for the substrate;

a substrate transport mechanism for transporting the substrate into and out of the testing chamber;

an image processing analyzer for detecting defects on the substrate;

a vibration isolation mechanism for the testing chamber;

a vacuum system for holding the testing chamber at a vacuum; and

a control system for displaying or storing positions of defects on the substrate.

A second embodiment of the present invention provides an electron beam apparatus suitable for a testing apparatus for testing an object under testing by irradiating the object with an electron beam, and a device manufacturing method using the electron beam apparatus.

A second embodiment of the present invention provides a testing apparatus comprising:

an electron-optical device having an electron-optical system for irradiating the object under testing with a primary electron beam from an electron source to project an image of secondary electrons emitted by the irradiation of the primary electron beam, and a detector for detecting the secondary electron image projected by the electron-optical system;

a stage device for holding the object under testing and moving the object under testing relative to the electron-optical system;

a mini-environment device for supplying a clean gas to the object under testing to prevent dust from attaching to the object under testing;

a working chamber for accommodating the stage device, said working chamber being controllable in a vacuum atmosphere;

at least two loading chambers disposed between the mini-environment device and the working chamber, and adapted to be independently controllable in a vacuum atmosphere;

a loader having a carrier unit capable of transferring the object under testing between the mini-environment device and one of the loading chambers, and another carrier unit capable of transferring the object under testing between the one loading chamber and the stage device; and

a vibration isolator through which the working chamber and the loading chamber are supported.

Further, the second embodiment of the present invention provides a testing apparatus comprising:

an electron-optical device having an electron-optical system for irradiating the object under testing with a primary electron beam from an electron source, and for accelerating secondary electrons emitted by the irradiation of the primary electron beam with a deceleration electric field type objective lens to project an image of the secondary electrons, a detector for detecting the secondary electron image projected by the electron-optical system, and electrodes disposed between the deceleration electric field type objective lens and the object under testing for controlling a field intensity on the surface of the object under testing which is irradiated with the primary electron beam;

a stage device for holding the object under testing and moving the object under testing relative to the electron-optical system;

a working chamber for accommodating the stage device, said working chamber being controllable in a vacuum atmosphere;

a loader for supplying the object under testing onto the stage device within the working chamber;

a precharge unit for irradiating a charged particle beam to the object under testing placed in the working chamber to reduce variations in charge on the object under testing;

a potential applying mechanism for applying a potential to the object under testing; and

a supporting device supported through a vibration isolator for supporting the working chamber.

In the testing apparatus described above, the loader may include a first loading chamber and a second loading chamber capable of independently controlling an atmosphere therein, a first carrier unit for carrying the object under testing between the first loading chamber and the outside of the first loading chamber, and a second carrier unit disposed in the second loading chamber for carrying the object under testing between the first loading chamber and the stage device. The electron beam apparatus may further comprise a partitioned mini-environment space for supplying a clean gas flowing to the object under testing carried by the loader to prevent dust from attaching to the object under testing, wherein the supporting device may support the loading chamber and the working chamber through the vibration isolator.

Also, the testing apparatus may further comprise an alignment controller for observing the surface of the object under testing for an alignment of the object under testing with respect to the electron-optical system to control the alignment, and a laser interference range finder for detecting coordinates of the object under testing on the stage device, wherein the coordinates of the object under testing is determined by the alignment controller using patterns formed on the object under testing. In this event, the alignment of the object under testing may include rough alignment performed within the mini-environment space, and alignment in XY-directions and alignment in a rotating direction performed on the stage device.

Further, the second embodiment of the present invention provides a method of manufacturing a device comprising the step of detecting defects on a wafer using the foregoing testing apparatus in the middle of a process or subsequent to the process.

A third embodiment of the present invention provides an electron beam apparatus for focusing electron beams emitted from a plurality of electron beam sources on the surface of a sample through an electron-optical system, characterized by comprising:

a partition wall for separating the electron beam sources from the electron-optical system, wherein the partition wall has holes in a large aspect ratio for the electron beams to pass therethrough.

The holes are provided two or more for each of the electron beam sources. Each of the holes is formed at a position which swerves from the irradiating axis of the beam source. Preferably, the partition wall is formed of a material having a high rigidity, and the electron beam source and the electron-optical system are attached to the partition wall.

The third embodiment of the present invention also provides a device manufacturing method for evaluating a wafer in the middle of a process using the electron beam apparatus.

A fourth embodiment of the present invention provides an evaluation apparatus for directing an electron beam into a sample using an electrostatic optical system including an electrostatic lens, detecting a secondary electron beam generated from the sample by the irradiation of the electron beam to form data, and evaluating the sample based on the data, characterized in that:

electrodes in the electron-optical system are coated with a metal having a work function of 5 eV or higher.

According to this evaluation apparatus, since the electrodes or some of the electrodes are coated with a metal having a work function of 5 eV or higher, no secondary electron beam will be emitted from the electrodes, a discharge will be less likely to occur between electrodes, and a breakdown will occur between electrodes less frequently.

Preferably, the metal coated on the electrodes in the electrostatic optical system is platinum or an alloy which includes platinum as a main material. In this case, as the electrodes or some of the electrodes are coated with platinum (work function: 5.3 [eV]) or an alloy which includes platinum as a main material, a smaller amount of secondary electron beam will be emitted from the electrodes, so that a discharge will be less likely to occur between the electrodes, and a breakdown will occur between electrodes less frequently. Also, even with the sample being a semiconductor wafer, the platinum coated on the electrodes, if attached on a pattern of the semiconductor wafer, will not deteriorate transistors, so that it is suitable for testing a semiconductor wafer.

The fourth embodiment of the present invention provides an evaluation apparatus for directing an electron beam into a sample using an electrostatic optical system including an electrostatic lens, detecting a secondary electron beam generated from the sample by the irradiation of the electron beam to form data, and evaluating the sample based on the data, characterized in that:

the electrostatic lens includes at least two electrodes having potential differences, and insulating materials positioned between the two electrodes for holding the at least two electrodes;

at least one of the at least two electrodes has a first electrode surface having a minimum inter-electrode distance between the at least two electrodes, a second electrode surface having an inter-electrode distance longer than the first electrode surface, and a step between the first electrode surface and the second electrode surface in a direction along the at least two electrodes; and

the insulating material substantially vertically supports the second electrode surface and an electrode surface of the other electrode between the at least two electrodes, and a minimum creeping distance of the insulating material between the at least two electrodes is substantially equal to an inter-electrode distance in the supported electrode portion.

According to this evaluation apparatus, the electrodes are supported by the insulating material which has long creeping distance, so that a discharge between electrodes, and hence a breakdown between electrodes can be made less probable. Further, at least one of the electrodes is shaped to have the first electrode surface, the second electrode surface and the step between these electrode surfaces, so that the surface of the insulating material need not be formed with crimps, resulting in a lower manufacturing cost.

Also, since the minimum creeping distance of the insulating material between the electrodes is substantially equal to the distance between the electrodes in the supported electrode portion, the surface of the insulating material is substantially free from ruggedness between the electrodes, and a gas exhausted from the insulating material will not be increased. Therefor the degree of vacuum will not be lowered in a beam path of the apparatus.

Preferably, the metal coated on the electrodes in the electrostatic optical system is platinum or an alloy which includes platinum as a main material. In this case, as the electrodes or some of the electrodes are coated with platinum or an alloy which includes platinum as a main material, a discharge between electrodes, and hence a breakdown between electrodes will occur less frequently. Also, even with the sample being a semiconductor wafer, the platinum coated on the electrodes, if attached on a pattern of the semiconductor wafer, will not deteriorate transistors, so that it is suitable for testing a semiconductor wafer.

Further, the fourth embodiment of the present invention also provides a device manufacturing method using the evaluation apparatus, characterized by evaluating patterns on a semiconductor wafer, which is the sample, using the evaluation apparatus in the middle of device manufacturing.

According to this device manufacturing method, by using the evaluation apparatus in the middle of device manufacturing, even if patterns on the semiconductor wafer, which is a sample, are evaluated, the evaluation can be made without breakdown between electrodes in the electrostatic optical system.

A fifth embodiment of the present invention provides an electron beam apparatus for irradiating a sample with a primary electron beam using a primary optical system, and separating a secondary electron beam emitted from the sample from the primary optical system by an ExB separator for introduction into a secondary optical system, characterized in that:

the amount of deflection of the secondary electron beam by a magnetic field of the ExB separator is twice the amount of deflection by an electric field, and the direction of deflection by the magnetic field is opposite to the direction of deflection by the electric field.

This electron beam apparatus is characterized in that, in the electron beam apparatus for irradiating the sample with the primary electron beam using a primary optical system, and separating the secondary electron beam emitted from the sample from the primary optical system by the ExB separator for introduction into the secondary optical system, the amount of deflection of the secondary electron beam by the magnetic field of the ExB separator is twice the amount of deflection by an electric field, and the directions of deflection are opposite to each other.

The fifth embodiment of the present invention also provides an electron beam apparatus for irradiating a sample with a primary electron beam using a primary optical system, and separating a secondary electron beam emitted from the sample from the primary optical system by an ExB separator for introduction into a secondary optical system, characterized in that the amount of deflection of the primary electron beam by a magnetic field of the ExB separator is twice the amount of deflection by an electric field, and the direction of deflection by the magnetic field is opposite to the direction of deflection by the electric field.

This electron beam apparatus is characterized in that the amount of deflection of the first electron beam by the magnetic field of the ExB separator is twice the amount of deflection by the electric field, and the directions of deflection are opposite to each other in the electron beam apparatus for irradiating the sample with the primary electron beam using a primary optical system, and separating the secondary electron beam emitted from the sample from the primary optical system by the ExB separator for introduction into the secondary optical system.

In this event, preferably, the primary electron beam comprised of a plurality of beams is formed by the primary optical system for irradiating the surface of the sample, and secondary electron beams emitted from the samples by the irradiation of the primary electron beam comprised of the plurality of beams are detected by a plurality of secondary electron beam detectors.

The aforementioned electron beam apparatus can be available in any of a defect testing apparatus, a line width measuring apparatus, an alignment accuracy measuring apparatus, and a high time resolution potential contrast measuring apparatus.

Also, the fifth embodiment of the present invention provides a device manufacturing method for testing a wafer in the middle of a process using the electron beam apparatus.

A sixth embodiment of the present invention provides an electron beam apparatus, characterized by comprising:

a measuring mechanism for measuring first data indicative of rising of a secondary charged particle beam signal waveform when a pattern edge parallel in a first direction is moved in a second direction in regard to an excitation voltage of an objective lens, and second data indicative of rising of the secondary charged particle beam signal waveform when a pattern edge parallel in the second direction is moved in the first direction;

means for approximating each of the first data and the second data using quadratics, finding an excitation condition for the objective lens indicative of a minimum value of each quadratic; and

means for fitting the objective lens to an algebraic mean of the found excitation condition.

A plurality of the electron beam apparatuses may be positioned opposite to the sample such that respective ones of the plurality of primary electron beams are converged by corresponding ones of the objective lens simultaneously on different locations on the sample.

Further, preferably, the electron beam apparatus comprises means for correcting astigmatism after exciting the objective lens using the exciting means with a voltage equal to the algebraic average with the pattern being charged, and then evaluating the pattern.

Also, the sixth embodiment provides an electron beam apparatus for converging an electron beam using an electron-optical system including an objective lens, and scanning a pattern with the electron beam to evaluate the pattern, characterized in that:

the objective lens comprises a first electrode applied with a voltage close to a ground, and a second electrode applied with a voltage remote from the ground;

a focal distance of the objective lens can be changed by changing the voltage applied to the first electrode; and

the exciting means comprises means for changing the voltage applied to the second electrode to largely change the focal distance of the objective lens, and means for changing the voltage applied to the first electrode to change the focal distance of the objective lens in a short time.

The sixth embodiment of the present invention also provides a device manufacturing method for evaluating a wafer in the middle of a process using the electron beam apparatus.

A seventh embodiment of the present invention provides an electron beam apparatus for irradiating an object with an electron beam to perform at least one of working, manufacturing, observation and testing of the object, comprises:

a mechanical construction for determining a position of an electronic beam with respect to the object, a piezoelectric element attached to the mechanical construction for receiving a force from vibrations of the mechanical construction; and a vibration attenuating circuit electrically connected to the piezoelectric element to attenuate electric energy output from the piezoelectric element.

When an object is irradiated with an electron beam to perform at least one of working, manufacturing, observation and testing of the object, an external force including a vibration component at a resonant frequency of proper vibration applied to a mechanical construction causes the mechanical construction to amplify the vibration component at a resonant magnification determined by its transfer function, and to vibrate. This vibration applies a force to the piezoelectric element. The piezoelectric element transduces the vibration energy of the mechanical construction into electric energy which is output. However, since the vibration attenuating circuit attenuates this electric energy, the piezoelectric element generates a force to cancel the external force applied to the piezoelectric element. In this way, the vibrations generated by the mechanical resonance can be canceled to reduce the resonant magnification.

The mechanical construction is a portion or entirety of an electron beam applied apparatus which generates problematic vibrations, and an arbitrary mechanical construction for aligning the electron beam. For example, the mechanical construction may be optics in an optical system for focusing an electron beam on an object, a barrel for containing such an optical system, a supporting stand for carrying an object, or optics in an optical system for focusing a secondary electron beam generated by irradiating the object with the electron beam on a detector, a barrel for containing such an optical system, a barrel for containing the detector, and so on.

The vibration attenuating circuit comprises at least inductive means as an element having an inductance or an equivalent circuit of the element, and the inductive means is connected to the piezoelectric element having a static capacitance to form a resonant circuit. The inductance of the inductive means is determined with respect to the static capacitance of the piezoelectric element such that a resonant frequency of the resonant circuit substantially matches a resonant frequency of the mechanical construction.

Preferably, a resistive element is included in the vibration attenuating circuit. In this event, the capacitive impedance of the piezoelectric element and the inductive impedance of the inductive means cancel each other at the resonant frequency, so that the impedance of the resonant circuit virtually has only a resistive element. Therefore, during resonance, the electric energy output from the piezoelectric element is substantially fully consumed by the resistive element.

The seventh embodiment of the present invention also provides a semiconductor manufacturing method which comprises a step of executing at least one of working and manufacturing of semiconductor devices, and observation and testing of semiconductor devices during working or finished ones, using the electron beam apparatus.

According to an eighth embodiment of the present invention, an electrostatic chuck for electrostatically sucking and holding a wafer is applied with a voltage which increases or decreases between zero volt to a predetermined voltage over time. The electrostatic chuck is comprised of a laminate of a substrate, an electrode plate, and an insulating layer. A voltage associated with a voltage applied to a wafer is applied to the electrode plate to generate an attractive force between the wafer and the chuck. The electrode plate is divided into a first electrode comprised of a central portion thereof and some of a peripheral portion thereof, and a second electrode comprised of the remaining portion. The first electrode is first applied with a voltage, the wafer is then placed at a low potential or a ground potential, and subsequently the second electrode is applied with a voltage.

According to the eighth embodiment of the present invention, in a combination of a wafer and the electrostatic chuck for electrostatically sucking and holding the wafer, the electrostatic chuck is formed of the laminate of the substrate, electrode plate and insulating layer, the wafer is applied with a voltage through a predetermined resistor or a contact, and the contact is in the shape of a needle, the leading end of which comes in contact with the back surface of the wafer, or in the shape of a knife edge, the edge of which comes in contact with the side surface of the wafer.

The eighth embodiment of the present invention also provides a device manufacturing method for sucking and holding a wafer using the electrostatic chuck or the combination.

A ninth embodiment of the present invention provides an apparatus for carrying a sample on an XY stage, moving the sample to an arbitrary position in a vacuum, and irradiating the surface of the sample with an electron beam, characterized in that:

the XY stage comprises a non-contact supporting mechanism by means of static pressure bearings, and a vacuum sealing mechanism through differential pumping;

a partition is disposed between a location of the sample which is irradiated with the beam and a static pressure bearing support of the stage for reducing a conductance; and

a pressure difference is produced between an electron beam irradiating region and the static pressure bearing support.

According to the ninth embodiment, the non-contact supporting mechanism by means of the static pressure bearings is applied to a supporting mechanism for the XY stage for carrying a sample thereon, and the vacuum sealing mechanism through differential exhaust is provided around the static pressure bearings such that a high pressure gas used for the static pressure bearing does not leak into a vacuum chamber, so that the stage device can demonstrate highly accurate positioning performance in vacuum. Further, by forming the partition between the electron beam irradiated position and the static pressure bearing support for reducing the conductance, even if a gas adsorbed on the surface of a sliding part of the stage is released each time the sliding part of the stage is moved from a high pressure gas section to a vacuum environment, the exhausted gas hardly reaches the electron beam irradiated position, thereby preventing the pressure at the electron beam irradiated position from rising. In other words, the employment of the foregoing configuration can stabilize the degree of vacuum at the electron beam irradiated position on the surface of the sample, and highly accurately drive the stage, thereby making it possible to accurately process the sample with the electron beam without contaminating the surface of the sample.

The partition may contain a differential exhaust structure. In this event, the partition is placed between the static pressure bearing support and the electron beam irradiating region, and a vacuum evacuation path is routed within the partition to provide a differential pumping function, so that a gas released from the static pressure bearing support cannot pass through the partition into the electron beam irradiating region. In this way, the degree of vacuum at the electron beam irradiated position can be further stabilized.

The partition may have a cold trap function. In this event, in a region at a pressure of 10 ⁻⁷Pa or higher, main components of a residual gas in the vacuum and a gas released from the surface of the material are water molecules. Therefore, if the water molecules can be efficiently exhausted, a high degree of vacuum can be readily maintained with stability. Therefore, a cold trap cooled at approximately −100° C. to −200° C., if provided in the partition, enables the released gas generated on the static pressure bearing side to be frozen and trapped by the cold trap, so that the released gas pass into the electron beam irradiating region with difficulty, and the degree of vacuum is readily maintained stable in the electron beam irradiating region. It goes without saying that the cold trap is effective not only for the water molecules but also for removing organic gas molecules such as a oil group which is a factor of hampering a clean vacuum.

Further, the partitions may be disposed at two locations, i.e., near the electron beam irradiated position and near the static pressure bearing. In this event, since the partitions which reduce the conductance are disposed at two locations, i.e., near the electron beam irradiated position and near the static pressure bearing, the vacuum chamber is divided into three chambers consisting of an electron beam irradiating chamber, a static pressure bearing chamber, and an intermediate chamber through small conductance. Then, a vacuum evacuation system is configured to set lower pressures from the charged particle beam irradiation chamber to the intermediate chamber and to the static pressure bearing chamber in this order. By doing so, even if the released gas causes a rise in pressure in the static pressure bearing chamber, a pressure fluctuating rate can be suppressed since this is a chamber in which the pressure has been initially set high. Therefore, fluctuations in pressure to the intermediate chamber are suppressed by the partition, thereby making it possible to reduce the fluctuations in pressure to a level at which substantially no problem arises.

The gas supplied to the static pressure bearings is preferably dry nitrogen or inert gas. Also preferably, at least surfaces of parts facing the static pressure bearings are applied with a surface treatment for reducing a released gas. As described above, on the sliding parts of the stage exposed to a high pressure gas atmosphere in the static pressure bering chamber, gas molecules included in the high pressure gas are adsorbed on their surfaces, and as the sliding parts are exposed to a vacuum environment, the adsorbed gas molecules are desorbed from the surfaces and act as a released gas which deteriorates the degree of vacuum. It is therefore necessary, for preventing the deterioration of the degree of vacuum, to reduce the amount of gas molecules to be adsorbed, and promptly exhaust adsorbed gas molecules.

For this purpose, it is effective that the static pressure bearings are supplied with a high pressure gas which is dry nitrogen, from which moisture has been sufficiently removed, or a highly pure inert gas (for example, a highly pure nitrogen gas) to remove gas components which are adsorbed to a surface with ease and desorbed therefrom with difficulty (organic substances, moisture and so on) from the high pressure gas. An inert gas such as nitrogen has a significantly low surface coverage to a surface and a significantly high desorbing speed from the surface, as compared with moisture and organic substance. Therefore, when a highly pure inert gas, from which moisture and organic components have been maximally removed, is used for the high pressure gas, a small amount of gas is released even when the sliding parts are moved from the static pressure bearing chamber to the vacuum environment. Also, since the released gas promptly attenuates, the deterioration of the degree of vacuum can be reduced. It is therefore possible to suppress a rise in pressure when the stage is moved.

Also effectively, at least surfaces of components, particularly, surfaces of parts which reciprocate between a high pressure gas atmosphere and a vacuum environment are applied with a surface treatment for reducing a released gas. As the surface treatment, when a base material is a metal, Tic (titanium carbide), TiN (titanium nitride), nickel plating, passivation, electrolytic polishing, composite electrolytic polishing, glass bead shot, and so on are contemplated. When a base material is Sic ceramics, coating of concise SiC layer by CVD and so on are contemplated. It is therefore possible to further suppress a rise in pressure when the stage is moved.

Also, the ninth embodiment of the present invention provides a wafer defect testing apparatus for testing the surface of a semiconductor wafer for defects using the electron beam apparatus. Since this can realize the testing apparatus which is highly accurate in stage positioning performance and stable in the degree of vacuum in the electron beam irradiating region, a testing apparatus which has high testing performance and is free from fear of contaminating the sample is provided.

In addition, the ninth embodiment of the present invention also provides an exposure apparatus for drawing a circuit pattern of a semiconductor device on the surface of a semiconductor wafer or a reticle using the electron beam apparatus. Since this can realize the exposure apparatus which is highly accurate in stage positioning performance and stable in the degree of vacuum in the electron beam irradiating region, an exposure apparatus which has high testing performance and is free from fear of contaminating the sample is provided.

Furthermore, the ninth embodiment of the present invention also provides a semiconductor manufacturing method for manufacturing semiconductors using the electron beam apparatus. Since this results in manufacturing semiconductors using the apparatus which is highly accurate in stage positioning performance and stable in the degree of vacuum in the electron beam irradiating region, fine semiconductor circuits can be formed.

A tenth embodiment of the present invention provides an apparatus for irradiating an electron beam to a sample carried on an XY stage, characterized in that:

the XY stage is contained in a housing and supported by static pressure bearings with respect to the housing in a non-contact manner;

the housing containing the stage is evacuated to vacuum; and

a differential exhaust mechanism is disposed around a portion of the electron beam apparatus for irradiating an electron beam to the surface of the sample for evacuating a region on the surface of the sample in which the electron beam is irradiated.

In this way, a high pressure gas for the static pressure bearings leaking into a vacuum chamber is first exhausted through a pipe for vacuum evacuation connected to the vacuum chamber. Then, by disposing the differential exhaust mechanism around the portion in which an electron beam is irradiated for evacuating a region in which the electron beam is irradiated, the pressure in the electron beam irradiating region is made largely lower than the pressure in the vacuum chamber, thereby making it possible to stably achieve a degree of vacuum at which the sample can be processed with the electron beam without problem. In other words, the sample on the stage can be stably processed with the electron beam using the stage having a structure similar to a static pressure bearing type stage which is generally used in the atmosphere (a stage supported by static pressure bearings, which does not have a differential exhaust mechanism).

The gas supplied to the static pressure bearings of the XY stage is preferably dry nitrogen or a highly pure inert gas. The highly pure inert gas is preferably pressurized after exhausted from the housing which contains the stage, and again supplied to the static pressure bearings. In this way, the remaining gas component in the vacuum housing is a highly pure inert gas, so that the surface of the construction within the vacuum chamber is not susceptible to contamination by moisture, oil component and so on. In addition, even if inert gas molecules are adsorbed on the surface of the sample, they are promptly desorbed from the surface of the sample if they are exposed to the differential exhaust mechanism or a high vacuum in the electron beam irradiating region, thereby making it possible to minimize the influence on the degree of vacuum in the electron beam irradiating region and stabilize the processing on the sample with the electron beam.

The tenth embodiment of the present invention provides a wafer defect testing apparatus for testing the surface of a semiconductor wafer for defects using the electron beam apparatus. It is therefore possible to provide a testing apparatus, at a low cost, which is highly accurate in stage positioning performance and stable in the degree of vacuum in the electron beam irradiating region.

The tenth embodiment of the present invention provides an exposure apparatus for drawing a circuit pattern of a semiconductor device on the surface of a semiconductor wafer or a reticle using the electron beam apparatus. It is therefore possible to provide an exposure apparatus, at a low cost, which is highly accurate in stage positioning performance and stable in the degree of vacuum in the electron beam irradiating region.

The tenth embodiment of the present invention provides a semiconductor manufacturing method for manufacturing semiconductors using the electron beam apparatus. Since this results in manufacturing semiconductors using the apparatus which is highly accurate in stage positioning performance and stable in the degree of vacuum in the electron beam irradiating region, fine semiconductor circuits can be formed.

An eleventh embodiment of the present invention provides an electron beam apparatus which comprises a plurality of optical systems each for generating a primary electron beam, converging the primary electron beam, scanning the primary electron beam on a sample for irradiation, and detecting a secondary electron beam emitted from an electron beam irradiated portion of the sample using a detector, characterized by comprising a retarding voltage applying unit for applying the sample with a retarding voltage, and a function for applying an optimal retarding voltage depending on the sample, wherein the optical system comprises at least one axially symmetric lens produced by working a bulk of insulating material, and having the surface applied with a metal coating.

The eleventh embodiment of the present invention also provides an electron beam apparatus which has a primary optical system for generating a primary electron beam, converging the primary electron beam, and scanning the primary electron beam on a sample for irradiation, wherein a secondary electron beam emitted from an electron beam irradiated portion of the sample is accelerated, separated from the primary optical system by an ExB separator, and detected by a detector, characterized by comprising a retarding voltage applying unit for applying the sample with a retarding voltage, a charge-up checking function unit for checking a charge-up state of the sample, and a function for determining an optimal retarding voltage based on information output from the charge-up checking function unit to apply the retarding voltage to the sample or to change it to an optimal beam current.

The eleventh embodiment of the present invention also provides an electron beam apparatus which is characterized by having an optical system for irradiating an electron beam to a sample, and a charge-up checking function, wherein the charge-up checking function evaluates a distorted pattern or a blurred pattern at a particular site of the sample, when the secondary electron beam generated from the sample irradiated with the primary electron beam is detected to form an image, and evaluates that charge-up is large when the result shows that the distorted pattern or the blurred pattern is large.

The charge-up checking function can apply the sample with a variable retarding voltage, and forms an image near a boundary where a pattern density largely varies on the sample which is applied with at least two retarding voltages, and may have a device for displaying the image such that an operator can evaluate the distorted pattern or the blurred pattern.

Also, the eleventh embodiment of the present invention provides a device manufacturing method characterized by detecting defects on a wafer in the middle of a process using the electron beam apparatus.

A twelfth embodiment of the present invention provides a defect testing apparatus for testing a sample for defects, characterized by comprising:

image capturing means for capturing each of images of a plurality of regions under testing displaced from one another while partially overlapping on the object under testing on the sample;

means for storing a reference image; and

defect determining means for comparing the images of the plurality of regions under testing captured by the image capturing means with the reference image stored in the storage means to determine defects on the sample. Here, while the sample under testing may be selected from arbitrary ones for which defects can be detected, the present invention can produce a distinct effect when a semiconductor wafer is intended.

In this embodiment, the image capturing means operates to capture each of the images of the plurality of regions under testing displaced from one another while partially overlapping on the object under testing on the sample, and the defect determining means operates to compare the images of the plurality of regions under testing captured by the image capturing means with the reference image stored in the storage means to determine defects on the sample.

In this way, since the twelfth embodiment of the present invention can capture a plurality of images of regions under testing at different positions, an image under testing with less discrepancy in position with the reference image can be selectively utilized in a subsequent process, thereby making it possible to prevent a degraded defect detecting accuracy due to misalignment. Moreover, even if the sample and the image capturing means is in such a positional relationship that a portion of a pattern under testing is normally lost from the image region under testing, it is highly likely that the entire pattern under testing lies in any of regions covered by the plurality of images of the regions under testing displaced from one another, thereby making it possible to prevent erroneous detection of defect due to such partial loss of the pattern.

The comparing means performs a so-called matching operation between each of the captured images of the plurality of regions under testing and the reference image, and operates to determine that the sample is non-defective if there is substantially no difference between at least one image of the plurality of regions under testing and the reference image. Conversely, if there is a substantial difference between all the images of the regions under testing and the reference image, the sample is determined as defective, thereby detecting defects at a higher accuracy.

In the twelfth embodiment, electron irradiating means is further provided for irradiating a primary electron beam to each of a plurality of regions under testing to emit secondary electron beams from the sample, wherein the image capturing means detects the secondary electron beams emitted from the plurality of regions under testing, thereby making it possible to sequentially capture the images of the plurality of regions under testing.

Further, the electron irradiating means preferably comprises a particle beam source for emitting primary electrons, and deflecting means for deflecting the primary electrons, such that a primary electron beam emitted from the particle beam source is deflected by the deflecting means to sequentially irradiate the primary electron beam to the plurality of regions under testing. In this event, since the position of an input image can be readily changed by the deflecting means, a plurality of images under testing at different positions can be captured at a high speed.

The twelfth embodiment of the present invention also provides a semiconductor device manufacturing method which includes a step of testing a wafer during working or a finished one for defects, using the electron beam apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram generally illustrating the configuration of a testing apparatus which is a first embodiment of a charged particle beam apparatus according to the present invention;

FIG. 2( a ) is a plan view of an electron deflection system, and FIG. 2( b ) is a cross-sectional view of the same;

FIG. 3 is a flow chart illustrating an embodiment of a semiconductor device manufacturing method according to the present invention;

FIG. 4( a ) is a flow chart illustrating a lithography step which forms the core of wafer processing steps in FIG. 3, and FIG. 4( b ) is a flow chart illustrating a wafer testing step in the wafer processing steps in FIG. 3;

FIG. 5 is an elevation illustrating the main components of a testing apparatus which is a second embodiment of the charged particle beam apparatus according to the present invention, viewed along a line A-A in FIG. 6;

FIG. 6( a ) is a plan view of the main components of the testing apparatus illustrated in FIG. 5, viewed along a line B-B in FIG. 5, and FIG. 6( b ) is a diagram illustrating an exemplary modification to the configuration illustrated in FIG. 6( a );

FIG. 7 is a cross-sectional view illustrating an mini-environment device in FIG. 5, viewed along a line C-C;

FIG. 8 is a diagram illustrating a loader housing in FIG. 5, viewed along a line D-D in FIG. 6( a );

FIGS. 9 [A] and 9 [B] are an enlarged view of a wafer rack, wherein FIG. 9 [A] is a side view and FIG. 9 [B] is a cross-sectional view taken along a line E-E in FIG. 9 [A];

FIGS. 10 [A] and 10 [B] are diagrams illustrating exemplary modifications to a method of supporting a main housing;

FIG. 11 is a schematic diagram illustrating a general configuration of an electron-optical device in the testing apparatus of FIG. 5;

FIG. 12 is a diagram illustrating a potential applying mechanism;

FIGS. 13 [A] and 13 [B] show diagrams for explaining an electron beam calibration mechanism, where FIG. 13 [A] is a side view and FIG. 13 [B] is a plan view;

FIG. 14 is a schematic explanatory view of a wafer alignment controller;

FIG. 15 is a cross-sectional view generally illustrating a third embodiment of the charged electron beam apparatus according to the present invention;

FIG. 16 is a configuration diagram schematically illustrating an evaluation apparatus which is a fourth embodiment of the charged electron beam apparatus according to the present invention;

FIG. 17 is a table showing a breakdown occurrence probability for each metal;

FIG. 18 is a perspective view and a cross-sectional view of an electrode;

FIG. 19 is a partial cross-sectional view of the electrode illustrated in FIG. 18;

FIG. 20 is a top plan view and a cross-sectional view of the electrode illustrated in FIG. 18;

FIG. 21 is an enlarged cross-sectional view of a main portion of the electrode illustrated in FIG. 20;

FIG. 22 is a diagram generally illustrating a fifth embodiment of the charged particle beam apparatus according to the present invention;

FIG. 23 is a diagram illustrating in detail the configuration of the electron beam apparatus illustrated in FIG. 22;

FIG. 24 is a diagram generally illustrating a sixth embodiment of the charged particle beam apparatus according to the present invention;

FIG. 25( a ) is a graph showing the relationship between a negative voltage applied to an objective lens and a rising width of an electric signal, and FIG. 25( b ) is a diagram for explaining the rising width of the electric signal;

FIG. 26 is a configuration diagram of an electron beam testing apparatus which is a seventh embodiment of the charged particle beam apparatus according to the present invention;

FIGS. 27 ( a ) to 27 ( c ) are diagrams generally illustrating blocks in a mechanical construction of the electron beam testing apparatus illustrated in FIG. 26, where FIG. 27( a ) shows the relationship between the electron beam testing apparatus and coordinate axes; FIG. 27( b ) shows the proper vibration of a barrel; and FIG. 27( c ) shows an actuator attached to cancel the proper vibrations;

FIG. 28 is a schematic diagram illustrating an actuator and a vibration attenuating circuit used in the electron beam testing apparatus illustrated in FIG. 26, as well as the configuration of an equivalent circuit of a formed series resonant circuit;

FIG. 29 is a graph showing a transfer function of the barrel in the electron beam testing apparatus illustrated in FIG. 26;

FIG. 30 is a graph showing the transfer function of the barrel, electric frequency characteristic of the series resonant circuit, and a total transfer function in the electron beam testing apparatus illustrated in FIG. 26;

FIGS. 31( a ) to 31 ( c ) are diagrams for explaining a wafer testing method according to the present invention, where FIG. 37( a ) shows pattern defect detection; FIG. 37( b ) line width measurement; and FIG. 37( c ) potential contrast measurement, respectively;

FIG. 32 is a schematic plan view of an electrostatic chuck in an eighth embodiment of the electron beam apparatus according to the present invention, i.e., a plan view with a wafer removed to show electrodes;

FIG. 33 is a schematic vertical cross-sectional view taken along a straight line M-M in FIG. 32, a cross-sectional view showing a state in which a wafer is carried but not applied with a voltage;

FIGS. 34( a ) and 34 ( b ) are time charts of voltages applied to electrodes and a wafer;

FIG. 35 is a block diagram illustrating an exemplary configuration of an electron beam apparatus which uses the electrostatic chuck illustrated in FIG. 32;

FIGS. 36 [A] and 36 [B] are diagrams illustrating a vacuum chamber and an XY stage of a conventional electron beam apparatus, where FIG. 36 [A] is a front view and FIG. 36 [B] is a side view;

FIG. 37 is a diagram for explaining a differential pumping mechanism in FIG. 36;

FIGS. 38 [A] and 38 [B] are diagrams illustrating a vacuum chamber and an XY stage in a ninth embodiment of the charged particle beam apparatus according to the present invention, where FIG. 38 [A] is a front view and FIG. 38 [B] is a side view;

FIG. 39 is a diagram illustrating a vacuum chamber and an XY stage in a first exemplary modification to the ninth embodiment of the present invention;

FIG. 40 is a diagram illustrating a vacuum chamber and an XY stage in a second exemplary modification to the ninth embodiment of the present invention;

FIG. 41 is a diagram illustrating a vacuum chamber and an XY stage in a third exemplary modification to the ninth embodiment of the present invention;

FIG. 42 is a diagram illustrating a vacuum chamber and an XY stage in a fourth exemplary modification to the ninth embodiment of the present invention;

FIG. 43 is a schematic diagram showing an example of an optical system and a detection system disposed in a barrel illustrated in FIGS. 38-42;

FIG. 44 is a diagram illustrating a vacuum chamber and an XY stage in a tenth embodiment of the charged particle beam apparatus according to the present invention;

FIG. 45 is a diagram illustrating an example of a differential pumping mechanism disposed in the apparatus illustrated in FIG. 44;

FIG. 46 is a diagram illustrating a gas circulation piping system installed in the apparatus illustrated in FIG. 44;

FIG. 47 is a schematic diagram of an optical system in an eleventh embodiment of the charged electron beam apparatus according to the present invention;

FIG. 48 is a diagram illustrating a state of arrayed barrels of the electron beam apparatus illustrated in FIG. 47;

FIG. 49 is a diagram for explaining a site at which charge-up is evaluated, and an evaluation method;

FIG. 50 is a schematic configuration diagram of a defect testing apparatus which is a twelfth embodiment of the charged particle beam apparatus according to the present invention;

FIG. 51 is a diagram illustrating examples of a plurality of images under testing captured by the defect testing apparatus of FIG. 50 and a reference image;

FIG. 52 is a flow chart illustrating the flow of a main routine of wafer testing in the defect testing apparatus of FIG. 50;

FIG. 53 is a flow chart illustrating in detail the flow of a subroutine for a step of acquiring data on a plurality of images under testing (step 1904 ) in FIG. 52;

FIG. 54 is a flow chart illustrating in detail the flow of a subroutine for a comparing step (step 1908 ) in FIG. 52;

FIG. 55 is a diagram illustrating a specific example of the configuration of a detector in the defect testing apparatus in FIG. 50; and

FIG. 56 is a diagram conceptually illustrating a plurality of regions under testing which are shifted in position from one another while partially overlapping with one another on the surface of a semiconductor wafer.

BEST MODE FOR IMPLEMENTING THE INVENTION

In the following, a variety of embodiments of a charged particles beam apparatus according to the present invention will be described for an electron beam based apparatus which is taken as an example. Any embodiment is suitable for use in a sheet beam based testing apparatus.

Embodiment Relating to Overall Structure of Apparatus (First Embodiment)

A first embodiment of the charged particle beam apparatus according to the present invention relates to an electron beam based projection system, so that the projection system will be described first.

The projection system involves collectively irradiating a region under observation on a sample with a primary electron beam, i.e., irradiating a fixed area without scanning, and focusing a secondary electron beam from the irradiated region collectively on a detector (a combination of a micro-channel plate and a fluorescent plate) through a lens system as an image of the secondary electron beam. This image is transduced into an electric signal by a two-dimensional CCD (solid-state imager device) or TDI-CCD (line image sensor) to output on a CRT or to store in a storage device. From this image information, defects on the sample wafer (a semiconductor (Si) wafer in the middle of a process) are detected. With a CCD, a stage is moved in the minor axis direction or major axis direction, and movements are made on a step-and-repeat basis. With TDI-CCD, the stage is continuously moved in an integrating direction. Since the TDI-CCD can sequentially capture images, the TDI-CCD is used when a defect testing is conducted continuously. The resolution is determined by a scaling factor, accuracy and so on of a focusing optical system (secondary optical system), and the resolution of 0.05 μm has been achieved, by way of example. In this event, with the resolution of 0.1 μm, when 1.6 μA is applied to an area of 200 μm×50 μm as an electron beam irradiating condition, approximately one hour of testing time is required for every 20 cm wafer, which is faster than the SEM system by a factor of eight. The specifications of the TDI-CCD used herein define 2048 pixels×512 stages, and a line rate at 3.3 microseconds (line frequency at 300 kHz). While the irradiated area in this example is fitted to the specifications of the TDI-CCD, the irradiated area may be changed depending on an object under irradiation.

Now, the relationship between main functions of the map projection system, and its general figure will be described with reference to FIG. 1. In FIG. 1, the testing apparatus has a primary column 2001 , a secondary column 2002 , and a chamber 2003 . In the primary column 2001 , an electronic gun 2004 is arranged, and a primary optical system 2005 is positioned on the optical axis of an electron beam (primary electron beam) emitted from the electron gun 2004 . In the chamber 2003 , in turn, a stage 2006 is arranged, and a sample 2007 is carried on the stage 2006 .

On the other hand, in the secondary column 2002 , a cathode lens 2008 , a numerical aperture (NA) 2009 , a Wien filter (ExB filter) 2010 , a second lens 2011 , a field aperture 2012 , a third lens 2013 , a fourth lens 2014 , and a detector 2015 are positioned on the optical axis of a secondary electron beam generated from the sample 2007 . The numerical aperture 2009 , which corresponds to a diagram, is made of a thin plate of metal (Mo or the like) formed with a circular hole extending therethrough, and is positioned such that its opening is at a convergence position of the primary electron beam as well as a focus position of the cathode lens 2008 . Therefore, the cathode lens 2008 and the numerical aperture 2009 constitute a telecentric electron-optical system.

The output of the detector 2015 is input to a control unit 2016 , while the output of the control unit 2016 is input to a CPU 2017 . A control signal of the CPU 2017 is input to a primary column control unit 2018 , a secondary column control unit 2019 , and a stage driving mechanism 2020 . The primary column control unit 2018 controls a lens voltage for the primary optical system 2005 , while the secondary column control unit 2019 controls lens voltages for the cathode lens 2008 and second lens 2011 -fourth lens 2014 , as well as controls an electromagnetic field applied to the Wien filter 2010 .

The stage driving mechanism 2020 transfers stage position information to the CPU 2017 . Also, the primary column 2001 , secondary column 2002 and chamber 2003 are connected to a vacuum exhaust system (not shown), such that they are evacuated by a turbo molecular pump in the vacuum exhaust system to maintain a vacuum state therein.

A primary electron beam emitted from the electron gun 2004 impinges on the Wien filter 2010 while receiving a lens action by the primary optical system 2005 . As a chip for the electron gun, L _aB ₆, capable of drawing a large current with a rectangular cathode, is preferably used.

The primary optical system 2005 uses quadrupole or octpole electrostatic (or electromagnetic) lenses which are asymmetric about the optical axis. This can give rise to convergence and divergence on each of the X-axis and Y-axis, similarly to a so-called cylindrical lens. The lenses are configured in two stages or in three stages to optimize conditions for the respective lenses, thereby making it possible to shape an electron beam irradiated region on the surface of a sample into an arbitrary rectangle or ellipse without losing the irradiated electron beam. Specifically, when electro-static lenses are used, four cylindrical rods are used to place opposing electrodes (a and b, c and d) at an equal potential and impart them opposite voltage characteristics. Instead of cylindrical ones, a lens having a shape resulting from dividing a circular plate generally used in an electrostatic deflector into four may be used as the quadrupole lens. In this event, the lenses can be reduced in size.

The primary electron beam passing through the primary optical system 2005 has its trajectory deflected by a deflecting action of the Wien filter 2010 . As described later, the Wien filter 2010 can generate a magnetic field and an electric field orthogonal to each other. Assuming now that an electric field is E, a magnetic field is B, and the velocity of electrons is v, the Wien filter allows only electrons which satisfy the Wien condition E=vB to go straight, and deflects the trajectories of the remaining electrons. For the primary electron beam, a force FB is generated from the magnetic field and a force FE is generated from the electric field to deflect the beam trajectory. On the other hand, for the secondary electron beam, since the forces FB and FE act in the opposite directions, they cancel each other, allowing the secondary electron beam to go straight therethrough as it is.

A lens voltage for the primary optical system 2005 has been previously set such that the primary electron beam is focused on the opening of the numerical aperture 2009 . The numerical aperture 2009 acts to prevent excessive electron beams dispersed within the apparatus from reaching the surface of the sample, and to prevent the sample 2007 from charging and contamination. Further, since the numerical aperture 2009 and the cathode lens 2008 constitute a telecentric electron-optical system, the primary electron beam transmitting the cathode lens 2008 is transformed into a parallel beam which is uniformly and evenly irradiated to the sample 2007 . In other words, Koehler illumination, so called in the optical microscope, is implemented.

As the sample 2007 is irradiated with the primary electron beam, secondary electrons, reflected electrons or back-scattered electrons are emitted from the beam irradiated surface of the sample 2007 as a secondary electron beam. The secondary electron beam transmits the cathode lens 2008 while receiving a lens action thereof. The cathode lens 2008 comprises three electrodes. The lowermost electrode is designed to form a positive electric field between itself and a potential close to the sample 2007 to draw electrons (particularly, less directional secondary electrons) and efficiently introduce the electrons into the lens. The lens action is generated by applying voltages to the first and second electrodes of the cathode lens 2008 , and placing the third electrode at a zero potential.

On the other hand, the numerical aperture 2009 is placed at a focus position of the cathode lens 2008 , i.e., a back focus position from the sample 2007 . Therefore, light flux of an electron beam emitted out of the center of the view field (out of axis) is transformed into a parallel beam which passes through the central position of the numerical aperture 2009 without eclipse. The numerical aperture 2009 serves to reduce lens aberration of the second lens 2011 -fourth lens 2014 for the secondary electron beam.

The secondary electron beam passing through the numerical aperture 2009 goes straight as it is without receiving a deflecting action of the Wien filter 2010 . By changing the electromagnetic field applied to the Wien filter 2010 , electrons having particular energy (for example, secondary electrons, reflected electrons or back-scattered electrons) alone can be introduced into the detector 2015 from the secondary electron beam.

If the secondary electron beam is focused only with the cathode lens 2008 , aberration is more likely to occur due to a stronger lens action. Therefore, image formation is performed once in combination of the second lens 2011 . The secondary electron beam provides intermediate image formation on the field aperture 2012 by the cathode lens 2008 and second lens 2011 . In this event, generally, the magnification required as the secondary optical system is often insufficient, so that the third lens 2013 and forth lens 2014 are added to the configuration as lenses for enlarging the intermediate image. The secondary electron beam is enlarged by the third lens 2013 , fourth lens 2014 and forms an image. Here, the secondary electron beam forms images a total of three times. Alternatively, the third lens 2013 and fourth lens 2014 may be combined to force the secondary electron beam to form an image once (a total of two times).

All of the second lens 2011 , third lens 2013 and fourth lens 2014 are lenses symmetric about the optical axis, which are called uni-potential lenses or Einzel lenses. Each of the lenses comprises three electrodes, where the two outer electrodes are generally placed at zero potential, and a voltage applied to the central electrode generates a lens action for controlling. Also, the field aperture 2012 is positioned at an intermediate image formation point. While the field aperture 2012 limits the field of view to a required range, similar to a viewing diaphragm of an optical microscope, it blocks excessive beams together with the third lens 2013 and fourth lens 2014 , for electronic beams, to prevent the detector 2015 from charging and contamination. The magnification is set by changing lens conditions (focal lengths) of the third lens 2013 and fourth lens 2014 .

The secondary electron beam is enlarged and projected by the secondary optical system, and is focused on a detecting face of the detector 2015 . The detector 2015 is comprised of a micro-channel plate (MCP) for amplifying electrons; a fluorescent plate for transducing electrons into light; a lens and other optics for relaying a vacuum system to the outside to transmit an optical image; and an imager device (CCD or the like). The secondary electron beam is focused on the MCP detecting face, amplified, transduced into an optical signal by the fluorescent plate, and opto-electrically transduced into an electric signal by the imager device.

The control unit 2016 reads an image signal of the sample from the detector 2015 for transmission to the CPU 2017 . The CPU 2017 conducts a pattern defect testing from the image signal through template matching or the like. The stage 2006 is movable in the XY directions by the stage driving mechanism 2020 . The CPU 2017 reads the position of the stage 2006 , outputs a driving control signal to the stage driving mechanisms 2020 to drive the stage 2006 , and sequentially detects an image and conducts the testing.

In this way, in the testing apparatus in the first embodiment, the numerical aperture 2009 and the cathode lens 2008 constitute a telecentric electron-optical system, so that the sample can be uniformly irradiated with the primary electron beam. In other words, the Koehler illumination can be readily implemented. Further, for the secondary electron beam, an overall primary beam from the sample 2007 impinges perpendicularly on the cathode lens 2008 (parallel with the optical axis of the lens) and passes through the numerical aperture 2009 , so that peripheral light will not eclipsed or the luminance of an image will not be degraded in a peripheral portion of the sample. In addition, although so-called magnification chromatism, i.e., difference in the position of image formation due to variations in energy possessed by electrons, occurs (particularly, large magnification chromatism occurs since the secondary electron beam has largely varying energy), the numerical aperture 2009 is placed at the focus position of the cathode lens 2008 , so that this magnification chromatism can be suppressed.

Since the magnification is changed after the passage through the numerical aperture 2009 , a uniform image can be generated over the entire field of view on the detection side, even if set magnifications are changed in the lens conditions for the third lens 2013 and fourth lens 2014 .

While an even and uniform image can be captured in this embodiment, generally, as the magnification is increased, a problem arises that the brightness of image is reduced. To improve this, the lens conditions for the primary optical system may be designed such that when the magnification is changed by modifying the lens conditions for the secondary optical system, an effective field of view on the surface of a sample determined thereby is identical in size to an electron beam irradiated onto the surface of the sample. Specifically, while the field of view becomes narrower as the magnification is larger, the irradiated energy density of the electron beam is increased simultaneously with this, so that a signal density of detected electrons is held constant at all times to avoid the reduced brightness of image even if the field of view is enlarged and projected in the secondary optical system.

Also, in the testing apparatus of the first embodiment, the Wien filter 2010 is used to deflect the trajectory of the primary electron beam and allow the secondary electron beam to go straight therethrough, the present invention is not limited to that, but a Wien filter may be used for allowing the primary electron beam to go straight therethrough while deflecting the trajectory of the secondary electron beam. Further, while a rectangular beam is formed from a rectangular cathode and a quadrupole lens in this embodiment, the present invention is not limited to this. For example, a rectangular beam or an elliptic beam may be created from a circular beam, or a circular beam may be passed through a slit to extract a rectangular beam. Also, a plurality of beams may be scanned such that electron beams are generally irradiated uniformly to an irradiated region. The scanning in this event may be performed such that the plurality of beams arbitrarily scan respective regions allocated thereto (however with a uniform amount of irradiation).

Explaining now the electron gun as an electron beam source, a thermal electron beam source may be used as the electron beam source in this embodiment. An electron emitter (cathode) is made of L _aB ₆. However, another material may be used as long as it is refractory (the vapor pressure is low at high temperatures) and small in work function. Preferably, the tip is formed in the shape of cone or truncated cone resulting from cutting off the tip of a cone. The tip of the truncated cone may have a diameter of approximately 100 μm. While an field emission type or thermal field emission type electron beam source may be used as another system, an L _aB ₆based thermal electron source is optimal for this embodiment in which a relatively wide region (for example, 100×25-400×100 μm ²) is irradiated with a large current (approximately 1 μA). (In the SEM system, a thermal electric field electron beam source is generally used).

The thermal electron beam source is based on a method of emitting electrons by heating an electron emitting material, while the thermal field emission electron beam source means a method for emitting electrons by applying the electron emitting material with a high electric field, and stabilizing the emission of electrons by heating the electron beam emitter.

As will be understood from the description with reference to FIG. 1, the functions of main components in the projection system are as follows. First, as to the primary electron-optical system, a section for forming electron radiations emitted from an electron gun into a beam shape and irradiating a wafer surface with a rectangular or circular (elliptic) electron beam is called the “primary electron-optical system.” The size and current density of the electron beam can be controlled by controlling the lens conditions for the primary electron-optical system. Also, the primary electron beam is directed perpendicular to the wafer by a Wien filter positioned at a junction of the primary/secondary electron-optical systems.

Thermal electrons emitted from an L _aB ₆cathode of the electron gun is focused as a cross-over image on a gun diaphragm by a Wehnelt, triple anode lens. An electron beam with an incident angle adapted to the lens with an illumination field diagram is focused on a numerical aperture diagram in the form of rotational asymmetry by controlling the primary electrostatic lens, and subsequently two-dimensionally irradiated onto a wafer surface. A rear stage of the primary electrostatic lens is comprised of a three-stage quadrupole (QL) and a one-stage electrode for correcting geometrical aberration. While the quadrupole lens has limitations such as strict alignment accuracy, it characteristically has a strong converging action as compared with a rotationally symmetrical lens, so that it can correct the geometrical aberration corresponding to spherical aberration of a rotationally symmetric lens by applying an appropriate voltage to the geometrical aberration correcting electrode. In this way, a uniform surface beam can be irradiated to a predetermined region.

Next, as to the secondary electron-optical system, a focusing/projection optical system for focusing a two-dimensional secondary electron image produced by processing a secondary electron beam generated from a wafer irradiated with a primary electron beam at the position of a field diaphragm by electrostatic lenses (CL, TL) corresponding to an objective lens, and enlarging and projecting the secondary electron image using a lens (PL) at a rear stage, is called the “secondary electron-optical system.” In this event, the wafer is applied with a minus bias voltage (decelerating electric field voltage). A decelerating electric field has a decelerating effect for an irradiated beam, and also has effects of reducing a damage on a wafer (sample), accelerating the secondary electron beam generated from the surface of the sample due to a potential difference between CL and the wafer, and reducing chromatism. Electrons converged by CL is focused on FA by TL, and the resulting image is enlarged and projected by PL, and formed on a secondary electron beam detector (MCP). In the secondary electron-optical system, NA is positioned between CL-TL and optimized to constitute an optical system which is capable of reducing off-axis aberration.

In addition, for correcting errors caused by the manufacturing of the electron-optical system, and astigmatism and anisotropic magnification of an image produced by passing a Wien filter, an electrostatic octpole (STIG) is disposed for correction, and preferably, a deflector (OP) positioned between respective lenses may be used to correct misalignment. In this way, a projection optical system can be achieved with a uniform resolution in the field of view.

The Wien filter 2010 is a unit based on an electromagnetic prism optical system which has electrodes and magnetic poles positioned in orthogonal directions to generate an electric field and a magnetic field in an orthogonal relationship. As an electromagnetic field is selectively applied, an electron beam incident from one direction into the field is deflected, while an electron beam incident from the opposite direction is allowed to go straight. This is achieved because of the ability to create conditions (Wien conditions) for canceling a force received by electrons from the electric field and a force received thereby from the magnetic field, whereby the primary electron beam is deflected and irradiated perpendicularly onto a wafer, while the secondary electron beam goes straight toward the detector.

The detailed structure of the Wien filter 2010 as an electron beam deflector will be described with reference to FIGS. 2( a ) and 2 ( b ). As illustrated in these figures, a field generated by the electron beam deflector has a structure in which an electric field is oriented orthogonal to a magnetic field in a plane perpendicular to the optical axis of he aforementioned projection optical system, i.e., an ExB structure.

Here, the electric field is generated by electrodes 2030 a , 2030 b which have concave curved surfaces. The electric fields generated by the electrodes 2030 a , 2030 b are controlled by controllers 2031 a , 2031 b , respectively. Electromagnetic coils 2032 a , 2032 b are arranged orthogonal to the electrodes 2030 a , 2030 b for generating the magnetic field. In this event, for improving the uniformity of the magnetic field, a pole piece having a parallel flat plate shape is provided to form a magnetic path. While the electrodes 2030 a , 2030 b for generating the electric field may be arranged symmetric about a point 2034 , they may be concentrically arranged.

FIG. 2( b ) is a vertical cross-sectional view on a plane which passes the point 2034 in FIG. 2( a ) and perpendicular to the electrodes 2030 a , 2030 b . Referring to FIG. 2( b ), behaviors of electron beams will be described. Irradiated electron beams 2035 a , 2035 b are deflected by an electric field generated by the electrodes 2030 a , 2030 b and a magnetic field generated by the electromagnetic coils 2031 a , 2031 b , and then impinge on the surface of a sample in a direction perpendicular thereto. Here, incident positions and angles of the irradiated electron beams 2035 a , 2035 b to the Wien filter 2010 are uniquely determined as the energy of electrons is determined. Further, by controlling conditions of the electric field and magnetic field, i.e., the electric field generated by the electrodes 2030 a , 2030 b and the magnetic field generated by the electromagnetic coils 2031 a , 2031 b by their respective controllers 2031 a , 2031 b , 2033 a , 2033 b such that the secondary electron beams 2036 a , 2036 b go straight, i.e., vB=E stands, secondary electron beams go straight through the Wien filter 2010 and impinges on the projection optical system, where v is the velocity of electrons (m/s), B is the magnetic field (T), e is the amount of charge (C), and E is the electric field (V/m).

Finally, the detector will be described. The image of the secondary electron beam from the wafer, focused by the secondary optical system is first amplified by the micro-channel plate (MCP), then strikes the fluorescent screen, and transduced into a light image. The MCP is comprised of several millions of very thin conductive glass capillaries of 6-25 μm in diameter and 0.24-1.0 mm in length which are bundled and shaped into a thin plate. Each of the capillaries acts as an independent secondary electron amplifier, when a predetermined voltage is applied, to form, as a whole, the secondary electron amplifier. An image transduced into light by this detector is projected through a vacuum transmission window onto TDI-CCD on a one-to-one basis in an FOP system which is placed in the atmosphere.

As will be understood from the foregoing description, the testing apparatus, which is the first embodiment, can improve the throughput of the electron beam based testing apparatus.

FIG. 3 illustrates an example of a semiconductor device manufacturing method which uses the first embodiment of the present invention, and includes the following main processes.

(1) a wafer manufacturing process for manufacturing a wafer (or a wafer preparing process for preparing a wafer);

(2) a mask manufacturing process for manufacturing masks for use in exposure (or mask preparing process for preparing masks);

(3) a wafer processing process for performing processing required to the wafer;

(4) a chip assembling process for excising one by one chips formed on the wafer and making them operable; and

(5) a chip testing process for testing complete chips.

The respective main processes are further comprised of several sub-processes.

Among these main processes, the wafer processing process set forth in (3) exerts critical affections to the performance of resulting semiconductor devices. This process involves sequentially laminating designed circuit patterns on the wafer to form a large number of chips which operate as memories, MPUs and so on. The wafer processing process includes the following sub-processes:

(A) a thin film forming sub-process for forming dielectric thin films serving as insulating layers, metal thin films for forming wirings or electrodes, and so on (using CVD, sputtering and so on);

(B) an oxidization sub-process for oxidizing the thin film layers and the wafer substrate;

(C) a lithography sub-process for forming a resist pattern using masks (reticles) for selectively processing the thin film layers and the wafer substrate;

(D) an etching sub-process for processing the thin film layers and the substrate in conformity to the resist pattern (using, for example, dry etching techniques);

(E) an ion/impurity injection/diffusion sub-process;

(F) a resist striping sub-process; and

(G) a sub-process for testing the processed wafer.

The wafer processing process is repeated a number of times equal to the number of required layers to manufacture semiconductor devices which operate as designed.

FIG. 4( a ) is a flow chart illustrating the lithography process (C) which forms the core of the wafer processing process in FIG. 3. The lithography process includes the following steps:

(a) a resist coating step for coating a resist on the wafer on which circuit patterns have been formed in the previous process;

(b) a step of exposing the resist;

(d) an annealing step for stabilizing the developed resist pattern.

When the defect testing apparatus of the present invention is used in the testing sub-process set forth in (G), any semiconductor devices even having miniature patterns can be tested at a high throughput, so that a total inspection can also be conducted, thereby making it possible to improve the yield rate of products and prevent defective products from being shipped. In this respect, description will be made with reference to FIG. 4( b ).

Generally, an electron beam based testing apparatus is expensive and low in throughput as compared with other process apparatuses, so that such a defect testing apparatus is presently used after critical steps for which testing is most required (for example, etching, deposition or CMP (chemical-mechanical polishing) planarization processing). In this event, a wafer under testing is aligned on a super precise X-Y stage through an atmosphere transport system and a vacuum transport system, and fixed by an electrostatic chuck mechanism or the like. Subsequently, testing for defects and so on is conducted in accordance with a procedure illustrated in FIG. 4( b ).

In FIG. 4( b ), first, an optical microscope is used to confirm the position of each die, and detect the height of each location for storage as required. Other than this, the optical microscope is used to capture an optical microscopic image of a desired site such as defects for comparison with an electron beam image. Next, information on prescription is input to the apparatus in accordance with the type of a wafer (after which process, whether the size of the wafer is 20 cm or 30 cm, and so on) to specify a testing location, set electron-optical systems, set testing conditions, and so on. Subsequently, the defect testing is conducted generally in real time while images are captured. Through comparison of cells with one another, comparison of dies, and so on, a high speed information processing system installed with algorithms conducts the testing to output the result to a CRT and so on and stores the result in a memory as required.

Defects include particle defect, anomalous shape (pattern defect), electrical defects (disconnected wires or vias, defective conduction and the like), and so on. Distinction of these defects, and classification of the defects by size, and identification of killer defects (critical defects which disable chips to be used) may be automatically performed in real time.

The detection of electrical defects can be carried out by detecting anomalous potential contrasts. For example, a defectively conducted location is generally charged in positive by irradiation of electron beams (at approximately 500 eV) and presents a lower contrast, so that it can be distinguished from normal locations. An electron beam irradiating means in this case refers to a low potential (energy) electron beam generating means (generation of thermal electrons, UV/photoelectrons) which is separately provided for emphasizing the contrast caused by a potential difference, other than the normal electron beam irradiating means for testing. Before irradiating a region under testing with a testing electron beam, a low potential (energy) electron beam is generated for irradiation. For the projection system which can positively charge a sample by irradiating the same with a testing electron beam, the low potential electron beam generating means need not be provided in separation depending on specifications. Also, defects can be detected from a difference in contrast which is produced by applying a sample such as a wafer with a positive or a negative potential with respect to a reference potential (due to a difference in the ease of flow in a forward direction or a backward direction of the device). Such a defect testing apparatus can be utilized as well in a line width measuring apparatus and an alignment precision measurement.

A method of testing electrical defects of a sample under testing may take advantage of the fact that a voltage at an essentially electrically insulated portion is different from a voltage when this portion is conducted. For this purpose, charges are previously supplemented to a sample under testing to produce a difference in potential between the essentially electrically insulated portion and a portion which should have been electrically insulated but is conducted by some cause. Subsequently, a charged particle beam is irradiated from the charged particle beam apparatus according to the present invention to acquire data with the difference in potential, and the acquired data is analyzed to detect the conducted state.

Embodiment Relating to Testing Apparatus (Second Embodiment)

The second embodiment of the present invention relates to an electron beam apparatus suitable for testing, using an electron beam, defects in patterns formed on the surface of an object under testing, and more particularly, to an electron beam apparatus suitable for a testing apparatus useful, for example, in detecting defects on a wafer in a semiconductor manufacturing process, which includes irradiating an object under testing with an electron beam, capturing secondary electrons which vary in accordance with the properties of the surface thereof to form image data, and testing patterns formed on the surface of the object under testing based on the image data at a high throughput, and a method of manufacturing devices at a high yield rate using such an electron beam apparatus.

As an apparatus for testing defects of a wafer using an electron beam, an apparatus using a scanning electron microscope (SEM) already commercially available is known. This apparatus involves raster scanning an object under testing with a narrowed electron beam at very narrow intervals of raster width, detecting secondary electrons emitted fro

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