DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0033] FIGS. 3 and 4 illustrate simulated contaminant distribution in an EFEM 40 and FOUP 13 . FIG. 3 illustrates the distribution of contaminants, which in this exemplary illustration include NH 3 contaminants, from outside the EFEM 40 . FIG. 4 illustrates the distribution of contaminants, which in this exemplary illustration include Cl 2 contaminants, introduced into the EFEM 40 and FOUP 13 from the adjacent wafer processing equipment.

[0034] FIG. 3 illustrates contaminants outside and inside the EFEM. The concentration of contaminants, in this example NH 3 contaminants, is indicated by spatial concentration contour lines 105 . Contaminants, including NH 3 and molecular contaminants such as Cl, F, Br, etc., are introduced into the EFEM 40 and the FOUP 13 . Even if particles are filtered, molecular contaminants penetrate the filter and enter the EFEM and FOUP. The molecular contaminants degrade the efficiency and operational characteristics of the devices formed in the semiconductor substrates exposed to the contaminants.

[0035] The simulative graph of FIG. 3 simulates the conditions of 0.4 m/sec of air stream from the topside of the frame 12 and 1000 ppm of NH 3 contaminant source of the EFEM. As a result, 1000 ppm of NH 3 is detected inside the EFEM 40 , outside the EFEM 40 and inside the FOUP 13 .

[0036] FIG. 4 shows contaminants introduced into the EFEM 40 and FOUP 13 from process equipment such as chemical vapor deposition (CVD) equipment, dry etch equipment, thermal furnace, developing equipment or metrology equipment. Contaminants, such as Cl 2 , are dispersed into the EFEM 40 and the FOUP 13 . These contaminants not only produce an undesired native oxide layer on wafers but also degrade operational characteristics and yield of semiconductor chips.

[0037] The simulative graph of FIG. 4 simulates the conditions of 0.4 m/sec of air stream from the topside of the frame 12 and 1000 ppm of Cl 2 contaminant from wafer process equipment which enters the EFEM 40 through the fram 12 at the location marked “A”. As a result, as shown by the contaminant concentration contour lines 105 , contaminants are detected inside the EFEM 40 , and 100 ppm of Cl 2 is detected in the FOUP 13 .

[0038] FIG. 5 contains an image which illustrates a simulated profile of conventional air flow from the top side of the EFEM 40 in a conventional configuration. As shown in the figure, a portion of the air stream flows into and circulates within a wafer storage container, for example, the FOUP 13 , through an opening at a side wall of the EFEM 40 . Even if the air stream is clean, the air may contain oxides, moisture, etc., and, therefore, could produce undesired native oxide on the in the container. This native oxide can degrade the performance and yield of semiconductor devices formed in the wafer. For example, if the native oxide forms on a contact hole including polysilicon, the resistance of the contact increases.

[0039] FIG. 6 contains a schematic perspective view illustrating an embodiment of an EFEM 100 in accordance with the present invention. In accordance with the invention, in addition to the gas, e.g., air, introduced into the EFEM 100 from the top side, an additional gas flow is introduced into the EFEM 100 of the invention to substantially reduce or eliminate the flow of contaminants into the FOUP. In accordance with the invention, the EFEM 100 includes a gas nozzle 110 in the frame 160 , which allows for the introduction of an additional flow of gas into the EFEM 100 . Specifically, a stable, inert gas such as N 2 , Ar, He, clean dry air, etc., is allowed to flow into the EFEM 100 . In one embodiment, the flow of the second gas into the EFEM 100 is accomplished with little or no interruption in the laminar flow of the gas entering the EFEM 100 at its top side. This combined flow of gases prevents the flow of gas and contaminants into the FOUP. As a result, contamination of the wafers stored in the FOUP is virtually eliminated.

[0040] Referring to FIG. 6 , FOUPs 120 are loaded on the wafer load station 130 . A transfer mechanism or platform 140 is installed in the frame 160 . Wafers are transferred into process equipment 150 , such as, for example, CVD equipment, dry etch equipment, thermal furnace, metrology equipment, etc., by the transfer mechanism 140 . The FOUP 2 120 are loaded or unloaded on the wafer load station 130 by a container transfer mechanism such as an overhead transfer (OHT) or overhead conveyor (OHC) system and an automatic guided vehicle (AGV or RGV) system. Wafers are transferred to the process equipment 150 via an opening 170 in a side wall of the frame 160 . In one embodiment, the inert gas nozzle 110 is installed at a side of the frame 160 in order to inject inert gas and comply with air stream or air flow into the FOUP 120 . A preferred position of the inert gas nozzle 110 is adjacent to and above the opening 170 in the frame 160 , as shown in the figure.

[0041] A fan (not shown) is installed the upper portion of the frame 160 in order to create an air stream from the upper portion to the bottom portion of the frame 160 . A filter (not shown) may be installed in the frame 160 for cleaning the air stream. Using this system of the invention, the clean room is separated to International Standard Organization (hereinafter as “ISO”) Class 5 and ISO Class 2 for economic maintenance. The semiconductor process path, such as the FOUP and EFEM environments are above ISO Class 2, and the outside of the process path is under ISO Class 5.

[0042] FIG. 7 illustrates a simulated contaminant distribution in the FOUP 120 and the EFEM 100 in the configuration of the present invention, that is, with the additional gas flow introduced into the EFEM 100 . In particular, FIG. 7 illustrates, via the concentration contour lines 105 , spatial distribution of NH 3 contaminants. The simulated graph of the contaminant distribution is simulated by conditions of 0.4 m/sec of air stream from the top side of the frame 160 and 1000 ppm of NH 3 contaminant source from the clean room, that is, outside of the frame 160 . As shown in the figure, in the configuration of the invention, less than 500 ppm (480 ppm) of NH 3 is detected in the FOUP 120 . This is an large improvement over the NH 3 concentration in the conventional configuration, as illustrated in FIG. 3 , where 1000 ppm of NH 3 was detected in the FOUP.

[0043] When the manufacturing process steps are performed in the configuration of the present invention, wafers in the FOUP 120 , which is filled with inert gas such as nitrogen, helium or argon, are transferred into the EFEM 100 , in which the lamina-flow air stream flows from the upper side of the frame 160 to the bottom side of the frame 160 . The inert gas introduced via the gas nozzle 110 protects wafers from oxidation and prevents contamination from wafer to wafer. The inert gas with the air stream from upper side of the EFEM 100 can flow as laminar flow and does not interfere with the environment of the EFEM 100 .

[0044] If the inert gas introduced in accordance with the invention interrupts the laminar flow of the air stream by introducing turbulence, it is possible that the wafer and the inside environment of the EFEM may be contaminated by a contaminant introduced by the process equipment 150 or entering the EFEM 100 by other routes, such as the air fan at the top side of the frame 160 . Also, if the injection of inert gas is performed at too high a pressure, second contamination caused from contaminates of the FOUP can occur. Accordingly, in the preferred embodiment of the invention, the flow of inert gas does not interfere with the flow of the air stream. The speed of air flow and inert gas can be reciprocally determined for laminar flow.

[0045] FIG. 8 illustrates a simulated contaminant distribution in the FOUP 120 and the EFEM 100 in the configuration of the present invention, that is, with the additional gas flow introduced into the EFEM 100 . In particular, FIG. 8 illustrates, via the concentration contour lines 105 , spatial distribution of Cl 2 contaminants. As shown in the figure, even though there are contaminants in the process equipment and the EFEM, there are virtually no contaminants in the FOUP 120 . In accordance with the invention, the clean gas or inert gas, e.g., nitrogen, argon, helium, clean dry air, etc., prevents contaminants from reaching the FOUP 120 . FIG. 8 illustrates conditions of 0.4 m/sec of air stream and 1000 ppm of Cl 2 as contaminant from process equipment 150 . As illustrated by the concentration contour lines 105 , almost zero ppm of Cl 2 is detected in the FOUP 120 . The concentration of contaminant is greatly reduced, compared to that of the conventional configuration illustrated in FIG. 4 .

[0046] FIG. 9 illustrates another embodiment of the invention showing inert gas nozzles installed in the EFEM 400 . The drawings in FIG. 9 are two views of the EFEM 400 rotated ninety degrees to each other. Inert gas nozzles, 200 and 300 are installed in the EFEM 400 . The inert gas nozzle 200 introduces inert gas such as nitrogen, argon, helium, etc., or clean dry air into a FOUP 220 and prevents air flowing in the frame from flowing into the FOUP 220 . The inert gas nozzle 300 injects inert gas or clean dry air into the FOUP 220 . The EFEM 400 in FIG. 9 may be coupled with a wet station as shown in FIG. 10 .

[0047] Referring to FIGS. 9 and 10 , in a semiconductor manufacturing process, wafers are cleaned at wet baths 250 and stocked in the FOUP 220 . While the FOUP 220 is empty, the inert gas nozzle 200 introduces gas into the FOUP 220 for about 20 seconds. After gas fills the FOUP 220 via a control valve, wafers are transferred into the FOUP 220 by a robot 240 .

[0048] During manufacturing of semiconductor devices, wafers having sources, drains, gate electrodes and isolation areas such as shallow trench isolation (STI) are deposited with a dielectric layer by a conventional chemical vapor deposition (CVD) method. Then contact holes (or self-aligned contacts) are formed to expose surfaces of sources/drains by etching the dielectric layer. After etching with chemicals, the residue on the contact hole should be removed and cleaned in the wet baths. The wafers are transferred for subsequent manufacturing process steps, such as filling the contact hole with polysilicon.

[0049] In conventional processing systems, however, wafers with contact holes have a tendency to grow undesired silicon dioxide because the silicon surface of the contact holes is exposed to air. To eliminate this problem, the purpose of filling gas in the FOUP is to prevent the growth of silicon dioxide in the contact hole. After wafers 230 are stocked in the FOUP 220 , the inert gas nozzle 300 purges air out of the FOUP and prevents intake from the outside of the FOUP 220 by a control valve. A FOUP opener closes the FOUP with a lid and the FOUP 220 is unloaded. The shapes of inert gas nozzles 200 , 300 can be rectangular, cylindrical, elongated triangle, etc., which may have a plurality of holes or elongated slits for the gas.

[0050] FIGS. 11A and 11B contain schematic cross-sectional views of semiconductor devices in a manufacturing process of forming a self-aligned contact (SAC) and depositing a conductive layer, in accordance with the present invention. After gate electrodes 410 and an interdielectric layer 430 are formed on the semiconductor substrate 401 , a SAC (contact hole) 420 is formed by a conventional method. The interdielectric layer 430 can be Boron Phosphorus Silicon Glass (BPSG). After etching the interdielectric layer 430 , a cleaning process is conventionally performed with chemicals such as dilute HF for removing polymer on the contact hole 420 in order to prevent increase in the contact resistance. When contaminants such as polymer or silicon dioxide are present, a polysilicon layer 440 of about 3000 Å of thickness and the surface of the contact hole can deteriorate. So, after cleaning wafers in chemical baths 250 , wafers 230 are transferred into the EFEM 400 and are transferred into the FOUP 220 by a robot 240 shown in FIG. 10 . During the transfer in the EFEM 400 shown in FIG. 10 , wafers may be exposed to air and native oxide may form in the contact hole as a result. In accordance with the invention, the inert has nozzles 200 and 300 can prevent wafers from becoming contaminated and having native oxide formed on them.

[0051] While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.