DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] The following is a detailed explanation of the preferred embodiments of the present invention, given in reference to the attached drawings. It is to be noted that in the specification and the drawings, the same reference numerals are assigned to components having substantially identical functions and structural features to preclude the necessity for a repeated explanation thereof.

[0038] The process control system achieved in the first embodiment controls semiconductor device manufacturing processes. FIG. 1 schematically illustrates the overall structure of the process control system. The process control system 100 is installed in a clean room at, for instance, a semiconductor manufacturing plant.

[0039] The space inside the clean room is divided into a plurality of areas (to be referred to as “bays” in this document) 110 (110A, 110B . . . ). The number of bays in the clean room corresponds to the manufacturing steps that need to be executed to manufacture semiconductor devices.

[0040] In each bay 110 (110A, 110B . . . ), a plurality of processing apparatuses 120 (120A, 120B . . . ), 122 (122A, 122B . . . ), 124 (124A, 124B . . . ) that process wafers are installed. The processing apparatuses 120, 122, 124 . . . may be, for instance, etching apparatuses, CVD (chemical vapor deposition) apparatuses, coaters/developers, washing apparatuses, CMP (chemical mechanical polishing) apparatuses, PVD (physical vapor deposition) apparatuses, exposure apparatuses or ion implanters. It is to be noted that in the following explanation, all the processing apparatuses 120, 122, 124 . . . in a given bay 110 may be simply referred to as the processing apparatuses 120, unless specifically stated otherwise.

[0041] In each bay 110, at least one measuring apparatus 130 that executes a measuring operation on wafers processed in the bay 110 is installed. The measuring apparatus 130 may execute the measuring operation on the wafers before and after they undergo the processing or only before or after they undergo the processing. The measuring apparatus may be a film thickness measuring apparatus, an ODP (optical digital profiler) or an FTIR. It is to be noted that a plurality of measuring apparatuses 130 may be installed in each bay 110. In addition, the measuring apparatus 130 may include a self-diagnosis unit 132 which embodies an example of a means for self-diagnosis that executes a self-diagnosis to determine whether or not any abnormality exists in the circuits constituting the measuring apparatus itself.

[0042] A transfer apparatus is installed in each bay 110. The transfer apparatus includes a bay transfer path 140 (140A, 140B . . . ) installed at the bay 110. The bay transfer path 140 is a transfer path through which wafers are transferred among the individual processing apparatuses 120 or between the processing apparatus 120 and the measuring apparatus 130 in the bay 110. The bay transfer paths 140 are connected to a main transfer path 142 which is a transfer path connecting the individual bays 110. The transfer apparatuses may be, for instance, OHTs (overhead hoist transports) or AGBs (automatic guided vehicles). The transfer paths 140 and 142 may each be constituted of a rail so that the wafers held in, for instance, FOUPs or wafer cassettes are transported on vehicles guided along the rails.

[0043] A process control device 150, which embodies an example of a control device that individually controls the processing apparatuses 120, 122, 124, the measuring apparatus 130 and the transfer apparatus in the bay 110 is installed in each bay 110. The process control device 150 (150A, 150B . . . ), the individual processing apparatuses 120 (120a , 120B . . . ), 122 (122A, 122B . . . ), 124 (124A, 124B . . . ) . . . , the measuring apparatus (130A, 130B . . . ) and the transfer apparatus in a given bay 110 ((110A, 110B . . . ) are all connected via a network 152 (152A, 152B . . . ) so as to enable data and signal exchange among the process control device 150, the individual processing apparatuses 120, the measuring apparatus 130 and the transfer apparatus via the network 152.

[0044] The process control device 150 engages the measuring apparatus 130 in a measuring operation on wafers processed by, for instance, a processing apparatus 120 and sets processing conditions for the processing apparatus 120 based upon the results of the measuring operation. More specifically, it may determine the processing conditions under which a model expression with regard to the processing results is generated based upon the results of the measuring operation by the measuring apparatus 130. A specific example of the processing executed by the processing apparatus 120 is to be explained in detail later.

[0045] The process control device 150 includes a microprocessor having, for instance, a CPU (central processing unit), a ROM (read only memory) having stored therein programs used to control various circuits and a RAM (random access memory) with a memory area where a program read out by the CPU from the ROM (read only memory) as necessary is stored in an expanded form. It may also include a means for recording such as a hard disk device, a means for input such as a keyboard, a means for display such as a display device and a means for warning that issues a warning in the event of an abnormality and the like.

[0046] Next, an etching apparatus which embodies an example of the processing apparatus 120 is explained in reference to a drawing. FIG. 2 is a schematic sectional view of the structure adopted in the etching apparatus. The etching apparatus 201 is a capacitive coupling type plane parallel etching apparatus having an upper electrode plate and a lower electrode plate that extend parallel to each other and face opposite each other with a plasma forming source connected to one of the electrode plates.

[0047] The etching apparatus 201 includes a cylindrical chamber (processing chamber) 202 constituted of aluminum and having anodized surfaces (anodic-oxide coated surfaces), and the chamber 202 is grounded. Inside the chamber 202, a susceptor stage 204 assuming a substantially columnar shape, on which a wafer W is placed, is provided at the bottom via an insulating plate 203 constituted of ceramic or the like. A susceptor 205 constituting a lower electrode is disposed atop the susceptor stage 204. A high pass filter (HPF) 206 is connected to the susceptor 205.

[0048] A temperature control medium chamber 207 is formed inside the susceptor stage 204. The temperature control medium is supplied into the temperature control medium chamber 207 via a supply pipe 208 to circulate in the temperature control medium chamber 207 therein, and the temperature control medium is then discharged through a discharge pipe 209. By circulating the temperature control medium in this manner, the temperature of the susceptor 205 can be controlled to maintain a desirable level.

[0049] The susceptor 205 is formed in a disk shape and includes a projecting central portion on the upper side thereof. An electrostatic chuck 211 assuming a shape substantially identical to that of the wafer W is provided atop the susceptor 205. The electrostatic chuck 211 adopts a structure achieved by inserting an electrode 212 between insulating members. As a DC voltage of, for instance, 1.5 kV is applied to the electrostatic chuck 211 from a DC source 213 connected to the electrode 212, the electrostatic chuck 211 holds the wafer W through electrostatic force.

[0050] A gas passage 214, through which a heat transfer medium (e.g., a backside gas such as He gas) is supplied to the rear surface of the wafer W undergoing the processing is formed at the insulating plate 203, the susceptor stage 204, the susceptor 205 and the electrostatic chuck 211, and heat is transferred between the susceptor 205 and the wafer W via the heat transfer medium to sustain the temperature of the wafer W at a specific level.

[0051] At the edge of the susceptor 205 at the upper end, a circular focus ring 215 is disposed so as to surround the wafer W placed on the electrostatic chuck 211. The focus ring 215, which is constituted of an insulating material such as ceramic or quartz or an electrically conductive material, improves the uniformity of etching.

[0052] In addition, above the susceptor 205, an upper electrode 221 is provided so as to run parallel to and face opposite the susceptor 205. The upper electrode 221 is supported in the chamber 202 via an insulating member 222. The upper electrode 221 comprises an electrode plate 224 facing opposite the susceptor 205 and having numerous outlet holes 223 and an electrode support member 225 that supports the electrode plate 224. The electrode plate may be constituted of, for instance, quartz, whereas the electrode support member 225 is constituted of an electrically conductive material such as aluminum having anodic-oxide coated surfaces. It is to be noted that the distance between the susceptor 205 and the upper electrode 221 can be adjusted.

[0053] At the center of the electrode support member 225 of the upper electrode 221, a gas supply port 226 is formed. A gas supply pipe 227 is connected to the gas supply port 226. In addition, a process gas supply source 230 is connected to the gas supply pipe 227 via a valve 228 and a mass flow controller 229.

[0054] An etching gas with which plasma etching is executed is supplied from the process gas supply source 230. It is to be noted that while a single process gas supply system constituted of the process gas supply source 230 and the like described above is shown in FIG. 2, a plurality of such process gas supply systems are installed in reality so as to supply the etching gas into the chamber 202 by individually controlling the flow rates of the gases constituting the etching gas, e.g., CF₄, O₂, N₂ and CHF₃.

[0055] An evacuation pipe 231 is connected at the bottom of the chamber 202, and an evacuation device 235 is connected to the evacuation pipe 231. The evacuation device 235 includes a vacuum pump such as a turbo molecular pump and is capable of evaluating the chamber 202 so that the atmosphere inside the chamber 202 achieves a specific lowered pressure level (e.g., 0.67 Pa or lower). In addition, a gate valve 232 is provided at the side wall of the chamber 202. The wafer W in a wafer cassette or the like is transferred between the bay transfer path 140 and the chamber while the gate valve 232 is in an open state.

[0056] A first high-frequency source 240 is connected to the upper electrode 221 and a matcher 241 is inserted in the power supply line. A low pass filter (LPF) 242 is connected to the upper electrode 221, as well. The power from the first high-frequency source 240 has a frequency within a range of 50 to 150 MHz. By applying power with such a high frequency, plasma achieving a desirable state of disassociation is formed in high density inside the chamber 202, and thus, plasma processing can be executed under lower pressure conditions compared to the related art. It is desirable to set the frequency of the power from the first high-frequency source 240 to 50 to 80 MHz, and typically, the frequency is set to approximately 60 MHz, as shown in the figure.

[0057] A second high-frequency source 250 is connected to the susceptor 205 constituting the lower electrode, and a matcher 251 is inserted in the power supply line. The power from the second high-frequency source 250 has a frequency within a range of several hundred kHz to 10-plus MHz. By applying the power with the frequency set within this range, desirable ionization is achieved without damaging the wafer W undergoing the processing. The frequency of the power from the second high-frequency source 250 is typically set to 13.56 MHz, as shown in the figure, or to 2 MHz or the like.

[0058] Next, a specific example of the process control executed in the process control system in the embodiment is explained. In this example, the etching apparatus 201 described above constitutes the processing apparatus 120, the measuring apparatus 130 measures pattern shape elements on the wafer and the extent to which the mask (e.g., an organic reflection-reducing film) is trimmed is controlled.

[0059] Such mask trimming is an effective means for achieving finer wiring or the like on the wafer. Namely, when a specific pattern is formed on the wafer through a photolithography step, it is normally difficult to form a mask layer with a line width equal to or smaller than approximately 0.07 μm due to technological limits imposed in the exposure/development steps. However, by setting an initial line width of the mask layer greater than the line width to be ultimately achieved and reducing the line width (trimming the mask layer) through an etching step, wiring achieving a smaller line width can be formed without having to assure a very small mask layer line width while the mask layer is exposed and developed.

[0060] Through tests and the like, it has been confirmed that the extent to which the mask is trimmed can be controlled by, for instance, adjusting the flow rate ratio (O₂ flow rate/CF₄+O ₂ flow rate). Accordingly, pattern shape elements of the pattern formed on a wafer are measured by the measuring apparatus 130, the flow rate ratio ((O₂ flow rate/(CF₄+O₂) flow rate) is controlled based upon the results of the measurement and a pattern conforming to the design specifications is formed on the wafer in the embodiment.

[0061] First, the relationship between the extent to which the mask (e.g., an organic reflection-reducing film) is trimmed and the flow rate ratio (O₂ flow rate/(CF₄+O₂) flow rate) is explained. In this example, the mask is constituted of an ArF resist. FIG. 3 presents schematic enlargements of a portion of a longitudinal section of a wafer with an ArF resist deposited thereupon.

[0062] In the wafer shown in FIG. 3, a silicon oxide film 322 is formed so as to achieve a predetermined film thickness (50 nm in the embodiment) on top of a polysilicon film 321 and an organic reflection-reducing film 323 is formed over the silicon oxide film 322 to achieve a specific film thickness (80 nm in the embodiment), as shown in FIG. 3A. In addition, atop the organic reflection-reducing film 323, an ArF resist 324 with a specific film thickness (240 nm in the embodiment) having been patterned to achieve a specific pattern through the exposure step and the development step mentioned earlier is formed. It is to be noted that the line width (indicated by “d” in the figure) is 80 nm in the embodiment.

[0063] The organic reflection-reducing film 323 is first etched via the ArF resist 324 (mask layer) through plasma etching executed by using an etching gas constituted of CF₄ gas and 02 gas in the state shown in FIG. 3A, thereby patterning the organic reflection-reducing film 323 to achieve a specific pattern, as shown in FIG. 3B.

[0064] Subsequently, the silicon oxide film 322 in the state shown in FIG. 3B undergoes plasma etching executed by using an etching gas constituted of CF₄ gas and CHF₃ gas via the ArF resist 324 (mask layer) and the organic reflection-reducing film 323 and, as a result, the silicon oxide film 322 is patterned to achieve a specific pattern as shown in FIG. 3C.

[0065] Afterwards, the ArF resist 324 and the organic reflection-reducing film 323 are removed through ashing or the like.

[0066] In addition, while the organic reflection-reducing film 323 undergoing the etching step can be trimmed as described above, the extent to which the organic reflection-reducing film 323 is trimmed can be controlled with ease, and the etching step can be subsequently executed on the silicon oxide film 322 practically without changing the trimmed line width at all.

[0067] Wafers having a diameter of 200 mm were each etched under the following conditions through the steps described above. In addition, the etching step was executed a plurality of times by varying the flow rate ratio (O₂ flow rate/(CF₄+O₂) flow rate) in order to ascertain how the trimming quantity changed as the flow rate ratio of the O₂ gas relative to the total flow rate of the etching gas (CF₄+O₂) changed.

[0068] The organic reflection-reducing film was etched under the following conditions.

[0069] Etching gas: CF₄+O₂ (total flow rate 40 sccm)

[0070] Pressure: 0.67 Pa (5 mTorr)

[0071] High-frequency power applied to the upper electrode: 300 W

[0072] High-frequency power applied to the lower electrode: 60 W

[0073] Distance between the electrodes: 140 mm

[0074] Temperatures at top/wall/bottom: 80/60/75° C.

[0075] He gas pressure (center/edge): 400/400 Pa (3 Torr)

[0076] over-etching: 10%

[0077] The silicon oxide film was etched under the following conditions.

[0078] Etching gas: CF₄ (flow rate 20 sccm)+CHF₃ (flow rate 20 sccm)

[0079] Pressure: 5.3 Pa (40 mTorr)

[0080] High-frequency power applied to the upper electrode: 600 W

[0081] High-frequency power applied to the lower electrode: 100 W

[0082] Distance between the electrodes: 140 mm

[0083] Temperatures at top/wall/bottom: 80/30/65° C.

[0084] He gas pressure (center/edge): 1300/1300 Pa (10 Torr)

[0085] over-etching: 10%

[0086] The results of control on the trimming quantity are shown in FIG. 4. The graph presented in FIG. 4 indicates the relationship between the trimming quantity (nm) which is indicated along the vertical axis and the flow rate ratio (O₂ flow rate/(CF₄+O₂) flow rate; %) which is indicated along the horizontal axis. The triangles in the figure each indicate the results of the actual etching processes executed as described above. It is to be noted that the level of the high-frequency power (the RF power density) applied to the lower electrode per unit area was 0.19 w/cm². It was learned that a substantially linear change in the trimming quantity could be achieved by changing the flow rate ratio (O₂ flow rate/(CF₄+O₂) flow rate), as shown in the figure.

[0087] Next, formation of a desired pattern on the wafer achieved by controlling the mask trimming quantity with the process control system according to the present invention based upon the substantially linear change in the trimming quantity resulting from a change in the flow rate ratio (O₂ flow rate/(CF₄+O₂) flow rate) is explained in reference to FIG. 5. FIG. 5 presents a flowchart of the processing condition adjustment processing executed by the process control device 150.

[0088] First, the pattern shape of the pattern on the wafer which has not yet undergone the processing is measured in step S 100. Namely, the wafer with the organic reflection-reducing film 323 still unetched is transferred to the measuring apparatus 130 via the transfer path 140, and the measuring apparatus 130 measures the line width d shown in FIG. 3A. After the measuring apparatus 130 finishes the measuring operation, the process control device 150 receives the measurement value from the measuring apparatus 130.

[0089] In response, the process control device 150 may determine an optimal condition with regard to the flow rate ratio based upon the relationship between the trimming quantity and the flow rate ratio shown in FIG. 4 which is stored in memory in advance, in correspondence to the difference between the pre-etching measurement value having been received and a target value and transmit information indicating the optimal processing condition to the processing apparatus 120 (step S 110). For instance, if the pre-etching measurement value is 80 nm and the target line width to be achieved through the etching processes is 50 nm, i.e., if the target trimming quantity is −30 nm, the process control device 150 can determine the flow rate ratio condition of 50% based upon the relationship between the trimming quantity and the flow rate ratio shown in FIG. 4 which is stored in memory in advance and transmit information indicating this optimal processing condition to the processing apparatus 120.

[0090] Once the pre-etching measurement is completed, the wafer is transferred to the processing apparatus 120 via the transfer path 140 and the processing apparatus 120 etches the organic reflection-reducing film 323 under the optimal processing condition.

[0091] Next, the pattern shape after the processing is measured in step S 120. Namely, after the processing apparatus 120 etches the organic reflection-reducing film 323 on the wafer is again transferred to the measuring apparatus 130 which then measures the line width d′ shown in FIG. 3B and transmits data indicating the measurement value.

[0092] In step S 130, the difference between the values indicating the line width measured before and after the processing is calculated in step S 130. Namely, the difference (e.g., d′−d) between the line widths measured before and after etching the organic reflection-reducing film 323 is calculated. This difference between the measurement values represents the trimming quantity.

[0093] In the following step S 140, a decision is made as to whether or not the error of the difference between the measurement values, i.e., the trimming quantity, relative to the target value (the target trimming quantity) is equal to or greater than a specific value. If it is decided in step S 140 that the error of the difference between the measurement values (the trimming quantity) relative to the target value is not equal to or greater than the predetermined value, the processing ends.

[0094] If, on the other hand, it is decided in step S 140 that the error of the difference between the measurement values (the trimming quantity) relative to the target value is equal to or greater than the predetermined value, the self-diagnosis unit 132 of the measuring apparatus 130 is engaged in operation in step S 150 to execute a self-diagnosis on the measuring apparatus 130 and a decision is made in step S 160 as to whether or not any abnormality has occurred in the measuring apparatus 130 itself.

[0095] If it is decided in step S 160 that no abnormality has occurred in the measuring apparatus 130 and wafers with substantially equal pre-etching pattern shape measurement values which are measured by the measuring apparatus 130 are to be continuously processed, the processing condition for the etching apparatus 201 constituting the processing apparatus 120 are adjusted in step S 170. More specifically, based upon the relationship between the trimming quantity and the flow rate ratio (O₂ flow rate/(CF₄+O₂) flow rate) shown in FIG. 4, the flow rate ratio (O₂ flow rate/(CF₄+O₂) flow rate) is adjusted in correspondence to the error. As a result, the trimming quantity is controlled to achieve a value closer to the target value if there has been an error equal to or greater than the predetermined value manifesting between the trimming quantity and the target value.

[0096] It is to be noted that the state of the fluctuation of the error in the difference between the two measurement values relative to the target value may be observed so as to predict the tendency of the fluctuation and in such a case, the processing condition set for the processing apparatus may be adjusted in conformance to the tendency of the fluctuation error before the error actually exceeds the predetermined value. For instance, if the tendency indicates a gradual increase in the error, the processing condition may be gradually adjusted in correspondence to the tendency, whereas if the tendency indicates a significant increase in the error, the control may be implemented to adjust the processing condition by a greater extent in correspondence to the tendency. By adjusting the processing condition in advance in this manner, control is achieved to ensure that the error never exceeds the predetermined value.

[0097] If, on the other hand, it is decided in step S 160 that an abnormality has occurred in the measuring apparatus 130, error processing is executed in step S 180. The process control device 150 engages the means for warning to issue a warning that an abnormality has occurred in the measuring apparatus 130 or engages the means for display to bring up an error display, for instance, as the error processing.

[0098] As described above, if there is an abnormality in the measuring apparatus 130 itself, the processing condition set for the etching apparatus 201 is not adjusted, since accurate control cannot be achieved even by adjusting the processing condition in the event of an error in the measuring apparatus 130 itself.

[0099] It is to be noted that while the processing in step S 160 and step S 180 is not essential in the processing shown in FIG. 5, the processing in step S 160 and step S 180 prevents any abnormality having occurred in the measuring apparatus 130 from adversely affecting the process control to ensure even more accurate control. In addition, while the measuring apparatus 130 executes the measuring operation both before and after the processing in the flowchart presented in FIG. 5, the present invention is not limited to this example and the measuring operation may be executed only after the processing. For instance, when the processing is executed continuously on successive wafers, the measurement value obtained after the immediately preceding wafer may be stored in memory and the difference between the measurement value stored in memory and the measurement value obtained after processing the current wafer may be calculated.

[0100] By providing a measuring apparatus 130 in each bay 110 as described above, the process control device 150 in the bay is enabled to reset the processing conditions for the processing apparatuses based upon the results of measuring operations executed by the measuring apparatus 130 to measure the shapes of the patterns on wafers processed by the processing apparatuses 120, 122, 124 . . . . As a result, accurate process control is assured at all times in each bay.

[0101] In addition, a necessary measuring operation can be executed by the measuring apparatus installed in each bay 110 whenever the need arises in the area. As a result, workpieces are not left in a measurement wait state to wait in standby before they can be measured by the measuring apparatus 130 or left in a transfer wait state. In addition, the length of time to elapse between the processing and the measuring operation can be reduced. Thus, the operating rate of each processing apparatus can be improved. Furthermore, since only a measuring instrument that is required to enable the process control in a given area needs to be mounted at the measuring apparatus 130, the equipment investment cost can be lowered.

[0102] Also, by providing a measuring apparatus 130 in each bay 110 and controlling the processing executed in the bay with the corresponding process control device 150, the quality of the processed wafers, which eventually become products, indicated by the line width of the pattern formed on the wafers, the film thickness, the dope quantity, the film density and the degree of stress and the distribution state within the wafers can be automatically measured by the measuring apparatus 130 to determine whether or not the wafers have been processed within target specification ranges, instead of using separate wafers for the inspection and the analysis. By implementing the control described above, it becomes possible to adjust the processing conditions so as to correct any significant error relative to the target value. Since such a correction is enabled, optimal processing conditions can be set at all times even when the states of workpieces are not consistent or the state of a given processing apparatus changes somewhat and, as a result, the processing can be executed to meet even the most rigorous design specifications. Furthermore, workpieces can be processed to become products while they are individually measured by the measuring apparatus 130, and the measuring operation can be executed on a specific lot alone or on all the wafers.

[0103] Next, the second embodiment of the present invention is explained in reference to the drawings. In this embodiment, the process control device 150 generates a model expression for predicting the results of the processing executed by the processing apparatuses 120, 122, 124 . . . through a multivariate analysis and implements the process control based upon the model expression.

[0104] The processing apparatuses 120 in the embodiment are each identical to the etching apparatus 201 shown in FIG. 2. In addition, the process control device 150 includes a means for multivariate analysis 400 in the embodiment.

[0105] As shown in FIG. 6, the means for multivariate analysis 400 includes an operation data storage unit 410, a processing result data storage unit 420, a multivariate analysis program storage unit 430, a multivariate analysis processing unit 440 and a multivariate analysis result storage unit 450.

[0106] The operation data storage unit 410 constitutes a means for storing it in memory operation data, whereas the processing result data storage unit 420 constitutes a means for storing in memory processing result data. The multivariate analysis processing unit 440 constitutes both a means for ascertaining the correlation (e.g., a predictive expression or a recurrence expression) between the operation data and the processing result data and a means for predicting the processing results based upon the correlation. The multivariate analysis result storage unit 450 constitutes a means for storing in memory the correlation determined by the multivariate analysis processing unit 440.

[0107] In more specific terms, the means for multivariate analysis 400 may be constituted of a microprocessor or the like that engages in operation in conformance to a program read out from the multivariate analysis program storage unit 430. In addition, the microprocessor constituting the process control device 150 may be utilized as the means for multivariate analysis 400 to execute the multivariate analysis processing. The operation data storage unit 410, the processing result data storage unit 420 and the multivariate analysis result storage unit 450 may each be constituted of a means for recording such as a memory installed in the process control device 150, or they may be constituted by allocating corresponding memory areas at a means for recording such as a hard disk.

[0108] After the means for multivariate analysis 400 stores the operation data and process characteristics data input thereto into the operation data storage unit 410 and the processing result data storage unit 420 respectively, it reads out the data and a program stored in the multivariate analysis program storage unit 430 into the multivariate analysis processing unit 440. The operation data and the process characteristics data undergo a multivariate analysis at the multivariate analysis processing unit 440, and the results of the multivariate analysis processing are stored into the multivariate analysis result storage unit 450.

[0109] More specifically, the means for multivariate analysis 400 obtains relational expression (1) below (a predictive expression such as a recurrence expression, a model) in which a plurality of types of operation data represent explanatory variable quantities (relating variables) and the processing result data represent related variable quantities (target variable quantities or target variables) by using the multivariate analysis program. In the recurrence expression presented in (1) below, X indicates a matrix of the explanatory variable quantities and Y indicates a matrix of the related variable quantities. In addition, B indicates a recurrent matrix constituted of coefficients (weights) set for the relating variable quantities and E represents a residual matrix.

Y=BX+E (1)

[0110] Expression (1) above may be defined through, for instance, the PLS (partial least squares) method described in the JOURNAL OF CHEMOMETRICS, vol. 2 (pp211 ˜228) (1998). By adopting the PLS method, a relational expression for matrices X and Y can be ascertained as long as small numbers of measurement values for X and Y are available even when the matrices X and Y include numerous relating variable quantities and related variable quantities. A marked advantage to the PLS method is that even a relational expression defined based upon a small number of measurement values assures a high degree of stability and reliability.

[0111] A program for executing the multivariate analysis processing through the PLS method is stored in the multivariate analysis program storage unit 430, the operation data and the process characteristics data are processed at the multivariate analysis processing unit 440 through the sequence of the program to obtain expression (1) and the results of the multivariate analysis processing are stored into the multivariate analysis result storage unit 450. As a result, once expression (1) is defined, process characteristics can be predicted by applying subsequent operation data in the matrix X as relating variable quantities in the second embodiment. The predictive value thus obtained is highly reliable.

[0112] The means for multivariate analysis 400 executes a multivariate analysis by using trace data constituted of measurement data obtained at various monitors (such as various types of measuring instruments) during the actual operation which include gas flow rate measurement data such as the data indicating the flow rate ratio (O₂ flow rate/(CF₄+O₂) flow rate) described earlier and by using pattern measurement values including the trimming quantity of the mask (e.g., an organic reflection-reducing film) formed on the wafer as the processing result data to predict the mask trimming quantity. It is to be noted that instead of the trace data, data indicating various types of operating condition settings including gas flow rate setting data may be used as the operation data.

[0113] In addition to the gas flow rate measurement data, data obtained by measuring the temperatures at a plurality of points (an upper electrode temperature T1, a wall surface temperature T2, a lower electrode temperature T3) inside the chamber 202 may be used as the trace data. The following data may also be incorporated as the trace data.

[0114] For instance, an APC (auto pressure controller) valve may be provided at the evacuation device 235 shown in FIG. 2 so as to automatically control the degree of openness of the APC valve in correspondence to the gas pressure inside the chamber 202. The degree of APC opening at the APC valve may then be detected to be incorporated in the trace data.

[0115] In addition, a power meter that detects the current and the voltage applied to the electrostatic chuck 211 may be provided so as to incorporate the data indicating the current and the voltage applied to the electrostatic chuck 211 which are detected by the power meter into the trace data.

[0116] Also, a mass flow controller, for instance, may be installed in the gas passage 214, through which the heat transfer medium (e.g., He gas) is supplied, to detect the gas flow rate of the heat transfer gas with the mass flow controller. Together with data indicating the gas pressure of the heat transfer gas detected by a pressure gauge, the data indicating the heat transfer gas flow rate may then be incorporated into the trace data.

[0117] The matchers 241 and 251 may each comprise two internal variable capacitors and a coil to achieve impedance matching via the variable capacitors C 1 and C 2. Data indicating the positions of the variable capacitors C 1 and C 2 in the impedance matched state may be included in the trace data as well. Furthermore, a power meter may be provided at the matcher 241 or 251 to measure the voltage Vdc between the high-frequency power supply line (electric wire) and the ground of the etching apparatus 201 with the power meter. Data indicating the voltage Vdc between the high-frequency power supply line (electric wire) and the ground may be incorporated into the trace data.

[0118] An electric measuring instrument (e.g., a VI probe) may be installed at the matcher 241 on the side toward the upper electrode 221 or at the matcher 251 on the side either toward the susceptor (the lower electrode) 205 i.e., the high-frequency voltage output side, to detect, via the electric measuring instrument, high-frequency voltages V, high-frequency currents I, high-frequency phases P and impedances Z of the fundamental waves (the advancing wave and the reflected wave of the high-frequency power) and the higher harmonic wave attributable to the plasma generated by the high-frequency power P applied to the upper electrode 221 or the susceptor (the lower electrode) 205 as electrical data. The electrical data corresponding to the advancing wave and the reflected wave of the high-frequency power may then be incorporated into the trace data.

[0119] An integrating unit that totals the accumulated length of time over which the high-frequency power has been applied may be connected between the high-frequency source 250 and a power meter, and the accumulated length of high-frequency power application detected by the integrating unit may be included in the trace data. The accumulated length of high-frequency power application time refers to the sum of the lengths of time the high-frequency power has been applied to process individual wafers W.

[0120] It is to be noted that the integrating unit mentioned above resets the accumulated length of high-frequency power application to 0 every time the etching apparatus 201 undergoes maintenance work. Accordingly, the accumulated length of high-frequency power application time in this context refers to the accumulated application time for a given maintenance cycle. During the maintenance work, wet cleaning may be performed to remove byproducts (such as particles) of the etching processes executed in the etching apparatus 201 and consumables and measuring instruments may be replaced.

[0121] The means for multivariate analysis 400 described above ascertains the relational expression (a recurrence expression) presented in (1) with a multivariate analysis program that enables a multivariate analysis through, for instance, the PLS method by using the trace data or the setting data, i.e., the operation data as explanatory variables and the mask trimming quantity indicated by the pattern measurement values (the difference between the line width d and the line width d′ in FIG. 3) constituting the processing result data as a related variable (a target variable). Then, it predicts the subsequent mask trimming quantity by applying new operation data in the recurrence expression thus ascertained.

[0122] In addition, prior to executing the multivariate analysis including the calculation of the relational expression (a recurrence expression) in (1), the multivariate analysis processing unit 440 may execute preliminary processing on the operation data and the processing result data such as MSC (multiplicative signal correction). Such MSC preliminary processing is normally executed to minimize the variance among samples by obtaining an ideal spectrum from the samples. Specifically, in the MSC preliminary processing, an average (ideal spectrum) is calculated along the wavelength for each sample and a linear regression line is calculated for the ideal spectrum in correspondence to the sample. Then, using the inclination and a section obtained from the linear regression line, the data of the sample are corrected. It is to be noted that details of the MSC preliminary processing are provided in, for instance, in Gelad, et al., (1985), Linearization and Scatter-infrared Reflectance Spectra of Meat, Applied Spectroscopy, 3,491-500.

[0123] Next, the operation of the etching apparatus 201 is explained. As the etching apparatus 201 starts operating, detection data indicating values intermittently detected with the various measuring instruments such as those mounted at the matchers 241 and 251 at the etching apparatus 201 are sequentially input to the means for multivariate analysis 400 of the process control device 150. Then, the average values are calculated each in correspondence to a specific type of operation data on individual wafers via the multivariate analysis processing unit 440. Next, the average values of the various types of operation data on the individual wafers are stored into the operation data storage unit 410, or the operation waits in standby for the next processing without storing the average values.

[0124] A wafer having undergone the etching process is then taken out of the etching apparatus 201 and is transferred to the measuring apparatus 130 via the transfer path 140. The measuring apparatus 130, in turn, calculates the mask trimming quantity for the wafer having undergone the etching processes. In more specific terms, the difference between the line width d shown in FIG. 3A having been measured by the measuring apparatus 130 prior to the etching processes and the line width d′ shown in FIG. 3B measured by the measuring apparatus 130 following the etching processes is calculated as the trimming quantity. After the trimming quantity calculated by the measuring apparatus 130 is input to the means for multivariate analysis 400 of the process control device 150, the input value is stored into the processing result data storage unit 420 as processing result data. Then, a recurrence expression (the relational expression in (1)) is defined through the PLS method by directly using the data without executing any preliminary processing or by using the data having undergone the preliminary processing described earlier.

[0125] When the etching apparatus 201 is engaged in the actual etching processes, the means for multivariate analysis 400 at the process control device 150 uses the trace data intermittently detected at the various measuring instruments or the setting data, which are input to the process control device 150 as relating variables to calculate a predictive value for the trimming quantity, i.e., the target variable, with the recurrence expression obtained through the PLS method as explained earlier.

[0126] Next, model expression update processing executed in the process control system in the embodiment to update the recurrence expression (model expression) defined through the PLS method is explained in reference to the drawings. FIG. 5 presents a flowchart of the model expression update processing executed by the process control device 150.

[0127] First, the pattern shape of a wafer that has not undergone the processing is measured in step S 200. Namely, a wafer with its organic reflection-reducing film 323 still unetched is transferred to the measuring apparatus 130 via the transfer path 140 and the measuring apparatus 130 measures the line width d shown in FIG. 3A. Once the measuring apparatus 130 completes the measuring operation, the process control device 150 receives the measurement value from the measuring apparatus 130.

[0128] Subsequently, an optimal condition for, at least, the flow rate ratio that greatly affects the trimming quantity may be determined based upon the correlation between the trimming quantity and various types of setting data including the flow rate ratio stored in advance in the multivariate analysis result storage unit 450 and the optimal condition thus determined may be transmitted to the processing apparatus 120 (step S 210).

[0129] Once the pre-etching measurement is completed, the wafer is transferred to the processing apparatus 120 via the transfer path 140 and the processing apparatus 120 etches the organic reflection-reducing film 323 under the optimal processing condition.

[0130] Next, the pattern shape after the processing is measured in step S 220. Namely, after the processing apparatus 120 etches the organic reflection-reducing film 323 on the wafer, the wafer is again transferred to the measuring apparatus 130 which then measures the line width d′ shown in FIG. 3B and transmits data indicating the measurement value to the process control device 150.

[0131] In step S 230, the difference between the values indicating the line width measured before and after the processing is calculated in step S 230. Namely, the difference (e.g., d′−d) in between the line widths measured before and etching the organic reflection-reducing film 323 is calculated. This difference between the measurement values represents the trimming quantity.

[0132] In the following step S 240, a decision is made as to whether or not the error of the difference between the measurement values, i.e., the trimming quantity relative to the predictive value for the trimming quantity calculated by the means for multivariate analysis 400 is equal to or greater than a specific value. If it is decided in step S 240 that the error of the difference between the measurement values (the trimming quantity) relative to the predictive value is not equal to or greater than the predetermined value, the processing ends.

[0133] If, on the other hand, it is decided in step S 240 that the error of the difference between the measurement values (the trimming quantity) relative to the predictive value is equal to or greater than the predetermined value, the self-diagnosis unit 132 of the measuring apparatus 130 is engaged in operation in step S 250 to execute a self-diagnosis on the measuring apparatus 130 and a decision is made in step S 260 as to whether or not any abnormality has occurred in the measuring apparatus 130.

[0134] If it is decided in step S 260 that no abnormality has occurred in the measuring apparatus 130, the means for multivariate analysis 400 regenerates a model expression to update the initial model expression in step S 270. Thus, after the initial model expression (recurrence expression) is obtained through the PLS method, the model expression (recurrence expression) is updated by automatically generating a new model expression if the wafer processing results greatly deviate from the predictive value and, as a result, the accuracy of the prediction can be maintained at a high level at all times.

[0135] It is to be noted that the state of the fluctuation of the error in the difference between the measurement values relative to the predictive value may be observed so as to predict the tendency of the fluctuation and in such a case, the processing condition set for the processing apparatus may be adjusted in conformance to the tendency of the fluctuation error before the error actually exceeds the predetermined value. For instance, if the tendency indicates a gradual increase in the error, the processing condition may be gradually adjusted in correspondence to the tendency, whereas if the tendency indicates a significant increase in the error, the control may be implemented to adjust the processing condition by a greater extent in correspondence to the tendency. By adjusting the processing condition in advance in this manner, control is achieved to ensure that the error never exceeds the predetermined value.

[0136] If, on the other hand, it is decided in step S 260 that an abnormality has occurred in the measuring apparatus 130, error processing is executed in step S 280. The process control device 150 engages the means for warning to issue a warning that an abnormality has occurred in the measuring apparatus 130 or engages the means for display to bring up an error display, for instance, as the error processing. It is to be noted that while the processing in step S 260 and step S 280 is not essential in the processing shown in FIG. 7, the processing in step S 260 and step S 280 prevents any abnormality having occurred in the measuring apparatus 130 from adversely affecting the correlation (model expression) to ensure even more accurate prediction, as in the first embodiment. In addition, while the measuring apparatus 130 executes the measuring operation both before and after the processing in the flowchart presented in FIG. 7 as in the flowchart in FIG. 5, too, the present invention is not limited to this example and the measuring operation may be executed only after the processing. For instance, when the processing is executed continuously on successive wafers, the measurement value obtained after processing the immediately proceeding wafer may be stored in memory and the difference between the measurement value stored in memory and the measurement value obtained after processing the current wafer may be calculated.

[0137] By providing the measuring apparatus 130 in each bay 110 as described above, the process control device 150 in the bay is enabled to regenerate the model expression for the processing apparatuses based upon the results of measuring operations executed by the measuring apparatus 130 to measure the shapes of the patterns on wafers proc