Method for creating reference spectrum library used for estimation of film thickness of work-piece

Abstract

To provide a reference spectrum library creation method that can improve correctness of a plurality of film thicknesses corresponding to a plurality of reference spectra.SOLUTION: A reference spectrum library creation method generates a plurality of reference spectra of reflectance from a reference work-piece obtained at a plurality of polishing times during polishing of the reference work-piece, calculates a plurality of polishing index values indicating progress of polishing of the reference work-piece from the plurality of reference spectra, determines a polishing rate line indicating a relationship between a film thickness and a polishing time of the reference work-piece from an initial film thickness of the reference work-piece, the plurality of polishing index values, and a final film thickness of the reference work-piece, determines a plurality of film thicknesses corresponding to the plurality of polishing index value on the basis of the polishing rate line, and associates the plurality of reference film thicknesses with the plurality of reference spectra, thereby creating a reference spectrum library.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a method for creating a reference spectral library for use in estimating film thickness on a workpiece such as a wafer or substrate, and more particularly to a method for creating a reference spectral library containing a plurality of reference spectra that are compared with a measured spectrum of light reflected from the workpiece. [Background technology]

[0002] The optical film thickness measurement device is configured to generate a measurement spectrum of light reflected from a wafer, determine a reference spectrum from a reference spectrum library whose shape is closest to the measurement spectrum, and determine a film thickness pre-associated with the determined reference spectrum. Figure 17 is a diagram illustrating the process of determining a film thickness by comparing the measurement spectrum with multiple reference spectra. The optical film thickness measurement device compares the measurement spectrum generated during polishing of a workpiece with multiple reference spectra prepared in advance, determines the reference spectrum whose shape is closest to the measurement spectrum, and determines a film thickness pre-associated with the determined reference spectrum. The reference spectrum whose shape is closest to the measurement spectrum is the spectrum whose shape difference between the reference spectrum and the measurement spectrum is the smallest.

[0003] The multiple reference spectra are obtained by pre-polishing a reference wafer having the same surface structure as the wafer to be polished. Each reference spectrum is associated with the film thickness at the time the reference spectrum was obtained. That is, the multiple reference spectra were obtained when the film thickness of the reference wafer was different, and the multiple reference spectra correspond to multiple different film thicknesses. Therefore, by identifying the reference spectrum whose shape most closely resembles the measured spectrum, the current film thickness of the wafer can be estimated.

[0004] An example of a process for acquiring multiple reference spectra and corresponding film thicknesses will be described. First, a reference wafer having the same surface structure as the wafer to be polished is prepared. The reference wafer is transferred to a film thickness measuring instrument, where the initial film thickness Tini of the reference wafer is measured. Next, the reference wafer is transferred to a polishing apparatus, where the reference wafer is polished. While the reference wafer is being polished, light is irradiated onto the surface of the reference wafer, and a spectrum of the reflected light from the reference wafer (i.e., a reference spectrum) is generated. The reference spectrum is generated periodically while the reference wafer is being polished. Therefore, while the reference wafer is being polished, multiple reference spectra are acquired as the film thickness decreases. After polishing of the reference wafer is completed, the reference wafer is transferred back to the film thickness measuring instrument, where the film thickness of the polished reference wafer (i.e., the final film thickness Tfin) is measured.

[0005] Figure 18 is a graph showing the relationship between the film thickness of a reference wafer and polishing time. When the polishing rate (also called the removal rate) of the reference wafer is constant, as shown in Figure 18, the film thickness decreases linearly with polishing time from the initial film thickness Tini to the final film thickness Tfin. In other words, the film thickness can be expressed by a linear function that includes polishing time as a variable. The polishing rate can be calculated by dividing the difference between the initial film thickness Tini and the final film thickness Tfin by the difference between the polishing time tfin at the final film thickness Tfin and the polishing time tini at the initial film thickness Tini (polishing rate = [Tini - Tfin] / [tfin - tini]).

[0006] The times t1, t2, . . . , tn at which multiple reference spectra are generated are within the range from polishing time tini to polishing time tfin. The film thicknesses corresponding to the reference spectra can be calculated from the initial film thickness Tini, the final film thickness Tfin, and the times t1 to tn at which the reference spectra were generated. For example, the film thickness corresponding to the reference spectrum generated at time t2 can be calculated using the following formula: Tini-[Tini-Tfin]·[[t2-tini] / [tfin-tini]]

[0007] In this way, multiple reference spectra corresponding to different film thicknesses are obtained. Each reference spectrum is associated with (linked to) a corresponding film thickness. By identifying the reference spectrum whose shape is closest to the measured spectrum during wafer polishing, the optical film thickness measurement device can estimate the current film thickness of the wafer from the film thickness associated with that reference spectrum. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2015 / 163164 [Patent Document 2] Japanese Patent Application Publication No. 2022-156879 Summary of the Invention [Problem to be solved by the invention]

[0009] In the conventional film thickness estimation described above, the polishing rate of the reference wafer is assumed to be constant, as shown in Fig. 18. However, the actual polishing rate of the reference wafer may not be constant, as shown in Fig. 19. Therefore, the multiple film thicknesses corresponding to the multiple reference spectra may differ from the actual film thickness of the reference wafer, resulting in a decrease in the accuracy of wafer film thickness estimation.

[0010] Therefore, the present invention provides a method for creating a reference spectrum library that can improve the accuracy of a plurality of film thicknesses corresponding to a plurality of reference spectra. [Means for solving the problem]

[0011] In one aspect, there is provided a method for creating a reference spectral library used to estimate a film thickness of a workpiece, the method comprising: measuring an initial film thickness of a reference workpiece before polishing; polishing the reference workpiece with a polishing apparatus; generating a plurality of reference spectra of reflected light from the reference workpiece obtained at a plurality of polishing times during polishing of the reference workpiece; measuring a final film thickness of the reference workpiece after polishing the reference workpiece; calculating a plurality of polishing index values ​​indicating progress of polishing of the reference workpiece from the plurality of reference spectra; determining a polishing rate line indicating a relationship between the film thickness of the reference workpiece and polishing time from the initial film thickness, the plurality of polishing index values, and the final film thickness; determining a plurality of reference film thicknesses corresponding to the plurality of polishing index values ​​based on the polishing rate line; and associating the plurality of reference film thicknesses with the plurality of reference spectra, thereby creating a reference spectral library.

[0012] In one embodiment, calculating the plurality of polishing index values ​​includes calculating a plurality of change amounts between the plurality of reference spectra, each change amount being two change amounts adjacent in time among the plurality of reference spectra, and calculating the plurality of polishing index values ​​by accumulating the plurality of change amounts one by one that are arranged according to the polishing time of the reference workpiece. In one embodiment, determining the polishing rate line includes calculating a tentative polishing rate line from the initial film thickness and the final film thickness when it is assumed that the polishing rate of the reference workpiece is constant, and determining the polishing rate line by correcting the tentative polishing rate line based on changes in the plurality of polishing index values ​​with polishing time. In one embodiment, the calculation of the plurality of polishing index values ​​includes calculating a plurality of tentative film thicknesses of the reference workpiece when the polishing rate of the reference workpiece is assumed to be constant from the initial film thickness, the final film thickness, and the plurality of polishing times, and performing principal component analysis on each of the plurality of reference spectra to obtain a plurality of principal components including a first principal component to a k-th principal component (k is a natural number of 2 or more) for each reference spectrum, classifying the plurality of principal components obtained for the plurality of reference spectra into a plurality of groups of the first principal component to the k-th principal component, and classifying a plurality of principal components included in each of the plurality of groups. The method includes: determining a plurality of correlation coefficients corresponding to the plurality of groups by calculating correlation coefficients between principal components and the plurality of temporary film thicknesses; determining a first group having the largest absolute value of the correlation coefficient and a second group having the second largest absolute value of the correlation coefficient among the plurality of correlation coefficients; arranging the plurality of principal components included in the first group on a first coordinate axis of a coordinate system; arranging the plurality of principal components included in the second group on a second coordinate axis of the coordinate system; and determining the plurality of polishing index values, which are a plurality of data points identified from the plurality of principal components on the first coordinate axis and the plurality of principal components on the second coordinate axis.

[0013] In one aspect, there is provided a method for creating a reference spectral library used to estimate film thickness of a workpiece, the method comprising: measuring an initial film thickness of a reference workpiece before polishing; polishing the reference workpiece with a polishing device; generating a plurality of reference spectra of reflected light from the reference workpiece obtained at a plurality of polishing times during polishing of the reference workpiece; measuring an intermediate film thickness of the reference workpiece at least once during polishing of the reference workpiece; measuring a final film thickness of the reference workpiece after polishing of the reference workpiece; determining a polishing rate line indicating the relationship between the film thickness of the reference workpiece and polishing time from the initial film thickness, the intermediate film thickness, and the final film thickness; determining a plurality of reference film thicknesses at the plurality of polishing times from the polishing rate line; and associating the reference film thicknesses with the plurality of reference spectra to create a reference spectral library. [Effects of the Invention]

[0014] According to the above aspect, the reference spectrum is generated from light reflected from the reference workpiece during polishing. Therefore, the polishing index values ​​calculated from the reference spectra reflect the progress of polishing the reference workpiece. The polishing rate line determined from the initial film thickness, the polishing index values, and the final film thickness reflects changes in the actual polishing rate of the reference workpiece. Therefore, the accuracy of the reference film thicknesses determined using the polishing rate line can be improved.

[0015] According to the above aspect, the polishing rate line is created based on a plurality of measurements of the film thickness of the reference workpiece, thereby improving the accuracy of the plurality of reference film thicknesses determined using the polishing rate line. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram illustrating an embodiment of a polishing apparatus. [Figure 2] FIG. 2 is a cross-sectional view showing a detailed configuration of the optical film thickness measurement device. [Figure 3] FIG. 4 is a schematic diagram showing an example of a measured spectrum generated from light intensity measurement data. [Figure 4] FIG. 1 is a schematic diagram illustrating one embodiment of a workpiece processing system including a polishing apparatus and a film thickness measurement apparatus used in a method for creating a reference spectral library. [Figure 5] 1 is a graph showing two temporally adjacent reference spectra. [Figure 6] 10 is a graph showing the amount of change in the reference spectrum calculated for each unit time during the polishing time of the reference workpiece. [Figure 7] 10 is a graph showing a plurality of polishing index values ​​calculated by integrating a plurality of amounts of change in a reference spectrum one by one. [Figure 8] 10 is a graph showing an example of a provisional polishing rate line when the polishing rate of a reference workpiece is assumed to be constant. [Figure 9]FIG. 10 is a diagram illustrating a process of determining a polishing rate line by correcting a temporary polishing rate line based on changes in a plurality of polishing index values ​​with respect to polishing time. [Figure 10] 1 is a flow chart illustrating one embodiment of a method for creating a reference spectral library. [Figure 11] FIG. 10 is a diagram showing an example of a plurality of polishing index values ​​identified from a plurality of first principal components and a plurality of second principal components. [Figure 12] FIG. 10 is a diagram illustrating a process of determining a polishing rate line by correcting a temporary polishing rate line based on changes in a plurality of polishing index values ​​with respect to polishing time. [Figure 13] 1 is a flow chart illustrating one embodiment of a method for creating a reference spectral library. [Figure 14] 1 is a flowchart illustrating the embodiment. [Figure 15] 1 is a graph showing an example of a polishing rate line indicating the relationship between the film thickness of a reference workpiece and polishing time. [Figure 16] 1 is a flow chart illustrating one embodiment of a method for creating a reference spectral library. [Figure 17] FIG. 10 is a diagram illustrating a process for determining a film thickness from a comparison of a measured spectrum with multiple reference spectra. [Figure 18] 10 is a graph showing the relationship between film thickness and polishing time of a reference wafer. [Figure 19] 10 is a graph showing an example in which the polishing rate of a reference wafer is not constant. DETAILED DESCRIPTION OF THE INVENTION

[0017] Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram illustrating one embodiment of a polishing apparatus. As shown in FIG. 1, a polishing apparatus 100 includes a polishing table 3 supporting a polishing pad 2, a polishing head 1 pressing a workpiece W against the polishing pad 2, a table motor 6 rotating the polishing table 3, a polishing liquid supply nozzle 5 for supplying a polishing liquid such as slurry onto the polishing pad 2, and an operation control unit 9 for controlling the operation of the polishing apparatus 100. The upper surface of the polishing pad 2 forms a polishing surface 2a for polishing the workpiece W. The workpiece W has a film on its surface that forms an interconnect structure. Examples of the workpiece W include wafers, substrates, wiring boards, and square substrates used in the manufacture of semiconductor devices. In one example, the workpiece W is a product wafer on which a multilayer film is formed.

[0018] The polishing head 1 is connected to a head shaft 10, and the head shaft 10 is connected to a polishing head rotating device 15. The polishing head rotating device 15 is configured to rotate the polishing head 1 together with the head shaft 10 in the direction indicated by the arrow. The configuration of the polishing head rotating device 15 is not particularly limited, but in one example, the polishing head rotating device 15 includes an electric motor, a belt, a pulley, etc. The polishing table 3 is connected to a table motor 6, and the table motor 6 is configured to rotate the polishing table 3 and the polishing pad 2 in the direction indicated by the arrow. The polishing head 1, the polishing head rotating device 15, and the table motor 6 are connected to an operation control unit 9.

[0019] The workpiece W is polished as follows. The table motor 6 and polishing head rotating device 15 rotate the polishing table 3 and polishing head 1 in the directions indicated by the arrows in FIG. 1, while a polishing liquid is supplied from the polishing liquid supply nozzle 5 to the polishing surface 2a of the polishing pad 2 on the polishing table 3. While the workpiece W is rotated by the polishing head 1, the polishing head 1 presses the workpiece W against the polishing surface 2a of the polishing pad 2 with the polishing liquid present on the polishing pad 2. The surface of the workpiece W is polished by the chemical action of the polishing liquid and the mechanical action of the abrasive grains contained in the polishing liquid and / or the polishing pad 2.

[0020] The operation control unit 9 includes a storage device 9a storing a program and an arithmetic unit 9b that executes calculations according to instructions included in the program. The operation control unit 9 is composed of at least one computer. The storage device 9a includes a main storage device such as a random access memory (RAM) and an auxiliary storage device such as a hard disk drive (HDD) or a solid state drive (SSD). Examples of the arithmetic unit 9b include a CPU (central processing unit) and a GPU (graphics processing unit). However, the specific configuration of the operation control unit 9 is not limited to these examples.

[0021] The polishing apparatus 100 is equipped with an optical film thickness measuring device 20 that measures the film thickness of the workpiece W. The optical film thickness measuring device 20 is equipped with a light source 22 that emits light, an optical sensor head 25 that irradiates the workpiece W with the light from the light source 22 and receives the light reflected from the workpiece W, a spectrometer 27 connected to the optical sensor head 25, and a processing system 30 that determines the film thickness of the workpiece W based on the spectrum of the light reflected from the workpiece W. The optical sensor head 25 is disposed within the polishing table 3 and rotates together with the polishing table 3.

[0022] The processing system 30 includes a storage device 30a that stores a program and an arithmetic device 30b that executes calculations according to instructions included in the program. The processing system 30 is composed of at least one computer. The storage device 30a includes a main storage device such as a random access memory (RAM) and an auxiliary storage device such as a hard disk drive (HDD) or a solid state drive (SSD). Examples of the arithmetic device 30b include a CPU (central processing unit) and a GPU (graphics processing unit). However, the specific configuration of the processing system 30 is not limited to these examples.

[0023] Each of the operation control unit 9 and the processing system 30 may be configured with multiple computers. For example, each of the operation control unit 9 and the processing system 30 may be configured with a combination of an edge server and a cloud server. In one embodiment, the operation control unit 9 and the processing system 30 may be configured with a single computer.

[0024] 2 is a cross-sectional view showing the detailed configuration of the optical film thickness measurement device 20. The optical film thickness measurement device 20 includes a light-projecting fiber optic cable 31 connected to the light source 22 and a light-receiving fiber optic cable 32 connected to the spectrometer 27. The tip 31a of the light-projecting fiber optic cable 31 and the tip 32a of the light-receiving fiber optic cable 32 form the optical sensor head 25. That is, the light-projecting fiber optic cable 31 guides light emitted by the light source 22 to the workpiece W on the polishing pad 2, and the light-receiving fiber optic cable 32 receives the light reflected from the workpiece W and transmits it to the spectrometer 27.

[0025] The spectrometer 27 is connected to a processing system 30. The light-emitting fiber optic cable 31, the light-receiving fiber optic cable 32, the light source 22, and the spectrometer 27 are attached to the polishing table 3 and rotate integrally with the polishing table 3 and the polishing pad 2. The optical sensor head 25, which is composed of the tip 31a of the light-emitting fiber optic cable 31 and the tip 32a of the light-receiving fiber optic cable 32, is positioned facing the surface of the workpiece W on the polishing pad 2.

[0026] The optical sensor head 25 is positioned at a position where it crosses the surface of the workpiece W on the polishing pad 2 every time the polishing table 3 and polishing pad 2 make one rotation. The polishing pad 2 has a through hole 2b located above the optical sensor head 25. The optical sensor head 25 irradiates light onto the workpiece W through the through hole 2b every time the polishing table 3 makes one rotation, and receives reflected light from the workpiece W through the through hole 2b.

[0027] In one embodiment, a flow of pure water may be formed in the through hole 2b of the polishing pad 2 to prevent the polishing liquid and polishing debris from contacting the optical sensor head 25. Light is guided from the optical sensor head 25 through the pure water to the workpiece W, and the reflected light from the workpiece W passes through the pure water and is received by the optical sensor head 25. In another embodiment, a transparent window (not shown) may be fitted in the through hole 2b of the polishing pad 2. The transparent window is made of a material (e.g., transparent resin) that allows light to pass through. In this case, light is guided from the optical sensor head 25 to the workpiece W through the transparent window, and the reflected light from the workpiece W passes through the transparent window and is received by the optical sensor head 25.

[0028] The light source 22 is a flash light source that repeatedly emits light at short time intervals. An example of the light source 22 is a xenon flash lamp. The light source 22 is electrically connected to the operation control unit 9 and emits light in response to a trigger signal sent from the operation control unit 9. More specifically, while the optical sensor head 25 traverses the surface of the workpiece W on the polishing pad 2, the light source 22 receives multiple trigger signals and emits light multiple times. Therefore, with each rotation of the polishing table 3, light is irradiated onto multiple film thickness measurement points on the workpiece W, including the center point.

[0029] The light emitted by the light source 22 is transmitted to the optical sensor head 25. That is, the light is transmitted to the optical sensor head 25 through the light-emitting fiber optic cable 31 and emitted from the optical sensor head 25. The light passes through the through hole 2b of the polishing pad 2 and is incident on the workpiece W on the polishing pad 2. The light reflected from the workpiece W passes through the through hole 2b of the polishing pad 2 again and is received by the optical sensor head 25. The light reflected from the workpiece W is transmitted to the spectrometer 27 through the light-receiving fiber optic cable 32.

[0030] The spectrometer 27 is configured to separate the reflected light according to wavelength and measure the intensity of the reflected light at each wavelength over a predetermined wavelength range. That is, the spectrometer 27 separates the reflected light from the workpiece W according to wavelength and measures the intensity of the reflected light at each wavelength over a predetermined wavelength range to generate light intensity measurement data. The intensity of the reflected light at each wavelength may also be expressed as a relative value such as reflectance or relative reflectance. The light intensity measurement data is sent to the processing system 30.

[0031] The processing system 30 generates a spectrum of reflected light as shown in FIG. 3 from the light intensity measurement data. In the following description, the spectrum of reflected light from the workpiece W is referred to as the measured spectrum. The measured spectrum of reflected light from the workpiece W contains information about the film thickness of the workpiece W. In other words, the measured spectrum of reflected light varies depending on the film thickness of the workpiece W. The processing system 30 is configured to determine the film thickness of the workpiece W based on the measured spectrum of reflected light. More specifically, the processing system 30 determines a reference spectrum from a reference spectrum library that has a shape that is closest to the measured spectrum of reflected light, and determines the film thickness associated with this determined reference spectrum. The reference spectrum library is created in advance before polishing the workpiece W and stored in a storage device 30a of the processing system 30.

[0032] An embodiment of the method for creating a reference spectral library will now be described. Fig. 4 is a schematic diagram showing an embodiment of a workpiece processing system including a polishing apparatus 100 and a film thickness measurement apparatus 101 used in the method for creating a reference spectral library.

[0033] First, a reference workpiece is prepared that has the same surface structure as the workpiece W. More specifically, the reference workpiece has an exposed surface made of the same material as the workpiece W and has the same layer structure. Next, the reference workpiece is transported by the transport device 103 to the film thickness measuring device 101, and the film thickness measuring device 101 measures the initial film thickness, which is the film thickness of the reference workpiece before polishing.

[0034] The film thickness measurement system 101 irradiates a stationary reference workpiece with light, generates a spectrum of reflected light from the reference workpiece, and analyzes the spectrum to determine the film thickness of the reference workpiece. The basic film thickness measurement principle of the film thickness measurement system 101 is the same as that of the optical film thickness measurement system 20, but differs from the optical film thickness measurement system 20 in that it measures the film thickness of a stationary reference workpiece. The initial film thickness measurement value is sent from the film thickness measurement system 101 to the processing system 30.

[0035] After measuring the initial film thickness, the reference workpiece is transported by transport device 103 to polishing apparatus 100, where it is polished. Polishing of the reference workpiece is performed in the same manner as polishing of workpiece W. That is, table motor 6 and polishing head rotation device 15 rotate polishing table 3 and polishing head 1 in the directions indicated by the arrows in FIG. 1, while polishing liquid is supplied from polishing liquid supply nozzle 5 to polishing surface 2a of polishing pad 2 on polishing table 3. While the reference workpiece is rotated by polishing head 1, the polishing head 1 presses the reference workpiece against polishing surface 2a of polishing pad 2 with polishing liquid present on polishing pad 2, thereby polishing the surface of the reference workpiece.

[0036] During polishing of the reference workpiece, similarly to polishing of workpiece W, light is irradiated onto the reference workpiece from optical sensor head 25, and a spectrum of reflected light from the reference workpiece is generated. In the following description, the spectrum of reflected light from the reference workpiece is referred to as the reference spectrum. With each rotation of polishing table 3, light is irradiated from optical sensor head 25 onto multiple film thickness measurement points on the reference workpiece, including the center point. With each rotation of polishing table 3, processing system 30 generates a reference spectrum from the light intensity measurement data generated by spectrometer 27.

[0037] In this way, multiple reference spectra corresponding to multiple polishing times are generated as the film thickness of the reference workpiece decreases during polishing of the reference workpiece. After polishing of the reference workpiece, the reference workpiece is transferred by the transfer device 103 to the film thickness measurement device 101, and the final film thickness, which is the film thickness of the reference workpiece after polishing, is measured by the film thickness measurement device 101. The measured value of the final film thickness is sent from the film thickness measurement device 101 to the processing system 30.

[0038] The processing system 30 calculates a plurality of polishing index values ​​indicating the progress of polishing the reference workpiece from the plurality of reference spectra. More specifically, the processing system 30 calculates a plurality of change amounts between the plurality of reference spectra and calculates a plurality of polishing index values ​​by integrating the plurality of change amounts arranged according to the polishing time of the reference workpiece one by one. Each of the plurality of change amounts between the plurality of reference spectra is a change amount between two of the plurality of reference spectra that are adjacent in time.

[0039] FIG. 5 is a graph showing two reference spectra adjacent in time. In FIG. 5, the vertical axis represents the intensity of reflected light from a reference workpiece, and the horizontal axis represents the wavelength of the reflected light. FIG. 5 shows a reference spectrum of reflected light at polishing time t and a reference spectrum of reflected light at polishing time t+Δt. Time Δt is a predetermined unit time. The two reference spectra adjacent in time are the reference spectrum of reflected light at a certain polishing time t and the reference spectrum of reflected light at polishing time t+Δt, a unit time Δt later.

[0040] In this embodiment, the reference spectrum is generated every time the polishing table 3 makes one rotation, and so the unit time Δt is the time it takes for the polishing table 3 to make one rotation. In another embodiment, the unit time Δt may be the time it takes for the polishing table 3 to make p rotations (p is a natural number).

[0041] Because the reference spectrum is generated from the light reflected from the reference workpiece being polished, the reference spectrum changes slightly as the film thickness decreases (i.e., with polishing time). Therefore, the shapes of multiple reference spectra generated from the light reflected at different polishing times during polishing of the reference workpiece are slightly different. In addition, these reference spectra reflect changes in the actual polishing rate of the reference workpiece.

[0042] The amount of change between two temporally adjacent reference spectra corresponds to the hatched area in Fig. 5. In other words, the amount of change between two temporally adjacent reference spectra is the amount of change in the reference spectra per unit time Δt. In one embodiment, the amount of change V(t) between two temporally adjacent reference spectra can be calculated using the following equation (1):

number

[0043] In this embodiment, a reference spectrum is generated each time the polishing table 3 makes one rotation, and therefore the amount of change between two temporally adjacent reference spectra is the amount of change in the reference spectra per one rotation of the polishing table 3. In one embodiment, the amount of change between two temporally adjacent reference spectra may be the amount of change in the reference spectra per p rotations (p is a natural number) of the polishing table 3.

[0044] The change amount V(t) of the reference spectrum expressed by the above formula (1) is calculated for each unit time Δt. FIG. 6 is a graph showing the change amount V(t) of the reference spectrum calculated for each unit time during the polishing time of the reference workpiece. In FIG. 6, the vertical axis represents the change amount V(t) of the reference spectrum, and the horizontal axis represents the polishing time of the reference workpiece. As shown in FIG. 6, multiple change amounts V(t) of the reference spectrum corresponding to multiple different polishing times during polishing of the reference workpiece are obtained.

[0045] The processing system 30 calculates multiple polishing index values ​​as shown in FIG. 7 by integrating multiple changes V(t) arranged according to the polishing time of the reference workpiece one by one. In FIG. 7, the vertical axis represents the polishing index value PI(t), and the horizontal axis represents the polishing time of the reference workpiece. The polishing index value PI(t1) at polishing time t1 is the change V(t1) at polishing time t1. The processing system 30 calculates the polishing index value PI(t2) at polishing time t2 by adding the change V(t2) at polishing time t2 to the change V(t1) at polishing time t1, and calculates the polishing index value PI(t3) at polishing time t3 by adding the change V(t3) at polishing time t3 to the polishing index value PI(t2) at polishing time t2. The processing system 30 calculates multiple polishing index values ​​PI(t) by repeating similar calculations. As can be seen from FIG. 7, the plurality of change amounts V(t) are integrated one by one for each unit time, so the polishing index value PI(t) gradually increases with the polishing time.

[0046] The processing system 30 calculates a tentative polishing rate line, assuming that the polishing rate of the reference workpiece is constant, from the initial film thickness, the final film thickness, and two polishing times corresponding to these film thicknesses. That is, as shown in Fig. 8, the processing system 30 calculates a tentative polishing rate line RL from the initial film thickness Tini, which is the film thickness of the reference workpiece before polishing, the polishing time at the initial film thickness Tini (i.e., the polishing start time of the reference workpiece), tini, the final film thickness Tfin, which is the film thickness of the reference workpiece after polishing, and the polishing time at the final film thickness Tfin (i.e., the polishing end time of the reference workpiece). This tentative polishing rate line RL decreases at a constant rate (linearly) with polishing time.

[0047] Next, as shown in FIG. 9 , the processing system 30 determines the polishing rate line RRL by correcting the provisional polishing rate line RL based on the changes with polishing time of the plurality of polishing index values ​​PI(t) shown in FIG. 7 . In one embodiment, the processing system 30 converts the plurality of polishing index values ​​PI(t) that increase with polishing time shown in FIG. 7 into a plurality of polishing index values ​​that decrease with polishing time, applies processing such as scaling to the plurality of converted polishing index values, and corrects the provisional polishing rate line RL so that it passes through the plurality of processed polishing index values, thereby determining the polishing rate line RRL. In another embodiment, an approximation curve of the plurality of polishing index values ​​after scaling processing is calculated, and the section of the provisional polishing rate line RL from time t1 to tn is replaced with the approximation curve, thereby correcting the provisional polishing rate line RL and determining the polishing rate line RRL. However, as long as the polishing rate line RRL reflects the changes with polishing time of the plurality of polishing index values ​​PI(t) shown in FIG. 7 , the method for determining the polishing rate line RRL is not limited to these embodiments.

[0048] The processing system 30 determines a plurality of reference film thicknesses corresponding to a plurality of polishing index values ​​based on the polishing rate line RRL. Specifically, the processing system 30 determines a plurality of reference film thicknesses RH(t1), RH(t2), RH(t3), ... RH(tn) at a plurality of polishing times t1, t2, t3, ... , tn corresponding to the plurality of polishing index values ​​from the polishing rate line RRL. Furthermore, the processing system 30 associates the plurality of reference film thicknesses with a plurality of reference spectra generated from reflected light from a reference workpiece being polished. More specifically, the processing system 30 associates the plurality of reference film thicknesses RH(t1), RH(t2), RH(t3), ... RH(tn) corresponding to a plurality of polishing times t1, t2, t3, ... , tn with a plurality of reference spectra generated from reflected light at a plurality of polishing times t1, t2, t3, ... , tn, respectively. The plurality of reference spectra and the corresponding plurality of reference film thicknesses thus obtained are added to a reference spectrum library. The reference spectrum library is stored in a storage device 30a of the processing system 30.

[0049] The reference spectrum is generated from light reflected from the reference workpiece during polishing. Therefore, the polishing index values ​​calculated from the reference spectra reflect the progress of polishing the reference workpiece. The polishing rate line determined from the initial film thickness, the polishing index values, and the final film thickness reflects changes in the actual polishing rate of the reference workpiece. Therefore, the accuracy of the reference film thicknesses determined using the polishing rate line can be improved.

[0050] FIG. 10 is a flow chart illustrating one embodiment of a method for creating a reference spectral library. In step S101, a reference workpiece is prepared that has the same surface structure as the workpiece W. More specifically, the reference workpiece has an exposed surface made of the same material as the workpiece W and has the same layer structure. In step S102, the film thickness measuring device 101 measures the initial film thickness, which is the film thickness of the reference workpiece before polishing.

[0051] In step S103, the reference workpiece is chemically mechanically polished by the polishing apparatus 100. In step S104, the reference workpiece is irradiated with light at different polishing times during polishing of the reference workpiece, and the processing system 30 generates a reference spectrum of the reflected light from the reference workpiece. In step S105, after the reference workpiece is polished, the final film thickness, which is the film thickness of the polished reference workpiece, is measured by film thickness measuring device 101. In step S106, the processing system 30 calculates a plurality of polishing index values ​​indicating the progress of polishing the reference workpiece from the plurality of reference spectra. In one embodiment, the processing system 30 calculates a plurality of change amounts between the plurality of reference spectra (see FIG. 6), and calculates a plurality of polishing index values ​​by integrating the plurality of change amounts arranged according to the polishing time of the reference workpiece one by one (see FIG. 7).

[0052] In step S107, the processing system 30 calculates a tentative polishing rate line from the initial film thickness and the final film thickness, assuming that the polishing rate of the reference workpiece is constant (see FIG. 8). In step S108, the processing system 30 determines (creates) the polishing rate line RRL by correcting the temporary polishing rate line RL based on changes in the multiple polishing index values ​​over polishing time (see FIG. 9). The polishing rate line RRL corresponds to the temporary polishing rate line RL corrected based on the multiple polishing index values.

[0053] In step S109, the processing system 30 determines a plurality of reference film thicknesses RH(t1), RH(t2), RH(t3), . . . RH(tn) corresponding to a plurality of polishing index values ​​based on the polishing rate line RRL. In step S110, the processing system 30 associates the plurality of reference film thicknesses with the plurality of reference spectra, respectively, and the plurality of reference spectra and the corresponding plurality of reference film thicknesses are added to a reference spectrum library.

[0054] Next, another embodiment of the method for creating a reference spectrum library will be described. Operations of this embodiment that are not specifically described are the same as those of the embodiment described with reference to Figures 1 to 10, and therefore redundant descriptions will be omitted. In this embodiment, the measurement of the initial film thickness of the reference workpiece, the polishing of the reference workpiece, the generation of multiple reference spectra of reflected light from the reference workpiece at different polishing times, and the measurement of the final film thickness of the reference workpiece are performed in the same manner as in the previously described embodiment.

[0055] The processing system 30 calculates a tentative polishing rate line from the initial film thickness and the final film thickness, assuming that the polishing rate of the reference workpiece is constant. The calculation of the tentative polishing rate line is performed in the same manner as in the embodiment described with reference to FIG. 8. The processing system 30 calculates multiple tentative film thicknesses of the reference workpiece, assuming that the polishing rate of the reference workpiece is constant, from the tentative polishing rate line and multiple polishing times corresponding to the multiple reference spectra. The multiple tentative film thicknesses can be calculated according to the method described with reference to FIG. 18. These tentative film thicknesses decrease linearly with polishing time.

[0056] The processing system 30 performs principal component analysis on each of the plurality of reference spectra to obtain the first principal component Z1 to the k-th principal component Z2. k (k is a natural number equal to or greater than 2) for each reference spectrum. More specifically, the processing system 30 performs principal component analysis on a data set including multiple intensities of reflected light at multiple wavelengths for each reference spectrum. As described with reference to FIG. 3, each reference spectrum indicates the relationship between the intensity of reflected light and wavelength, and is composed of multiple wavelengths of reflected light and corresponding multiple intensities. The data set for each reference spectrum includes data on the multiple intensities of that reference spectrum.

[0057] In the example described below, the processing system 30 performs principal component analysis on each reference spectrum to calculate the first principal component Z1, the second principal component Z2, the third principal component Z3, and the fourth principal component Z4. k The step of calculating is not limited to the following example, as long as k is a natural number of 2 or more.

[0058] Examples of calculation formulas for the first principal component Z1 to the fourth principal component Z4 are as follows: First principal component Z1==w 11 X1+w 12 X2+w 12 X3+... Second principal component Z2==w 21 X1+w 22 X2+w 22X3+... Third principal component Z3==w 31 X1+w 32 X2+w 32 X3+... Fourth principal component Z4==w 41 X1+w 42 X2+w 42 X3+... where X m (m is a natural number) is the wavelength λ of the reference spectrum m represents the intensity of reflected light at 1m is the intensity X used to calculate the first principal component Z1 m is the weighting factor for 2m is the intensity X used to calculate the second principal component Z2 m is the weighting factor for 3m is the intensity X used to calculate the third principal component Z3 m is the weighting factor for 4m is the intensity X used to calculate the fourth principal component Z4 m is the weighting factor for

[0059] In this manner, a first principal component Z1, a second principal component Z2, a third principal component Z3, and a fourth principal component Z4 are calculated for each reference spectrum. Thus, a plurality of first principal components Z1, a plurality of second principal components Z2, a plurality of third principal components Z3, and a plurality of fourth principal components Z4 are calculated for a plurality of reference spectra. Because the plurality of reference spectra are generated from light reflected from the reference workpiece as it is being polished, the plurality of reference spectra correspond to a plurality of provisional film thicknesses of the reference workpiece.

[0060] The processing system 30 divides the plurality of principal components acquired for the plurality of reference spectra into the first principal component Z1 to the k-th principal component Z2. kIn the above example, the principal components obtained for the plurality of reference spectra are classified into four groups: group G1 of the first principal component Z1, group G2 of the second principal component Z2, group G3 of the third principal component Z3, and group G4 of the fourth principal component Z4. Group G1 includes the first principal components Z1 obtained for the plurality of reference spectra, group G2 includes the second principal components Z2 obtained for the plurality of reference spectra, group G3 includes the third principal components Z3 obtained for the plurality of reference spectra, and group G4 includes the fourth principal components Z4 obtained for the plurality of reference spectra.

[0061] The processing system 30 determines multiple correlation coefficients corresponding to the multiple groups by calculating correlation coefficients between multiple principal components included in each of the multiple groups and the corresponding multiple temporary film thicknesses. The correlation coefficient is an index that represents the strength of the correlation between the multiple principal components belonging to each group and the corresponding multiple temporary film thicknesses. The larger the correlation coefficient, the stronger the correlation between the principal components and the temporary film thicknesses. The correlation coefficient is calculated according to a known method.

[0062] The processing system 30 determines the group with the largest absolute value of the correlation coefficient and the group with the second largest absolute value of the correlation coefficient from among the multiple correlation coefficients calculated for the multiple groups. For example, if the correlation coefficient of group G1 is 0.91, the correlation coefficient of group G2 is −0.89, the correlation coefficient of group G3 is −0.32, and the correlation coefficient of group G4 is −0.05, the group with the largest absolute value of the correlation coefficient is group G1, and the group with the second largest absolute value of the correlation coefficient is group G2.

[0063] 11, the processing system 30 arranges the first principal components included in the group G1 having the largest absolute value of the correlation coefficient on a first coordinate axis of the coordinate system, and arranges the second principal components included in the group G2 having the second largest absolute value of the correlation coefficient on a second coordinate axis of the coordinate system. The coordinate system of the embodiment shown in FIG. 11 is a Cartesian coordinate system having a first coordinate axis and a second coordinate axis. The processing system 30 determines a plurality of polishing index values ​​PI(t), which are a plurality of data points identified from the first principal components on the first coordinate axis and the second principal components on the second coordinate axis.

[0064] A plurality of polishing index values ​​PI(t) on the coordinate system are determined from a plurality of first principal components and a plurality of second principal components, which are calculated from a plurality of reference spectra of reflected light from the reference workpiece. Thus, the plurality of polishing index values ​​PI(t) on the coordinate system correspond to a plurality of polishing times t1, t2, t3, ..., tn during polishing of the reference workpiece. In the embodiment shown in Figure 11, the plurality of polishing index values ​​PI(t) on the coordinate system decrease with the polishing time of the reference workpiece.

[0065] The processing system 30 determines the polishing rate line by correcting the temporary polishing rate line used when calculating the temporary film thickness of the reference workpiece based on changes with polishing time in the multiple polishing index values ​​PI(t) shown in FIG. 11. In one embodiment, the processing system 30 determines the polishing rate line RRL by applying a process such as scaling to the multiple polishing index values ​​PI(t) as shown in FIG. 12 and correcting the temporary polishing rate line RL so that it passes through the multiple polishing index values ​​after the process. In another embodiment, the processing system 30 calculates an approximate curve of the multiple polishing index values ​​after the scaling process and replaces the section of the temporary polishing rate line RL from time t1 to tn with the approximate curve, thereby correcting the temporary polishing rate line RL and determining the polishing rate line RRL. However, as long as the polishing rate line RRL reflects changes with polishing time in the multiple polishing index values ​​PI(t) shown in FIG. 11, the method for determining the polishing rate line RRL is not limited to these embodiments.

[0066] The processing system 30 determines a plurality of reference film thicknesses corresponding to a plurality of polishing index values ​​based on the polishing rate line RRL. Specifically, the processing system 30 determines a plurality of reference film thicknesses RH(t1), RH(t2), RH(t3), ... RH(tn) at a plurality of polishing times t1, t2, t3, ... , tn corresponding to the plurality of polishing index values ​​from the polishing rate line RRL. Furthermore, the processing system 30 associates the plurality of reference film thicknesses with a plurality of reference spectra generated from reflected light from a reference workpiece being polished. More specifically, the processing system 30 associates the plurality of reference film thicknesses RH(t1), RH(t2), RH(t3), ... RH(tn) corresponding to a plurality of polishing times t1, t2, t3, ... , tn with a plurality of reference spectra generated from reflected light at a plurality of polishing times t1, t2, t3, ... , tn, respectively. The plurality of reference spectra and the corresponding plurality of reference film thicknesses thus obtained are added to a reference spectrum library. The reference spectrum library is stored in a storage device 30a of the processing system 30.

[0067] The reference spectrum is generated from light reflected from the reference workpiece during polishing. Therefore, the polishing index values ​​calculated from the reference spectra reflect the progress of polishing the reference workpiece. The polishing rate line determined from the initial film thickness, the polishing index values, and the final film thickness reflects changes in the actual polishing rate of the reference workpiece. Therefore, the accuracy of the reference film thicknesses determined using the polishing rate line can be improved.

[0068] FIG. 13 is a flow chart illustrating one embodiment of a method for creating a reference spectral library. Steps S201 to S205 are the same as steps S101 to S105 shown in FIG. 11, so a duplicated description will be omitted. In step S206, the processing system 30 calculates a tentative polishing rate line from the initial film thickness and the final film thickness, assuming that the polishing rate of the reference workpiece is constant. In step S207, the processing system 30 calculates a plurality of tentative film thicknesses of the reference workpiece, assuming that the polishing rate of the reference workpiece is constant, from the tentative polishing rate line and a plurality of polishing times corresponding to the plurality of reference spectra.

[0069] In step S208, the processing system 30 performs principal component analysis on each of the plurality of reference spectra to obtain the first principal component Z1 through the k-th principal component Z2. k (k is a natural number equal to or greater than 2) for each reference spectrum. In step S209, the processing system 30 divides the plurality of principal components obtained for the plurality of reference spectra into the first principal component Z1 to the k-th principal component Z2. k Classify into multiple groups. In step S210, the processing system 30 determines a plurality of correlation coefficients corresponding to the plurality of groups by calculating correlation coefficients between a plurality of principal components included in each of the plurality of groups and a corresponding plurality of tentative film thicknesses. In step S211, the processing system 30 determines the group with the largest absolute value of the correlation coefficient and the group with the second largest absolute value of the correlation coefficient from among the multiple correlation coefficients calculated for the multiple groups.

[0070] In step S212, the processing system 30 arranges the principal components included in the group with the largest absolute value of the correlation coefficient on the first coordinate axis of the coordinate system, and arranges the principal components included in the group with the second largest absolute value of the correlation coefficient on the second coordinate axis of the coordinate system. In step S213, the processing system 30 determines a plurality of polishing index values ​​PI(t), which are a plurality of data points identified from a plurality of principal components on the first coordinate axis and a plurality of principal components on the second coordinate axis (see FIG. 11).

[0071] In step S214, the processing system 30 determines (creates) a polishing rate line RRL by correcting the provisional polishing rate RL used when calculating the provisional film thickness of the reference workpiece based on changes in the plurality of polishing index values ​​PI(t) over polishing time (see FIG. 12). The polishing rate line RRL corresponds to the provisional polishing rate line RL corrected based on the plurality of polishing index values ​​PI(t). In step S215, the processing system 30 determines a plurality of reference film thicknesses RH(t1), RH(t2), RH(t3), . . . RH(tn) corresponding to a plurality of polishing index values ​​PI(t) based on the polishing rate line RRL. In step S216, the processing system 30 associates the plurality of reference film thicknesses with the plurality of reference spectra, respectively, and the plurality of reference spectra and the corresponding plurality of reference film thicknesses are added to a reference spectrum library.

[0072] Next, a further embodiment of the method for creating a reference spectrum library will be described. Operations of this embodiment that are not specifically described are the same as those of the embodiment described with reference to FIGS. 1 to 11, and therefore, redundant description will be omitted. In this embodiment, a polishing index value is not calculated. Instead, in this embodiment, the intermediate film thickness of the reference workpiece is measured at least once during polishing of the reference workpiece. In the embodiment described below, the intermediate film thickness of the reference workpiece is measured multiple times during polishing of the reference workpiece.

[0073] The measurement of the initial film thickness of the reference workpiece, the polishing of the reference workpiece, the generation of multiple reference spectra of reflected light from the reference workpiece at different polishing times, and the measurement of the final film thickness of the reference workpiece are performed in the same manner as in the previously described embodiment. The intermediate film thickness of the reference workpiece is the film thickness of the reference workpiece during polishing. The measurement of the intermediate film thickness is performed after the measurement of the initial film thickness and before the measurement of the final film thickness.

[0074] The initial film thickness and the final film thickness are measured by film thickness measuring device 101 shown in Fig. 4. The intermediate film thickness is measured by film thickness measuring device 101 shown in Fig. 4 or optical film thickness measuring device 20 shown in Fig. 2. When film thickness measuring device 101 is used to measure the intermediate film thickness, polishing of the reference workpiece by polishing apparatus 100 is temporarily stopped, and the reference workpiece is transported to film thickness measuring device 101 by transport device 103, and the intermediate film thickness of the reference workpiece is measured by film thickness measuring device 101. When optical film thickness measuring device 20 is used to measure the intermediate film thickness, the intermediate film thickness of the reference workpiece is measured by optical film thickness measuring device 20 while the reference workpiece is being polished by polishing apparatus 100.

[0075] The processing system 30 determines a polishing rate line showing the relationship between the film thickness of the reference workpiece and polishing time from the initial film thickness, multiple intermediate film thicknesses, and the final film thickness. FIG. 15 is a graph showing an example of a polishing rate line showing the relationship between the film thickness of the reference workpiece and polishing time. In FIG. 15, the vertical axis represents the film thickness of the reference workpiece, and the horizontal axis represents the polishing time of the reference workpiece. In the embodiment shown in FIG. 15, three intermediate film thicknesses Titr1, Titr2, and Titr3 are measured by the film thickness measurement device 101 or the optical film thickness measurement device 20 after polishing of the reference workpiece begins but before polishing ends. The polishing times ti1, ti2, and ti3 shown in FIG. 15 correspond to the intermediate film thicknesses Titr1, Titr2, and Titr3, respectively.

[0076] The processing system 30 determines (creates) a polishing rate line RRL determined from the initial film thickness Tini, intermediate film thicknesses Titr1, Titr2, Titr3, final film thickness Tfin, and polishing times tini, ti1, ti2, ti3, tfin corresponding to these film thicknesses. In one embodiment, the processing system 30 determines the polishing rate line RRL passing through film thickness data points identified from the initial film thickness Tini, intermediate film thicknesses Titr1, Titr2, Titr3, final film thickness Tfin, and the corresponding multiple polishing times tini, ti1, ti2, ti3, tfin. In another embodiment, the processing system 30 may determine the polishing rate line RRL as an approximation curve of film thickness data points identified from the initial film thickness Tini, intermediate film thicknesses Titr1, Titr2, Titr3, final film thickness Tfin, and the corresponding multiple polishing times tini, ti1, ti2, ti3, tfin.

[0077] The processing system 30 determines, from the polishing rate line RRL, a plurality of reference film thicknesses at a plurality of polishing times corresponding to a plurality of reference spectra of light reflected from the reference workpiece being polished. The plurality of reference film thicknesses can be determined in a manner similar to that described with reference to FIG. 9. Furthermore, the processing system 30 associates the plurality of reference film thicknesses with a plurality of reference spectra. The plurality of reference spectra thus obtained and the corresponding plurality of reference film thicknesses are added to a reference spectrum library. The reference spectrum library is stored in a storage device 30a of the processing system 30.

[0078] According to this embodiment, the polishing rate line RRL is created based on multiple measurements of the film thickness of the reference workpiece, thereby improving the accuracy of multiple reference film thicknesses determined using the polishing rate line RRL.

[0079] FIG. 16 is a flow chart illustrating one embodiment of a method for creating a reference spectral library. Steps S301 to S304 are the same as steps S101 to S104 shown in FIG. 11, so a duplicated description will be omitted. In step S305, the intermediate film thickness, which is the film thickness of the reference workpiece during polishing, is measured by film thickness measuring device 101 or optical film thickness measuring device 20 one or more times. In step S306, after the reference workpiece is polished, the final film thickness, which is the film thickness of the polished reference workpiece, is measured by film thickness measuring device 101.

[0080] In step S307, the processing system 30 determines (creates) a polishing rate line RRL indicating the relationship between the film thickness of the reference workpiece and the polishing time from the initial film thickness, intermediate film thickness, and final film thickness (see FIG. 14). In step S308, the processing system 30 determines a plurality of reference film thicknesses corresponding to a plurality of reference spectra based on the polishing rate line RRL. In step S309, the processing system 30 associates the plurality of reference film thicknesses with the plurality of reference spectra, respectively, and the plurality of reference spectra and the corresponding plurality of reference film thicknesses are added to a reference spectrum library.

[0081] The above-described embodiments have been described for the purpose of enabling a person of ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments would be obvious to a person skilled in the art, and the technical concept of the present invention may be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope in accordance with the technical concept defined by the claims. [Explanation of symbols]

[0082] 1 polishing head 2 polishing pads 2a Polished surface 3 Polishing table 5 Polishing liquid supply nozzle 6 Table Motor 9. Operation control section 10 Head shaft 15 Polishing head rotation device 20 Optical film thickness measuring device 22 Light source 25 Optical sensor head 27 Spectrometer 30 Processing System 31 Light-emitting fiber optic cable 32 Receiving optical fiber cable 100 Polishing equipment 101 Film Thickness Measuring Device 103 Conveyor equipment W Workpiece

Claims

1. 1. A method for creating a reference spectral library used to estimate a film thickness of a workpiece, comprising: measuring an initial film thickness of a reference workpiece before polishing; polishing the reference workpiece with a polishing device; generating a plurality of reference spectra of reflected light from the reference workpiece obtained at a plurality of polishing times during polishing of the reference workpiece; measuring a final film thickness of the reference workpiece after polishing the reference workpiece; determining a plurality of polishing indicator values ​​indicative of progress of polishing of the reference workpiece from the plurality of reference spectra; determining a polishing rate line indicating the relationship between the film thickness of the reference workpiece and polishing time from the initial film thickness, the plurality of polishing index values, and the final film thickness; determining a plurality of reference film thicknesses corresponding to the plurality of polishing index values ​​based on the polishing rate line; A method for creating a reference spectral library, comprising: creating a reference spectral library by relating the plurality of reference film thicknesses to the plurality of reference spectra.

2. The calculation of the plurality of polishing index values ​​includes: calculating a plurality of change amounts between the plurality of reference spectra, each change amount being a change amount between two temporally adjacent ones of the plurality of reference spectra; The method for creating a reference spectrum library according to claim 1 , further comprising calculating the plurality of polishing index values ​​by integrating the plurality of change amounts arranged according to the polishing time of the reference workpiece one by one.

3. The determination of the polishing rate line is Calculating a tentative polishing rate line from the initial film thickness and the final film thickness, assuming that the polishing rate of the reference workpiece is constant; The method for creating a reference spectrum library according to claim 1, further comprising determining the polishing rate line by correcting the provisional polishing rate line based on changes in the plurality of polishing index values ​​over polishing time.

4. The calculation of the plurality of polishing index values ​​includes: calculating a plurality of tentative film thicknesses of the reference workpiece from the initial film thickness, the final film thickness, and the plurality of polishing times, assuming that the polishing rate of the reference workpiece is constant; performing a principal component analysis on each of the plurality of reference spectra to obtain a plurality of principal components including a first principal component to a k-th principal component (k is a natural number of 2 or more) for each of the reference spectra; classifying the principal components acquired for the reference spectra into a plurality of groups of first to k-th principal components; determining a plurality of correlation coefficients corresponding to the plurality of groups by calculating correlation coefficients between a plurality of principal components included in each of the plurality of groups and the plurality of temporary film thicknesses; determining a first group having the largest absolute value of the correlation coefficients and a second group having the second largest absolute value of the correlation coefficients from among the plurality of correlation coefficients; arranging the plurality of principal components included in the first group on a first coordinate axis of a coordinate system; arranging the plurality of principal components included in the second group on a second coordinate axis of the coordinate system; 2. The method for creating a reference spectral library according to claim 1, further comprising determining the plurality of polishing index values, which are a plurality of data points identified from the plurality of principal components on the first coordinate axis and the plurality of principal components on the second coordinate axis.

5. 1. A method for creating a reference spectral library used to estimate a film thickness of a workpiece, comprising: measuring an initial film thickness of a reference workpiece before polishing; polishing the reference workpiece with a polishing device; generating a plurality of reference spectra of reflected light from the reference workpiece obtained at a plurality of polishing times during polishing of the reference workpiece; measuring an intermediate film thickness of the reference workpiece at least once during polishing of the reference workpiece; measuring a final film thickness of the reference workpiece after polishing the reference workpiece; determining a polishing rate line indicating the relationship between the film thickness of the reference workpiece and polishing time from the initial film thickness, the intermediate film thickness, and the final film thickness; determining a plurality of reference film thicknesses for the plurality of polishing times from the polishing rate line; A method for creating a reference spectral library, comprising: associating the reference film thickness with the plurality of reference spectra to create a reference spectral library.

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