Method for creating reference spectrum library for estimating film thickness of workpiece

Abstract

Provided is a method for creating a reference spectrum library capable of improving the accuracy of a plurality of film thicknesses corresponding to a plurality of reference spectrums. In the reference spectrum library creation method, a plurality of reference spectrums of reflected light from a reference workpiece obtained at a plurality of polishing times during polishing of the reference workpiece are generated, and a plurality of polishing index values indicating the polishing progress of the reference workpiece are calculated from the plurality of reference spectrums. On the basis of the initial film thickness of the reference workpiece, the plurality of polishing index values, and the final film thickness of the reference workpiece, a polishing rate line indicating the relationship between the film thickness of the reference workpiece and the polishing time is determined, and a plurality of reference film thicknesses corresponding to the plurality of polishing index values are determined on the basis of the polishing rate line. A reference spectrum library is created by associating a plurality of reference film thicknesses with a plurality of reference spectra.

Description

Technical Field

[0001] The present invention relates to a method for fabricating a reference spectral library for estimating the film thickness of workpieces such as wafers and substrates, and particularly to a method for fabricating a reference spectral library comprising multiple reference spectra that are compared with the measured spectrum of reflected light from the workpiece. Background Technology

[0002] The optical film thickness measuring device is configured to: generate a measurement spectrum of reflected light from the wafer, determine a reference spectrum whose shape is closest to the measurement spectrum from a reference spectrum library, and then determine the film thickness that is pre-associated with the determined reference spectrum. Figure 17 This is a flowchart illustrating how film thickness is determined by comparing a measured spectrum with multiple reference spectra. The optical film thickness measuring device compares the measured spectrum generated during workpiece grinding with multiple pre-prepared reference spectra, determines the reference spectrum whose shape is closest to the measured spectrum, and then determines the film thickness pre-associated with this determined reference spectrum. The reference spectrum whose shape is closest to the measured spectrum is the spectrum with the smallest shape difference between the reference spectrum and the measured spectrum.

[0003] Multiple reference spectra are obtained by pre-grinding a reference wafer having the same surface structure as the wafer being ground. The film thickness at the time of acquisition of the reference spectrum is correlated with each reference spectrum. That is, multiple reference spectra are acquired when the film thickness of the reference wafer is different, and multiple reference spectra correspond to multiple different film thicknesses. Therefore, the current film thickness of the wafer can be estimated by using the reference spectrum with a specific shape that is closest to the measured spectrum.

[0004] The following describes an example of the process for obtaining multiple reference spectra and their corresponding film thicknesses. First, a reference wafer with the same surface structure as the wafer to be ground is prepared. The reference wafer is transported to a film thickness measuring device, where its initial film thickness Tini is measured. Next, the reference wafer is transported to a grinding apparatus, where it is ground. During the grinding of the reference wafer, light is irradiated onto its surface, generating a spectrum of reflected light from the reference wafer (i.e., a reference spectrum). The reference spectrum is generated periodically during the grinding process. Therefore, multiple reference spectra are obtained while the film thickness decreases during the grinding process. After the grinding is complete, the reference wafer is again transported to the aforementioned film thickness measuring device, where the film thickness of the ground reference wafer (i.e., the final film thickness Tfin) is measured.

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

[0006] The times t1, t2, ..., tn for generating multiple reference spectra fall within the range from grinding time tini to grinding time tfin. Based on the initial film thickness Tini, the final film thickness Tfin, and the times t1 to tn for generating the reference spectra, the film thickness corresponding to the reference spectra can be calculated. For example, the film thickness corresponding to the reference spectrum generated at time t2 can be calculated using the following formula.

[0007] Tini-[Tini-Tfin]·[[t2-tini] / [tfin-tini]]

[0008] In this way, multiple reference spectra corresponding to different film thicknesses are obtained. Each reference spectrum is associated (linked) with its corresponding film thickness. The optical film thickness measuring device can estimate the current film thickness of the wafer based on the film thickness associated with the reference spectrum from the reference spectrum that is closest to the measured spectrum in a specific shape during wafer grinding.

[0009] Existing technical documents

[0010] Patent Literature

[0011] Patent Document 1: International Publication No. 2015 / 163164

[0012] Patent Document 2: Japanese Patent Application Publication No. 2022-156879

[0013] (The problem the invention aims to solve)

[0014] like Figure 18 As shown, the previously estimated film thicknesses assumed a constant polishing rate for the reference wafer. However, as... Figure 19 The actual polishing rate of the reference wafer is not constant. Therefore, the film thickness corresponding to multiple reference spectra will differ from the actual film thickness of the reference wafer, resulting in a decrease in the accuracy of the film thickness estimation. Summary of the Invention

[0015] Therefore, the present invention provides a method for fabricating a reference spectral library that can improve the accuracy of multiple film thicknesses corresponding to multiple reference spectra.

[0016] (Solutions)

[0017] In one approach, a method for creating a reference spectral library is provided for estimating the film thickness of a workpiece. This involves determining the initial film thickness of a reference workpiece before grinding, grinding the reference workpiece using a grinding apparatus, generating multiple reference spectra of reflected light from the reference workpiece obtained at multiple grinding times during the grinding process, measuring the final film thickness of the reference workpiece after grinding, calculating multiple grinding index values ​​representing the grinding progress of the reference workpiece based on the multiple reference spectra, determining a grinding rate line representing the relationship between the film thickness of the reference workpiece and grinding time based on the initial film thickness, the multiple grinding index values, and the final film thickness, determining multiple reference film thicknesses corresponding to the multiple grinding index values ​​based on the grinding rate line, and creating a reference spectral library by correlating the multiple reference film thicknesses with the multiple reference spectra.

[0018] In one approach, the calculation of the plurality of grinding index values ​​includes the following: calculating a plurality of variations among the plurality of reference spectra, each variation being two temporally adjacent variations in the plurality of reference spectra, and calculating the plurality of grinding index values ​​by accumulating the plurality of variations arranged according to the grinding time of the reference workpiece.

[0019] In one approach, the determination of the grinding rate line includes the following: based on the initial film thickness and the final film thickness, a false grinding rate line is calculated assuming that the grinding rate of the reference workpiece is constant; the false grinding rate line is corrected based on the changes of the plurality of grinding index values ​​with grinding time, thereby determining the grinding rate line.

[0020] In one approach, the estimation of the multiple grinding index values ​​includes the following: Based on the initial film thickness, the final film thickness, and the multiple grinding times, estimating multiple dummy film thicknesses of the reference workpiece assuming a constant grinding rate; performing principal component analysis on the multiple reference spectra to obtain multiple principal components containing a first principal component to a k-th principal component for each reference spectrum, where k is a natural number greater than 2; classifying the multiple principal components obtained from the multiple reference spectra into multiple groups of the first principal component to the k-th principal component; determining multiple correlation coefficients corresponding to the multiple groups by estimating the correlation coefficients between the multiple principal components contained in each group and the multiple dummy film thicknesses; determining the first group with the largest absolute value of the correlation coefficient and the second group with the second largest absolute value of the correlation coefficient; arranging the multiple principal components contained in the first group on the first coordinate axis of the coordinate system; arranging the multiple principal components contained in the second group on the second coordinate axis of the coordinate system; and determining the multiple grinding index values, which are specific data points based on the multiple principal components on the first coordinate axis and the multiple principal components on the second coordinate axis.

[0021] In one approach, the initial film thickness of a reference workpiece before grinding is measured, the reference workpiece is ground by a grinding device, and multiple reference spectra of reflected light from the reference workpiece are generated from multiple grinding times during the grinding process. During the grinding of the reference workpiece, the intermediate film thickness of the reference workpiece is measured at least once. After the grinding of the reference workpiece, the final film thickness of the reference workpiece is measured. Based on the initial film thickness, the intermediate film thickness, and the final film thickness, a grinding rate line representing the relationship between the film thickness of the reference workpiece and the grinding time is determined. Based on the grinding rate line, multiple reference film thicknesses are determined at the multiple grinding times. A reference spectral library is created by correlating the reference film thicknesses with the multiple reference spectra.

[0022] (Invention Effects)

[0023] When using one of the above methods, a reference spectrum is generated based on the reflected light from a reference workpiece during grinding. Therefore, multiple grinding index values ​​calculated from these reference spectra reflect the grinding progress of the reference spectra. A grinding rate line, determined by the initial film thickness, multiple grinding index values, and the final film thickness, reflects the change in the actual grinding rate of the reference workpiece. Therefore, the accuracy of using multiple reference film thicknesses determined by the grinding rate line can be improved.

[0024] When using one of the above methods, a grinding rate line is created based on multiple measured values ​​of the film thickness of a reference workpiece. Therefore, the accuracy of using multiple reference film thicknesses determined by the grinding rate line can be improved. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating one embodiment of the grinding apparatus.

[0026] Figure 2 This is a cross-sectional view showing the detailed configuration of an optical film thickness measuring device.

[0027] Figure 3 This is a schematic diagram representing a measured spectrum generated based on light intensity measurement data.

[0028] Figure 4 This is a schematic diagram illustrating one embodiment of a workpiece processing system that includes a grinding apparatus and a film thickness measuring apparatus used in the fabrication of a reference spectral library.

[0029] Figure 5 It is a graph representing two temporally adjacent reference spectra.

[0030] Figure 6 It is a graph representing the change in the reference spectrum calculated per unit time based on the grinding time of the reference workpiece.

[0031] Figure 7It is a graph representing multiple grinding index values ​​calculated by accumulating multiple changes in the reference spectrum one by one.

[0032] Figure 8 This is an example curve representing the pseudo-grind rate line when the grinding rate of the reference workpiece is assumed to be constant.

[0033] Figure 9 This is a process diagram that explains how the grinding rate line is determined by correcting the spurious grinding rate line based on the changes of multiple grinding index values ​​over grinding time.

[0034] Figure 10 This is a flowchart illustrating one implementation method for creating a reference spectral library.

[0035] Figure 11 This is a diagram illustrating an example of multiple grinding index values ​​specific to multiple first principal components and multiple second principal components.

[0036] Figure 12 This is a process diagram that explains how the grinding rate line is determined by correcting the spurious grinding rate line based on the changes of multiple grinding index values ​​with grinding time.

[0037] Figure 13 This is a flowchart illustrating one implementation method for creating a reference spectral library.

[0038] Figure 14 This is a flowchart illustrating the above implementation method.

[0039] Figure 15 This is a graph illustrating an example of the grinding rate curve, which represents the relationship between the film thickness of a reference workpiece and the grinding time.

[0040] Figure 16 This is a flowchart illustrating one implementation method for creating a reference spectral library.

[0041] Figure 17 This is a diagram illustrating the procedure for determining film thickness based on the comparison of the measured spectrum with multiple reference spectra.

[0042] Figure 18 This is a graph showing the relationship between the film thickness of the reference wafer and the polishing time.

[0043] Figure 19 This is an example of a graph showing that the polishing rate of the reference wafer is not constant. Detailed Implementation

[0044] Hereinafter, embodiments of the present invention will be described with reference to the figures. Figure 1 This is a schematic diagram illustrating one embodiment of the grinding apparatus. For example... Figure 1As shown, the polishing apparatus 100 includes: a polishing table 3 supporting the polishing pad 2; a polishing head 1 pressing the workpiece W onto the polishing pad 2; a table motor 6 for rotating the polishing table 3; a polishing slurry supply nozzle 5 for supplying polishing slurry, such as slurry, to 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 the polishing surface 2a of the workpiece W. The workpiece W has a film forming a wiring structure on its surface. Examples of workpiece W include wafers, substrates, wiring substrates, corner substrates, etc., used in the manufacture of semiconductor components. One example is a product wafer on which a multilayer film is formed.

[0045] The grinding head 1 is connected to the head shaft 10, and the head shaft 10 is connected to the grinding head rotating device 15. The grinding head rotating device 15 is configured to rotate the grinding head 1 and the head shaft 10 together in the direction indicated by the arrow. The configuration of the grinding head rotating device 15 is not particularly limited; however, in one example, the grinding head rotating device 15 includes a motor, a belt, and pulleys. The grinding table 3 is connected to the table motor 6, and the table motor 6 is configured to rotate the grinding table 3 and the grinding pad 2 in the direction indicated by the arrow. The grinding head 1, the grinding head rotating device 15, and the table motor 6 are connected to the motion control unit 9.

[0046] The workpiece W is ground as follows. The stage motor 6 and the grinding head rotation device 15 move the grinding table 3 and the grinding head 1 towards... Figure 1 The grinding head rotates in the direction indicated by the arrow, while simultaneously supplying grinding fluid from the grinding fluid supply nozzle 5 to the grinding surface 2a of the grinding pad 2 on the grinding table 3. The workpiece W rotates via the grinding head 1, and with grinding fluid present on the grinding pad 2, the grinding head 1 presses the workpiece W against the grinding surface 2a of the grinding pad 2. The surface of the workpiece W is ground by the chemical action of the grinding fluid and the abrasive particles contained in the grinding fluid, and / or the mechanical action of the grinding pad 2.

[0047] The motion control unit 9 includes: a storage device 9a storing a program; and a computing device 9b performing calculations according to the commands contained in the program. The motion control unit 9 is configured as at least one computer. The storage device 9a includes: a main storage device such as 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 computing device 9b include a CPU (central processing unit) and a GPU (graphics processing unit). However, the specific configuration of the motion control unit 9 is not limited to these examples.

[0048] The grinding apparatus 100 includes an optical film thickness measuring device 20 for measuring the film thickness of a workpiece W. The optical film thickness measuring device 20 includes: a light source 22 that emits light; an optical sensor head 25 that illuminates the workpiece W with light from the light source 22 and receives reflected light from the workpiece W; a beam splitter 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 reflected light from the workpiece W. The optical sensor head 25 is disposed within the grinding table 3 and rotates together with the grinding table 3.

[0049] The processing system 30 includes: a storage device 30a storing a program; and a processing unit 30b executing operations according to the commands contained in the program. The processing system 30 comprises at least one computer. The storage device 30a includes: a main storage device such as random access memory (RAM); and auxiliary storage devices such as hard disk drives (HDDs) and solid-state drives (SSDs). Examples of processing units 30b include CPUs (central processing units) and GPUs (graphics processing units). However, the specific configuration of the processing system 30 is not limited to these examples.

[0050] The motion control unit 9 and the processing system 30 can each be composed of multiple computers. For example, the motion control unit 9 and the processing system 30 can each be composed of a combination of an edge server and a cloud server. In one embodiment, the motion control unit 9 and the processing system 30 can also be composed of a single computer.

[0051] Figure 2 This is a cross-sectional view showing the detailed configuration of the optical film thickness measuring device 20. The optical film thickness measuring device 20 includes: a light-emitting fiber optic cable 31 connected to a light source 22; and a light-receiving fiber optic cable 32 connected to a beam splitter 27. The tip 31a of the light-emitting fiber optic cable 31 and the tip 32a of the light-receiving fiber optic cable 32 constitute an optical sensor head 25. That is, the light-emitting fiber optic cable 31 guides the 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 reflected light from the workpiece W and transmits it to the beam splitter 27.

[0052] The beam splitter 27 is connected to the processing system 30. The projection fiber optic cable 31, the receiving fiber optic cable 32, the light source 22, and the beam splitter 27 are mounted on the polishing table 3 and rotate integrally with the polishing table 3 and the polishing pad 2. The optical sensor head 25, which is formed by the tip 31a of the projection fiber optic cable 31 and the tip 32a of the receiving fiber optic cable 32, is positioned opposite to the surface of the workpiece W on the polishing pad 2.

[0053] The optical sensor head 25 is positioned across the surface of the workpiece W on the grinding pad 2 each time the grinding table 3 and grinding pad 2 rotate once. The grinding pad 2 has a through hole 2b located above the optical sensor head 25. Each time the grinding table 3 rotates once, the optical sensor head 25 transmits light through the through hole 2b to illuminate the workpiece W, and receives reflected light from the workpiece W through the through hole 2b.

[0054] In one embodiment, to prevent polishing fluid and polishing debris from contacting the optical sensor head 25, pure water can be introduced into the through-hole 2b of the polishing pad 2. Light is guided from the optical sensor head 25 to the workpiece W through the pure water, and reflected light from the workpiece W is received by the optical sensor head 25 through the pure water. In another embodiment, a transparent window (not shown) can be embedded in the through-hole 2b of the polishing pad 2. The transparent window is made of a light-transmitting material (e.g., transparent resin). In this case, light is guided from the optical sensor head 25 to the workpiece W through the transparent window, and reflected light from the workpiece W is received by the optical sensor head 25 through the transparent window.

[0055] Light source 22 is a flash light source that emits light repeatedly at short time intervals. An example of light source 22 is a xenon flash lamp. Light source 22 is electrically connected to the motion control unit 9 and emits light upon receiving trigger signals from the motion control unit 9. More specifically, light source 22 receives multiple trigger signals and emits light multiple times while the optical sensor head 25 traverses the surface of the workpiece W on the polishing pad 2. Therefore, each time the polishing table 3 rotates once, light is irradiated at multiple film thickness measurement points, including the center point on the workpiece W.

[0056] 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 projection fiber optic cable 31 and emitted from the optical sensor head 25. The light enters the workpiece W on the polishing pad 2 through the through hole 2b. 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 reflected light from the workpiece W is transmitted to the beam splitter 27 through the light-receiving fiber optic cable 32.

[0057] The beam splitter 27 is configured to analyze reflected light according to wavelength and measure the intensity of reflected light at each wavelength within a specified wavelength range. That is, the beam splitter 27 analyzes the reflected light from the workpiece W according to wavelength and generates light intensity measurement data by measuring the intensity of reflected light at each wavelength within a specified wavelength range. The intensity of reflected light at each wavelength can also be expressed as a relative value such as reflectivity or relative reflectivity. The light intensity measurement data is sent to the processing system 30.

[0058] Processing system 30 generates data such as light intensity measurement data. Figure 3The spectrum of reflected light is shown. In the following description, the spectrum of reflected light from workpiece W will be referred to as the measurement spectrum. The measurement spectrum of reflected light from workpiece W contains information about the film thickness of workpiece W. In other words, the measurement spectrum of reflected light varies depending on the film thickness of workpiece W. The processing system 30 is configured to determine the film thickness of workpiece W based on the measurement spectrum of reflected light. More specifically, the processing system 30 determines a reference spectrum from a reference spectrum library that has a shape closest to the measurement spectrum of reflected light, and determines the film thickness associated with the determined reference spectrum. The reference spectrum library is pre-made before grinding workpiece W and stored in the storage device 30a of the processing system 30.

[0059] The following describes one implementation method for creating a reference spectral library. Figure 4 This is a schematic diagram of one embodiment of a workpiece processing system that includes a grinding apparatus 100 and a film thickness measuring apparatus 101 used in the preparation of a reference spectral library.

[0060] First, a reference workpiece with the same surface structure as workpiece W is prepared. More specifically, the reference workpiece has an exposed surface made of the same material as workpiece W and has the same layered structure. Second, the reference workpiece is transported to the film thickness measuring device 101 via the transport device 103, and the initial film thickness of the reference workpiece before grinding is measured by the film thickness measuring device 101.

[0061] Film thickness measuring device 101 illuminates a stationary reference workpiece with light, generating a spectrum of reflected light from the reference spectrum. The film thickness of the reference workpiece is determined by analyzing the spectrum. The basic film thickness measuring principle of this device 101 is the same as that of the optical film thickness measuring device 20, except that it measures the film thickness of a stationary reference workpiece. The initial film thickness measurement value is transmitted from the film thickness measuring device 101 to the processing system 30.

[0062] After measuring the initial film thickness, the reference workpiece is transported to the grinding device 100 via the conveying device 103 and ground by the grinding device 100. The grinding of the reference workpiece is performed in the same way as the grinding of the workpiece W. That is, the table motor 6 and the grinding head rotation device 15 move the grinding table 3 and the grinding head 1 towards... Figure 1 The grinding head rotates in the direction indicated by the arrow, while grinding fluid is supplied from the grinding fluid supply nozzle 5 to the grinding surface 2a of the grinding pad 2 on the grinding table 3. The reference workpiece is rotated by the grinding head 1, and while grinding fluid is present on the grinding pad 2, the grinding head 1 presses the reference workpiece against the grinding surface 2a of the grinding pad 2 to grind the surface of the reference workpiece.

[0063] In the grinding of the reference workpiece, similarly to the grinding of workpiece W, light is irradiated from the optical sensor head 25 onto the reference workpiece, generating a spectrum of reflected light from the reference workpiece. In the following description, the spectrum of reflected light from the reference workpiece will be referred to as the reference spectrum. Each rotation of the grinding stage 3 irradiates light from the optical sensor head 25 onto multiple film thickness measurement points, including the center point on the reference workpiece. Each time the grinding stage 3 rotates, the processing system 30 generates the reference spectrum based on the light intensity measurement data generated by the spectrometer 27.

[0064] Thus, during the grinding of the reference workpiece, the film thickness of the reference workpiece decreases, and multiple reference spectra corresponding to multiple grinding times are generated. After grinding the reference workpiece, it is transported to the film thickness measuring device 101 via the transport device 103, and the final film thickness of the reference workpiece after grinding is measured by the film thickness measuring device 101. The measured value of the final film thickness is transmitted from the film thickness measuring device 101 to the processing system 30.

[0065] The processing system 30 calculates multiple grinding index values ​​representing the grinding progress of a reference workpiece from multiple reference spectra. More specifically, the processing system 30 calculates multiple grinding index values ​​by calculating multiple changes between multiple reference spectra and accumulating these changes one by one according to the grinding time of the reference workpiece. The multiple changes between multiple reference spectra are two temporally adjacent changes in the multiple reference spectra.

[0066] Figure 5 It is a graph representing two temporally adjacent reference spectra. Figure 5 In the diagram, the vertical axis represents the intensity of reflected light from the reference workpiece, and the horizontal axis represents the wavelength of the reflected light. Figure 5 The display shows: the reference spectrum of reflected light at polishing time t; and the reference spectrum of reflected light at polishing time t+Δt. Time Δt is a predetermined unit time. Two temporally adjacent reference spectra refer to the reference spectrum of reflected light at a certain polishing time t and the reference spectrum of reflected light at polishing time t+Δt after a unit time Δt.

[0067] Since the reference spectrum in this embodiment is generated every time the grinding table 3 rotates once, the unit time Δt is the time it takes for the grinding table 3 to rotate once. In one embodiment, the unit time Δt can also be the time it takes for the grinding table 3 to rotate p times (p is a natural number).

[0068] Since the reference spectrum is generated based on reflected light from the reference workpiece being ground, it changes slightly as the film thickness decreases (i.e., with grinding time). Therefore, during reference workpiece grinding, the shapes of the multiple reference spectra generated based on reflected light at different grinding times differ slightly. Furthermore, these reference spectra reflect the actual grinding rate of the reference workpiece.

[0069] The change in two adjacent reference spectra in time is equivalent to Figure 5 The area shown by the shaded line. In other words, the change in two temporally adjacent reference spectra is the change in the reference spectrum per unit time Δt. In one embodiment, the change V(t) in two temporally adjacent reference spectra can be calculated by the following formula (1).

[0070] [Mathematical Expression 1]

[0071]

[0072] Where Δλ represents the wavelength scale, λ1 represents the lower limit of the wavelength range of the reference spectrum, λ2 represents the upper limit of the wavelength range of the reference spectrum, R(λ,t+Δt) represents the intensity of reflected light from the reference workpiece at time t+Δt for wavelength λ, and R(λ,t) represents the intensity of reflected light from the reference workpiece at time t for wavelength λ.

[0073] In this embodiment, since the reference spectrum is generated each time the grinding table 3 rotates, the change in two temporally adjacent reference spectra is the change in the reference spectrum each time the grinding table 3 rotates. In one embodiment, the change in two temporally adjacent reference spectra can also be the change in the reference spectrum each time the grinding table 3 rotates p times (p is a natural number).

[0074] The change in the reference spectrum V(t) represented by the above formula (1) is calculated per unit time Δt. Figure 6 It is a graph representing the change in the reference spectrum V(t) of the reference workpiece per unit time during the grinding time. Figure 6 In the diagram, the vertical axis represents the change in the reference spectrum, V(t), and the horizontal axis represents the grinding time of the reference workpiece. For example... Figure 6 As shown, multiple variations V(t) of the reference spectrum corresponding to different grinding times during the grinding of the reference workpiece are obtained.

[0075] The processing system 30 accumulates multiple variations V(t) arranged according to the grinding time of a reference workpiece, such as... Figure 7 The values ​​of multiple grinding parameters are calculated as shown. Figure 7In the diagram, the vertical axis represents the grinding index value PI(t), and the horizontal axis represents the grinding time of the reference workpiece. The grinding index value PI(t1) at grinding time t1 is the change V(t1) over grinding time t1. The processing system 30 calculates the grinding index value PI(t2) at grinding time t2 by adding the change V(t2) over grinding time t1 to the change V(t1), and calculates the grinding index value PI(t3) at grinding time t3 by adding the change V(t3) over grinding time t3 to the grinding index value PI(t2) at grinding time t2. The processing system 30 calculates multiple grinding index values ​​PI(t) by repeatedly performing the same calculation. Figure 7 It can be seen that, as multiple variables V(t) accumulate one by one over each unit of time, the grinding index value PI(t) gradually increases along with the grinding time.

[0076] The processing system 30 calculates a pseudo-grinding rate curve based on the initial film thickness, the final film thickness, and two grinding times corresponding to these film thicknesses, assuming a constant grinding rate for the reference workpiece. That is, as... Figure 8 As shown, the processing system 30 calculates the spurious grinding rate line RL based on the initial film thickness Tini of the reference workpiece before grinding, the grinding time at the initial film thickness Tini (i.e., the time when the reference workpiece starts grinding) tini, the final film thickness Tfin of the reference workpiece after grinding, and the grinding time at the final film thickness Tfin (i.e., the time when the reference workpiece ends grinding) tfin. This spurious grinding rate line RL decreases at a constant ratio (linearly) along with the grinding time.

[0077] Secondly, such as Figure 9 As shown, the processing system 30 is based on Figure 7 The changes in multiple grinding index values ​​PI(t) with grinding time are shown to correct the pseudo-grinding rate line RL, thereby determining the grinding rate line RRL. In one embodiment, the processing system 30 determines the grinding rate line RRL by... Figure 7 The multiple grinding index values ​​PI(t) that increase with grinding time are converted into multiple grinding index values ​​that decrease with grinding time. Further calibration and other processing are applied to these converted grinding index values ​​to correct the false grinding rate line RL using these processed multiple grinding index values, thereby determining the grinding rate line RRL. In other embodiments, an approximate curve of the multiple calibrated grinding index values ​​is calculated, and the time interval from t1 to tn of the false grinding rate line RL is replaced with this approximate curve to correct the false grinding rate line RL, thereby determining the grinding rate line RRL. However, the grinding rate line RRL only needs to reflect... Figure 7 The method for determining the grinding rate line RRL is not limited to these implementations, as shown by the variation of multiple grinding index values ​​PI(t) with grinding time.

[0078] The processing system 30 determines multiple reference film thicknesses corresponding to multiple grinding index values ​​based on the grinding rate line RRL. Specifically, the processing system 30 determines multiple reference film thicknesses RH(t1), RH(t2), RH(t3), ..., RH(tn) corresponding to multiple grinding index values ​​at multiple grinding times t1, t2, t3, ..., tn based on the grinding rate line RRL. Furthermore, the processing system 30 associates the multiple reference film thicknesses with multiple reference spectra generated during grinding based on reflected light from a reference workpiece. More specifically, the processing system 30 associates the multiple reference film thicknesses RH(t1), RH(t2), RH(t3), ..., RH(tn) corresponding to multiple grinding times t1, t2, t3, ..., tn with the multiple reference spectra generated at multiple grinding times t1, t2, t3, ..., tn based on reflected light. The multiple reference spectra thus obtained and the corresponding multiple reference film thicknesses are added to a reference spectrum library. The reference spectrum library is stored in the storage device 30a of the processing system 30.

[0079] A reference spectrum is generated based on the reflected light from a reference workpiece during grinding. Therefore, multiple grinding index values ​​calculated from these reference spectra reflect the grinding progress of the reference workpiece. A grinding rate curve, determined by the initial film thickness, multiple grinding index values, and the final film thickness, reflects the actual grinding rate change of the reference workpiece. Therefore, the accuracy of multiple reference film thicknesses determined using the grinding rate curve can be improved.

[0080] Figure 10 This is a flowchart illustrating one implementation method for creating a reference spectral library.

[0081] In step S101, a reference workpiece with the same surface structure as workpiece W is prepared. More specifically, the reference workpiece has an exposed surface made of the same material as workpiece W and has the same layered structure.

[0082] In step S102, the initial film thickness of the reference workpiece before grinding is measured by the film thickness measuring device 101.

[0083] In step S103, the reference workpiece is chemically and mechanically ground by the grinding device 100.

[0084] In step S104, light is irradiated onto the reference workpiece at different grinding times during the grinding process. The processing system 30 generates a reference spectrum of the reflected light from the reference workpiece.

[0085] In step S105, after grinding the reference workpiece, the final film thickness of the reference workpiece after grinding is measured by the film thickness measuring device 101.

[0086] In step S106, the processing system 30 calculates multiple grinding index values ​​representing the grinding progress of a reference workpiece based on multiple reference spectra. In one embodiment, the processing system 30 calculates multiple variations (reference values) between the multiple reference spectra. Figure 6 And by accumulating multiple changes arranged according to the grinding time of a reference workpiece, multiple grinding index values ​​(reference) are calculated. Figure 7 ).

[0087] In step S107, the processing system 30 calculates the pseudo-grinding rate line (reference) based on the initial film thickness and the final film thickness, assuming the grinding rate of the reference workpiece is constant. Figure 8 ).

[0088] In step S108, the processing system 30 determines (creates) the grinding rate line RRL (reference) by correcting the dummy grinding rate line RL based on the changes of multiple grinding index values ​​with grinding time. Figure 9 The grinding rate line RRL is equivalent to a pseudo grinding rate line RL, which is modified based on multiple grinding index values.

[0089] In step S109, the processing system 30 determines multiple reference film thicknesses RH(t1), RH(t2), RH(t3), ...RH(tn) corresponding to multiple polishing index values ​​based on the polishing rate line RRL.

[0090] In step S110, the processing system 30 associates multiple reference film thicknesses with multiple reference spectra. The multiple reference spectra and their corresponding multiple reference film thicknesses are added to a reference spectral library.

[0091] Next, other embodiments of the method for creating the reference spectral library will be described. Since the operation of this embodiment is similar to that of the reference spectral library unless otherwise specified, Figures 1 to 10 The implementation method described is the same, so repeated descriptions are omitted. In this embodiment, the following steps are performed in the same way as the previously described embodiment: measuring the initial film thickness of the reference workpiece; grinding the reference workpiece; generating multiple reference spectra based on the reflected light from the reference workpiece at different grinding times; and measuring the final film thickness of the reference workpiece.

[0092] The processing system 30 calculates a false grinding rate curve based on the initial and final film thicknesses, assuming a constant grinding rate for the reference workpiece. The calculation of the false grinding rate curve is related to the reference... Figure 8 The described implementation method is performed similarly. The processing system 30 calculates multiple dummy film thicknesses of the reference workpiece assuming a constant grinding rate, based on dummy grinding rate lines and multiple grinding times corresponding to multiple reference spectra. The multiple dummy film thicknesses can be calculated according to the reference... Figure 18 The method described is used to extrapolate this. These pseudo-film thicknesses decrease linearly with polishing time.

[0093] The processing system 30 performs principal component analysis on multiple reference spectra separately, and for each reference spectrum, it obtains the principal components Z1 to Zkth principal components Z1. k Multiple principal components (k is a natural number greater than 2). More specifically, the processing system 30 performs principal component analysis on a dataset containing multiple intensities of reflected light at multiple wavelengths of each reference spectrum. Each reference spectrum is as follows: Figure 3 The description indicates the relationship between reflected light intensity and wavelength, and consists of multiple wavelengths of reflected light and their corresponding intensities. Each reference spectrum dataset contains multiple intensity data for that reference spectrum.

[0094] In the example described below, the processing system 30 calculates the first principal component Z1, the second principal component Z2, the third principal component Z3, and the fourth principal component Z4 by performing principal component analysis on each reference spectrum. However, the calculation of the first principal component Z1 to the k-th principal component Z4... k The process can proceed as long as k is a natural number greater than 2, and is not limited to the following examples.

[0095] Examples of calculation formulas for the first principal component Z1 to the fourth principal component Z4 are as follows.

[0096] The first principal component Z1 = W11X1 + W12X2 + W12X3 + ...

[0097] The second principal component Z2 = W21X1 + W22X2 + W22X3 + ...

[0098] The third principal component Z3 = W31X1 + W32X2 + W32X3 + ...

[0099] The fourth principal component Z4 = W41X1 + W42X2 + W42X3 + ...

[0100] Where Xm (m is a natural number) represents the intensity of reflected light at wavelength λm of the reference spectrum, W1m is the weighting coefficient for the intensity Xm used to calculate the first principal component Z1, W2m is the weighting coefficient for the intensity Xm used to calculate the second principal component Z2, W3m is the weighting coefficient for the intensity Xm used to calculate the third principal component Z3, and W4m is the weighting coefficient for the intensity Xm used to calculate the fourth principal component Z4.

[0101] Thus, the first principal component Z1, the second principal component Z2, the third principal component Z3, and the fourth principal component Z4 are calculated for each reference spectrum. Therefore, multiple first principal components Z1, second principal components Z2, third principal components Z3, and fourth principal components Z4 are calculated for multiple reference spectra. Since multiple reference spectra are generated based on reflected light from the reference workpiece during grinding, multiple reference spectra correspond to multiple dummy film thicknesses of the reference workpiece.

[0102] Processing system 30 classifies multiple principal components obtained from multiple reference spectra into first principal component Z1 to k-th principal component Z. k Multiple groups. In the example above, the multiple principal components obtained from multiple reference spectra are classified into four groups: group G1 for the first principal component Z1, group G2 for the second principal component Z2, group G3 for the third principal component Z3, and group G4 for the fourth principal component Z4. Group G1 contains multiple first principal components Z1 obtained from multiple reference spectra; group G2 contains multiple second principal components Z2 obtained from multiple reference spectra; group G3 contains multiple third principal components Z3 obtained from multiple reference spectra; and group G4 contains multiple fourth principal components Z4 obtained from multiple reference spectra.

[0103] The processing system 30 determines multiple correlation coefficients corresponding to multiple groups by calculating the correlation coefficients between multiple principal components contained in multiple groups and their corresponding spurious film thicknesses. The correlation coefficient is an indicator representing the strength of the correlation between multiple principal components belonging to each group and their corresponding spurious film thicknesses. The larger the correlation coefficient, the stronger the correlation between the principal components and the spurious film thickness. The correlation coefficients are calculated using known methods.

[0104] 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 among multiple correlation coefficients calculated for 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 G1 is -0.05, then 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.

[0105] like Figure 11 As shown, the processing system 30 arranges the multiple first principal components contained in the group G1 with the largest absolute value of the correlation coefficient on the first coordinate axis of the coordinate system, and arranges the multiple second principal components contained in the group G2 with the second largest absolute value of the correlation coefficient on the second coordinate axis of the coordinate system. Figure 11 The coordinate system of the illustrated embodiment is an orthogonal coordinate system with a first coordinate axis and a second coordinate axis. The processing system 30 determines multiple data points, i.e., multiple grinding index values ​​PI(t), based on multiple first principal components on the first coordinate axis and multiple second principal components on the second coordinate axis.

[0106] The multiple grinding index values ​​PI(t) in the coordinate system are specific based on multiple first principal components and multiple second principal components, which are derived from multiple reference spectra of reflected light from the reference workpiece. Therefore, the multiple grinding index values ​​PI(t) in the coordinate system correspond to multiple grinding times t1, t2, t3, ..., tn in the grinding of the reference workpiece. Figure 11In the embodiment shown, multiple grinding index values ​​PI(t) on the coordinate system decrease as the grinding time of the reference workpiece increases.

[0107] Processing system 30 based on Figure 11 The multiple grinding index values ​​PI(t) shown are adjusted as grinding time changes to correct the dummy grinding rate line used when calculating the dummy film thickness of the reference workpiece, thereby determining the grinding rate line. In one embodiment, as... Figure 12 As shown, the processing system 30 determines the grinding rate line RRL by applying calibration and other processing to multiple grinding index values ​​PI(t), thereby correcting the false grinding rate line RL using the processed multiple grinding index values. In other embodiments, the grinding rate line RRL is determined by calculating an approximate curve of the multiple grinding index values ​​after calibration, replacing the time interval t1 to tn of the false grinding rate line RL with the approximate curve, and correcting the false grinding rate line RL. However, as long as the grinding rate line RRL can reflect... Figure 11 The method for determining the grinding rate line RRL is not limited to these implementations, as the multiple grinding index values ​​PI(t) shown change with grinding time.

[0108] The processing system 30 determines multiple reference film thicknesses corresponding to multiple grinding index values ​​based on the grinding rate line RRL. Specifically, the processing system 30 determines multiple reference film thicknesses RH(t1), RH(t2), RH(t3), ..., RH(tn) at multiple grinding times t1, t2, t3, ..., tn corresponding to multiple grinding index values, based on the grinding rate line RRL. Furthermore, the processing system 30 associates the multiple reference film thicknesses with multiple reference spectra generated based on reflected light from a reference workpiece during grinding. More specifically, the processing system 30 associates the multiple reference film thicknesses RH(t1), RH(t2), RH(t3), ..., RH(tn) corresponding to multiple grinding times t1, t2, t3, ..., tn with the multiple reference spectra generated based on reflected light at the multiple grinding times t1, t2, t3, ..., tn, respectively. The multiple reference spectra thus obtained and the corresponding multiple reference film thicknesses are added to a reference spectrum library. The reference spectrum library is stored in the storage device 30a of the processing system 30.

[0109] The reference spectrum is generated based on the reflected light from the reference workpiece during grinding. Therefore, multiple grinding index values ​​calculated from multiple reference spectra reflect the grinding progress of the reference workpiece. The grinding rate line, determined based on the initial film thickness, multiple grinding index values, and the final film thickness, reflects the actual grinding rate change of the reference workpiece. Therefore, the accuracy of multiple reference film thicknesses determined using the grinding rate line can be improved.

[0110] Figure 13 This is a flowchart illustrating one implementation method for creating a reference spectral library.

[0111] Because steps S201 to S205 and Figure 11 The steps S101 to S105 shown are the same, so repeated descriptions are omitted.

[0112] In step S206, the processing system 30 calculates the pseudo-grinding rate line based on the initial film thickness and the final film thickness, assuming that the grinding rate of the reference workpiece is constant.

[0113] In step S207, the processing system 30 calculates multiple dummy film thicknesses of the reference workpiece when the grinding rate of the reference workpiece is assumed to be constant, based on the dummy grinding rate lines and multiple grinding times corresponding to multiple reference spectra.

[0114] In step S208, the processing system 30 performs principal component analysis on multiple reference spectra respectively, and obtains the first principal component Z1 to the kth principal component Z for each reference spectrum. k Multiple principal components (k is a natural number greater than 2).

[0115] In step S209, the processing system 30 classifies the multiple principal components obtained from multiple reference spectra into the first principal component Z1 to the kth principal component Z. k The group.

[0116] In step S210, the processing system 30 determines multiple correlation coefficients corresponding to multiple groups by calculating the correlation coefficients between the multiple principal components contained in the multiple groups and the corresponding multiple pseudo-film thicknesses.

[0117] 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 among the multiple correlation coefficients calculated for multiple groups.

[0118] In step S212, the processing system 30 arranges the principal components contained 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 contained in the group with the second largest absolute value of the correlation coefficient on the second coordinate axis of the coordinate system.

[0119] In step S213, the processing system 30 determines multiple data points, i.e., multiple grinding index values ​​PI(t), based on multiple principal components on the first coordinate axis and multiple principal components on the second coordinate axis (refer to...). Figure 11 ).

[0120] In step S214, the processing system 30 corrects the dummy grinding rate line RL used when calculating the dummy film thickness of the reference workpiece based on the changes of multiple grinding index values ​​PI(t) with grinding time, thereby determining (creating) the grinding rate line RRL (reference). Figure 12 The grinding rate line RRL is equivalent to a pseudo grinding rate line RL that is corrected based on multiple grinding index values ​​PI(t).

[0121] In step S215, the processing system 30 determines multiple reference film thicknesses RH(t1), RH(t2), RH(t3), ...RH(tn) corresponding to multiple polishing index values ​​PI(t) based on the polishing rate line RRL.

[0122] In step S216, the processing system 30 correlates multiple reference film thicknesses with multiple reference spectra. The multiple reference spectra and their corresponding multiple reference film thicknesses are then added to a reference spectral library.

[0123] Secondly, another embodiment of the method for creating the reference spectral library will be described. Since the operation of this embodiment is similar to that of the reference spectral library unless otherwise specified, the following will be explained: Figures 1 to 11 The implementation method described is the same, so repeated descriptions are omitted. Grinding index values ​​are not calculated in this embodiment. Instead, the intermediate film thickness of the reference workpiece is measured at least once during the grinding of the reference workpiece. In the embodiments described below, the intermediate film thickness of the reference workpiece is measured multiple times during the grinding of the reference workpiece.

[0124] The initial film thickness measurement of the reference workpiece, grinding the reference workpiece, generating multiple reference spectra based on the reflected light from the reference workpiece at different grinding times, and measuring the final film thickness of the reference workpiece are all 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 the grinding process. The measurement of the intermediate film thickness is performed after the initial film thickness measurement and before the final film thickness measurement.

[0125] Initial film thickness and final film thickness through Figure 4 The film thickness is measured by the film thickness measuring device 101 shown. The intermediate film thickness is measured by... Figure 4 The film thickness measuring device 101 shown or Figure 2 The optical film thickness measuring device 20 is used for measurement. When measuring the intermediate film thickness using the film thickness measuring device 101, the grinding of the reference workpiece by the grinding device 100 is paused, and the reference workpiece is transported to the film thickness measuring device 101 by the transport device 103, and the intermediate film thickness of the reference workpiece is measured by the film thickness measuring device 101. When measuring the intermediate film thickness using the optical film thickness measuring device 20, the reference workpiece is ground by the grinding device 100, and the intermediate film thickness of the reference workpiece is measured by the optical film thickness measuring device 20 at the same time.

[0126] The processing system 30 determines the grinding rate line, which represents the relationship between the film thickness of the reference workpiece and the grinding time, based on the initial film thickness, multiple intermediate film thicknesses, and the final film thickness. Figure 15 This is an example of a graph representing the relationship between the film thickness of a reference workpiece and the grinding time. Figure 15 In the diagram, the vertical axis represents the film thickness of the reference workpiece, and the horizontal axis represents the grinding time of the reference workpiece. Figure 15In the embodiment shown, three intermediate film thicknesses Titr1, Titr2, and Titr3 are measured by film thickness measuring device 101 or optical film thickness measuring device 20 after the grinding of the reference workpiece begins and before the grinding ends. Figure 15 The grinding times ti1, ti2, and ti3 shown correspond to the intermediate film thicknesses Titr1, Titr2, and Titr3, respectively.

[0127] The processing system 30 determines (creates) a polishing rate line RRL based on 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 using specific film thickness data points based on 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 other embodiments, the processing system 30 may also determine the polishing rate line RRL based on an approximate curve of specific film thickness data points based on 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.

[0128] The processing system 30 determines multiple reference film thicknesses corresponding to multiple reference spectra of reflected light from a reference workpiece being ground, and multiple grinding times, based on the grinding rate line RRL. These multiple reference film thicknesses can be compared with reference... Figure 9 The implementation method described is similarly determined. Furthermore, the processing system 30 associates multiple reference film thicknesses with multiple reference spectra. The multiple reference spectra thus obtained and the corresponding multiple reference film thicknesses are added to a reference spectral library. The reference spectral library is stored in the storage device 30a of the processing system 30.

[0129] In this embodiment, a grinding rate line (RRL) is created based on multiple measured values ​​of the film thickness of a reference workpiece. Therefore, the accuracy of the multiple reference film thicknesses determined using the grinding rate line (RRL) can be improved.

[0130] Figure 16 This is a flowchart illustrating one implementation method for creating a reference spectral library.

[0131] Because steps S301 to S304 and Figure 11 S101 to S104 are the same as shown, so their repeated descriptions are omitted.

[0132] In step S305, the intermediate film thickness is measured once or multiple times by the film thickness measuring device 101 or the optical film thickness measuring device 20, referring to the film thickness during the grinding of the workpiece.

[0133] In step S306, after grinding the reference workpiece, the final film thickness of the reference workpiece after grinding is measured by the film thickness measuring device 101.

[0134] In step S307, the processing system 30 determines (fabricates) a grinding rate line RRL (reference) representing the relationship between the film thickness and grinding time of a reference workpiece based on the initial film thickness, intermediate film thickness, and final film thickness. Figure 14 ).

[0135] In step S308, the processing system 30 determines multiple reference film thicknesses corresponding to multiple reference spectra based on the abrasion rate line RRL.

[0136] In step S309, the processing system 30 correlates multiple reference film thicknesses with multiple reference spectra. The multiple reference spectra and their corresponding multiple reference film thicknesses are then added to a reference spectral library.

[0137] The above embodiments are described with the aim of enabling those skilled in the art to implement the present invention. Various variations of the above embodiments can, of course, be implemented by those skilled in the art, and the technical concept of the present invention can be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is interpreted within the broadest scope of the technical concept defined by the claims.

[0138] Symbol Explanation

[0139] 1: Grinding head 2: Grinding pad 2a: Grinding surface 3: Grinding table 5: Grinding fluid supply nozzle 6: Table motor 9: Motion control unit 10: Head shaft 15: Grinding head rotation device 20: Optical film thickness measuring device 22: Light source 25: Optical sensor head 27: Spectrometer 30: Processing system 31: Fiber optic cable for projection 32: Fiber optic cable for receiving light 100: Grinding device 101: Film thickness measuring device 103: Handling device W: Workpiece.

Claims

1. A method for fabricating a reference spectral library, used for estimating the film thickness of a workpiece, characterized in that, Measure the initial film thickness of the reference workpiece before grinding. The reference workpiece is ground using a grinding device. Multiple reference spectra of the reflected light from the reference workpiece are generated from multiple grinding times during the grinding process. After grinding the reference workpiece, the final film thickness of the reference workpiece is measured. Based on the multiple reference spectra, multiple grinding index values ​​representing the grinding progress of the reference workpiece are calculated. Based on the initial film thickness, the multiple grinding index values, and the final film thickness, a grinding rate curve representing the relationship between the film thickness and grinding time of the reference workpiece is determined. Based on the polishing rate curve, multiple reference film thicknesses corresponding to the multiple polishing index values ​​are determined. A reference spectral library is created by associating the plurality of reference film thicknesses with the plurality of reference spectra.

2. The method for constructing the reference spectral library as described in claim 1, characterized in that, The calculation of the multiple grinding index values ​​includes the following: Multiple changes among the multiple reference spectra are calculated, where each change is a temporally adjacent change among the multiple reference spectra. The multiple grinding index values ​​are calculated by accumulating the multiple changes arranged according to the grinding time of the reference workpiece.

3. The method for constructing the reference spectral library as described in claim 1, characterized in that, The determination of the grinding rate line includes the following: Based on the initial film thickness and the final film thickness, a pseudo-grinding rate curve is calculated assuming the grinding rate of the reference workpiece is constant. The false grinding rate line is corrected based on the changes in the multiple grinding index values ​​with grinding time, thereby determining the grinding rate line.

4. The method for constructing the reference spectral library as described in claim 1, characterized in that, The calculation of the multiple grinding index values ​​includes the following: Based on the initial film thickness, the final film thickness, and the multiple grinding times, multiple dummy film thicknesses of the reference workpiece are calculated assuming a constant grinding rate. By performing principal component analysis on the multiple reference spectra respectively, multiple principal components containing the first principal component to the kth principal component are obtained for each reference spectrum, where k is a natural number greater than 2. The principal components obtained from the multiple reference spectra are classified into multiple groups from the first principal component to the kth principal component. By calculating the correlation coefficients between the principal components contained in the multiple groups and the multiple pseudo-film thicknesses, the multiple correlation coefficients corresponding to the multiple groups are determined. The first group with the largest absolute value of the correlation coefficient and the second group with the second largest absolute value of the correlation coefficient are determined from the plurality of correlation coefficients. Arrange the principal components contained in the first group on the first coordinate axis of the coordinate system. Arrange the principal components contained in the second group on the second coordinate axis of the coordinate system. The plurality of grinding index values ​​are determined based on a plurality of data points specific to the plurality of principal components on the first coordinate axis and the plurality of principal components on the second coordinate axis.

5. A method for preparing a reference spectral library, used for estimating the film thickness of a workpiece, characterized in that, Measure the initial film thickness of the reference workpiece before grinding. The reference workpiece is ground using a grinding device. Multiple reference spectra of the reflected light from the reference workpiece are generated from multiple grinding times during the grinding process. During the grinding of the reference workpiece, the intermediate film thickness of the reference workpiece is measured at least once. After grinding the reference workpiece, the final film thickness of the reference workpiece is measured. Based on the initial film thickness, the intermediate film thickness, and the final film thickness, a grinding rate curve representing the relationship between the film thickness of the reference workpiece and grinding time is determined. Based on the grinding rate curve, multiple reference film thicknesses are determined at the multiple grinding times. A reference spectral library is created by associating the reference film thickness with the plurality of reference spectra.

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