Polishing method and polishing apparatus

Abstract

The present invention provides a polishing method that can detect the polishing endpoint where the upper layer is polished and the lower layer is exposed, regardless of changes in torque current and polishing rate. [Solution] The polishing method involves rotating the polishing table 3, supplying polishing liquid to the polishing pad 2 on the polishing table 3, and pressing the workpiece W against the polishing pad 2 to polish the workpiece W in the presence of the polishing liquid. Each time the polishing table 3 rotates, light is irradiated onto the workpiece W to generate a spectrum of reflected light from the workpiece W, an index value indicating the similarity between the reflected light spectrum and the interface spectrum is calculated, and the polishing endpoint where the index value is maximum or minimum is determined. The interface spectrum is the spectrum of reflected light from the reference workpiece that is generated when the first film is removed during the polishing of the reference workpiece, exposing the second film underneath.

Description

Technical Field

[0001] The present invention relates to a technique for polishing workpieces such as wafers, substrates, wiring boards, and corner boards, and particularly to a technique for detecting the end point of polishing of a workpiece.

Background Art

[0002] In the manufacture of semiconductor devices, there is a process of polishing the surface of a wafer with a CMP (Chemical Mechanical Polishing) apparatus. The CMP apparatus performs wafer polishing as follows. While rotating a polishing table holding a polishing pad, a polishing liquid (typically, a slurry containing abrasive grains) is supplied onto the polishing pad. The wafer is pressed against the polishing pad by a polishing head and is brought into sliding contact with the polishing pad. The surface of the wafer is planarized by a combination of the chemical action of the polishing liquid and the mechanical action of the abrasive grains contained in the polishing liquid and the polishing pad.

[0003] The polishing of the wafer is stopped when the upper layer is polished and the lower layer is exposed. There are a torque monitoring method and a spectrum monitoring method for detecting the end point of such wafer polishing. The torque monitoring method monitors the current (hereinafter referred to as torque current) supplied to an electric motor that rotates the polishing table during wafer polishing, and detects the polishing end point at the time when the torque current changes across a threshold value. The spectrum monitoring method irradiates light on the wafer during wafer polishing, obtains the cumulative change amount of the spectrum of the reflected light from the wafer, and detects the polishing end point based on this cumulative change amount of the spectrum.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

[0005] The torque monitoring method described above relies on changes in torque current for detecting the polishing endpoint, while the spectrum monitoring method relies on changes in the wafer polishing rate for detecting the polishing endpoint. However, depending on the chemical properties of the polishing solution used to polish the wafer, the torque current or wafer polishing rate may not change significantly when the upper layer is removed and the lower layer is exposed, resulting in the above methods failing to detect the polishing endpoint.

[0006] Therefore, the present invention provides a polishing method and polishing apparatus that can detect the polishing endpoint where the upper layer is polished and the lower layer is exposed, regardless of changes in torque current and polishing rate. [Means for solving the problem]

[0007] In one embodiment, a polishing method is provided, in which a polishing liquid is supplied to a polishing pad on the polishing table while the polishing table is rotated, and the workpiece is polished in the presence of the polishing liquid by pressing the workpiece against the polishing pad, and each time the polishing table rotates, light is shone on the workpiece to generate a spectrum of reflected light from the workpiece, an index value indicating the similarity between the spectrum of reflected light and the interface spectrum is calculated, the interface spectrum being the spectrum of reflected light from the reference workpiece generated when the first film is removed during the polishing of the reference workpiece and the second film underneath is exposed, and the polishing endpoint where the index value is maximum or minimum is determined.

[0008] In one embodiment, the index value is a plurality of index values ​​calculated according to different calculation algorithms, and the polishing endpoint is the point in time when at least one of the plurality of index values ​​becomes the maximum or minimum. In one embodiment, the polishing endpoint is the point at which any one of the plurality of index values ​​first reaches its maximum or minimum value. In one embodiment, the polishing endpoint is the point at which all of the multiple index values ​​reach their maximum or minimum. In one embodiment, the reference workpiece has the same surface structure as the workpiece. In one embodiment, the polishing conditions for the reference workpiece are the same as the polishing conditions for the workpiece. In one embodiment, the interface spectrum is acquired in advance by an interface spectrum acquisition step before polishing the workpiece, and the interface spectrum acquisition step includes generating a theoretical interface spectrum of light reflected from the reference workpiece when the first film is removed and the second film is exposed, generating a plurality of spectra of reflected light from the reference workpiece while polishing the reference workpiece, calculating an index value indicating the similarity between each of the plurality of spectra and the theoretical interface spectrum, selecting the spectrum with the maximum or minimum index value from the plurality of spectra, and designating the selected spectrum as the interface spectrum.

[0009] In one embodiment, a polishing apparatus is provided comprising: a polishing table supporting a polishing pad; a table motor for rotating the polishing table; a polishing fluid supply nozzle for supplying polishing fluid to the polishing pad; a polishing head for polishing a workpiece in the presence of the polishing fluid by pressing the workpiece against the polishing pad; and an optical system that irradiates the workpiece with light each time the polishing table rotates and generates a spectrum of reflected light from the workpiece, wherein the optical system calculates an index value indicating the similarity between the spectrum of reflected light and an interface spectrum, the interface spectrum being the spectrum of reflected light from the reference workpiece generated when a first film is removed during polishing of the reference workpiece and a second film underneath is exposed, and the system is configured to determine the polishing endpoint where the index value is maximum or minimum.

[0010] In one embodiment, the optical system is configured to calculate a plurality of index values ​​according to different calculation algorithms and to determine the polishing endpoint where at least one of the plurality of index values ​​is the maximum or minimum. In one embodiment, the optical system is configured to determine the polishing endpoint where any one of the plurality of index values ​​first reaches its maximum or minimum value. In one embodiment, the optical system is configured to determine the polishing endpoint at which all of the plurality of index values ​​are at their maximum or minimum. [Effects of the Invention]

[0011] When the first layer of a workpiece is removed by polishing, exposing the second layer, the spectrum of the reflected light from the workpiece is closest to the interface spectrum. The point at which the similarity between the reflected light spectrum and the interface spectrum is maximized, i.e., the point at which the similarity index value is maximum or minimum, indicates the polishing endpoint where the first layer of the workpiece has been removed and the second layer is exposed. Therefore, the polishing endpoint of the workpiece can be accurately detected based on the similarity index value. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram showing one embodiment of a polishing apparatus. [Figure 2] This is a cross-sectional view showing the detailed configuration of the optical system. [Figure 3] An example of the spectrum of reflected light from a workpiece is shown. [Figure 4] This is a cross-sectional view showing an example of the surface structure of a workpiece before polishing. [Figure 5] Figures 5(a) to 5(c) show an example of how the surface structure shown in Figure 4 changes as the workpiece is polished. [Figure 6] This figure illustrates one embodiment of a method for calculating an index value indicating the similarity between multiple spectra generated during the polishing of a workpiece, one by one, and the interface spectrum. [Figure 7] This graph shows an example of how the index value indicating the similarity between two spectra changes with polishing time. [Figure 8]It is a flowchart for explaining an embodiment of determining the polishing end point of a workpiece described with reference to FIGS. 6 and 7. [Figure 9] It is a flowchart for explaining an embodiment of an interface spectrum determination step. [Figure 10] It is a diagram showing an example of a theoretical interface spectrum. [Figure 11] It is a schematic diagram for explaining step 203 shown in FIG. 9.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an embodiment of a polishing apparatus. As shown in FIG. 1, the polishing apparatus includes a polishing table 3 that supports a polishing pad 2, a polishing head 1 that presses a workpiece W against the polishing pad 2, a table motor 6 that rotates 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. The upper surface of the polishing pad 2 constitutes a polishing surface 2a for polishing the workpiece W. The workpiece W has a film forming a wiring structure on its surface. Examples of the workpiece W include a wafer, a substrate, a wiring board, a square substrate, etc. used in the manufacture of semiconductor devices. In one example, the workpiece W is a wafer on which a multilayer film is formed.

[0014] The polishing head 1 is connected to a head shaft 10, and the head shaft 10 is connected to a polishing head rotation device 15. The polishing head rotation 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 rotation device 15 is not particularly limited, but in one example, the polishing head rotation device 15 includes an electric motor, a belt, a pulley, etc. The polishing table 3 is connected to the 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 rotation device 15, and the table motor 6 are connected to the operation control unit 9.

[0015] The workpiece W is polished as follows. The table motor 6 and the polishing head rotating device 15 rotate the polishing table 3 and the polishing head 1 in the directions indicated by the arrows in FIG. 1 while 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 workpiece W is pressed against the polishing surface 2a of the polishing pad 2 by the polishing head 1 in a state where polishing liquid exists 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.

[0016] The operation control unit 9 includes a storage device 9a in which a program is stored and an arithmetic device 9b that executes arithmetic 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) and a solid state drive (SSD). Examples of the arithmetic device 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.

[0017] The polishing apparatus includes an optical system 20 that detects the polishing end point of the workpiece W. The optical system 20 includes a light source 22 that emits light, an optical sensor head 25 that irradiates the workpiece W with the light of the light source 22 and receives the reflected light from the workpiece W, a spectroscope 27 connected to the optical sensor head 25, and a spectrum of the reflected light from the workpiece W. And a spectrum processing unit 30 for generating. The optical sensor head 25 is disposed in the polishing table 3 and rotates together with the polishing table 3.

[0018] The spectrum processing unit 30 comprises a storage device 30a in which a program is stored, and an arithmetic unit 30b that performs calculations according to the instructions contained in the program. The spectrum processing unit 30 is composed of at least one computer. The storage device 30a comprises main memory such as random access memory (RAM) and auxiliary storage such as a hard disk drive (HDD) or solid-state drive (SSD). Examples of arithmetic units 30b include a CPU (central processing unit) and a GPU (graphics processing unit). However, the specific configuration of the spectrum processing unit 30 is not limited to these examples.

[0019] The motion control unit 9 and the spectrum processing unit 30 may each be composed of multiple computers. For example, the motion control unit 9 and the spectrum processing unit 30 may each be composed of a combination of edge servers and cloud servers. In one embodiment, the motion control unit 9 and the spectrum processing unit 30 may be composed of a single computer.

[0020] Figure 2 is a cross-sectional view showing the detailed configuration of the optical system 20. The optical system 20 includes a light-emitting optical fiber cable 31 connected to a light source 22 and a light-receiving optical fiber cable 32 connected to a spectrometer 27. The tip 31a of the light-emitting optical fiber cable 31 and the tip 32a of the light-receiving optical fiber cable 32 constitute an optical sensor head 25. That is, the light-emitting optical fiber cable 31 guides the light emitted by the light source 22 to the workpiece W on the polishing pad 2, and the light-receiving optical fiber cable 32 receives the reflected light from the workpiece W and transmits it to the spectrometer 27.

[0021] The spectrometer 27 is connected to the spectrum processing unit 30. The light-emitting optical fiber cable 31, the light-receiving optical fiber cable 32, the light source 22, and the spectrometer 27 are mounted on the polishing table 3 and rotate together with the polishing table 3 and the polishing pad 2. The optical sensor head 25, consisting of the tip 31a of the light-emitting optical fiber cable 31 and the tip 32a of the light-receiving optical fiber cable 32, is positioned facing the surface of the workpiece W on the polishing pad 2.

[0022] The optical sensor head 25 is positioned so that it crosses the surface of the workpiece W on the polishing pad 2 each time the polishing table 3 and polishing pad 2 rotate once. The polishing pad 2 has a through hole 2b located above the optical sensor head 25. The optical sensor head 25 irradiates the workpiece W with light through the through hole 2b and receives reflected light from the workpiece W through the through hole 2b each time the polishing table 3 rotates once.

[0023] In one embodiment, a flow of pure water may be formed within the through-hole 2b of the polishing pad 2 to prevent polishing fluid and polishing debris from coming into contact with the optical sensor head 25. Light is guided from the optical sensor head 25 through the pure water to the workpiece W, 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) may be fitted within the through-hole 2b of the polishing pad 2. The transparent window is made of a material that allows light transmission (e.g., a transparent resin). In this case, light is guided from the optical sensor head 25 through the transparent window to the workpiece W, and reflected light from the workpiece W is received by the optical sensor head 25 through the transparent window.

[0024] In one embodiment, the light source 22 is a flash light source that emits light repeatedly 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 moves across 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, each time the polishing table 3 rotates, light is irradiated onto multiple measurement points on the workpiece W, including the center point.

[0025] 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 optical fiber 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 of 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 reflected light from the workpiece W is transmitted to the spectrometer 27 through the light-receiving optical fiber cable 32.

[0026] The spectrometer 27 is configured to decompose reflected light according to its wavelength and measure the intensity of the reflected light at each wavelength over a predetermined wavelength range. That is, the spectrometer 27 decomposes the reflected light from the workpiece W according to its 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 can also be expressed as a relative value such as reflectance or relative reflectance. The light intensity measurement data is sent to the spectrum processing unit 30.

[0027] The spectrum processing unit 30 generates a reflected light spectrum from the light intensity measurement data. Figure 3 shows an example of a reflected light spectrum from a workpiece W. The reflected light spectrum from a workpiece W contains information about the film thickness of the workpiece W. In other words, the reflected light spectrum changes depending on the film thickness of the workpiece W. The spectrum processing unit 30 is configured to determine the film thickness of the workpiece W and the polishing endpoint based on the reflected light spectrum.

[0028] Figure 4 is a cross-sectional view showing an example of the surface structure of a workpiece W before polishing. As shown in Figure 4, the workpiece W before polishing has a surface structure including a first film 101 and a second film 102 formed beneath the first film 101. Examples of workpiece W include wafers, substrates, wiring boards, and square substrates used in the manufacture of semiconductor devices. The material constituting the first film 101 is different from the material constituting the second film 102. In one example, the first film 101 is an oxide film (e.g., an SiO2 film), and the second film 102 is a polishing stopper film (e.g., a SiN film).

[0029] Figures 5(a) to 5(c) illustrate an example of how the surface structure shown in Figure 4 changes as the workpiece W is polished. More specifically, Figure 5(a) is the initial stage of polishing the workpiece W, Figure 5(b) is the intermediate stage of polishing the workpiece W, and Figure 5(c) is the final stage of polishing the workpiece W. As shown in Figures 5(a) to 5(c), as the workpiece W is polished, the thickness of the first film 101 constituting the exposed surface of the workpiece W gradually decreases. Polishing of the workpiece W is carried out until the first film 101 is removed from the workpiece W and the second film 102 is exposed. That is, as shown in Figure 5(c), the final stage of polishing the workpiece W is when the first film 101 is removed and the second film 102 is exposed.

[0030] The optical system 20 is configured to irradiate the workpiece W with light each time the polishing table 3 rotates and generate a spectrum of reflected light from the workpiece W. More specifically, the optical sensor head 25 irradiates the workpiece W with light each time the polishing table 3 rotates and receives the reflected light from the workpiece W, and the spectrometer 27 measures the intensity of the reflected light from the workpiece W at each wavelength. The spectrum processing unit 30 generates a spectrum of reflected light from the light intensity measurement data and detects the polishing endpoint of the workpiece W based on the spectrum.

[0031] The following describes one embodiment for detecting the polishing endpoint of the workpiece W. The spectrum processing unit 30 compares the reflected light spectrum (hereinafter sometimes simply referred to as the reflected light spectrum) with the interface spectrum each time it generates a spectrum of reflected light from the workpiece W, and calculates an index value indicating the similarity between the reflected light spectrum and the interface spectrum. The interface spectrum is the spectrum of reflected light from the reference workpiece that is generated when the first film is removed during the polishing of the reference workpiece and the second film underneath is exposed. The interface spectrum is determined from the results of polishing the reference workpiece performed before polishing the workpiece W. The method for determining the interface spectrum using a reference workpiece will be described later.

[0032] The spectrum processing unit 30 is configured to calculate an index value indicating the similarity between the spectrum of reflected light from the workpiece W and the interface spectrum during the polishing of the workpiece W, and to determine the polishing endpoint where the index value is maximized or minimized. The index value is calculated according to a predetermined calculation algorithm.

[0033] The similarity between two spectra indicates how similar the shapes of the two spectra are. Each spectrum represents multiple intensities of reflected light corresponding to multiple wavelengths, as explained with reference to Figure 3. These multiple intensities of reflected light corresponding to multiple wavelengths can be treated as a data group representing the characteristics of that spectrum. Therefore, the similarity between two spectra can be calculated as the similarity between two data groups.

[0034] An index value indicating the similarity between two spectra can be calculated according to a calculation algorithm used to determine the similarity between two data groups. The calculation algorithm varies depending on the type of index value. Examples of index values ​​are listed below. Euclidean distance Mahalanobis distance • Normalized cross-correlation (NCC) Cosine similarity However, the index value is not limited to these examples, as long as it can demonstrate the similarity between the two spectra.

[0035] Figure 6 illustrates one embodiment in which multiple spectra generated during the polishing of a workpiece W are compared one by one with the interface spectrum, and an index value indicating the similarity between these two spectra is calculated. As shown in Figure 6, the spectrum processing unit 30 generates a spectrum of reflected light from the workpiece W each time the polishing table 3 rotates once. Furthermore, each time a spectrum of reflected light is generated, the spectrum processing unit 30 calculates an index value indicating the similarity between each spectrum of reflected light and the interface spectrum, according to a predetermined calculation algorithm.

[0036] Figure 7 is a graph showing an example of how index values ​​indicating similarity between two spectra change with polishing time. In the example shown in Figure 7, Euclidean distance, Mahalanobis distance, normalized cross-correlation (NCC), and cosine similarity are used as index values ​​to indicate similarity. As shown in Figure 7, the index values ​​change with polishing time. The way in which the index values ​​change differs depending on the calculation algorithm used to calculate the index values. For example, the Euclidean distance and Mahalanobis distance decrease as the similarity between the two spectra increases. In contrast, the normalized cross-correlation (NCC) and cosine similarity increase as the similarity between the two spectra increases.

[0037] The spectral processing unit 30 may calculate a single index value using a single calculation algorithm. For example, the spectral processing unit 30 may use Euclidean distance as the index value, calculate the index value according to a calculation algorithm for calculating Euclidean distance, and determine the polishing endpoint of the workpiece W, which is the point at which the index value is minimized. In another example, the spectral processing unit 30 may use cosine similarity as the index value, calculate the index value according to a calculation algorithm for calculating cosine similarity, and determine the polishing endpoint of the workpiece W, which is the point at which the index value is maximized.

[0038] In one embodiment, the spectral processing unit 30 may calculate multiple index values ​​using different calculation algorithms. For example, the spectral processing unit 30 may use Euclidean distance, Mahalanobis distance, normalized cross-correlation, and cosine similarity as multiple index values, calculate multiple index values ​​according to different calculation algorithms for calculating these index values, and determine the polishing endpoint of the workpiece W, which is the point in time when any one of the multiple index values ​​is first at its minimum or maximum. In another example, the spectral processing unit 30 determines the polishing endpoint of the workpiece W, which is the point in time when all of the above multiple index values ​​are at their minimum or maximum.

[0039] In one embodiment, the multiple index values ​​may be two or three index values ​​selected from Euclidean distance, Mahalanobis distance, normalized cross-correlation, and cosine similarity. In other embodiments, the index values ​​may be index values ​​other than Euclidean distance, Mahalanobis distance, normalized cross-correlation, and cosine similarity, as long as they can indicate the similarity between the two spectra.

[0040] When the first film 101 of the workpiece W is removed by polishing, exposing the second film 102, the spectrum of the reflected light from the workpiece W approaches the interface spectrum most closely. The point at which the similarity between the reflected light spectrum and the interface spectrum is maximized, i.e., the point at which the similarity index value is maximum or minimum, indicates the polishing endpoint where the first film 101 of the workpiece W has been removed and the second film 102 is exposed. Therefore, the optical system 20 can accurately determine the polishing endpoint of the workpiece W based on the similarity index value.

[0041] Figure 8 is a flowchart illustrating one embodiment for determining the polishing endpoint of the workpiece W, as described with reference to Figures 6 and 7. In step 101, while polishing the reference workpiece with the polishing apparatus shown in Figures 1 and 2, the spectral processing unit 30 generates multiple spectra of reflected light from the reference workpiece. These multiple spectra are generated from the start to the end of polishing the reference workpiece.

[0042] In step 102, the spectrum processing unit 30 determines an interface spectrum from among multiple spectra of reflected light from the reference workpiece. This interface spectrum is the spectrum of reflected light from the reference workpiece that is generated when the first film on the reference workpiece is removed during polishing, exposing the second film underneath. The interface spectrum is stored in the memory device 30a of the spectrum processing unit 30.

[0043] In step 103, while polishing the workpiece W using the polishing apparatus shown in Figures 1 and 2, the spectrum processing unit 30 generates a spectrum of reflected light from the workpiece W. The spectrum of reflected light is generated each time the polishing table 3 rotates during the polishing of the workpiece W. In step 104, the spectrum processing unit 30 calculates an index value indicating the similarity between the spectrum of reflected light from the workpiece W and the interface spectrum each time such a spectrum is generated. In step 105, the spectral processing unit 30 determines the polishing endpoint where the index value is maximum or minimum. In step 106, the spectrum processing unit 30 issues a command to the operation control unit 9 to terminate the polishing of the workpiece W.

[0044] Next, an embodiment for determining the interface spectrum will be described. The interface spectrum is one of several spectra of reflected light from the reference workpiece generated during the polishing of the reference workpiece. The reference workpiece has the same surface structure as workpiece W. That is, as shown in Figure 3, if workpiece W has a surface structure including a first film 101 and a second film 102 underneath it, then the reference workpiece also has a surface structure including a first film 101 and a second film 102 underneath it. The reference workpiece is polished using the polishing apparatus shown in Figures 1 and 2 under the same polishing conditions as workpiece W. The polishing conditions include the rotation speed of the polishing table 3, the rotation speed of the polishing head 1, the pressing force of the polishing head 1, and the polishing fluid used.

[0045] During the polishing of the reference workpiece, similar to the polishing of the workpiece W, the optical sensor head 25 irradiates the reference workpiece with light each time the polishing table 3 rotates, and the spectrum processing unit 30 generates a spectrum of reflected light from the reference workpiece. Multiple spectra of reflected light from the reference workpiece are generated from the start to the end of the polishing process.

[0046] The spectrum processing unit 30 determines the interface spectrum from among multiple spectra of reflected light from the reference workpiece. The interface spectrum is the spectrum of light reflected from the reference workpiece when the first film on the reference workpiece is removed and the second film is exposed during polishing of the reference workpiece. Known techniques such as torque monitoring methods or spectrum monitoring methods can be used to determine the interface spectrum from multiple spectra generated during the polishing of the reference workpiece.

[0047] The torque monitoring method involves monitoring the current supplied to the table motor 6 (hereinafter referred to as the torque current) during the polishing of the reference workpiece, and detecting the polishing endpoint when the torque current crosses a threshold. The spectrum monitoring method involves determining the cumulative change in the spectrum of reflected light from the reference workpiece during the polishing of the reference workpiece, and detecting the polishing endpoint when this cumulative change in the spectrum crosses a certain threshold. In addition to these known techniques, the interface spectrum may also be determined by considering the operator's judgment of changes in the torque current or changes in the cumulative change in the spectrum.

[0048] In other embodiments, the interface spectrum is determined by the interface spectrum determination process described below, instead of the technique described above. Figure 9 is a flowchart illustrating one embodiment of the interface spectrum determination process.

[0049] In step 201, the spectral processing unit 30 generates a theoretical interface spectrum of light reflected from the reference workpiece when the first film of the reference workpiece is removed and the second film is exposed. Figure 10 shows an example of a theoretical interface spectrum. The theoretical interface spectrum is generated by a light reflection simulation using optical coefficients such as the refractive index of the second film, the light absorption rate of the second film, and the thickness of the second film.

[0050] In step 202, while polishing the reference workpiece with the polishing apparatus shown in Figures 1 and 2, the spectral processing unit 30 generates multiple spectra of reflected light from the reference workpiece. In step 203, the spectral processing unit 30 calculates an index value indicating the similarity between each of the multiple spectra of reflected light from the reference workpiece and the theoretical interface spectrum. This index value is of the same type as the index value described above that indicates the similarity between the spectrum of reflected light from the workpiece W and the interface spectrum, and is calculated in the same manner. Figure 11 is a schematic diagram illustrating step 203.

[0051] In step 204, the spectrum processing unit 30 selects the spectrum with the maximum or minimum index value calculated in step 203 from the multiple spectra obtained in step 202. The selection of the spectrum with the maximum or minimum index value is performed after the polishing of the reference workpiece is completed. In step 205, the spectrum processing unit 30 designates the selected spectrum as the interface spectrum. The spectrum processing unit 30 stores the designated interface spectrum in the storage device 30a.

[0052] The interface spectrum determined in this way is used to detect (determine) the polishing endpoint of the workpiece W, as explained with reference to Figure 8.

[0053] The embodiments described above are intended to enable persons with ordinary skill in the art to implement the present invention. Various modifications of the above embodiments can be made naturally by those skilled in the art, and the technical idea of ​​the present invention can be applied to other embodiments as well. Therefore, the present invention is not limited to the embodiments described, but is to be interpreted in the broadest sense according to the technical idea defined by the claims. [Explanation of symbols]

[0054] 1 Polishing head 2 polishing pads 2a Polished surface 3 Polishing Table 5. Polishing fluid supply nozzle 6 Table motors 9. Operation Control Unit 10 Head Shaft 15. Polishing head rotation device 20 Optical Systems 22 Light source 25 Optical sensor heads 27 Spectrometer 30. Spectrum Processing Unit 31. Floodlight Fiber Optic Cable 32 Optical fiber receiving cable W Workpiece

Claims

1. While rotating the polishing table, polishing fluid is supplied to the polishing pad on the polishing table. The workpiece is polished in the presence of the polishing liquid by pressing the workpiece against the polishing pad. Each time the polishing table rotates, light is shone onto the workpiece, and the spectrum of the reflected light from the workpiece is generated. An index value indicating the similarity between the reflected light spectrum and the interface spectrum is calculated, and the interface spectrum is the spectrum of reflected light from the reference workpiece that is generated when the first film is removed during polishing of the reference workpiece, exposing the second film underneath. A polishing method for determining the polishing endpoint where the aforementioned index value is maximum or minimum.

2. The aforementioned index values ​​are multiple index values ​​calculated according to different calculation algorithms. The polishing endpoint is the point at which at least one of the plurality of index values ​​becomes the maximum or minimum, according to claim 1.

3. The polishing method according to claim 2, wherein the polishing endpoint is the point at which any one of the plurality of index values ​​first reaches the maximum or minimum.

4. The polishing endpoint is the point at which all of the plurality of index values ​​reach their maximum or minimum, according to claim 2.

5. The polishing method according to claim 1, wherein the reference workpiece has the same surface structure as the workpiece.

6. The polishing method according to claim 1, wherein the polishing conditions for the reference workpiece are the same as the polishing conditions for the workpiece.

7. The interface spectrum is obtained in advance by an interface spectrum acquisition process before polishing the workpiece. The interface spectrum acquisition step is, When the first film is removed and the second film is exposed, a theoretical interface spectrum of the light reflected from the reference workpiece is generated. While polishing the reference workpiece, multiple spectra of reflected light from the reference workpiece are generated. An index value indicating the similarity between each of the aforementioned plurality of spectra and the theoretical interface spectrum is calculated. Select the spectrum from the plurality of spectra that has the maximum or minimum index value. The polishing method according to claim 1, further comprising specifying the selected spectrum as the interface spectrum.

8. A polishing table that supports the polishing pad, A table motor for rotating the polishing table, A polishing fluid supply nozzle for supplying polishing fluid to the polishing pad, A polishing head that polishes a workpiece in the presence of the polishing liquid by pressing the workpiece against the polishing pad, The system includes an optical system that, each time the polishing table rotates, irradiates the workpiece with light and generates a spectrum of reflected light from the workpiece. The aforementioned optical system is An index value indicating the similarity between the reflected light spectrum and the interface spectrum is calculated, and the interface spectrum is the spectrum of reflected light from the reference workpiece that is generated when the first film is removed during polishing of the reference workpiece, exposing the second film underneath. A polishing device configured to determine the polishing endpoint at which the aforementioned index value is maximum or minimum.

9. The aforementioned optical system is Multiple indicator values ​​are calculated according to different calculation algorithms, The polishing apparatus according to claim 8, configured to determine the polishing endpoint where at least one of the plurality of index values ​​is the maximum or minimum.

10. The polishing apparatus according to claim 9, wherein the optical system is configured to determine the polishing endpoint where any one of the plurality of index values ​​first reaches the maximum or minimum.

11. The polishing apparatus according to claim 9, wherein the optical system is configured to determine the polishing endpoint where all of the plurality of index values ​​are at their maximum or minimum.

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