Polishing method and polishing device

Abstract

To provide a polishing method capable of stabilizing intensity of light emitted by flash light sources and polishing a substrate while measuring a film thickness at many measurement points.SOLUTION: In a polishing method, when an optical sensor head 7 moves across a substrate W, a first flash light source 44A and a second flash light source 44B are caused to emit light multiple times at different timing to guide light to the substrate W through the optical sensor head 7, reflection light from the substrate W is taken in a spectrometer 47 through the optical sensor head 7, a spectrum of the reflection light is generated, and a film thickness of the substrate W is determined from the spectrum.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a polishing method and polishing apparatus for polishing a substrate such as a wafer, and more particularly to a polishing method and polishing apparatus for polishing a substrate while measuring the film thickness of the substrate with an optical film thickness measurement system. [Background technology]

[0002] The semiconductor device manufacturing process includes various steps, such as polishing insulating films such as SiO2 and metal films such as copper and tungsten. Wafer polishing is performed using a polishing apparatus. A polishing apparatus generally includes a polishing table that supports a polishing pad, a polishing head that presses the wafer against the polishing pad, and a slurry supply nozzle that supplies slurry onto the polishing pad. While the polishing table is rotating, slurry is supplied to the polishing pad on the polishing table, and the polishing head presses the wafer against the polishing pad. The wafer is brought into sliding contact with the polishing pad in the presence of the slurry. The wafer surface is planarized by a combination of the chemical action of the slurry and the mechanical action of the abrasive grains contained in the slurry and the polishing pad.

[0003] Wafer polishing is terminated when the thickness of the film (insulating film, metal film, silicon layer, etc.) that constitutes the surface of the wafer reaches a predetermined target value. A polishing apparatus generally includes an optical film thickness measurement system to measure the thickness of non-metallic films such as insulating films and silicon layers. This optical film thickness measurement system is configured to direct light from an optical sensor head that rotates together with the polishing table to the wafer surface, measure the intensity of the light reflected from the wafer with a spectroscope, and analyze the spectrum of the reflected light to measure the wafer film thickness.

[0004] Fig. 7 is a schematic diagram showing an example of multiple measurement points of film thickness measured by an optical film thickness measurement system. As shown in Fig. 7, an optical sensor head 500 irradiates multiple measurement points MP with light while moving across the surface of a wafer W. The optical sensor head 500 is connected to a flash light source (not shown), and light emitted by the flash light source is transmitted to the optical sensor head 500. Each time the optical sensor head 500 moves across the surface of the wafer W, the film thickness is measured at the multiple measurement points MP, as shown in Fig. 7. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-23210 Summary of the Invention [Problem to be solved by the invention]

[0006] As can be seen from Figure 7, the more measurement points MP there are on the wafer W, the more precise the film thickness distribution (or film thickness profile) that can be obtained. However, if the light emission cycle of the flash light source is shortened, the light intensity of the flash light source may vary due to the principle of light emission of the flash light source. In other words, if the light emission cycle of the flash light source is too short, the power energy stored in the flash light source for light emission will not be stable, and as a result, the intensity of the light emitted from the flash light source will be unstable.

[0007] Therefore, the present invention provides a polishing method and polishing apparatus that can stabilize the intensity of light emitted by a flash light source and can polish a substrate while measuring film thickness at more measurement points. [Means for solving the problem]

[0008] In one aspect, there is provided a polishing method for polishing a substrate, the polishing method including rotating a polishing table together with an optical sensor head optically coupled to a spectrometer, a first flash light source, and a second flash light source, moving the optical sensor head across the substrate while pressing the substrate against a polishing pad on the polishing table with the polishing head to polish the substrate, and while the optical sensor head moves across the substrate, emitting light from the first flash light source and the second flash light source at different times to direct light toward the substrate through the optical sensor head, and capturing reflected light from the substrate into the spectrometer through the optical sensor head to generate a spectrum of the reflected light, and determining a film thickness of the substrate from the spectrum.

[0009] In one embodiment, the first flash light source and the second flash light source alternately fire while the optical sensor head moves across the substrate. In one embodiment, the optical sensor head is composed of an end of a light-projecting fiber optic cable and an end of a light-receiving fiber optic cable, the light-projecting fiber optic cable being connected to a plurality of branched fiber optic cables, and the first flash light source and the second flash light source being respectively connected to the plurality of branched fiber optic cables.

[0010] In one aspect, a polishing apparatus for polishing a substrate includes: a polishing table for supporting a polishing pad; a table motor for rotating the polishing table; an optical sensor head installed in the polishing table; a spectrometer, a first flash light source, and a second flash light source optically coupled to the optical sensor head; a polishing head for pressing a substrate against the polishing pad to polish the substrate; and an operation controller for controlling operation of the spectrometer, the first flash light source, and the second flash light source, wherein the operation controller is configured to issue commands to the first flash light source and the second flash light source to emit light at different times while the optical sensor head moves across the substrate and direct the light toward the substrate through the optical sensor head, and to issue commands to the spectrometer to capture reflected light from the substrate through the optical sensor head into the spectrometer, generate a spectrum of the reflected light, and determine the film thickness of the substrate from the spectrum.

[0011] In one aspect, the motion controller is configured to command the first flash light source and the second flash light source to alternately emit light while the optical sensor head moves across the substrate. In one embodiment, the optical sensor head is composed of an end of a light-projecting fiber optic cable and an end of a light-receiving fiber optic cable, the light-projecting fiber optic cable being connected to a plurality of branched fiber optic cables, and the first flash light source and the second flash light source being respectively connected to the plurality of branched fiber optic cables. [Effects of the Invention]

[0012] Since multiple flash light sources including at least a first flash light source and a second flash light source are used, the light emission period of each of the first flash light source and the second flash light source can be lengthened. As a result, the intensity of light emitted from each of the first flash light source and the second flash light source is stabilized. Furthermore, since light is emitted multiple times from both the first flash light source and the second flash light source while the optical sensor head moves across the substrate once, the film thickness of the substrate can be measured at many measurement points. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram illustrating an embodiment of a polishing apparatus. [Figure 2] 2 is a cross-sectional view showing an embodiment of a detailed configuration of the polishing apparatus shown in FIG. 1. [Figure 3] 10 is a time chart showing an embodiment of the light emission operations of the first flash light source and the second flash light source and the capture operation of the reflected light by the spectroscope. [Figure 4] FIG. 1 is a diagram showing an example of light irradiation points on the surface of a wafer. [Figure 5] FIG. 1 is a schematic diagram illustrating an embodiment of an optical film thickness measurement system equipped with three flash light sources. [Figure 6] 10 is a time chart showing an embodiment of the light emission operations of three flash light sources and the capture operation of the reflected light by the spectroscope. [Figure 7] FIG. 2 is a diagram showing an example of measurement points of a film thickness on a wafer. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a schematic diagram showing one 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 wafer W, which is an example of a substrate, against the polishing pad 2, a table motor 6 that rotates the polishing table 3, and a slurry supply nozzle 5 that supplies slurry onto the polishing pad 2.

[0015] The polishing head 1 is connected to a head shaft 10, and the polishing head 1 rotates together with the head shaft 10 in the direction indicated by the arrow. The polishing table 3 is connected to a table motor 6, and the table motor 6 is configured to rotate the polishing table 3 and polishing pad 2 in the direction indicated by the arrow. The polishing apparatus is equipped with a rotary encoder 11 that detects the rotation angle of the polishing table 3. The rotary encoder 11 is connected to the table motor 6.

[0016] The wafer W is polished as follows: While the polishing table 3 and polishing head 1 are rotated in the directions indicated by the arrows in Figure 1, slurry is supplied from the slurry supply nozzle 5 to the polishing surface 2a of the polishing pad 2 on the polishing table 3. While the wafer W is rotated by the polishing head 1, the wafer W is pressed against the polishing surface 2a of the polishing pad 2 with the slurry present on the polishing pad 2. The surface of the wafer W is polished by the chemical action of the slurry and the mechanical action of the abrasive grains contained in the slurry and the polishing pad 2.

[0017] The polishing apparatus is equipped with an optical film thickness measurement system 40 that measures the film thickness of the wafer W. The optical film thickness measurement system 40 includes an optical sensor head 7, a first flash light source 44A, a second flash light source 44B, a spectrometer 47, and an operation control unit 9. The optical sensor head 7, the first flash light source 44A, the second flash light source 44B, and the spectrometer 47 are attached to the polishing table 3 and rotate integrally with the polishing table 3 and the polishing pad 2. The optical sensor head 7 is positioned so that it crosses the surface of the wafer W on the polishing pad 2 every time the polishing table 3 and the polishing pad 2 rotate once.

[0018] The operation control unit 9 is composed of at least one computer. The polishing control unit 9 includes a storage device 9a that stores a program for controlling the operation of the polishing apparatus, and a processor 9b that executes calculations according to instructions included in the program. The storage device 9a includes a main storage device such as a random access memory (RAM) and an auxiliary storage device such as a hard disk drive (HDD) or a solid state drive (SSD). Examples of the processor 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.

[0019] Fig. 2 is a cross-sectional view showing one embodiment of the detailed configuration of the polishing apparatus shown in Fig. 1. The head shaft 10 is connected to a polishing head motor 18 via a connecting means 17 such as a belt, and is rotated. The rotation of the head shaft 10 causes the polishing head 1 to rotate in the direction indicated by the arrow.

[0020] The spectrometer 47 includes a photodetector 48. In one embodiment, the photodetector 48 is an image sensor such as a CCD or CMOS, or a photodiode. The optical sensor head 7 is optically coupled to the first flash light source 44A, the second flash light source 44B, and the photodetector 48. The photodetector 48 is electrically connected to the operation control unit 9. In FIG. 2, for the sake of explanation, the second flash light source 44B is depicted below the first flash light source 44A, but the arrangement of the first flash light source 44A and the second flash light source 44B is not particularly limited.

[0021] The optical film thickness measurement system 40 further includes a light-projecting optical fiber cable 31 that guides light emitted from the first flash light source 44A and the second flash light source 44B to the surface of the wafer W, and a light-receiving optical fiber cable 32 that receives the light reflected from the wafer W and sends the reflected light to a spectrometer 47. The ends of the light-projecting optical fiber cable 31 and the light-receiving optical fiber cable 32 are located within the polishing table 3.

[0022] The tip of the light-projecting optical fiber cable 31 and the tip of the light-receiving optical fiber cable 32 form an optical sensor head 7 that guides light to the surface of the wafer W and receives reflected light from the wafer W. The other end of the light-receiving optical fiber cable 32 is connected to a spectroscope 47. The spectroscope 47 is configured to resolve the reflected light from the wafer W according to wavelength and measure the intensity of the reflected light over a predetermined wavelength range.

[0023] The light projecting optical fiber cable 31 is optically connected to a first branch optical fiber cable 61 and a second branch optical fiber cable 62. An end of the first branch optical fiber cable 61 is connected to the first flash light source 44A. An end of the second branch optical fiber cable 62 is connected to the second flash light source 44B. The configurations of the light projecting optical fiber cable 31, the first branch optical fiber cable 61, and the second branch optical fiber cable 62 are not particularly limited as long as the light projecting optical fiber cable 31 is optically connected to both the first branch optical fiber cable 61 and the second branch optical fiber cable 62. In one embodiment, the two optical fiber cables constituting the first branch optical fiber cable 61 and the second branch optical fiber cable 62 may be joined to form the light projecting optical fiber cable 31.

[0024] The first flash light source 44A and the second flash light source 44B send light to the optical sensor head 7 at different times via the light-projecting optical fiber cable 31, the first branched optical fiber cable 61, and the second branched optical fiber cable 62, and the optical sensor head 7 emits the light toward the wafer W. The light reflected from the wafer W is received by the optical sensor head 7 and sent to the photodetector 48 of the spectroscope 47 via the light-receiving optical fiber cable 32. The spectroscope 47 separates the reflected light according to its wavelength and measures the intensity of the reflected light at each wavelength. The spectroscope 47 sends measurement data of the intensity of the reflected light to the operation control unit 9.

[0025] The operation control unit 9 generates a spectrum of the reflected light from the measurement data of the intensity of the reflected light. This spectrum indicates the relationship between the intensity of the reflected light and the wavelength, and the shape of the spectrum changes according to the film thickness of the wafer W. The operation control unit 9 determines the film thickness of the wafer W from the spectrum of the reflected light. A known technique is used to determine the film thickness of the wafer W from the spectrum of the reflected light. For example, a Fourier transform is performed on the spectrum of the reflected light, and the film thickness is determined from the obtained frequency spectrum. In another example, the operation control unit 9 searches a spectrum library storing multiple reference spectra associated with multiple film thicknesses, determines the reference spectrum whose shape is closest to the spectrum of the reflected light, and determines the film thickness associated with this determined reference spectrum.

[0026] During polishing of the wafer W, the optical sensor head 7 irradiates light onto multiple measurement points on the wafer W while crossing the surface of the wafer W on the polishing pad 2 with each rotation of the polishing table 3, and receives reflected light from the wafer W. The operation control unit 9 determines the film thickness of the wafer W from the measurement data of the intensity of the reflected light, and controls the polishing operation of the wafer W based on the film thickness. For example, the operation control unit 9 determines the polishing endpoint, which is the point at which the film thickness of the wafer W reaches a target film thickness.

[0027] The polishing table 3 has a hole 50 that opens on its upper surface. Furthermore, a through-hole 51 is formed in the polishing pad 2 at a position corresponding to the hole 50. The hole 50 communicates with the through-hole 51, which opens on the polishing surface 2a. The optical sensor head 7, which is composed of the tip of the light-emitting fiber optic cable 31 and the tip of the light-receiving fiber optic cable 32, is disposed in the hole 50 and is located below the through-hole 51. To prevent the slurry from entering the hole 50, a flow of pure water may be formed in the hole 50, or the through-hole 51 may be blocked with a transparent window (not shown).

[0028] In this embodiment, xenon flash lamps are used as the first flash light source 44A and the second flash light source 44B. The optical sensor head 7, which is made up of the ends of the light-projecting optical fiber cable 31 and the light-receiving optical fiber cable 32, is disposed facing the wafer W held by the polishing head 1. Each time the polishing table 3 rotates once, the first flash light source 44A and the second flash light source 44B emit light multiple times, and the optical sensor head 7 irradiates light onto multiple measurement points on the wafer W. In this embodiment, only one optical sensor head 7 is provided, but multiple optical sensor heads 7 may be provided.

[0029] During polishing of the wafer W, the optical sensor head 7 moves across the wafer W with each rotation of the polishing table 3. While the optical sensor head 7 is below the wafer W, the first flash light source 44A and the second flash light source 44B emit light multiple times at different timings. The light is guided to the surface (surface to be polished) of the wafer W through the light-projecting optical fiber cable 31, the first branched optical fiber cable 61, and the second branched optical fiber cable 62. The reflected light from the wafer W is received by the spectrometer 47 through the light-receiving optical fiber cable 32 and captured by the photodetector 48. The spectrometer 47 measures the intensity of the reflected light at each wavelength over a predetermined wavelength range and sends the resulting measurement data to the operation control unit 9. This measurement data is a film thickness signal that changes according to the film thickness of the wafer W. The operation control unit 9 generates a spectrum of the reflected light representing the light intensity at each wavelength from the measurement data and further determines the film thickness of the wafer W from the spectrum of the reflected light.

[0030] The rotary encoder 11 is electrically connected to the operation control unit 9, and the output signal of the rotary encoder 11 (i.e., the detected value of the rotation angle of the polishing table 3) is sent to the operation control unit 9. The operation control unit 9 determines the relative position of the optical sensor head 7 with respect to the polishing head 1 from the output signal of the rotary encoder 11, i.e., the rotation angle of the polishing table 3, and controls the light emission timing of the first flash light source 44A, the light emission timing of the second flash light source 44B, and the light detection timing of the spectroscope 47 based on the relative position of the optical sensor head 7.

[0031] During polishing of the wafer W, the operation control unit 9 issues commands to the first flash light source 44A, the second flash light source 44B, and the spectroscope 47 to control the light emission operations of the first flash light source 44A and the second flash light source 44B and the light detection operation of the spectroscope 47. That is, when the optical sensor head 7 is below the wafer W, the operation control unit 9 sends a light emission trigger signal to the first flash light source 44A and the second flash light source 44B and a light detection trigger signal to the spectroscope 47. Upon receiving the light emission trigger signal, the first flash light source 44A and the second flash light source 44B momentarily emit light. Upon receiving the light detection trigger signal, the spectroscope 47 starts capturing reflected light, and stops capturing reflected light when the transmission of the light detection trigger signal is stopped.

[0032] The operation control unit 9 generates a light emission trigger signal and a light detection trigger signal that are synchronized with each other. While the optical sensor head 7 moves across the wafer W, the first flash light source 44A and the second flash light source 44B receive the multiple light emission trigger signals and emit light multiple times, and at the same time, the photodetector 48 of the spectroscope 47 receives the multiple light detection trigger signals and captures the reflected light from the wafer W multiple times.

[0033] 3 is a time chart showing one embodiment of the light emission operations of the first flash light source 44A and the second flash light source 44B and the reflected light capture operation of the spectroscope 47. The first flash light source 44A and the second flash light source 44B alternately emit light, and the spectroscope 47 captures the reflected light from the wafer W at the same timing as the first flash light source 44A and the second flash light source 44B emit light. In the embodiment shown in FIG. 3, the first flash light source 44A and the second flash light source 44B emit light at the same cycle (same time interval).

[0034] FIG. 4 is a diagram showing an example of a light irradiation point on the surface of the wafer W. The light irradiation point corresponds to a film thickness measurement point MP on the wafer W. While the optical sensor head 7 moves across the wafer W, the operation control unit 9 issues commands (sends light emission trigger signals) to the first flash light source 44A and the second flash light source 44B to cause the first flash light source 44A and the second flash light source 44B to emit light multiple times at different timings. As shown in FIG. 4, the light emitted from the first flash light source 44A and the second flash light source 44B is alternately directed toward the surface of the wafer W.

[0035] Because the first flash light source 44A and the second flash light source 44B emit light at different times, the light emission cycle of each of the first flash light source 44A and the second flash light source 44B can be lengthened. As a result, the intensity of light emitted from each of the first flash light source 44A and the second flash light source 44B is stabilized. Furthermore, because light is emitted multiple times from both the first flash light source 44A and the second flash light source 44B while the optical sensor head 7 moves once across the surface of the wafer, the film thickness of the wafer W can be measured at many measurement points MP.

[0036] In one embodiment, the optical film thickness measurement system 40 may further include one or more flash light sources in addition to the first flash light source 44A and the second flash light source 44B. For example, as schematically shown in Fig. 5, the optical film thickness measurement system 40 may include the first flash light source 44A, the second flash light source 44B, and the third flash light source 44C. The third flash light source 44C is connected to a third branched optical fiber cable 63 that is optically connected to the light projecting optical fiber cable 31.

[0037] The operation control unit 9 issues commands to the first flash light source 44A, the second flash light source 44B, and the third flash light source 44C to cause the first flash light source 44A, the second flash light source 44B, and the third flash light source 44C to emit light at different timings.

[0038] Fig. 6 is a time chart showing one embodiment of the light emission operations of the three flash light sources 44A, 44B, and 44C and the reflected light capture operation of the spectroscope 47. As shown in Fig. 6, the three flash light sources 44A, 44B, and 44C repeatedly emit light in the order of the first flash light source 44A, the second flash light source 44B, and the third flash light source 44C, and the spectroscope 47 captures the reflected light from the wafer W at the same timing as the three flash light sources 44A, 44B, and 44C emit light. In the embodiment shown in Fig. 6, the flash light sources 44A, 44B, and 44C emit light at the same cycle (same time interval).

[0039] The embodiment shown in Figures 5 and 6 is the same as the above-described embodiment including two flash light sources 44A and 44B in that the three flash light sources 44A, 44B, and 44C emit light at different times while the optical sensor head 7 moves once across the surface of the wafer W. Furthermore, the embodiment shown in Figures 5 and 6 is the same as the above-described embodiment including two flash light sources 44A and 44B in that any two of the three flash light sources 44A, 44B, and 44C emit light alternately while the optical sensor head 7 moves once across the surface of the wafer W. The embodiment including three flash light sources 44A, 44B, and 44C can extend the emission period of each flash light source and / or increase the number of film thickness measurement points. Four or more flash light sources may be provided.

[0040] The above-described embodiments have been described for the purpose of enabling a person of ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments would be obvious to a person skilled in the art, and the technical concept of the present invention may be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope in accordance with the technical concept defined by the claims. [Explanation of symbols]

[0041] 1 polishing head 2 polishing pads 3 Polishing table 5 Slurry supply nozzle 6 Table Motor 7 Optical sensor head 9. Operation control section 10 Head shaft 17 Connection means 18 Polishing head motor 31 Optical fiber cable for light projection 32 Receiving optical fiber cable 40 Optical Film Thickness Measurement System 44A, 44B, 44C Flash light source 47 Spectrometer 48 Photodetector 50 holes 51 Through hole 61, 62, 63 Branched fiber optic cable

Claims

1. 1. A polishing method for polishing a substrate, comprising: rotating the polishing table together with an optical sensor head optically coupled to the spectrometer, the first flash light source, and the second flash light source; While moving the optical sensor head across the substrate, the substrate is pressed against a polishing pad on the polishing table by a polishing head to polish the substrate; While the optical sensor head moves across the substrate, the first flash light source and the second flash light source are caused to emit light a plurality of times at different timings, so that light is guided to the substrate through the optical sensor head, and reflected light from the substrate is taken into the spectroscope through the optical sensor head; generating a spectrum of the reflected light; A polishing method in which a film thickness of the substrate is determined from the spectrum.

2. 2. The polishing method of claim 1, wherein the first flash light source and the second flash light source alternately emit light while the optical sensor head moves across the substrate.

3. the optical sensor head is composed of an end of a light-emitting fiber optic cable and an end of a light-receiving fiber optic cable; the light projecting optical fiber cable is connected to a plurality of branched optical fiber cables; 2. The polishing method according to claim 1, wherein the first flash light source and the second flash light source are respectively connected to the plurality of branched optical fiber cables.

4. A polishing apparatus for polishing a substrate, comprising: a polishing table for supporting the polishing pad; a table motor for rotating the polishing table; an optical sensor head installed in the polishing table; a spectrometer, a first flash light source, and a second flash light source optically coupled to the optical sensor head; a polishing head for pressing a substrate against the polishing pad to polish the substrate; an operation control unit that controls operations of the spectroscope, the first flash light source, and the second flash light source; The operation control unit while the optical sensor head moves across the substrate, instructing the first flash light source and the second flash light source to emit light at different times to direct light through the optical sensor head to the substrate, and instructing the spectrometer to capture reflected light from the substrate through the optical sensor head into the spectrometer; generating a spectrum of the reflected light; a polishing apparatus configured to determine a film thickness of the substrate from the spectrum;

5. 5. The polishing apparatus of claim 4, wherein the motion control unit is configured to issue commands to the first flash light source and the second flash light source to alternately emit light while the optical sensor head moves across the substrate.

6. the optical sensor head is composed of an end of a light-emitting fiber optic cable and an end of a light-receiving fiber optic cable; the light projecting optical fiber cable is connected to a plurality of branched optical fiber cables, 5. The polishing apparatus according to claim 4, wherein the first flash light source and the second flash light source are respectively connected to the plurality of branched optical fiber cables.

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