Method for cleaning an optical surface monitoring device

Abstract

To provide a washing method capable of removing abrasive grains adhered to an optical passage in a polishing table.SOLUTION: A washing method slides a substrate W on an abrasive pad 2 while supplying a slurry containing abrasive grains on the abrasive pad 2 supported by a polishing table 3 and polishes the substrate W, leads light to the substrate W through an optical path 50A provided in the polishing table 3 while polishing the substrate W, passes reflecting light from the substrate W through the optical path 50A, removes the polished substrate W from the abrasive pad 2, supplies chemical liquid in the optical path 50A in the state that there is no substrate on the abrasive pad 2, and removes the abrasive grains adhered to the optical path 50A.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for cleaning an optical surface monitoring device provided in a polishing apparatus for polishing substrates such as wafers, and more particularly to a method for removing abrasive particles of a slurry that have adhered to an optical path provided in a polishing table. [Background technology]

[0002] The manufacturing process of semiconductor devices includes various steps such as polishing insulating films such as SiO2 and polishing metal films such as copper and tungsten. Wafers are polished 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 rotating the polishing table, 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 surface of the wafer is planarized by a combination of the chemical action of the slurry and the mechanical action of the abrasive grains contained in the slurry.

[0003] Wafer polishing is terminated when the thickness of a film (insulating film, metal film, silicon layer, etc.) constituting the surface of the wafer reaches a predetermined target value. A polishing apparatus is generally equipped with an optical surface monitoring device to measure the thickness of a non-metallic film such as an insulating film or silicon layer. This optical surface monitoring device is configured to detect the surface condition of the wafer (for example, to measure the film thickness of the wafer or to detect the removal of a film constituting the wafer surface) by directing light emitted from a light source to the wafer surface, measuring the intensity of the light reflected from the wafer with a spectroscope, and analyzing the spectrum of the reflected light.

[0004] The polishing table is provided with an optical fiber cable connected to the light source and the spectrometer, and an optical path connected to the optical fiber cable. Light travels through the optical path and is incident on the wafer, and the reflected light from the wafer travels in the opposite direction through the optical path. A flow of pure water is formed in the optical path during polishing of the wafer to prevent the slurry supplied to the polishing pad from entering the optical path. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2006-525878 Summary of the Invention [Problem to be solved by the invention]

[0006] However, if the supply of pure water to the optical path is interrupted due to a malfunction of the pure water supply system, the slurry supplied to the polishing pad penetrates into the optical path, and the abrasive grains contained in the slurry adhere to the inner surface of the optical path. The abrasive grains change the way the light passing through the optical path travels, and as a result, the spectrometer cannot correctly measure the intensity of the reflected light from the wafer. In particular, the abrasive grains firmly attached to the inner surface of the optical path cannot be washed away with pure water, and it was necessary to replace the entire optical path and the optical fiber cable with new ones.

[0007] Therefore, the present invention provides a cleaning method capable of removing abrasive grains adhering to the light path in the polishing table. [Means for solving the problem]

[0008] In one embodiment, a substrate is polished by sliding the substrate against a polishing pad supported on a rotating polishing table while supplying a slurry containing abrasive grains onto the polishing pad, and while the substrate is being polished, light is guided to the substrate through an optical path provided in the polishing table, and reflected light from the substrate is passed through the optical path, and after the substrate is polished, the rotation of the polishing table is stopped, and with the rotation of the polishing table stopped and with no substrate present on the polishing pad, a chemical solution is supplied into the optical path, and the abrasive grains adhering to the optical path are removed by the chemical solution, After the supply of the chemical liquid is stopped, pure water is supplied into the optical path while keeping a pure water discharge valve on a pure water discharge line communicating with the optical path closed, and the chemical liquid remaining in the optical path is discharged together with the pure water through the chemical liquid discharge line communicating with the optical path, and then A cleaning method is provided, which includes supplying a dry gas to the optical path to dry the optical path, and the chemical liquid has a chemical property that etches an inner surface of the optical path.

[0009] one In one embodiment, after the rotation of the polishing table is stopped and before the chemical liquid is supplied into the optical path, pure water is supplied into the optical path.

[0010] In one embodiment, a substrate is polished by sliding it against a polishing pad supported on a rotating polishing table while supplying a slurry containing abrasive grains onto the polishing pad, and while polishing the substrate, light is guided to the substrate through an optical path provided in the polishing table and reflected light from the substrate is passed through the optical path, and after polishing the substrate, rotation of the polishing table is stopped, and pure water is supplied into the optical path with the polishing table stopped from rotating and no substrate is present on the polishing pad to remove the abrasive grains adhering to the optical path. After the substrate has been polished and the supply of the pure water has been stopped, A cleaning method is provided that includes supplying a dry gas to the optical path to dry the optical path. Effect of the Invention

[0011] The chemical solution slightly etches the inner surface of the optical path, and the abrasive grains can be removed from the optical path by a lift-off effect. Therefore, light can travel through the optical path without being affected by the abrasive grains. As a result, the optical surface monitoring device can accurately detect the surface condition of a substrate such as a wafer. Furthermore, the optical path is dried by the dry gas, so that the optical path can be maintained in good condition.

[0012] If the abrasive particles contained in the slurry do not adhere firmly to the optical path, for example, immediately after the slurry has entered the optical path, the abrasive particles can be washed out of the optical path with pure water instead of a chemical solution. Light can travel through the optical path without being affected by the abrasive particles. As a result, the optical surface monitoring device can accurately detect the surface condition of a substrate such as a wafer. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram illustrating an embodiment of a polishing apparatus. [Diagram 2] 2 is a cross-sectional view showing an embodiment of a detailed configuration of the polishing apparatus shown in FIG. 1. [Diagram 3] 13 is a flow chart illustrating one embodiment of removing abrasive particles from a light path. [Figure 4] 13 is a flow chart illustrating another embodiment for removing abrasive particles from a light path. [Diagram 5] 13 is a flow chart illustrating yet another embodiment for removing abrasive particles from a light path. [Figure 6] 13 is a flow chart illustrating yet another embodiment for removing abrasive particles from a light path. [Figure 7] 13 is a flow chart illustrating yet another embodiment for removing abrasive particles from a light path. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment 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 a 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 the polishing pad 2 in the direction indicated by the arrow. The upper surface of the polishing pad 2 forms a polishing surface 2a for polishing a wafer W.

[0016] The wafer W is polished as follows. While the polishing table 3 and polishing head 1 are rotated in the direction indicated by the arrow in Fig. 1, slurry is supplied from a 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.

[0017] The polishing apparatus is equipped with an optical surface monitoring device 40 that detects the surface condition of the wafer W. The optical surface monitoring device 40 includes an optical sensor head 7, a light source 44, a spectroscope 47, and a processing device 9. The optical sensor head 7, the light source 44, and the spectroscope 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 at a position where 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] Fig. 2 is a cross-sectional view showing an 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 rotates the polishing head 1 in the direction indicated by the arrow.

[0019] The optical sensor head 7 is optically coupled to a light source 44 and a spectrometer 47. The spectrometer 47 is electrically connected to a processing device 9. The processing device 9 is composed of a computer having a storage device that stores a program and an arithmetic device (e.g., a CPU) that executes calculations according to instructions included in the program.

[0020] The optical surface monitoring device 40 further includes a light-projecting optical fiber cable 31 that guides the light emitted from the light source 44 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.

[0021] The tip of the light-projecting fiber optic cable 31 and the tip of the light-receiving fiber optic cable 32 constitute 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-projecting fiber optic cable 31 is connected to a light source 44, and the other end of the light-receiving fiber optic cable 32 is connected to a spectroscope 47. The spectroscope 47 is configured to resolve the light reflected from the wafer W according to wavelength and measure the intensity of the reflected light over a predetermined wavelength range.

[0022] The light source 44 transmits light to the optical sensor head 7 via the light-projecting optical fiber cable 31, 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 transmitted to the spectrometer 47 via the light-receiving optical fiber cable 32. The spectrometer 47 separates the reflected light according to its wavelength and measures the intensity of the reflected light at each wavelength. The spectrometer 47 transmits measurement data of the intensity of the reflected light to the processing device 9.

[0023] The processing device 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 processing device 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.

[0024] During polishing of the wafer W, the optical sensor head 7 irradiates light to multiple measurement points on the wafer W while crossing the surface of the wafer W on the polishing pad 2 each time the polishing table 3 rotates once, and receives reflected light from the wafer W. The processing device 9 generates a spectrum of the reflected light from measurement data of the intensity of the reflected light, determines the film thickness of the wafer W from the spectrum of the reflected light, and controls the polishing operation of the wafer W based on the film thickness. For example, the processing device 9 determines the polishing end point of the wafer W, which is the point at which the film thickness of the wafer W reaches a target film thickness.

[0025] In one embodiment, the processing device 9 may detect the time when the film constituting the surface of the wafer W is removed from a change in the spectrum of the reflected light. In this case, the processing device 9 determines the polishing end point based on the time when the film constituting the surface of the wafer W is removed. The processing device 9 does not need to determine the film thickness of the wafer W from the spectrum of the reflected light.

[0026] The polishing table 3 has a light path 50A and a drain hole 50B that open on its upper surface. The light path 50A is formed of a cylinder 52 made of metal, resin, or the like. The ends of the light projecting optical fiber cable 31 and the light receiving optical fiber cable 32 are optically connected to the light path 50A. The drain hole 50B is adjacent to the light path 50A and is located within the polishing table 3.

[0027] The polishing pad 2 has a through hole 51 communicating with both the light path 50A and the drain hole 50B. This through hole 51 is located above the light path 50A and the drain hole 50B. The through hole 51 opens at the polishing surface 2a. The light path 50A is connected to a pure water supply line 53, and the drain hole 50B is connected to a pure water discharge line 54. The optical sensor head 7, which is composed of the tip of the light projecting optical fiber cable 31 and the tip of the light receiving optical fiber cable 32, is located below the light path 50A and the through hole 51.

[0028] The light emitted from the light source 44 passes through the light projecting optical fiber cable 31, travels further through the optical path 50A, and is incident on the surface of the wafer W. The light is reflected by the surface (surface to be polished) of the wafer W, and travels in the opposite direction through the optical path 50A as reflected light. The reflected light from the wafer W passes through the light receiving optical fiber cable 32 and is received by the spectroscope 47. The spectroscope 47 measures the intensity of the reflected light at each wavelength over a predetermined wavelength range, and sends the obtained intensity measurement data to the processing device 9. This intensity measurement data is a film thickness signal that changes according to the film thickness of the wafer W. The processing device 9 generates a spectrum of the reflected light representing the intensity of light for each wavelength from the intensity measurement data, and further determines the film thickness of the wafer W from the spectrum of the reflected light.

[0029] An optical sensor head 7 constituted by the respective ends of a light-projecting optical fiber cable 31 and a 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, light is irradiated onto a plurality of measurement points on the wafer W. In this embodiment, only one optical sensor head 7 is provided, but a plurality of optical sensor heads 7 may be provided.

[0030] During polishing of the wafer W, pure water is supplied as a rinsing liquid to the light path 50A via the pure water supply line 53, and is further supplied to the through hole 51 through the light path 50A. The pure water fills the space between the surface (polished surface) of the wafer W and the optical sensor head 7. The pure water flows into the drain hole 50B and is discharged through the pure water discharge line 54. The pure water flowing through the light path 50A and the through hole 51 can prevent slurry from entering the light path 50A.

[0031] One end of the pure water supply line 53 is connected to the optical path 50A, and the other end of the pure water supply line 53 is connected to a pure water supply source 61. One end of the pure water discharge line 54 is connected to the drain hole 50B. The pure water supplied to the through hole 51 flows through the drain hole 50B and further through the pure water discharge line 54 to be discharged outside the polishing apparatus.

[0032] A chemical liquid supply line 63 and a dry gas supply line 65 are further connected to the optical path 50A. A chemical liquid discharge line 68 is further connected to the drain hole 50B. One end of each of the pure water supply line 53, the chemical liquid supply line 63, the dry gas supply line 65, the pure water discharge line 54, and the chemical liquid discharge line 68 is located inside the polishing table 3, and the other end is located outside the polishing table 3. The pure water supply line 53, the chemical liquid supply line 63, the dry gas supply line 65, the pure water discharge line 54, and the chemical liquid discharge line 68 extend through the rotary joint 19.

[0033] A pure water supply valve 72 is attached to the pure water supply line 53, and a pure water discharge valve 74 is attached to the pure water discharge line 54. A chemical supply valve 78 is attached to the chemical supply line 63, and a chemical discharge valve 79 is attached to the chemical discharge line 68. A dry gas supply valve 81 is attached to the dry gas supply line 65. Each of the pure water supply valve 72, the pure water discharge valve 74, the chemical supply valve 78, the chemical discharge valve 79, and the dry gas supply valve 81 is an actuator-driven valve such as an electric valve, an electromagnetic valve, or an air-operated valve.

[0034] The pure water supply valve 72, the pure water discharge valve 74, the chemical solution supply valve 78, the chemical solution discharge valve 79, and the dry gas supply valve 81 are connected to a valve control unit 90. The operations of the pure water supply valve 72, the pure water discharge valve 74, the chemical solution supply valve 78, the chemical solution discharge valve 79, and the dry gas supply valve 81 are controlled by the valve control unit 90. The valve control unit 90 is composed of a computer having a storage device that stores a program, and an arithmetic unit (e.g., a CPU) that executes calculations according to instructions included in the program.

[0035] The chemical solution has a chemical property of etching the inner surface of the light path 50A. That is, the chemical solution can slightly etch the inner surface of the light path 50A and remove the abrasive grains from the light path 50A by a lift-off effect. An example of the chemical solution used in this embodiment is a solution containing potassium hydroxide. However, the type of chemical solution is not limited to this embodiment as long as it can etch the inner surface of the light path 50A. The chemical solution supply line 63 is connected to a chemical solution supply source 84.

[0036] The dry gas is a gas for expelling liquid (pure water and / or chemical liquid) from the optical path 50A and further drying the optical path 50A. Examples of the dry gas used in this embodiment include dry air and inert gas (e.g., nitrogen gas). The dry gas supply line 65 is connected to a dry gas supply source 88, such as an air supply source or an inert gas supply source.

[0037] During polishing of the wafer W, the chemical supply valve 78, the chemical discharge valve 79, and the dry gas supply valve 81 are closed, and the pure water discharge valve 74 is open. The pure water supply valve 72 is opened and closed in synchronization with the rotation of the polishing table 3. More specifically, the valve control unit 90 opens the pure water supply valve 72 when the through hole 51 of the polishing pad 2 rotating with the polishing table 3 is located under the wafer W. The pure water flows into the light path 50A through the pure water supply line 53, and flows through the light path 50A and the through hole 51. Furthermore, the pure water flows from the through hole 51 into the drain hole 50B, and is discharged from the polishing apparatus through the pure water discharge line 54. When the through hole 51 of the polishing pad 2 rotating with the polishing table 3 is not under the wafer W, the valve control unit 90 closes the pure water supply valve 72.

[0038] When the through hole 51 is under the wafer W, i.e., when the optical path 50A is under the wafer W, the light-projecting optical fiber cable 31 guides light to the surface of the wafer W through the optical path 50A, and the light-receiving optical fiber cable 32 receives the reflected light from the wafer W passing through the optical path 50A. Since the optical path 50A is filled with pure water, which is a transparent liquid, slurry does not enter the optical path 50A, and a good optical path is secured.

[0039] When polishing of the wafer W using the slurry is completed, the polished wafer W is removed from the polishing pad 2 by the polishing head 1. The polished wafer W is transferred from the polishing head 1 to a transport device (not shown) and cleaned by a cleaning unit (not shown).

[0040] If the supply of pure water to the optical path 50A is interrupted due to a malfunction of the pure water supply source 61 or a breakdown of the pure water supply valve 72, the slurry supplied to the polishing pad 2 will enter the optical path 50A, and the abrasive grains contained in the slurry will adhere to the inner surface of the optical path 50A. The abrasive grains will change the way the light passing through the optical path 50A travels, and as a result, the spectroscope 47 will not be able to correctly measure the intensity of the reflected light from the wafer W.

[0041] Thus, in one embodiment, the abrasive particles are removed from the light path 50A according to the flow chart shown in FIG. In step 1, after the wafer W is polished, the rotation of the polishing table 3 is stopped. In step 2, the valve control unit 90 opens the pure water supply valve 72 without the wafer W on the polishing pad 2. The chemical supply valve 78, the chemical discharge valve 79, the pure water discharge valve 74, and the dry gas supply valve 81 are closed. The pure water flows into the light path 50A through the pure water supply line 53, and then flows through the through hole 51 and overflows onto the polishing pad 2. The slurry in the light path 50A flows onto the polishing pad 2 together with the pure water. Since the pure water discharge valve 74 is closed, the slurry does not flow through the pure water discharge line 54. This is to prevent the pure water discharge line 54 from being clogged by the abrasive grains contained in the slurry.

[0042] In step 3, after a predetermined pure water supply time has elapsed, the valve control unit 90 closes the pure water supply valve 72 and opens the pure water discharge valve 74. The pure water in the through hole 51 is discharged through the drain hole 50B and the pure water discharge line 54. Since almost no slurry remains in the through hole 51, the pure water discharge line 54 is not clogged with abrasive grains. In step 4, the valve control unit 90 closes the pure water drain valve 74 and opens the chemical supply valve 78 and the chemical drain valve 79. The chemical is supplied to the light path 50A through the chemical supply line 63 and fills the light path 50A. The chemical flows into the drain hole 50B through the through hole 51 and is drained through the chemical drain line 68. The abrasive grains adhered to the inner surface of the light path 50A are removed by the chemical.

[0043] In step 5, the valve control unit 90 closes the chemical supply valve 78 while keeping the chemical discharge valve 79 open, thereby stopping the supply of the chemical to the light path 50A. The chemical in the through hole 51 is discharged through the drain hole 50B and the chemical discharge line 68. In step 6, the valve control unit 90 opens the pure water supply valve 72 while keeping the chemical discharge valve 79 open. The pure water pushes out the chemical remaining in the optical path 50A, and the chemical is discharged together with the pure water through the drain hole 50B and the chemical discharge line 68. The optical path 50A is rinsed with the pure water.

[0044] In step 7, the valve control unit 90 closes the pure water supply valve 72 and the chemical solution discharge valve 79, and opens the pure water discharge valve 74. The pure water in the through hole 51 is discharged through the drain hole 50B and the pure water discharge line . In step 8, the valve control unit 90 closes the pure water discharge valve 74 and opens the dry gas supply valve 81. Dry gas, such as dry air or nitrogen gas, is supplied to the optical path 50A through the dry gas supply line 65 to push out the pure water present in the optical path 50A. The supply of the dry gas is continued for a predetermined gas supply time. This gas supply time is long enough for the dry gas to push out the pure water from the optical path 50A and to dry the inside of the optical path 50A. In step 9, after the gas supply time has elapsed, the valve control unit 90 closes the dry gas supply valve 81.

[0045] According to this embodiment, the abrasive grains are removed from the light path 50A by the chemical liquid, and the light path 50A is further dried by the dry gas. Therefore, the light path 50A can be maintained in a good condition. In particular, this embodiment is suitable for a case where the polishing apparatus is not used for a long period of time after the abrasive grains are removed from the light path 50A. This embodiment is performed, for example, immediately before replacing the polishing pad 2 with a new polishing pad.

[0046] FIG. 4 is a flow chart illustrating another embodiment for removing abrasive particles from the light path 50A. In step 1, after the wafer is polished, the rotation of the polishing table 3 is stopped. In step 2, without a wafer on the polishing pad 2, the valve control unit 90 opens the chemical supply valve 78 and the chemical discharge valve 79. The pure water supply valve 72, the pure water discharge valve 74, and the dry gas supply valve 81 are closed. The chemical flows into the light path 50A through the chemical supply line 63, and then flows through the through hole 51 and overflows onto the polishing pad 2. The slurry in the light path 50A flows onto the polishing pad 2 together with the chemical. The abrasive grains adhered to the inner surface of the light path 50A are removed by the chemical.

[0047] In step 3, the valve control unit 90 closes the chemical supply valve 78 while keeping the chemical discharge valve 79 open, thereby stopping the supply of the chemical to the light path 50A. The chemical in the through hole 51 is discharged through the drain hole 50B and the chemical discharge line 68. In step 4, the valve control unit 90 closes the chemical solution discharge valve 79 and opens the dry gas supply valve 81. Dry gas, such as dry air or nitrogen gas, is supplied to the optical path 50A through the dry gas supply line 65 to push out the chemical solution present in the optical path 50A. The supply of the dry gas is continued for a predetermined gas supply time. This gas supply time is long enough for the dry gas to push out the chemical solution from the optical path 50A and to dry the inside of the optical path 50A. In step 5, after the gas supply time has elapsed, the valve control unit 90 closes the dry gas supply valve 81.

[0048] This embodiment is carried out when a type of chemical solution is used that does not require a rinsing process of washing the chemical solution from the optical path 50A with pure water. In this embodiment, the abrasive grains are also removed from the optical path 50A by the chemical solution, and the optical path 50A is further dried by dry gas. Therefore, the optical path 50A can be maintained in a good condition. This embodiment is particularly suitable for a case where the polishing apparatus is not used for a long period of time after the abrasive grains are removed from the optical path 50A. This embodiment is carried out, for example, immediately before replacing the polishing pad 2 with a new polishing pad.

[0049] FIG. 5 is a flow chart illustrating yet another embodiment for removing abrasive particles from light path 50A. In step 1, after the wafer is polished, the rotation of the polishing table 3 is stopped. In step 2, without a wafer on the polishing pad 2, the valve control unit 90 opens the pure water supply valve 72. The chemical supply valve 78, the chemical discharge valve 79, the pure water discharge valve 74, and the dry gas supply valve 81 are closed. The pure water flows into the optical path 50A through the pure water supply line 53, and further flows through the through hole 51, overflowing onto the polishing pad 2. The slurry in the optical path 50A flows onto the polishing pad 2 together with the pure water.

[0050] In step 3, after a predetermined pure water supply time has elapsed, the valve control unit 90 closes the pure water supply valve 72 and opens the pure water discharge valve 74. The pure water in the through hole 51 is discharged through the drain hole 50B and the pure water discharge line . In step 4, the valve control unit 90 closes the pure water discharge valve 74 and opens the dry gas supply valve 81. Dry gas, such as dry air or nitrogen gas, is supplied to the optical path 50A through the dry gas supply line 65 to push out the pure water present in the optical path 50A. The supply of the dry gas is continued for a predetermined gas supply time. This gas supply time is long enough for the dry gas to push out the pure water from the optical path 50A and to dry the inside of the optical path 50A. In step 5, after the gas supply time has elapsed, the valve control unit 90 closes the dry gas supply valve 81.

[0051] In this embodiment, no chemical solution is used to remove the abrasive grains. This embodiment is performed immediately after the slurry enters the light path 50A. More specifically, the operation of this embodiment is performed before the abrasive grains contained in the slurry are fixed to the light path 50A. The abrasive grains are removed from the light path 50A by pure water, and the light path 50A is further dried by dry gas. Therefore, the light path 50A can be maintained in good condition. In particular, this embodiment is suitable for the case where the polishing apparatus is not used for a long period of time after the abrasive grains are removed from the light path 50A.

[0052] FIG. 6 is a flow chart illustrating yet another embodiment for removing abrasive particles from light path 50A. In step 1, after the wafer is polished, the rotation of the polishing table 3 is stopped. In step 2, without a wafer on the polishing pad 2, the valve control unit 90 opens the pure water supply valve 72. The chemical supply valve 78, the chemical discharge valve 79, the pure water discharge valve 74, and the dry gas supply valve 81 are closed. The pure water flows into the optical path 50A through the pure water supply line 53, and further flows through the through hole 51, overflowing onto the polishing pad 2. The slurry in the optical path 50A flows onto the polishing pad 2 together with the pure water.

[0053] In step 3, after a predetermined pure water supply time has elapsed, the valve control unit 90 closes the pure water supply valve 72 and opens the pure water discharge valve 74. The pure water in the through hole 51 is discharged through the drain hole 50B and the pure water discharge line . In step 4, the valve control unit 90 closes the pure water drain valve 74 and opens the chemical supply valve 78 and the chemical drain valve 79. The chemical is supplied to the light path 50A through the chemical supply line 63 and fills the light path 50A. The chemical flows into the drain hole 50B through the through hole 51 and is drained through the chemical drain line 68. The abrasive grains adhered to the inner surface of the light path 50A are removed by the chemical.

[0054] In step 5, the valve control unit 90 closes the chemical supply valve 78 while keeping the chemical discharge valve 79 open, thereby stopping the supply of the chemical to the light path 50A. The chemical in the through hole 51 is discharged through the drain hole 50B and the chemical discharge line 68. In step 6, the valve control unit 90 opens the pure water supply valve 72 while keeping the chemical discharge valve 79 open. The pure water pushes out the chemical remaining in the optical path 50A, and the chemical is discharged together with the pure water through the drain hole 50B and the chemical discharge line 68. The optical path 50A is rinsed with the pure water.

[0055] In step 7, the valve control unit 90 closes the pure water supply valve 72 and the chemical solution discharge valve 79, and opens the pure water discharge valve 74. The pure water in the through hole 51 is discharged through the drain hole 50B and the pure water discharge line . In step 8, the valve control unit 90 closes the pure water discharge valve 74.

[0056] In this embodiment, the abrasive grains are removed by the chemical solution, but the optical path 50A is not dried. This embodiment is suitable for polishing the next wafer immediately after removing the abrasive grains with the chemical solution and rinsing the optical path 50A with pure water.

[0057] FIG. 7 is a flow chart illustrating yet another embodiment for removing abrasive particles from light path 50A. In step 1, after the wafer is polished, the rotation of the polishing table 3 is stopped. In step 2, without a wafer on the polishing pad 2, the valve control unit 90 opens the chemical supply valve 78 and the chemical discharge valve 79. The pure water supply valve 72, the pure water discharge valve 74, and the dry gas supply valve 81 are closed. The chemical flows into the light path 50A through the chemical supply line 63, and then flows through the through hole 51 and overflows onto the polishing pad 2. The slurry in the light path 50A flows onto the polishing pad 2 together with the chemical. The abrasive grains adhered to the inner surface of the light path 50A are removed by the chemical.

[0058] In step 3, the valve control unit 90 closes the chemical supply valve 78 while keeping the chemical discharge valve 79 open, thereby stopping the supply of the chemical to the light path 50A. The chemical in the through hole 51 is discharged through the drain hole 50B and the chemical discharge line 68. In step 4, the valve control unit 90 closes the chemical solution discharge valve 79.

[0059] This embodiment is implemented when a type of chemical solution is used that does not require a rinsing step of washing the chemical solution from the optical path 50A with pure water. In this embodiment, the abrasive grains are also removed by the chemical solution, but the optical path 50A is not dried. This embodiment is suitable for polishing the next wafer immediately after removing the abrasive grains with the chemical solution.

[0060] As described above, according to each of the above-mentioned embodiments, the abrasive grains are removed from the light path 50A by the chemical solution or pure water. The light can travel through the light path 50A without being affected by the abrasive grains. As a result, the optical surface monitoring device 40 can accurately measure the film thickness of a substrate such as a wafer.

[0061] The cleaning method according to each of the above-mentioned embodiments is performed with the polishing table 3 stopped from rotating in order to prevent the chemical liquid and / or the pure water from scattering. Depending on the flow rate of the chemical liquid and / or the pure water, the cleaning method according to each of the above-mentioned embodiments may be performed with the polishing table 3 kept rotating.

[0062] The above-described embodiments have been described for the purpose of enabling a person having ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments are naturally possible for a person skilled in the art, and the technical idea of ​​the present invention can 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 according to the technical idea defined by the claims. [Explanation of symbols]

[0063] 1 Polishing head 2 Polishing Pads 3 Polishing table 5 Slurry supply nozzle 6 Table Motor 7 Optical Sensor Head 9 Processing Equipment 10 Head shaft 17 Connection means 19 Rotary joint 31 Optical fiber cable for floodlight 32 Receiving optical fiber cable 40 Optical surface monitoring device 44 Light source 47 Spectrometer 50A Optical path 50B Drain hole 51 Through hole 52 Cylinder 53 Pure water supply line 54 Pure water discharge line 61 Pure water source 63 Chemical supply line 65 Dry gas supply line 68 Chemical Discharge Line 72 Pure water supply valve 74 Pure water discharge valve 78 Chemical supply valve 79 Chemical Discharge Valve 81 Dry gas supply valve 84 Chemical Supply Source 88 Dry Gas Supply Source 90 Valve control section

Claims

1. a substrate is polished by bringing the substrate into sliding contact with a polishing pad supported on a rotating polishing table while supplying a slurry containing abrasive grains onto the polishing pad; During polishing of the substrate, light is guided to the substrate through an optical path provided in the polishing table, and reflected light from the substrate is passed through the optical path; After the substrate is polished, the rotation of the polishing table is stopped; supplying a chemical solution into the optical path while the rotation of the polishing table is stopped and no substrate is present on the polishing pad, thereby removing the abrasive grains adhering to the optical path with the chemical solution; After the supply of the chemical liquid is stopped, pure water is supplied into the optical path while keeping a pure water discharge valve on a pure water discharge line communicating with the optical path closed, and the chemical liquid remaining in the optical path is discharged together with the pure water through the chemical liquid discharge line communicating with the optical path, and then supplying a dry gas to the optical path to dry the optical path; A cleaning method, wherein the chemical solution has a chemical property that etches the inner surface of the optical path.

2. 2. The cleaning method according to claim 1, further comprising the step of supplying pure water into said optical path after stopping the rotation of said polishing table and before supplying said chemical liquid into said optical path.

3. The cleaning method described in claim 1, further comprising: after discharging the chemical solution remaining in the optical passage together with the pure water, and before supplying dry gas to the optical passage, opening the pure water discharge valve to discharge the pure water through a hole formed in the polishing pad via the pure water discharge line, the hole being connected to the optical passage.

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