Polishing device

Abstract

To provide a polishing device which can prevent abrasive grains of a polishing liquid and swarf of a workpiece from adhering to an optical sensor head and improve measurement accuracy of a film thickness of the workpiece.SOLUTION: A polishing device includes: a polishing table 3 supporting a polishing pad 2 provided with a through hole 4; an optical film thickness measurement system 20 having an optical sensor head 25 attached to the polishing table 3; a transparent liquid inflow passage 50 for supplying a transparent liquid to the through hole 4; and a light projection side transparent liquid outflow passage 51 and a light receiving side transparent liquid outflow passage 52 communicating with the through hole 4. The optical sensor head 25 has: a light projection surface 71 which emits light to the oblique upper side; and a light receiving surface 72 which receives reflection light from a workpiece W. The light projection surface 71 faces the light projection side transparent liquid outflow passage 51 and the light receiving surface 72 faces a light receiving side transparent liquid outflow passage 28.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a technique for polishing workpieces such as wafers, wiring boards, and square substrates, and more particularly to a technique for guiding light to the workpiece through holes in a polishing pad for polishing the workpiece and measuring the film thickness of the workpiece based on the spectrum of the light reflected from the workpiece. [Background technology]

[0002] In the manufacturing process of semiconductor devices, a chemical mechanical polishing (CMP) apparatus is used to polish the surface of a workpiece such as a wafer. The CMP apparatus is equipped with a polishing table to which a polishing pad is attached, and a polishing head for pressing the workpiece against the polishing surface of the polishing pad. The CMP apparatus presses the workpiece against the polishing surface of the polishing pad with the polishing head while supplying a polishing liquid (e.g., slurry) onto the polishing pad, thereby bringing the surface of the workpiece into sliding contact with the polishing surface of the polishing pad. The surface of the workpiece 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.

[0003] Polishing of a workpiece is terminated when the thickness of a film (such as an insulating film or a silicon layer) constituting the surface of the workpiece reaches a target film thickness. The polishing apparatus is equipped with an optical film thickness measurement system for measuring the film thickness of the workpiece. The optical film thickness measurement system is configured to irradiate light onto the workpiece using an optical sensor head arranged in the polishing table, receive reflected light from the workpiece, generate a spectrum of the reflected light from the intensity of the reflected light, and determine the film thickness of the workpiece based on the spectrum of the reflected light.

[0004] In order to stabilize film thickness measurements using an optical film thickness measurement system, it is necessary to keep the light path clean. For example, Patent Document 1 describes how the light path is filled with a transparent liquid to prevent the intrusion of polishing liquid and polishing debris. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2003-197587 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the abrasive grains contained in the polishing liquid and the polishing debris from the workpiece usually have a higher specific gravity than the transparent liquid, and the abrasive grains and the polishing debris may adhere to the optical sensor head. If the abrasive grains and the polishing debris adhere to the optical sensor head, the measured value of the intensity of the reflected light from the workpiece decreases, and the optical film thickness measurement system cannot accurately measure the film thickness.

[0007] Therefore, the present invention provides a polishing apparatus that can prevent abrasive grains in the polishing liquid and polishing debris from the workpiece from adhering to an optical sensor head, thereby improving the measurement accuracy of the film thickness of the workpiece. [Means for solving the problem]

[0008] In one aspect, a polishing apparatus is provided that includes a polishing table that supports a polishing pad having a through hole formed therein, a polishing head that presses a workpiece against the polishing pad, an optical film thickness measurement system having an optical sensor head attached to the polishing table, a transparent liquid inlet path that supplies transparent liquid to the through hole, and a light-projecting side transparent liquid outlet path and a light-receiving side transparent liquid outlet path that communicate with the through hole, wherein the optical sensor head has a light-projecting surface that emits light diagonally upward and a light-receiving surface that receives reflected light from the workpiece, wherein the light-projecting surface faces the light-projecting side transparent liquid outlet path and the light-receiving surface faces the light-receiving side transparent liquid outlet path.

[0009] In one embodiment, the light projecting surface and the light receiving surface face obliquely upward. In one embodiment, the light projecting surface is located within the light projecting side transparent liquid outlet channel, and the light receiving surface is located within the light receiving side transparent liquid outlet channel. In one embodiment, the transparent liquid inflow channel is located between the light-emitting side transparent liquid outflow channel and the light-receiving side transparent liquid outflow channel. In one embodiment, the light-emitting side transparent liquid outflow channel and the light-receiving side transparent liquid outflow channel are disposed symmetrically with respect to the transparent liquid inflow channel. In one embodiment, the transparent liquid inlet channel is connected to a transparent liquid supply source, the transparent liquid supply source being a pure water supply source or a chemical liquid supply source. In one embodiment, the liquid ejection device further includes an ultrasonic transducer that applies ultrasonic waves to the transparent liquid flowing through the transparent liquid inflow channel. In one embodiment, the polishing apparatus further includes a flow control valve connected to the transparent liquid inlet path and an operation control unit that controls the operation of the flow control valve, and the operation control unit is configured to: when the workpiece is located on the through hole during polishing of the workpiece, command the flow control valve to supply the transparent liquid to the through hole at a first flow rate; and when the workpiece is not located on the through hole during polishing of the workpiece, command the flow control valve to supply the transparent liquid to the through hole at a second flow rate, the second flow rate being smaller than the first flow rate. Effect of the Invention

[0010] The transparent liquid supplied from the transparent liquid supply path into the through hole of the polishing pad forms a flow toward the light-projecting side transparent liquid outflow path and the light-receiving side transparent liquid outflow path. Since the light-projecting surface and the light-receiving surface of the optical sensor head face the light-projecting side transparent liquid outflow path and the light-receiving side transparent liquid outflow path, respectively, the flow of transparent liquid in the light-projecting side transparent liquid outflow path and the light-receiving side transparent liquid outflow path can contact the light-projecting surface and the light-receiving surface of the optical sensor head and clean the light-projecting surface and the light-receiving surface. The optical sensor head guides light to the workpiece and receives the reflected light from the workpiece, and the optical film thickness measurement system can accurately measure the film thickness of the workpiece based on the intensity of the reflected light from the workpiece. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram illustrating an embodiment of a polishing apparatus. [Diagram 2] FIG. 2 is a cross-sectional view showing a detailed configuration of the optical film thickness measurement system. [Diagram 3] 1 is an enlarged cross-sectional view showing an embodiment of an optical sensor head, a transparent liquid inflow path, a light-emitting side transparent liquid outflow path, and a light-receiving side transparent liquid outflow path. FIG. [Figure 4] FIG. 11 is an enlarged cross-sectional view showing another embodiment of the polishing apparatus. [Diagram 5] FIG. 11 is an enlarged cross-sectional view showing still another embodiment of the polishing apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] 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 pad 2 having a through hole 4 formed therein, a polishing table 3 supporting the polishing pad 2, a polishing head 1 pressing a workpiece W against the polishing pad 2, a table motor 6 rotating the polishing table 3, a polishing liquid supply nozzle 5 for supplying a polishing liquid such as a slurry onto the polishing pad 2, and an operation control unit 9 for controlling the operation of the polishing apparatus.

[0013] The upper surface of the polishing pad 2 constitutes a polishing surface 2a for polishing a workpiece W. Through holes 4 penetrate the polishing pad 2. The workpiece W has a film that constitutes its surface. Examples of the workpiece W to be polished include wafers, wiring boards, square boards, etc. used in the manufacture of semiconductor devices.

[0014] The polishing head 1 is connected to a head shaft 10, and the head shaft 10 is connected to a polishing head rotating device 15. The polishing head rotating device 15 is configured to rotate the polishing head 1 together with the head shaft 10 in the direction indicated by the arrow. The configuration of the polishing head rotating device 15 is not particularly limited, but in one example, the polishing head rotating device 15 includes an electric motor, a belt, a pulley, and the like. The polishing table 3 is connected to a table motor 6, and the table motor 6 is configured to rotate the polishing table 3 and the polishing pad 2 in the direction indicated by the arrow. The polishing head 1, the polishing head rotating device 15, and the table motor 6 are electrically connected to an operation control unit 9.

[0015] The workpiece W is polished as follows. A polishing liquid is supplied from a polishing liquid supply nozzle 5 to the polishing surface 2a of the polishing pad 2 on the polishing table 3 while the table motor 6 and the polishing head rotating device 15 rotate the polishing table 3 and the polishing head 1 in the directions shown by the arrows in Fig. 1. 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 with the polishing liquid present on the polishing pad 2. The surface of the workpiece W is polished by the chemical action of the polishing liquid and the mechanical action of the abrasive grains contained in the polishing liquid and / or the polishing pad 2.

[0016] The operation control unit 9 includes a storage device 9a in which a program is stored, and a calculation device 9b that executes calculations according to instructions included in the program. The operation control unit 9 includes at least one computer. The storage device 9a includes a main storage device such as a random access memory (RAM), and an auxiliary storage device such as a hard disk drive (HDD) or a solid state drive (SSD). Examples of the calculation 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 is equipped with an optical film thickness measurement system 20 that measures the film thickness of the workpiece W. The optical film thickness measurement system 20 is equipped with a light source 22 that emits light, an optical sensor head 25 that irradiates the workpiece W with the light from the light source 22 and receives the light reflected from the workpiece W, a spectrometer 23 connected to the optical sensor head 25, and a spectrum processing unit 30 that determines the film thickness of the workpiece W based on the spectrum of the light reflected from the workpiece W. The optical sensor head 25 is attached to the polishing table 3 and rotates together with the polishing table 3.

[0018] The spectrum processing unit 30 includes a storage device 30a in which a program is stored, and an arithmetic unit 30b that executes calculations according to instructions included in the program. The spectrum processing unit 30 includes at least one computer. The storage device 30a includes a main storage device such as a random access memory (RAM), and an auxiliary storage device such as a hard disk drive (HDD) or a solid state drive (SSD). Examples of the arithmetic unit 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] Each of the operation control unit 9 and the spectrum processing unit 30 may be composed of a plurality of computers. For example, each of the operation control unit 9 and the spectrum processing unit 30 may be composed of a combination of an edge server and a cloud server. In one embodiment, the operation control unit 9 and the spectrum processing unit 30 may be composed of a single computer.

[0020] 2 is a cross-sectional view showing a detailed configuration of the optical film thickness measurement system 20. The optical sensor head 25 is disposed in the polishing table 3, and the light source 22 and the spectroscope 23 are attached to the polishing table 3. The optical sensor head 25, the light source 22, and the spectroscope 23 rotate together with the polishing table 3 and the polishing pad 2. The position of the optical sensor head 25 is a position where it crosses the surface of the workpiece W on the polishing pad 2 every time the polishing table 3 and the polishing pad 2 rotate once. The optical sensor head 25 is connected to the light source 22 and the spectroscope 23, and the spectroscope 23 is connected to the spectrum processing unit 30.

[0021] The optical film thickness measuring device 20 includes a light projecting fiber optic cable 27 that guides light emitted from the light source 22 to the surface of the workpiece W, and a light receiving fiber optic cable 28 that receives the light reflected from the workpiece W and sends the reflected light to the spectroscope 23. An end 27a of the light projecting fiber optic cable 27 and an end 28a of the light receiving fiber optic cable 28 constitute an optical sensor head 25 that guides light to the surface of the workpiece W and receives the light reflected from the workpiece W. The other end of the light projecting fiber optic cable 27 is connected to the light source 22, and the other end of the light receiving fiber optic cable 28 is connected to the spectroscope 23. The spectroscope 23 is configured to resolve the light reflected from the workpiece W according to wavelength and measure the intensity of the reflected light over a predetermined wavelength range.

[0022] The optical sensor head 25, which is composed of an end 27a of a light-projecting optical fiber cable 27 and an end 28a of a light-receiving optical fiber cable 28, is located below the through hole 4 of the polishing pad 2 and faces the through hole 4. Light emitted by the light source 22 passes through the light-projecting optical fiber cable 27, and is guided from the optical sensor head 25 through the through hole 4 to the workpiece W. The reflected light from the workpiece W is received by the optical sensor head 25 through the through hole 4 and sent to the spectrometer 23 through the light-receiving optical fiber cable 28. The spectrometer 23 breaks down the reflected light according to its wavelength and generates reflected light intensity measurement data by measuring the intensity of the reflected light at each wavelength. The reflected light intensity measurement data is sent from the spectrometer 23 to a spectrum processing unit 30.

[0023] The spectrum processor 30 is configured to generate a spectrum of the reflected light from the workpiece W from the reflected light intensity measurement data. The spectrum of the reflected light is expressed as a line graph (i.e., a spectral waveform) showing the relationship between the wavelength and intensity of the reflected light. The intensity of the reflected light can also be expressed as a relative value such as reflectance or relative reflectance.

[0024] The spectrum processor 30 is configured to determine the film thickness of the workpiece W based on the spectrum of the reflected light. A known method is used to determine the film thickness of the workpiece W based on the spectrum. For example, the spectrum processor 30 determines a reference spectrum from a reference spectrum library that has a shape closest to the spectrum of the reflected light, and determines the film thickness associated with the determined reference spectrum. In another example, the spectrum processor 30 performs a Fourier transform on the spectrum of the reflected light, and determines the film thickness from the obtained frequency spectrum.

[0025] The polishing table 3 has a transparent liquid inflow path 50, a light-emitter side transparent liquid outflow path 51, and a light-receiving side transparent liquid outflow path 52, which communicate with the through hole 4. The transparent liquid inflow path 50, the light-emitter side transparent liquid outflow path 51, and the light-receiving side transparent liquid outflow path 52 are provided inside the polishing table 3 and rotate integrally with the polishing table 3. The polishing apparatus 1 includes a transparent liquid supply line 35 connected to the transparent liquid inflow path 50, a transparent liquid discharge line 36 connected to the light-emitter side transparent liquid outflow path 51 and the light-receiving side transparent liquid outflow path 52, and a supply pump 37 and a flow rate adjustment valve 41 connected to the transparent liquid supply line 35.

[0026] One end of the transparent liquid supply line 35 is connected to the transparent liquid inlet path 50, and the other end is connected to a transparent liquid supply source 55. The transparent liquid inlet path 50 may be configured integrally with the transparent liquid supply line 35. An example of the transparent liquid supply source 55 is a pure water supply source that supplies pure water as the transparent liquid. The pure water, which is a transparent liquid, is supplied into the through hole 4 of the polishing pad 2 through the transparent liquid supply line 35 and the transparent liquid inlet path 50.

[0027] The pure water supplied into the through hole 4 of the polishing pad 2 passes through the light-emitter-side transparent liquid outflow path 51 and the light-receiving-side transparent liquid outflow path 52, is discharged from the through hole 4, and is further discharged through the transparent liquid discharge line 36. The light-emitter-side transparent liquid outflow path 51 and the light-receiving-side transparent liquid outflow path 52 may be configured integrally with the transparent liquid discharge line 36.

[0028] In one embodiment, the transparent liquid may be a liquid other than pure water as long as it does not impede the transmission of light. The supply pump 37 is configured to pressurize the pure water flowing through the transparent liquid supply line 35. The pure water pressurized by the supply pump 37 is supplied to the through hole 4 through the transparent liquid supply line 35 and the transparent liquid inflow path 50.

[0029] The flow rate control valve 41 is an actuator-driven valve such as an electric valve, a solenoid valve, or an air-operated valve. The flow rate control valve 41 is electrically connected to the operation control unit 9, and the operation of the flow rate control valve 41 is controlled by the operation control unit 9.

[0030] Fig. 3 is an enlarged cross-sectional view showing one embodiment of the optical sensor head 25, the transparent liquid inflow path 50, the light-projecting side transparent liquid outflow path 51, and the light-receiving side transparent liquid outflow path 52. As shown in Fig. 3, the optical sensor head 25, which is composed of the end 27a of the light-projecting fiber optic cable 27 and the end 28a of the light-receiving fiber optic cable 28, is located below the through-hole 4 of the polishing pad 2. The end 27a of the light-projecting fiber optic cable 27 is inclined upward, and the end 28a of the light-receiving fiber optic cable 28 is also inclined upward at the same angle.

[0031] The optical sensor head 25 has a light projecting surface 71 that emits light and a light receiving surface 72 that receives reflected light from the workpiece W. In this embodiment, the light projecting surface 71 is formed from the tip surface of the light projecting optical fiber cable 27, and the light receiving surface 72 is formed from the tip surface of the light receiving optical fiber cable 28. In one embodiment, the light projecting surface 71 and the light receiving surface 72 may be formed from optical elements such as lenses, glass, or mirrors arranged opposite the tip surfaces of the light projecting optical fiber cable 27 and the light receiving optical fiber cable 28.

[0032] The light-projecting surface 71 and the light-receiving surface 72 face obliquely upward at the same angle. More specifically, the light-projecting surface 71 and the light-receiving surface 72 face the same measurement point MP on the surface of the workpiece W on the polishing pad 2. Therefore, the light-projecting surface 71 of the optical sensor head 25 emits light obliquely upward and guides the light to the measurement point MP on the surface of the workpiece W. The reflected light from the measurement point MP travels obliquely downward toward the light-receiving surface 72 of the optical sensor head 25 and is incident on the light-receiving surface 72.

[0033] The upper ends of the transparent liquid inflow path 50, the light-emitter-side transparent liquid outflow path 51, and the light-receiving-side transparent liquid outflow path 52 open at the upper surface of the polishing table 3 and communicate with the through-hole 4. The transparent liquid inflow path 50, the light-emitter-side transparent liquid outflow path 51, and the light-receiving-side transparent liquid outflow path 52 extend downward from the upper surface of the polishing table 3. The transparent liquid inflow path 50 is connected to the transparent liquid supply line 35, and the light-emitter-side transparent liquid outflow path 51 and the light-receiving-side transparent liquid outflow path 52 are connected to the transparent liquid discharge line 36.

[0034] During polishing of the workpiece W, the through hole 4 is filled with pure water, which is a transparent liquid. Light emitted from an optical sensor head 25 consisting of an end 27a of a light-projecting optical fiber cable 27 and an end 28a of a light-receiving optical fiber cable 28 passes through the pure water filling the through hole 4 and is irradiated onto the workpiece W on the polishing pad 2. The reflected light from the workpiece W passes through the pure water filling the through hole 4 and is received by the optical sensor head 25.

[0035] An end 27a of the light-projecting fiber optic cable 27 constituting the optical sensor head 25 is connected to the light-projecting side transparent liquid outflow path 51, and a light-projecting surface 71 of the optical sensor head 25 faces the light-projecting side transparent liquid outflow path 51. An end 28a of the light-receiving fiber optic cable 28 constituting the optical sensor head 25 is connected to the light-receiving side transparent liquid outflow path 52, and a light-receiving surface 72 of the optical sensor head 25 faces the light-receiving side transparent liquid outflow path 52.

[0036] The transparent liquid inlet path 50 is located directly below the measurement point MP of the workpiece W (i.e., the point irradiated with light from the optical sensor head 25). The transparent liquid inlet path 50 is located between the light-emitter side transparent liquid outlet path 51 and the light-receiving side transparent liquid outlet path 52, and pure water as the transparent liquid flows upward from the transparent liquid inlet path 50. The light-emitter side transparent liquid outlet path 51 and the light-receiving side transparent liquid outlet path 52 are disposed symmetrically with respect to the transparent liquid inlet path 50.

[0037] The pure water, which is a transparent liquid, flows from the transparent liquid inflow path 50 into the through hole 4 and flows toward the measurement point MP on the surface of the workpiece W on the polishing pad 2. The pure water changes direction inside the through hole 4 and flows into the light-projecting side transparent liquid outflow path 51 and the light-receiving side transparent liquid outflow path 52. The flow of the pure water in the light-projecting side transparent liquid outflow path 51 and the light-receiving side transparent liquid outflow path 52 contacts the light-projecting surface 71 and the light-receiving surface 72 of the optical sensor head 25, and can prevent the abrasive grains contained in the polishing liquid and the polishing debris of the workpiece W from adhering to the light-projecting surface 71 and the light-receiving surface 72. Therefore, the light-projecting surface 71 and the light-receiving surface 72 of the optical sensor head 25 can be kept clean.

[0038] The light receiving surface 72 of the optical sensor head 25 receives the reflected light from the measurement point MP of the workpiece W. The optical film thickness measurement system 20 can accurately measure the film thickness at the measurement point MP of the workpiece W based on the intensity of the reflected light from the workpiece W.

[0039] In the embodiment shown in Fig. 3, in order to improve the cleaning effect of the light-projecting surface 71 and the light-receiving surface 72 of the optical sensor head 25 by the flow of pure water, the end 27a of the light-projecting optical fiber cable 27 protrudes into the light-projecting side transparent liquid outflow path 51, and the light-projecting surface 71 of the optical sensor head 25 is located in the light-projecting side transparent liquid outflow path 51. Similarly, the end 28a of the light-receiving optical fiber cable 28 protrudes into the light-receiving side transparent liquid outflow path 52, and the light-receiving surface 72 of the optical sensor head 25 is located in the light-receiving side transparent liquid outflow path 52. The pure water forms a fast flow in the light-projecting side transparent liquid outflow path 51 and the light-receiving side transparent liquid outflow path 52, and this flow of pure water can maintain the cleanliness of the light-projecting surface 71 and the light-receiving surface 72 of the optical sensor head 25.

[0040] During polishing of the workpiece W, the flow rate control valve 41 is opened, and pure water as a transparent liquid is supplied into the through hole 4 through the transparent liquid supply line 35 and the transparent liquid inlet path 50. During polishing of the workpiece W, the polishing pad 2 rotates together with the polishing table 3, whereas the workpiece W held by the polishing head 1 does not rotate together with the polishing table 3. Therefore, there are times when the workpiece W is on the through hole 4 and times when the workpiece W is not on the through hole 4. In other words, as the polishing pad 2 and the polishing table 3 rotate, the workpiece W periodically covers the through hole 4.

[0041] The flow rate control valve 41 is connected to the transparent liquid inlet passage 50 via the transparent liquid supply line 35. The flow rate control valve 41 can adjust the flow rate of the pure water supplied into the through hole 4. The operation of the flow rate control valve 41 is controlled by the operation control unit 9. In one embodiment, the flow rate of the pure water supplied into the through hole 4 is maintained constant by the flow rate control valve 41 during polishing of the workpiece W. In another embodiment, the operation control unit 9 is configured to give a command to the flow rate control valve 41 to supply the pure water to the through hole 4 at a first flow rate when the workpiece W is on the through hole 4 during polishing of the workpiece W, and to give a command to the flow rate control valve 41 to supply the pure water to the through hole 4 at a second flow rate smaller than the first flow rate when the workpiece W is not on the through hole 4 during polishing of the workpiece W.

[0042] When the workpiece W is on the through hole 4, the through hole 4 is closed by the workpiece W. Therefore, by supplying pure water to the through hole 4 at a first flow rate that is greater than the second flow rate, a fast flow of pure water can be formed in the light-projecting side transparent liquid outflow path 51 and the light-receiving side transparent liquid outflow path 52. This fast flow of pure water can improve the cleaning effect of the light-projecting surface 71 and the light-receiving surface 72 of the optical sensor head 25.

[0043] In the embodiment shown in FIG. 3, the light-projecting surface 71 and the light-receiving surface 72 of the optical sensor head 25 are located below the polishing pad 2. In one embodiment, as shown in FIG. 4, the polishing table 3 has a protrusion 3a located in the through hole 4 of the polishing pad 2, and the light-projecting surface 71 and the light-receiving surface 72 of the optical sensor head 25, the upper end of the transparent liquid inflow path 50, the light-projecting side transparent liquid outflow path 51, and the upper end of the light-receiving side transparent liquid outflow path 52 may be located in the protrusion 3a. The protrusion 3a protrudes upward and fits into the lower part of the through hole 4. The transparent liquid inflow path 50, the light-projecting side transparent liquid outflow path 51, and the light-receiving side transparent liquid outflow path 52 open at the upper surface of the protrusion 3a.

[0044] The embodiment shown in Figure 4 is the same as the embodiment shown in Figure 3 in that the light-projecting surface 71 and the light-receiving surface 72 of the optical sensor head 25 are located within the light-projecting side transparent liquid outflow path 51 and the light-receiving side transparent liquid outflow path 52, but differs in that the light-projecting surface 71 and the light-receiving surface 72 of the optical sensor head 25 are located within the polishing pad 2.

[0045] 4, the flows of pure water in the light-projecting-side transparent liquid outflow path 51 and the light-receiving-side transparent liquid outflow path 52 come into contact with the light-projecting surface 71 and the light-receiving surface 72 of the optical sensor head 25, and can prevent the abrasive grains contained in the polishing liquid and the polishing debris of the workpiece W from adhering to the light-projecting surface 71 and the light-receiving surface 72. Therefore, the light-projecting surface 71 and the light-receiving surface 72 of the optical sensor head 25 can be kept clean.

[0046] 5 is an enlarged cross-sectional view showing still another embodiment of the polishing apparatus. The configuration and operation of this embodiment not specifically described are the same as those of the embodiment described with reference to FIGS. 1 to 3, and therefore the duplicated description will be omitted.

[0047] 5, the polishing apparatus includes an ultrasonic transducer 80 that applies ultrasonic waves to pure water, which serves as a transparent liquid, flowing through a transparent liquid inlet path 50. The ultrasonic transducer 80 is installed within the polishing table 3 and is adjacent to the transparent liquid inlet path 50.

[0048] According to this embodiment, the pure water to which ultrasonic waves are applied by the ultrasonic vibrator 80 fills the through hole 4, and then flows through the light-projecting side transparent liquid outlet path 51 and the light-receiving side transparent liquid outlet path 52, thereby effectively cleaning the light-projecting surface 71 and the light-receiving surface 72 of the optical sensor head 25. The ultrasonic vibrator 80 can also be applied to the embodiment described with reference to FIG.

[0049] In one embodiment, the transparent liquid source 55 (see FIG. 2) may be a chemical liquid source instead of a pure water source. A transparent chemical liquid is used as the transparent liquid instead of pure water. An example of the chemical liquid is a potassium hydroxide (KOH) solution that has an etching effect.

[0050] When a chemical liquid is used as the transparent liquid, in order to prevent the chemical liquid from flowing onto the polishing pad 2 during polishing of the workpiece W, the light-emitting surface 71 and the light-receiving surface 72 of the optical sensor head 25 may be cleaned before or after polishing the workpiece W.

[0051] 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]

[0052] W Workpiece 1 Polishing head 2 Polishing Pads 2a Polished surface 3 Polishing table 4 through hole 5 Polishing fluid supply nozzle 6 Table Motor 9. Operation control section 10 Head shaft 15 Polishing head rotation device 20 Optical Film Thickness Measurement System 22 Light source 23 Spectrometer 25 Optical sensor head 27 Optical fiber cable for floodlight 28 Receiving optical fiber cable 30 Spectral Processing Section 35 Transparent liquid supply line 36 Transparent liquid discharge line 37 Supply Pump 41 Flow control valve 50 Clear liquid inlet channel 51 Transparent liquid outflow path on the emitter side 52 Transparent liquid outflow path on light receiving side 71 Light-projecting surface 72 Light-receiving surface 80 Ultrasonic vibrator

Claims

1. a polishing table supporting a polishing pad having a through hole; a polishing head for pressing a workpiece against the polishing pad; an optical film thickness measurement system having an optical sensor head attached to the polishing table; a transparent liquid inlet channel for supplying a transparent liquid to the through hole; a light-emitting side transparent liquid outlet path and a light-receiving side transparent liquid outlet path communicating with the through hole, the optical sensor head has a light projection surface that emits light obliquely upward and a light receiving surface that receives reflected light from the workpiece; A polishing apparatus, wherein the light-projecting surface faces the light-projecting side transparent liquid outflow path, and the light-receiving surface faces the light-receiving side transparent liquid outflow path.

2. 2. The polishing apparatus according to claim 1, wherein the light projecting surface and the light receiving surface face obliquely upward.

3. 2. The polishing apparatus according to claim 1, wherein said light projecting surface is located within said light projecting side transparent liquid outlet channel, and said light receiving surface is located within said light receiving side transparent liquid outlet channel.

4. 2. The polishing apparatus according to claim 1, wherein the transparent liquid inlet channel is located between the light-emitter side transparent liquid outlet channel and the light-receive side transparent liquid outlet channel.

5. 5. The polishing apparatus according to claim 4, wherein the light-emitting side transparent liquid outlet channel and the light-receiving side transparent liquid outlet channel are disposed symmetrically with respect to the transparent liquid inlet channel.

6. 2. The polishing apparatus according to claim 1, wherein the transparent liquid inlet passage is connected to a transparent liquid supply source, the transparent liquid supply source being a pure water supply source or a chemical liquid supply source.

7. 2. The polishing apparatus according to claim 1, further comprising an ultrasonic vibrator that applies ultrasonic waves to the transparent liquid flowing through the transparent liquid inflow path.

8. a flow control valve connected to the transparent liquid inlet channel; An operation control unit that controls the operation of the flow rate control valve is further provided.

2. The polishing apparatus of claim 1, wherein the operation control unit is configured to: when the workpiece is located on the through hole during polishing of the workpiece, give a command to the flow rate control valve to supply the transparent liquid to the through hole at a first flow rate, and when the workpiece is not located on the through hole during polishing of the workpiece, give a command to the flow rate control valve to supply the transparent liquid to the through hole at a second flow rate, the second flow rate being smaller than the first flow rate.

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