Transparent liquid filling method

Abstract

To provide a transparent liquid filling method that can achieve accurate measurement of a film thickness of a workpiece by stabilizing an optical path within a space existing between a transparent window of an abrasive pad and an optical sensor head.SOLUTION: Negative pressure is formed within a space 32 by performing evacuation of the space 32 that is formed between a transparent window 4 constituting a part of an abrasive pad 2 for polishing a workpiece W and an optical sensor head 25 of an optical film thickness measurement system 20 for measuring a film thickness of the workpiece W. In a state in which the negative pressure is formed within the space 32, a transparent liquid is supplied into the space 32 through a transparent liquid feed line 35.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a technology for polishing workpieces such as wafers, wiring boards, and square substrates, and more particularly to a technology for guiding light to the workpiece through a transparent window of a polishing pad for polishing the workpiece and measuring the film thickness of the workpiece based on the spectrum of the reflected light 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 pad attached to a polishing table 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] The polishing pad on the polishing table has a transparent window that constitutes a part of the polishing pad. The transparent window can prevent the polishing liquid and polishing debris on the polishing pad from contacting the optical sensor head. A space exists between the optical sensor head and the transparent window. Light emitted from the optical sensor head is guided to the workpiece through the space and the transparent window, and reflected light from the workpiece reaches the optical sensor head through the transparent window and the space. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-24036 A Summary of the Invention [Problem to be solved by the invention]

[0006] In addition to the polishing liquid, pure water is supplied onto the polishing pad for use in dressing and cleaning the polishing pad. Liquids such as the polishing liquid or pure water may penetrate into the polishing pad made of a foam material and enter the space between the optical sensor head and the transparent window. The liquid in the space may change the direction of light or scatter the light. In particular, if there are bubbles in the liquid in the space, the liquid may change the intensity of the reflected light from the workpiece and prevent accurate film thickness measurement.

[0007] Therefore, the present invention provides a transparent liquid filling method that can stabilize the optical path in the space between the transparent window of the polishing pad and the optical sensor head, thereby achieving accurate film thickness measurement of the workpiece. [Means for solving the problem]

[0008] In one aspect, a transparent liquid filling method is provided, which comprises evacuating a space formed between a transparent window that constitutes part of a polishing pad for polishing a workpiece and an optical sensor head of an optical film thickness measurement system for measuring the film thickness of the workpiece, thereby creating a negative pressure in the space, and supplying the transparent liquid into the space through a transparent liquid supply line while the negative pressure is created in the space.

[0009] In one embodiment, the transparent liquid is supplied into the space through the transparent liquid supply line while the space is being evacuated to a vacuum. In one aspect, after the evacuation of the space is stopped and in a state in which a negative pressure is formed in the space, the transparent liquid is supplied into the space through the transparent liquid supply line. In one embodiment, after the entire space is filled with the transparent liquid, the supply of the transparent liquid into the space is stopped. Effect of the Invention

[0010] By evacuating the space between the transparent window of the polishing pad and the optical sensor head, moisture and dust present in the space can be removed. After evacuating the space, transparent liquid is supplied into the space, so that the space is filled with transparent liquid. The transparent liquid filling the space forms a stable optical path in the space. Therefore, the optical film thickness measurement system can accurately measure the film thickness of 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] FIG. 2 is an enlarged cross-sectional view of one embodiment of a transparent window and an optical sensor head. [Figure 4] 11 is an enlarged cross-sectional view showing another embodiment of a transparent window and an optical sensor head. FIG. [Diagram 5]FIG. 1 illustrates an embodiment in which the space between the transparent window and the optical sensor head is filled with pure water. [Figure 6] FIG. 13 illustrates an embodiment in which a flow of pure water is formed in the space between the transparent window and the optical sensor head. [Figure 7] 11A and 11B are diagrams showing an embodiment of a transparent liquid filling method for filling the space between the transparent window and the optical sensor head with pure water; [Figure 8] 1 is a flowchart illustrating an embodiment of a transparent liquid filling method. [Figure 9] 13 is a flowchart illustrating another embodiment of a transparent liquid filling method. [Figure 10] FIG. 11 is an enlarged cross-sectional view showing another embodiment of the polishing apparatus. [Figure 11] FIG. 11 is an enlarged cross-sectional view showing still another embodiment of the polishing apparatus. [Figure 12] FIG. 11 is an enlarged cross-sectional view showing still another embodiment of the polishing apparatus. [Figure 13] FIG. 11 is an enlarged cross-sectional view showing still another embodiment of the polishing apparatus. [Figure 14] FIG. 11 is an enlarged cross-sectional view showing still another embodiment of the polishing apparatus. [Figure 15] FIG. 11 is a cross-sectional view showing another embodiment of a transparent window. [Figure 16] FIG. 11 is a cross-sectional view showing yet another embodiment of a transparent window. [Figure 17] FIG. 11 is an enlarged cross-sectional view showing still another embodiment of the polishing apparatus. [Figure 18] 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 transparent window 4, 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 the workpiece W. The transparent window 4 constitutes a part of the polishing pad 2 and is made of a transparent material (e.g., transparent resin) that allows light to pass through. The workpiece W has a film that constitutes its surface. Examples of the workpiece W to be polished include wafers, wiring boards, and square boards 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 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 disposed within 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 measurement system 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. The ends of the light projecting fiber optic cable 27 and the light receiving fiber optic cable 28 are exposed on the polishing table 3. The ends of the light projecting fiber optic cable 27 and the light receiving fiber optic cable 28 form 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] An optical sensor head 25 , which is constituted by the tip of a light-projecting optical fiber cable 27 and the tip of a light-receiving optical fiber cable 28 , is positioned below the transparent window 4 of the polishing pad 2 .

[0023] 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 transparent window 4 to the workpiece W. Light reflected from the workpiece W is received by the optical sensor head 25 through the transparent window 4 and sent to the spectrometer 23 through the light-receiving optical fiber cable 28. The spectrometer 23 resolves 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.

[0024] 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.

[0025] 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.

[0026] The polishing apparatus includes a transparent liquid supply line 35 that supplies pure water, which is a transparent liquid, to a space 32 formed between the transparent window 4 and the optical sensor head 25, a transparent liquid discharge line 36 that discharges pure water from the space 32, a supply pump 37 and a transparent liquid supply valve 41 connected to the transparent liquid supply line 35, and a transparent liquid discharge valve 42 connected to the transparent liquid discharge line 36. The transparent liquid supply line 35 and the transparent liquid discharge line 36 communicate with the space 32. The transparent liquid supply line 35 and the transparent liquid discharge line 36 extend within the polishing table 3. In one embodiment, a plurality of transparent liquid discharge lines 36 may be provided.

[0027] Pure water flows as a transparent liquid from a transparent liquid supply source (not shown) in the transparent liquid supply line 35. 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 space 32 through the transparent liquid supply line 35. The pure water supplied to the space 32 is discharged from the space 32 through the transparent liquid discharge line 36.

[0028] In one embodiment, the polishing apparatus includes a pressure regulator 39 connected to the transparent liquid supply line 35. The pressure regulator 39 is configured to adjust the pressure of pure water as the transparent liquid supplied to the space 32 through the transparent liquid supply line 35. The pressure of the transparent liquid supplied to the space 32 can also be adjusted by the supply pump 37. When a utility facility of a factory in which the polishing apparatus is installed is used as a transparent liquid supply source, the supply pump 37 does not need to be provided.

[0029] Each of the transparent liquid supply valve 41 and the transparent liquid discharge valve 42 is an actuator-driven valve such as an electric valve, a solenoid valve, or an air-operated valve. The transparent liquid supply valve 41 and the transparent liquid discharge valve 42 are electrically connected to the operation control unit 9, and the operations of the transparent liquid supply valve 41 and the transparent liquid discharge valve 42 are controlled by the operation control unit 9. In one embodiment, the transparent liquid supply valve 41 and the transparent liquid discharge valve 42 may be manual valves.

[0030] 3 is an enlarged cross-sectional view showing one embodiment of the transparent window 4 and the optical sensor head 25. As shown in FIG. 3, the transparent window 4 is disposed in a through hole 45 formed in the polishing pad 2 and closes the through hole 45. The thickness of the transparent window 4 is smaller than the thickness of the polishing pad 2, and the lower surface of the transparent window 4 is located higher than the lower surface of the polishing pad 2. The optical sensor head 25, which is composed of the tip of the light-projecting fiber optic cable 27 and the tip of the light-receiving fiber optic cable 28, is located below the transparent window 4 of the polishing pad 2 and faces the space 32.

[0031] In the embodiment shown in FIG. 3, the space 32 between the transparent window 4 and the optical sensor head 25 is formed in the polishing pad 2. That is, the space 32 is formed by the lower surface of the transparent window 4, the through hole 45 of the polishing pad 2, and the upper surface of the polishing table 3. In one embodiment, as shown in FIG. 4, the space 32 between the transparent window 4 and the optical sensor head 25 is formed in the polishing table 3. That is, the space 32 is formed by the lower surface of the transparent window 4 and a recess 46 formed in the upper surface of the polishing table 3. In the embodiment shown in FIG. 4, the thickness of the transparent window 4 may be the same as the thickness of the polishing pad 2. In one embodiment, the embodiment shown in FIG. 3 and the embodiment shown in FIG. 4 may be combined.

[0032] In one embodiment shown in FIG. 5, the space 32 is filled with pure water, which is a transparent liquid. Both the transparent liquid supply valve 41 and the transparent liquid discharge valve 42 are closed. Therefore, the pure water is confined in the space 32, and no flow of pure water is formed in the space 32 during polishing of the workpiece W. Light emitted from the optical sensor head 25 composed of the tip of the light-projecting optical fiber cable 27 and the tip of the light-receiving optical fiber cable 28 passes through the pure water filling the space 32 and the transparent window 4, and is irradiated onto the workpiece W on the polishing pad 2. The reflected light from the workpiece W passes through the transparent window 4 and the pure water filling the space 32, and is received by the optical sensor head 25.

[0033] 5, the space 32 is filled with pure water during polishing of the workpiece W. Therefore, a stable optical path for measuring the film thickness of the workpiece W is secured in the space 32. As a result, the optical film thickness measurement system 20 can accurately measure the film thickness of the workpiece W.

[0034] In one embodiment shown in Fig. 6, the space 32 is filled with pure water, which is a transparent liquid, and both the transparent liquid supply valve 41 and the transparent liquid discharge valve 42 are open. During polishing of the workpiece W, a flow of pure water is formed in the space 32. That is, the pure water flows into the space 32 through the transparent liquid supply line 35, flows within the space 32, and then flows out through the transparent liquid discharge line 36. Since the space 32 is filled with pure water during polishing of the workpiece W, an optical path for measuring the film thickness of the workpiece W is secured. As a result, the optical film thickness measurement system 20 can accurately measure the film thickness of the workpiece W.

[0035] In the embodiment shown in Figures 3 to 6, the transparent window 4 has a flat lower surface. The lower surface of the transparent window 4 is perpendicular to the orientation of the optical sensor head 25. More specifically, it is perpendicular to the tip of the light projecting optical fiber cable 27 and the tip of the light receiving optical fiber cable 28 that constitute the optical sensor head 25. Since the lower surface of the transparent window 4 is perpendicular to the optical path of the light generated from the optical sensor head 25, the light from the optical sensor head 25 is perpendicularly incident on the lower surface of the transparent window 4. In one embodiment, the optical sensor head 25 may be disposed obliquely with respect to the lower surface of the transparent window 4, and the light from the optical sensor head 25 may be obliquely incident on the lower surface of the transparent window 4.

[0036] Next, an embodiment of a transparent liquid filling method for filling the space 32 between the transparent window 4 and the optical sensor head 25 with pure water, which is an example of a transparent liquid, before polishing the workpiece W will be described with reference to Fig. 7. First, the transparent liquid discharge line 36 is connected to a discharge pump 50. The discharge pump 50 is configured to be capable of transporting liquid and gas. An example of the discharge pump 50 is a piezoelectric pump equipped with a piezoelectric vibrator.

[0037] The transparent liquid supply valve 41 is closed, and the transparent liquid discharge valve 42 is opened. When the discharge pump 50 is operated, a negative pressure is generated in the space 32. By evacuating the space 32 with the discharge pump 50, it is possible to remove moisture and dust present in the space 32. In particular, the liquid containing air bubbles present in the space 32 can be removed by operating the discharge pump 50.

[0038] When the transparent liquid supply valve 41 is opened while negative pressure is formed in the space 32, pure water as a transparent liquid is supplied into the space 32 through the transparent liquid supply line 35. After the entire space 32 is filled with pure water, the transparent liquid supply valve 41 is closed to stop the supply of pure water into the space 32. The pure water filling the space 32 forms a stable optical path within the space 32. Therefore, the optical film thickness measurement system 20 can measure the film thickness of the workpiece W accurately.

[0039] The operation of the transparent liquid supply valve 41 and the transparent liquid discharge valve 42 is performed by the operation control unit 9. In one embodiment, the transparent liquid supply valve 41 and the transparent liquid discharge valve 42 are manual valves, and the operation of the transparent liquid supply valve 41 and the transparent liquid discharge valve 42 may be performed manually.

[0040] 8 is a flow chart for explaining one embodiment of a transparent liquid filling method. In this embodiment, while evacuating the space 32, pure water as the transparent liquid is supplied into the space 32 through the transparent liquid supply line 35. Specifically, the process is as follows. In step 101, the clear liquid supply valve 41 is closed and the clear liquid discharge valve 42 is opened, and the discharge pump 50 is operated to generate a negative pressure in the space 32. In step 102, while the transparent liquid discharge valve 42 is open and the discharge pump 50 is operating, the transparent liquid supply valve 41 is opened. Pure water as the transparent liquid is supplied into the space 32 through the transparent liquid supply line 35. In step 103, after the entire space 32 is filled with pure water, the transparent liquid supply valve 41 and the transparent liquid discharge valve 42 are closed, and the operation of the discharge pump 50 is stopped. This stops the supply of pure water into the space 32.

[0041] In one embodiment, instead of the operation of step 103, after the entire space 32 is filled with pure water, the transparent liquid supply valve 41 and the transparent liquid discharge valve 42 may be kept open and the discharge pump 50 may be continued to operate. In this embodiment, the supply and discharge of pure water to and from the space 32 continues even after the entire space 32 is filled with pure water. Therefore, a flow of pure water is formed in the space 32 when the entire space 32 is filled with pure water.

[0042] 9 is a flow chart for explaining another embodiment of the transparent liquid filling method. In this embodiment, after the evacuation of the space 32 is stopped and negative pressure is formed in the space 32, pure water as the transparent liquid is supplied into the space 32 through the transparent liquid supply line 35. Specifically, the process is as follows. In step 201, the clear liquid supply valve 41 is closed and the clear liquid discharge valve 42 is opened, and the discharge pump 50 is operated to generate a negative pressure in the space 32. In step 202, the clear liquid discharge valve 42 is closed and the discharge pump 50 is stopped. In step 203, the transparent liquid supply valve 41 is opened while a negative pressure is formed in the space 32. Pure water as the transparent liquid is supplied into the space 32 through the transparent liquid supply line . In step 204, after the entire space 32 is filled with pure water, the transparent liquid supply valve 41 is closed, whereby the supply of pure water into the space 32 is stopped.

[0043] 7 to 9 is performed before polishing the workpiece W. In one example, the transparent liquid filling method described with reference to Fig. 7 to 9 is performed after a new polishing pad 2 that has not been used for polishing a workpiece is placed on the polishing table 3 and before the workpiece is polished with the new polishing pad 2.

[0044] 10 is an enlarged cross-sectional view showing another embodiment of the polishing apparatus including the transparent window 4 and the optical sensor head 25. The configuration and operation of this embodiment that are not specifically described are the same as those of the above-mentioned embodiment, so duplicated descriptions will be omitted. The polishing apparatus of this embodiment includes an inlet side measuring device 52 provided in the transparent liquid supply line 35. The inlet side measuring device 52 is disposed downstream of the transparent liquid supply valve 41.

[0045] The inlet side measuring device 52 is configured to measure a physical quantity (flow rate or pressure) of the transparent liquid flowing through the transparent liquid supply line 35. The inlet side measuring device 52 is electrically connected to the operation control unit 9, and the measurement value of the physical quantity (flow rate or pressure) of the transparent liquid acquired by the inlet side measuring device 52 is sent to the operation control unit 9.

[0046] In one embodiment, the inlet side measuring device 52 is a flow measuring device that measures the flow rate of the transparent liquid. The operation control unit 9 is configured to generate an alarm signal when the measured value of the flow rate of the transparent liquid falls outside a preset flow rate range. The flow rate of the transparent liquid is expected to increase or decrease significantly when a malfunction occurs in the transparent liquid supply system. For example, the flow rate of the transparent liquid is expected to decrease when the transparent liquid supply line 35 is clogged or the supply pump 37 breaks down. On the other hand, the flow rate of the transparent liquid is expected to increase when the pressure regulator 39 breaks down or when the transparent liquid leaks through the gap around the transparent window 4. If the flow rate of the transparent liquid changes significantly, air bubbles may enter the transparent liquid, degrading the quality of the reflected light intensity measurement data used for film thickness measurement. A change in the flow rate of the transparent liquid may also change the pressure of the transparent liquid. If the pressure of the transparent liquid in the space 32 increases, the transparent window 4 may be deformed.

[0047] In one embodiment, the inlet side measuring device 52 is a pressure measuring device that measures the pressure of the transparent liquid. The operation control unit 9 is configured to generate an alarm signal when the measured value of the pressure of the transparent liquid is outside a preset pressure range.

[0048] The operation control unit 9 generates an alarm signal when the measured value of the flow rate of the transparent liquid falls outside a preset flow rate range or when the measured value of the pressure of the transparent liquid falls outside a preset pressure range. In one embodiment, the operation control unit 9 issues a command to the optical film thickness measurement system 20 to stop the measurement operation of the film thickness of the workpiece W when the measured value of the flow rate of the transparent liquid falls outside a preset flow rate range or when the measured value of the pressure of the transparent liquid falls outside a preset pressure range.

[0049] 11 is an enlarged cross-sectional view showing yet another embodiment of the polishing apparatus including the transparent window 4 and the optical sensor head 25. The configuration and operation of this embodiment that are not specifically described are the same as those of the above-mentioned embodiment, so duplicated descriptions will be omitted. The polishing apparatus of this embodiment includes an outlet side measuring device 53 provided in the transparent liquid discharge line 36. The outlet side measuring device 53 is disposed upstream of the transparent liquid discharge valve 42.

[0050] The outflow side measuring device 53 is configured to measure a physical quantity (flow rate or pressure) of the transparent liquid flowing through the transparent liquid discharge line 36. The outflow side measuring device 53 is electrically connected to the operation control unit 9, and the measurement value of the physical quantity (flow rate or pressure) of the transparent liquid acquired by the outflow side measuring device 53 is sent to the operation control unit 9.

[0051] In one embodiment, the outlet side measurement device 53 is a flow measurement device that measures the flow rate of the transparent liquid. The operation control unit 9 is configured to generate an alarm signal when the measured flow rate of the transparent liquid falls outside a preset flow rate range.

[0052] In one embodiment, the outflow side measurement device 53 is a pressure measurement device that measures the pressure of the transparent liquid. The operation control unit 9 is configured to generate an alarm signal when the measured value of the pressure of the transparent liquid is outside a preset pressure range.

[0053] The operation control unit 9 generates an alarm signal when the measured value of the flow rate of the transparent liquid falls outside a preset flow rate range or when the measured value of the pressure of the transparent liquid falls outside a preset pressure range. In one embodiment, the operation control unit 9 issues a command to the optical film thickness measurement system 20 to stop the measurement operation of the film thickness of the workpiece W when the measured value of the flow rate of the transparent liquid falls outside a preset flow rate range or when the measured value of the pressure of the transparent liquid falls outside a preset pressure range.

[0054] In one embodiment, as shown in Figure 12, the outflow side measuring device 53 may be disposed downstream of the transparent liquid discharge valve 42 and the discharge pump 50. In one embodiment, as shown in Figure 13, the inflow side measuring device 52 shown in Figure 10 may be combined with the outflow side measuring device 53 shown in Figure 11, or as shown in Figure 14, the inflow side measuring device 52 shown in Figure 10 may be combined with the outflow side measuring device 53 shown in Figure 12.

[0055] FIG. 15 is a cross-sectional view showing another embodiment of the transparent window 4. The configuration of this embodiment not specifically described is the same as the embodiment described with reference to FIG. 3 or FIG. 4, so the overlapping description will be omitted. As shown in FIG. 15, the lower surface of the transparent window 4 includes a light receiving surface 61 that receives light from the optical sensor head 25, and a receding surface 62 that is located higher than the light receiving surface 61. The receding surface 62 is adjacent to the light receiving surface 61. In the embodiment shown in FIG. 15, the receding surface 62 is connected to the light receiving surface 61 and is inclined upward toward the outside.

[0056] The light receiving surface 61 is located at the center of the lower surface of the transparent window 4, and the receding surface 62 surrounds the light receiving surface 61. In one embodiment, the receding surface 62 has the shape of an inverted truncated cone. The light receiving surface 61 is a flat surface and perpendicular to the orientation of the optical sensor head 25. The light receiving surface 61 is perpendicular to the optical path of the light generated from the optical sensor head 25, and the light from the optical sensor head 25 is perpendicularly incident on the light receiving surface 61. In one embodiment, the portion of the transparent window 4 that constitutes the receding surface 62 may be made of a material different from the transparent material that constitutes the light receiving surface 61.

[0057] If any air bubbles are present on the light-receiving surface 61, the air bubbles move from the light-receiving surface 61 to the receding surface 62, and then move outward along the inclined receding surface 62 and are collected on the outer region of the receding surface 62. Therefore, the air bubbles are removed from the light-receiving surface 61, and a stable optical path can be maintained. As a result, the optical film thickness measurement system 20 can accurately measure the film thickness of the workpiece W.

[0058] FIG. 16 is a cross-sectional view showing another embodiment of the transparent window 4. The configuration of this embodiment not specifically described is the same as the embodiment described with reference to FIG. 15, and therefore the duplicated description will be omitted. In the embodiment shown in FIG. 16, there is a step between the light receiving surface 61 and the receding surface 62. The receding surface 62 is a flat surface that is located higher than the light receiving surface 61. In one embodiment, the receding surface 62 may be inclined upward toward the outside as in the embodiment shown in FIG. 15, or may be curved.

[0059] If air bubbles are present on the light-receiving surface 61, the air bubbles move from the light-receiving surface 61 to the receding surface 62 and are collected on the receding surface 62. Therefore, the air bubbles are removed from the light-receiving surface 61 and a stable optical path can be maintained. As a result, the optical film thickness measurement system 20 can accurately measure the film thickness of the workpiece W.

[0060] The embodiment described with reference to FIGS. 15 and 16 is applicable to the embodiment described with reference to FIGS.

[0061] FIG. 17 is a cross-sectional view showing another embodiment of the polishing apparatus. The configuration of this embodiment that is not particularly described is the same as the embodiment described with reference to FIGS. 1 to 6, so the overlapping description will be omitted. In the embodiment shown in FIG. 17, the transparent window 4 has a transparent liquid outlet 70 communicating with the space 32. The transparent liquid outlet 70 is a through hole penetrating the transparent window 4 and extends from the lower surface to the upper surface of the transparent window 4. The transparent liquid outlet 70 is located outside the light receiving surface 61 that receives light from the optical sensor head 25, and is away from the optical path. In this embodiment, the transparent liquid outlet line 36 and the transparent liquid outlet valve 42 are not provided.

[0062] During polishing of the workpiece W, the transparent liquid supply valve 41 is opened, and pure water as a transparent liquid is supplied into the space 32 through the transparent liquid supply line 35. The space 32 is filled with pure water, and the pure water flows out of the space 32 through the transparent liquid outlet 70. During polishing of the workpiece W, the transparent window 4 and the space 32 rotate together with the polishing table 3, so that there are times when the workpiece W is on the transparent window 4 and times when the workpiece W is not on the transparent window 4. When the workpiece W is not on the transparent window 4, the pure water in the space 32 flows out onto the polishing pad 2 through the transparent liquid outlet 70. Therefore, a flow of pure water is formed in the space 32. The flow rate of the pure water (transparent liquid) supplied into the space 32 through the transparent liquid supply line 35 is set to a flow rate at which the polishing rate of the workpiece W does not decrease due to the polishing liquid supplied onto the polishing pad 2 being diluted with the pure water.

[0063] According to this embodiment, if air bubbles are present in the space 32, the air bubbles are discharged from the space 32 through the transparent liquid outlet 70 together with the pure water. Therefore, a stable optical path for measuring the film thickness of the workpiece W is ensured in the space 32. As a result, the optical film thickness measurement system 20 can accurately measure the film thickness of the workpiece W. In one embodiment, the transparent window 4 may have a plurality of transparent liquid outlets 70 communicating with the space 32.

[0064] As shown in FIG. 18, in one embodiment, a check valve 80 connected to the transparent liquid outlet 70 may be provided. The check valve 80 is disposed in the polishing pad. In the embodiment shown in FIG. 18, the check valve 80 is disposed in the space 32. The check valve 80 is configured to allow the transparent liquid in the space 32 to flow out through the transparent liquid outlet 70, while not allowing the transparent liquid to flow into the space 32 through the transparent liquid outlet 70. For example, the check valve 80 is configured of a flap valve. The check valve 80 can prevent the polishing liquid on the polishing surface 2a of the polishing pad 2 and the pure water used for dressing the polishing pad 2 from flowing into the space 32.

[0065] The embodiment described with reference to Figures 17 and 18 may be applied to the embodiment described with reference to Figures 15 and 16. Specifically, the clear liquid outlet 70 may open in the recessed surface 62 shown in Figures 15 and 16.

[0066] 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]

[0067] W Workpiece 1 Polishing head 2 Polishing Pads 2a Polished surface 3 Polishing table 4 Transparent window 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 32 Space 35 Transparent liquid supply line 36 Transparent liquid discharge line 37 Supply Pump 39 Pressure Regulator 41 Transparent liquid supply valve 42 Transparent liquid discharge valve 45 Through hole 46 Depression 50 Discharge Pump 52 Inlet side measuring device 53 Outlet Measuring Device 61 Photosensitive surface 62 Retraction plane 70 Clear liquid outlet 80 Check valve

Claims

1. a space formed between a transparent window constituting a part of a polishing pad for polishing a workpiece and an optical sensor head of an optical film thickness measurement system for measuring a film thickness of the workpiece is evacuated to a vacuum, thereby forming a negative pressure in the space; a transparent liquid filling method for supplying the transparent liquid into the space through a transparent liquid supply line while a negative pressure is formed in the space.

2. 2. The method for filling with transparent liquid according to claim 1, wherein the transparent liquid is supplied into the space through the transparent liquid supply line while the space is being evacuated to a vacuum.

3. 2. The transparent liquid filling method according to claim 1, further comprising the step of supplying the transparent liquid into the space through the transparent liquid supply line after the evacuation of the space has been stopped and in a state in which a negative pressure has been formed in the space.

4. 2. The transparent liquid filling method according to claim 1, wherein the supply of the transparent liquid into the space is stopped after the entire space is filled with the transparent liquid.

Images