Method and apparatus for polishing a workpiece

Abstract

To provide a polishing method that can suppress polishing liquid such as slurry from influencing accuracy in measuring a film thickness of a work-piece, so as to enable the film-thickness to be measured accurately.SOLUTION: In a polishing method, a work-piece W is pressed by a polishing head 1 against a polishing pad 2 in a state where there is polishing liquid on the polishing pad 2 so as to polish the work-piece W; the work-piece W is irradiated with light by an optical sensor head 7 arranged in the polishing table 3 during polishing of the work-piece W, and a film thickness of the work-piece W is determined based on a spectrum of reflected light received from the work-piece W; cleaning liquid is supplied from a cleaning nozzle 8 to a target position TP just above the optical sensor head 7, during polishing of the work-piece W.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a technique for polishing workpieces such as wafers, substrates, and panels used in the manufacture of semiconductor devices, and more particularly to a technique for reducing the effect of a polishing liquid such as a slurry on the measurement accuracy of the film thickness of the workpiece. [Background technology]

[0002] In the manufacturing process of semiconductor devices, various materials are repeatedly deposited as films on silicon wafers to form a layered structure. To form this layered structure, it is important to have a technology that can flatten the surface of the top layer. Chemical mechanical polishing (CMP) is used as a method for achieving this flattening.

[0003] Chemical mechanical polishing (CMP) is performed using a polishing apparatus. This type of polishing apparatus generally includes a polishing table that supports a polishing pad, a polishing head that holds a workpiece (e.g., a wafer with a film), and a polishing liquid supply nozzle that supplies a polishing liquid (e.g., a slurry) onto the polishing pad. When polishing the workpiece, the polishing head presses the surface of the workpiece against the polishing pad while supplying the polishing liquid from the polishing liquid supply nozzle onto the polishing pad. The polishing head and polishing table are rotated to move the workpiece and polishing pad relative to each other, thereby polishing the film that forms the surface of the workpiece.

[0004] To measure the thickness of non-metallic films such as insulating films and silicon layers, polishing machines are typically equipped with an optical film thickness measurement device that is configured to direct light emitted from a light source to the surface of the workpiece during polishing and analyze the spectrum of the light reflected from the workpiece to determine the film thickness of the workpiece. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2020-104191 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the spectrum obtained during polishing of a workpiece is easily affected by the polishing liquid present on the polishing pad. For example, under polishing conditions with an increased polishing liquid flow rate or a polishing liquid with a high concentration, the intensity of the light reflected from the workpiece decreases, and as a result, the film thickness calculated from the spectrum of the reflected light may differ significantly from the actual film thickness.

[0007] Therefore, the present invention provides a polishing method and polishing apparatus that can reduce the influence of a polishing liquid such as a slurry on the measurement accuracy of the film thickness of a workpiece and achieve accurate film thickness measurement. [Means for solving the problem]

[0008] In one aspect, there is provided a method for polishing a workpiece, the method including: supplying a polishing liquid onto a polishing pad while rotating a polishing table supporting the polishing pad; polishing the workpiece by pressing the workpiece against the polishing pad with a polishing head while the polishing liquid is present on the polishing pad; irradiating the workpiece with light using an optical sensor head disposed in the polishing table while polishing the workpiece and receiving reflected light from the workpiece; determining a film thickness of the workpiece based on a spectrum of the reflected light; and supplying a cleaning liquid from a cleaning nozzle to a target position directly above the optical sensor head while polishing the workpiece, the cleaning nozzle being disposed above the polishing pad and located upstream of the polishing head in the direction of rotation of the polishing table.

[0009] In one aspect, the supply of the cleaning liquid from the cleaning nozzle starts when the target position is upstream of the polishing head. In one aspect, the supply of the cleaning liquid from the cleaning nozzle is stopped before the target position moves under the polishing head. In one aspect, the cleaning liquid is supplied intermittently from the cleaning nozzle to the target position in synchronization with the rotation of the polishing table. In one embodiment, the supply time of the cleaning liquid per one rotation of the polishing table is shorter than half the time for one rotation of the polishing table. In one aspect, the polishing method further includes supplying gas to the target position from a gas nozzle while polishing the workpiece, the gas nozzle being positioned above the polishing pad and upstream of the cleaning nozzle in the direction of rotation of the polishing table. In one embodiment, the gas and the cleaning liquid are alternately supplied to the target position from the gas nozzle and the cleaning nozzle while the polishing table makes one rotation.

[0010] In one aspect, a polishing apparatus for a workpiece is provided, the polishing apparatus comprising: a polishing table that supports a polishing pad; a table motor that rotates the polishing table; a polishing liquid supply nozzle that supplies a polishing liquid onto the polishing pad; a polishing head that polishes the workpiece by pressing the workpiece against the polishing pad with the polishing liquid present on the polishing pad; an optical sensor head that is positioned to irradiate the workpiece with light and receive light reflected from the workpiece while the workpiece is being polished; the optical sensor head is positioned within the polishing table; a spectral processing device that determines a film thickness of the workpiece based on the spectrum of the reflected light; a cleaning nozzle that supplies a cleaning liquid to a target position directly above the optical sensor head; a cleaning liquid supply valve connected to the cleaning nozzle; and a fluid supply control unit that controls the operation of the cleaning liquid supply valve, wherein the cleaning nozzle is positioned above the polishing pad and is located upstream of the polishing head in the rotation direction of the polishing table, and the fluid supply control unit is configured to issue a command to the cleaning liquid supply valve to supply the cleaning liquid from the cleaning nozzle to the target position while the workpiece is being polished.

[0011] In one aspect, the fluid supply control unit is configured to instruct the cleaning liquid supply valve to start supplying the cleaning liquid from the cleaning nozzle when the target position is upstream of the polishing head. In one aspect, the fluid supply control unit issues a command to the cleaning liquid supply valve to stop supplying the cleaning liquid from the cleaning nozzle before the target position moves under the polishing head. In one aspect, the fluid supply control unit is configured to issue a command to the cleaning liquid supply valve to intermittently supply the cleaning liquid from the cleaning nozzle to the target position in synchronization with the rotation of the polishing table. In one embodiment, the supply time of the cleaning liquid per one rotation of the polishing table is shorter than half the time for one rotation of the polishing table. In one aspect, the polishing apparatus further includes a gas nozzle that supplies gas to the target position and a gas supply valve connected to the gas nozzle, the fluid supply control unit is configured to control the operation of the gas supply valve, and the gas nozzle is positioned above the polishing pad and upstream of the cleaning nozzle in the rotation direction of the polishing table. In one aspect, the fluid supply control unit is configured to issue commands to the cleaning liquid supply valve and the gas supply valve to alternately supply the gas and the cleaning liquid from the gas nozzle and the cleaning nozzle to the target position during one rotation of the polishing table. In one embodiment, the polishing apparatus further includes a flow rate control valve that controls the flow rate of the cleaning liquid supplied from the cleaning nozzle to the target position. [Effects of the Invention]

[0012] According to the present invention, a cleaning liquid is supplied to the target location from above the polishing pad to remove the polishing liquid (e.g., slurry) from the target location. Therefore, the reflected light from the workpiece that is incident on the optical sensor head is less affected by the polishing liquid, and as a result, the film thickness of the workpiece can be accurately determined during polishing of the workpiece. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram illustrating an embodiment of a polishing apparatus. [Figure 2] FIG. 10 is a diagram illustrating an example of a spectrum. [Figure 3] FIG. 10 is a top view for explaining an example of the positional relationship between the cleaning nozzle and the polishing head. [Figure 4] FIG. 2 is a cross-sectional view of the polishing apparatus. [Figure 5] FIG. 10 is a schematic view showing another embodiment of the polishing apparatus. [Figure 6] FIG. 10 is a schematic view showing still another embodiment of the polishing apparatus. DETAILED DESCRIPTION OF THE INVENTION

[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 workpiece W, such as a wafer, substrate, or panel used in semiconductor device manufacturing, against the polishing pad 2, a table motor 6 that rotates the polishing table 3, a polishing liquid supply nozzle 5 that supplies a polishing liquid such as slurry onto the polishing pad 2, and a cleaning nozzle 8 that supplies a cleaning liquid onto the polishing pad 2. The upper surface of the polishing pad 2 forms a polishing surface 2a that polishes the workpiece W. In this embodiment, the workpiece W to be polished is a circular wafer, but the workpiece W may have other shapes, such as a rectangular, square, or polygonal shape.

[0015] The polishing head 1 is connected to a head shaft 10, which is connected to a polishing head motor (not shown). The polishing head motor rotates the polishing head 1 together with the head shaft 10 in the direction indicated by the arrow. The polishing table 3 is connected to a table motor 6, which is configured to rotate the polishing table 3 and polishing pad 2 in the direction indicated by the arrow.

[0016] The workpiece W is polished as follows. While the polishing table 3 and polishing head 1 are rotated in the directions indicated by the arrows in FIG. 1, a polishing liquid is supplied from the polishing liquid supply nozzle 5 to the polishing surface 2a of the polishing pad 2 on the polishing table 3. While the workpiece W is rotated by the polishing head 1, the polishing head 1 presses the workpiece W against the polishing surface 2a of the polishing pad 2 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. The polishing apparatus of this embodiment is a face-down type polishing apparatus in which the workpiece W is pressed against the polishing surface 2a of the polishing pad 2 with its surface to be polished facing downward.

[0017] The polishing apparatus is equipped with an optical film thickness measuring device 20 that measures the film thickness of the workpiece W while the workpiece W is being polished. The optical film thickness measuring device 20 is equipped with a light source 22 that emits light, an optical sensor head 7 that irradiates the workpiece W with the light from the light source 22 and receives the light reflected from the workpiece W, a spectrometer 24 that measures the intensity of the light reflected from the workpiece W, and a spectral processing device 27 that determines the film thickness of the workpiece W based on the measurement data of the intensity of the light reflected from the workpiece W. The light source 22 and the spectrometer 24 are connected to the optical sensor head 7. The light source 22, the spectrometer 24, and the optical sensor head 7 are attached to the polishing table 3 and rotate together with the polishing table 3.

[0018] The polishing pad 2 has through holes 30 for passing light. With each rotation of the polishing table 3, light emitted by the light source 22 is transmitted to the optical sensor head 7 and directed from the optical sensor head 7 through the through holes 30 to the surface of the workpiece W. The light is reflected by the surface of the workpiece W, and the reflected light from the surface of the workpiece W is received by the optical sensor head 7 through the through holes 30. The reflected light is sent from the optical sensor head 7 to the spectrometer 24. The spectrometer 24 resolves the reflected light according to wavelength over a predetermined wavelength range and measures the intensity of the reflected light at each wavelength to generate reflected light intensity measurement data. The reflected light intensity measurement data is sent from the spectrometer 24 to a spectral processing device 27.

[0019] The spectrum processor 27 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.

[0020] The spectrum processing device 27 is configured to determine the film thickness of the workpiece W from the spectrum of the reflected light. A known technique is used to determine the film thickness of the workpiece W based on the spectrum. For example, the spectrum processing device 27 determines a reference spectrum from a reference spectrum library that has a shape that is closest to the spectrum of the reflected light, and determines the film thickness associated with this determined reference spectrum. In another example, the spectrum processing device 27 performs a Fourier transform on the spectrum of the reflected light and determines the film thickness from the resulting frequency spectrum.

[0021] FIG. 2 shows an example of a spectrum generated by the spectrum processing device 27. The spectrum is expressed as a line graph (i.e., a spectral waveform) showing the relationship between light wavelength and intensity. In FIG. 2, the horizontal axis represents the wavelength of light reflected from the workpiece W, and the vertical axis represents the relative reflectance derived from the intensity of the reflected light. Relative reflectance is an index value indicating the intensity of reflected light, and is the ratio of the light intensity to a predetermined reference intensity. By dividing the light intensity (measured intensity) at each wavelength by the predetermined reference intensity, unnecessary noise such as variations in intensity inherent to the optical system of the device or the light source can be removed from the measured intensity.

[0022] In the example shown in Figure 2, the spectrum of reflected light is a spectral waveform that shows the relationship between the relative reflectance and the wavelength of the reflected light, but the spectrum of reflected light may also be a spectral waveform that shows the relationship between the intensity of the reflected light itself and the wavelength of the reflected light.

[0023] 1, the spectrum processing device 27 is connected to a polishing control unit 9 for controlling the polishing operation of the workpiece W. The polishing control unit 9 controls the polishing operation of the workpiece W based on the film thickness of the workpiece W determined by the spectrum processing device 27. For example, the polishing control unit 9 is configured to determine a polishing end point, which is the point at which the film thickness of the workpiece W reaches a target film thickness, or to change the polishing conditions for the workpiece W when the film thickness of the workpiece W reaches a predetermined value.

[0024] The spectrum processing device 27 includes a storage device 27a storing a program and an arithmetic device 27b that executes calculations according to instructions included in the program. The spectrum processing device 27 includes at least one computer. The storage device 27a 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 device 27b include a CPU (central processing unit) and a GPU (graphics processing unit). However, the specific configuration of the spectrum processing device 27 is not limited to these examples.

[0025] 1, the cleaning nozzle 8 is disposed above the polishing table 3 and the polishing pad 2. More specifically, the cleaning nozzle 8 is disposed above the orbit HP of the optical sensor head 7 that rotates together with the polishing table 3, and faces the orbit HP. The cleaning nozzle 8 is located upstream of the polishing head 1 in the rotation direction of the polishing table 3 and the polishing pad 2.

[0026] The cleaning nozzle 8 is positioned to supply cleaning liquid onto the polishing pad 2 from above the polishing pad 2. More specifically, the cleaning nozzle 8 supplies cleaning liquid to a target position TP directly above the optical sensor head 7. An example of the cleaning liquid is pure water. The target position TP is within the polishing surface 2a of the polishing pad 2. More specifically, the target position TP is the position of a through hole 30 formed in the polishing pad 2. In one embodiment, the cleaning liquid may be supplied to an arc-shaped area including the target position TP directly above the optical sensor head 7. The arc-shaped area is an arc-shaped area that follows the trajectory HP of the optical sensor head 7.

[0027] The polishing apparatus includes a cleaning liquid supply line 35 connected to the cleaning nozzle 8, a cleaning liquid supply valve 36 attached to the cleaning liquid supply line 35, and a fluid supply control unit 39 that controls the operation of the cleaning liquid supply valve 36. The cleaning liquid supply line 35 is connected to a cleaning liquid supply source (not shown) and supplies a cleaning liquid (e.g., deionized water) to the cleaning nozzle 8. The cleaning liquid supply valve 36 is an actuator-driven valve such as an electric valve, a solenoid valve, or an air-pumped valve. In one embodiment, the cleaning liquid supply valve 36 may be directly connected to the cleaning nozzle 8.

[0028] The fluid supply control unit 39 is configured to issue a command to the cleaning liquid supply valve 36 to supply cleaning liquid from the cleaning nozzle 8 to the target position TP during polishing of the workpiece W. The cleaning liquid emitted from the cleaning nozzle 8 can remove the polishing liquid from the target position TP. Therefore, the reflected light from the workpiece W that enters the optical sensor head 7 is less affected by the polishing liquid, and as a result, the spectral processing device 27 can determine an accurate film thickness of the workpiece W during polishing of the workpiece W.

[0029] The polishing apparatus further includes a flow rate control valve 37 attached to the cleaning liquid supply line 35. This flow rate control valve 37 is disposed upstream of the cleaning liquid supply valve 36 and is configured to adjust the flow rate of the cleaning liquid supplied from the cleaning nozzle 8. The flow rate control valve 37 is connected to a fluid supply control unit 39, and the operation of the flow rate control valve 37 is controlled by the fluid supply control unit 39. The operation of the flow rate control valve 37, i.e., the flow rate of the cleaning liquid supplied from the cleaning nozzle 8 to the target position TP, is set based on the rotation speed of the polishing table 3, the type of polishing pad 2, the type and / or concentration of the polishing liquid, the structure of the polishing pad 2 (for example, the presence or absence of a transparent window, which will be described later), etc.

[0030] During polishing of the workpiece W, both the polishing liquid and the cleaning liquid are supplied onto the polishing pad 2. That is, while the polishing liquid (e.g., slurry) is supplied onto the polishing surface 2a of the polishing pad 2, the cleaning liquid is supplied to the target position TP within the polishing pad 2. In order to prevent the cleaning liquid once supplied to the target position TP from being replaced by the polishing liquid, it is preferable to supply the cleaning liquid to the target position TP from the cleaning nozzle 8 when the target position TP approaches the polishing head 1.

[0031] Therefore, the fluid supply control unit 39 is configured to issue a command to the cleaning liquid supply valve 36 during polishing of the workpiece W to start supplying the cleaning liquid from the cleaning nozzle 8 when the target position TP is upstream of the polishing head 1. In one embodiment, the fluid supply control unit 39 is configured to issue a command to the cleaning liquid supply valve 36 during polishing of the workpiece W to stop supplying the cleaning liquid from the cleaning nozzle 8 before the target position TP moves below the polishing head 1. Such a supply operation of the cleaning liquid can prevent the polishing liquid from being diluted with the cleaning liquid, and prevent a decrease in the polishing rate (also referred to as the removal rate) of the workpiece W.

[0032] In this embodiment, the fluid supply control unit 39 is configured to issue a command to the cleaning liquid supply valve 36 to intermittently supply the cleaning liquid from the cleaning nozzle 8 to the target position TP in synchronization with the rotation of the polishing table 3. That is, the supply of the cleaning liquid is started and stopped each time the polishing table 3 rotates. The supply of the cleaning liquid may be started and stopped multiple times each time the polishing table 3 rotates, so that the polishing liquid is removed from the target position TP by the pressure of the cleaning liquid. The supply time of the cleaning liquid per rotation of the polishing table 3 is shorter than half the time required for one rotation of the polishing table 3. In one embodiment, in order to prevent dilution of the polishing liquid, the supply time of the cleaning liquid per rotation of the polishing table 3 is shorter than one-third of the time required for one rotation of the polishing table 3.

[0033] The fluid supply control unit 39 includes a storage device 39a storing a program and an arithmetic unit 39b that executes calculations according to instructions included in the program. The fluid supply control unit 39 is composed of at least one computer. The storage device 39a 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 39b include a CPU (central processing unit) and a GPU (graphics processing unit). However, the specific configuration of the fluid supply control unit 39 is not limited to these examples.

[0034] 3 is a top view illustrating an example of the positional relationship between the cleaning nozzle 8 and the polishing head 1. If L1 is a line extending from the center of rotation CP of the polishing table 3 to the upstream end face of the polishing head 1, and L2 is a line extending from the center of rotation CP of the polishing table 3 to the outlet of the cleaning nozzle 8, the angle α between the lines L1 and L2 is within a range of 0 to 120 degrees, preferably 20 to 90 degrees, and even more preferably 30 to 60 degrees. A cleaning nozzle 8 positioned in this way can apply the cleaning liquid to the target position TP immediately before the target position TP moves below the polishing head 1, thereby preventing the cleaning liquid once supplied to the target position TP from being replaced by the polishing liquid.

[0035] The optical film thickness measuring device 20 will be described in detail with reference to Fig. 4. The spectrometer 24 includes a photodetector 25. In one embodiment, the photodetector 25 is configured with a photodiode, a CCD, a CMOS, or the like. The optical sensor head 7 is optically coupled to the light source 22 and the photodetector 25. The photodetector 25 is electrically connected to a spectrum processing device 27.

[0036] The optical film thickness measuring device 20 includes a light-projecting optical fiber cable 41 that guides light emitted from the light source 22 to the surface of the workpiece W, and a light-receiving optical fiber cable 42 that receives the light reflected from the workpiece W and sends the reflected light to the spectrometer 24. The ends of the light-projecting optical fiber cable 41 and the light-receiving optical fiber cable 42 are located within the polishing table 3.

[0037] The tip of the light-projecting fiber optic cable 41 and the tip of the light-receiving fiber optic cable 42 form an optical sensor head 7 that guides light to the surface of the workpiece W and receives light reflected from the workpiece W. The other end of the light-projecting fiber optic cable 41 is connected to the light source 22, and the other end of the light-receiving fiber optic cable 42 is connected to the spectrometer 24. The spectrometer 24 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.

[0038] The polishing table 3 has a first hole 50A and a second hole 50B opening on its upper surface. The polishing pad 2 also has a through-hole 30 formed at a position corresponding to the holes 50A and 50B. The holes 50A and 50B communicate with the through-hole 30, which opens on the polishing surface 2a. The first hole 50A is connected to a liquid supply line 54, and the second hole 50B is connected to a drain line 55. The optical sensor head 7, which is composed of the tip of the light-emitting fiber optic cable 41 and the tip of the light-receiving fiber optic cable 42, is disposed in the first hole 50A and is located below the through-hole 30.

[0039] During polishing of the workpiece W, pure water is supplied as a rinse liquid to the first hole 50A via the liquid supply line 54, and then further supplied to the through hole 30 through the first hole 50A. The pure water fills the space between the surface of the workpiece W (the surface to be polished) and the optical sensor head 7. The pure water flows into the second hole 50B and is discharged through the drain line 55. The pure water flowing through the first hole 50A and the through hole 30 prevents the polishing liquid from entering the first hole 50A, thereby maintaining the optical path.

[0040] Light emitted from the optical sensor head 7 is irradiated onto the workpiece W through the through hole 30, and light reflected from the workpiece W passes through the through hole 30 and is received by the optical sensor head 7. In this embodiment, the position of the through hole 30 is a target position TP to which a cleaning liquid is supplied from the cleaning nozzle 8. Therefore, the cleaning nozzle 8 supplies the cleaning liquid to the through hole 30, and the cleaning liquid can remove the polishing liquid (e.g., slurry) from the through hole 30. In particular, according to this embodiment, the pure water supplied from the liquid supply line 54 and the cleaning liquid supplied from the cleaning nozzle 8 can remove the polishing liquid present above the optical sensor head 7.

[0041] The light-projecting fiber optic cable 41 is an optical transmission section that guides light emitted by the light source 22 to the surface of the workpiece W. The tips of the light-projecting fiber optic cable 41 and the light-receiving fiber optic cable 42 are located within the first hole 50A and are positioned near the surface of the workpiece W to be polished. The optical sensor head 7, which is composed of the tips of the light-projecting fiber optic cable 41 and the light-receiving fiber optic cable 42, is positioned facing the workpiece W held by the polishing head 1. Light is irradiated onto a predetermined measurement point on the workpiece W each time the polishing table 3 rotates. In this embodiment, only one optical sensor head 7 is provided within the polishing table 3, but multiple optical sensor heads 7 may be provided within the polishing table 3. For example, two optical sensor heads 7 may be provided, one positioned to pass through the center and the other positioned to pass through the edge of the workpiece W, respectively.

[0042] Figure 5 is a schematic diagram showing another embodiment of a polishing apparatus. The configuration and operation of this embodiment, which are not specifically described, are the same as those of the embodiment described with reference to Figures 1 to 4, and therefore, redundant description will be omitted. In the embodiment shown in Figure 5, the polishing apparatus further includes a gas nozzle 61 that supplies gas to the target position TP, a gas supply line 62 connected to the gas nozzle 61, and a gas supply valve 63 attached to the gas supply line 62. Examples of the gas include air and an inert gas (e.g., nitrogen gas).

[0043] The gas supply line 62 is connected to a gas supply source (not shown) and supplies gas to the gas nozzle 61. The gas supply valve 63 is an actuator-driven valve such as an electric valve, a solenoid valve, or an air-pumped valve. In one embodiment, the gas supply valve 63 may be directly connected to the gas nozzle 61.

[0044] The gas nozzle 61 is disposed above the polishing table 3 and the polishing pad 2. More specifically, the gas nozzle 61 is disposed above the orbit HP of the optical sensor head 7, which rotates together with the polishing table 3, and faces the orbit HP. The gas nozzle 61 is located upstream of the cleaning nozzle 8 in the rotation direction of the polishing table 3 and the polishing pad 2. The gas nozzle 61 is disposed so as to supply gas onto the polishing pad 2 from above. More specifically, the gas nozzle 61 supplies gas to a target position TP directly above the optical sensor head 7.

[0045] The fluid supply control unit 39 is configured to control the operation of the gas supply valve 63 in addition to the cleaning liquid supply valve 36. The fluid supply control unit 39 is configured to give a command to the gas supply valve 63 to supply gas from the gas nozzle 61 to the target position TP during polishing of the workpiece W. More specifically, the fluid supply control unit 39 is configured to give a command to the cleaning liquid supply valve 36 and the gas supply valve 63 to alternately supply gas and cleaning liquid from the gas nozzle 61 and the cleaning nozzle 8 to the target position TP during one rotation of the polishing table 3.

[0046] During one rotation of the polishing table 3, the gas is first supplied to the target position TP, and then the cleaning liquid is supplied to the target position TP. The gas jet can remove the polishing liquid present at the target position TP. The cleaning liquid not only removes the polishing liquid remaining at the target position TP, but also wets the portion of the polishing pad 2 that was dried by the gas jet.

[0047] Like the cleaning liquid, the gas can remove the polishing liquid from the target position TP, but supplying the gas can dry out the polishing pad 2. A dried polishing pad 2 may cause scratches on the workpiece W. According to this embodiment, after the gas is supplied to the polishing pad 2, the polishing pad 2 is returned to a wet state with the cleaning liquid, thereby preventing the polishing pad 2 from drying out.

[0048] In one embodiment, the fluid supply control unit 39 is configured to issue a command to the gas supply valve 63 to stop gas injection from the gas nozzle 61 during polishing of the workpiece W before the target position TP moves under the polishing head 1. Such a gas supply operation can reduce the amount of gas supplied to remove the polishing liquid.

[0049] In this embodiment, the fluid supply control unit 39 is configured to issue commands to the gas supply valve 63 and the cleaning liquid supply valve 36 to alternately and intermittently supply gas and liquid from the gas nozzle 61 and the cleaning nozzle 8 to the target position TP in synchronization with the rotation of the polishing table 3. That is, the gas supply and the liquid supply are started and stopped each time the polishing table 3 rotates. The gas supply time per rotation of the polishing table 3 is shorter than half the time required for one rotation of the polishing table 3. To prevent the polishing pad 2 from drying out, the gas supply time per rotation of the polishing table 3 is shorter than one-third the time required for one rotation of the polishing table 3. The gas supply may be started and stopped multiple times each time the polishing table 3 rotates, and the polishing liquid may be removed from the target position TP by the pressure of the gas jet.

[0050] FIG. 6 is a schematic diagram showing another embodiment of the polishing apparatus. The configuration and operation of this embodiment, which are not specifically described, are the same as those of the embodiment described with reference to FIGS. 1 to 4, and therefore, redundant description will be omitted. In the embodiment shown in FIG. 6, the polishing apparatus includes a transparent window 70 disposed in the polishing pad 2 instead of the liquid supply line 54 and the drain line 55. The transparent window 70 is disposed in a through hole 30 formed in the polishing pad 2. The transparent window 70 completely closes the through hole 30 of the polishing pad 2, and the through hole 30 prevents the polishing liquid and polishing debris from contacting the optical sensor head 7.

[0051] The transparent window 70 is located directly above the optical sensor head 7. Therefore, the optical sensor head 7 emits light through the transparent window 70 to the workpiece W and receives reflected light from the workpiece W that has passed through the transparent window 70. The transparent window 70 is a window made of a material that transmits light. The material of the transparent window 70 is not particularly limited, but it may be made of a transparent resin, for example.

[0052] In this embodiment, the target position TP to which the cleaning liquid should be supplied is the position of the upper surface of the transparent window 70. Similar to the embodiment described with reference to FIGS. 1 to 4, the cleaning nozzle 8 supplies the cleaning liquid to the target position TP, i.e., the upper surface of the transparent window 70, while the workpiece W is being polished. The cleaning liquid emitted from the cleaning nozzle 8 can remove the polishing liquid from the target position TP, i.e., the upper surface of the transparent window 70. Therefore, the reflected light from the workpiece W that enters the optical sensor head 7 is less affected by the polishing liquid, and as a result, the spectral processing device 27 can accurately determine the film thickness of the workpiece W while the workpiece W is being polished.

[0053] The embodiment of the transparent window 70 shown in Fig. 6 can be similarly applied to the embodiment including both the gas nozzle 61 and the cleaning nozzle 8 described with reference to Fig. 5. The arrangement of the gas nozzle 61 and the cleaning nozzle 8, the timing of supplying the gas and liquid, and the like are the same as those in the embodiment described with reference to Fig. 5, and therefore redundant description will be omitted.

[0054] The above-described embodiments have been described for the purpose of enabling a person of ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments would be obvious to a person skilled in the art, and the technical concept of the present invention may be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope in accordance with the technical concept defined by the claims. [Explanation of symbols]

[0055] W Workpiece TP Target Position 1 polishing head 2 polishing pads 2a Polished surface 3 Polishing table 5 Polishing liquid supply nozzle 6 Table Motor 7 Optical sensor head 8 Cleaning nozzle 9 Polishing control unit 10 Head shaft 20 Optical film thickness measuring device 22 Light source 24 Spectrometer 25 Photodetector 27 Spectral Processing Device 30 through hole 35 Cleaning solution supply line 36 Cleaning liquid supply valve 37 Flow control valve 39 Fluid supply control unit 41 Optical fiber cable for floodlight 42 Receiving optical fiber cable 50A First hole 50B Second hole 54 Liquid supply line 55 Drain line 61 Gas nozzle 62 Gas supply line 63 Gas supply valve 70 Transparent Window

Claims

1. 1. A method of polishing a workpiece, comprising: supplying a polishing liquid onto the polishing pad while rotating a polishing table supporting the polishing pad; a polishing head pressing the workpiece against the polishing pad with the polishing liquid present on the polishing pad to polish the workpiece; an optical sensor head disposed within the polishing table irradiating light onto the workpiece and receiving reflected light from the workpiece while the workpiece is being polished; determining a film thickness of the workpiece based on the spectrum of the reflected light; supplying a cleaning liquid from a cleaning nozzle to a target position directly above the optical sensor head while the workpiece is being polished; the cleaning nozzle is disposed above the polishing pad and is located upstream of the polishing head in a rotation direction of the polishing table; a cleaning nozzle that starts supplying the cleaning liquid when the target position is located upstream of the polishing head in the rotation direction of the polishing table;

2. The polishing method according to claim 1 , wherein the supply of the cleaning liquid from the cleaning nozzle is stopped before the target position moves under the polishing head.

3. 3. The polishing method according to claim 1, wherein the cleaning liquid is intermittently supplied from the cleaning nozzle to the target position in synchronization with rotation of the polishing table.

4. A method for polishing a workpiece, comprising: supplying a polishing liquid onto the polishing pad while rotating a polishing table supporting the polishing pad; a polishing head pressing the workpiece against the polishing pad with the polishing liquid present on the polishing pad to polish the workpiece; an optical sensor head disposed within the polishing table irradiating light onto the workpiece and receiving reflected light from the workpiece while the workpiece is being polished; determining a film thickness of the workpiece based on the spectrum of the reflected light; supplying a cleaning liquid from a cleaning nozzle to a target position directly above the optical sensor head while the workpiece is being polished; the cleaning nozzle is disposed above the polishing pad and is located upstream of the polishing head in a rotation direction of the polishing table; the cleaning liquid is intermittently supplied from the cleaning nozzle to the target position in synchronization with the rotation of the polishing table; A polishing method, wherein the supply time of the cleaning liquid per one rotation of the polishing table is shorter than half the time for one rotation of the polishing table.

5. A method for polishing a workpiece, comprising: supplying a polishing liquid onto the polishing pad while rotating a polishing table supporting the polishing pad; a polishing head pressing the workpiece against the polishing pad with the polishing liquid present on the polishing pad to polish the workpiece; an optical sensor head disposed within the polishing table irradiating light onto the workpiece and receiving reflected light from the workpiece while the workpiece is being polished; determining a film thickness of the workpiece based on the spectrum of the reflected light; supplying a cleaning liquid from a cleaning nozzle to a target position directly above the optical sensor head while the workpiece is being polished; supplying gas from a gas nozzle to the target location while polishing the workpiece; the cleaning nozzle is disposed above the polishing pad and is located upstream of the polishing head in a rotation direction of the polishing table; The polishing method, wherein the gas nozzle is disposed above the polishing pad and is located upstream of the cleaning nozzle in the rotation direction of the polishing table.

6. 6. The polishing method according to claim 5, wherein the gas and the cleaning liquid are alternately supplied to the target position from the gas nozzle and the cleaning nozzle while the polishing table makes one rotation.

7. 1. A polishing apparatus for a workpiece, comprising: a polishing table supporting a polishing pad; a table motor for rotating the polishing table; a polishing liquid supply nozzle that supplies a polishing liquid onto the polishing pad; a polishing head that presses the workpiece against the polishing pad with the polishing liquid present on the polishing pad to polish the workpiece; an optical sensor head disposed to irradiate light onto the workpiece and receive reflected light from the workpiece while the workpiece is being polished, the optical sensor head being disposed within the polishing table; a spectral processing device for determining a film thickness of the workpiece based on the spectrum of the reflected light; a cleaning nozzle for supplying a cleaning liquid to a target position directly above the optical sensor head; a cleaning liquid supply valve connected to the cleaning nozzle; a fluid supply control unit for controlling the operation of the cleaning liquid supply valve; the cleaning nozzle is disposed above the polishing pad and is located upstream of the polishing head in a rotation direction of the polishing table; the fluid supply control is configured to command the cleaning liquid supply valve to supply the cleaning liquid from the cleaning nozzle to the target location during polishing of the workpiece; a fluid supply control unit configured to give a command to the cleaning liquid supply valve to start supplying the cleaning liquid from the cleaning nozzle when the target position is upstream of the polishing head in the rotation direction of the polishing table.

8. 8. The polishing apparatus according to claim 7, wherein the fluid supply control unit issues a command to the cleaning liquid supply valve to stop the supply of the cleaning liquid from the cleaning nozzle before the target position moves under the polishing head.

9. 9. The polishing apparatus according to claim 7, wherein the fluid supply control unit is configured to give a command to the cleaning liquid supply valve to intermittently supply the cleaning liquid from the cleaning nozzle to the target position in synchronization with rotation of the polishing table.

10. A polishing apparatus for a workpiece, comprising: a polishing table supporting a polishing pad; a table motor for rotating the polishing table; a polishing liquid supply nozzle that supplies a polishing liquid onto the polishing pad; a polishing head that presses the workpiece against the polishing pad with the polishing liquid present on the polishing pad to polish the workpiece; an optical sensor head disposed to irradiate light onto the workpiece and receive reflected light from the workpiece while the workpiece is being polished, the optical sensor head being disposed within the polishing table; a spectral processing device for determining a film thickness of the workpiece based on the spectrum of the reflected light; a cleaning nozzle for supplying a cleaning liquid to a target position directly above the optical sensor head; a cleaning liquid supply valve connected to the cleaning nozzle; a fluid supply control unit for controlling the operation of the cleaning liquid supply valve; the cleaning nozzle is disposed above the polishing pad and is located upstream of the polishing head in a rotation direction of the polishing table; the fluid supply control is configured to command the cleaning liquid supply valve to supply the cleaning liquid from the cleaning nozzle to the target location during polishing of the workpiece; the fluid supply control unit is configured to issue a command to the cleaning liquid supply valve to intermittently supply the cleaning liquid from the cleaning nozzle to the target position in synchronization with rotation of the polishing table, The polishing apparatus, wherein the supply time of the cleaning liquid per one rotation of the polishing table is shorter than half the time for one rotation of the polishing table.

11. A polishing apparatus for a workpiece, comprising: a polishing table supporting a polishing pad; a table motor for rotating the polishing table; a polishing liquid supply nozzle that supplies a polishing liquid onto the polishing pad; a polishing head that presses the workpiece against the polishing pad with the polishing liquid present on the polishing pad to polish the workpiece; an optical sensor head disposed to irradiate light onto the workpiece and receive reflected light from the workpiece while the workpiece is being polished, the optical sensor head being disposed within the polishing table; a spectral processing device for determining a film thickness of the workpiece based on the spectrum of the reflected light; a cleaning nozzle for supplying a cleaning liquid to a target position directly above the optical sensor head; a cleaning liquid supply valve connected to the cleaning nozzle; a gas nozzle for supplying gas to the target position; a gas supply valve connected to the gas nozzle; a fluid supply control unit that controls operations of the cleaning liquid supply valve and the gas supply valve; the cleaning nozzle is disposed above the polishing pad and is located upstream of the polishing head in a rotation direction of the polishing table; the fluid supply control is configured to command the cleaning liquid supply valve to supply the cleaning liquid from the cleaning nozzle to the target location during polishing of the workpiece; The gas nozzle is disposed above the polishing pad and is located upstream of the cleaning nozzle in the rotation direction of the polishing table.

12. 12. The polishing apparatus according to claim 11, wherein the fluid supply control unit is configured to issue commands to the cleaning liquid supply valve and the gas supply valve to alternately supply the gas and the cleaning liquid to the target position from the gas nozzle and the cleaning nozzle during one rotation of the polishing table.

13. 8. The polishing apparatus according to claim 7, further comprising a flow rate control valve for controlling the flow rate of the cleaning liquid supplied from the cleaning nozzle to the target position.

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