POLISHING METHOD AND POLISHING APPARATUS FOR WORKPIECE

Abstract

A polishing method that can reduce influence of polishing liquid (e.g., slurry) on measuring of a film thickness of a workpiece and can achieve accurate measuring of the film thickness is disclosed. The polishing method includes pressing the workpiece against a polishing pad by a polishing head while polishing liquid is present on the polishing pad to polish the workpiece; during polishing of the workpiece, directing light from an optical sensor head onto the workpiece and receiving reflected light from the workpiece by the optical sensor head, the optical sensor head being disposed in the polishing table; determining a film thickness of the workpiece based on a spectrum of the reflected light; and during polishing of the workpiece, supplying cleaning liquid from a cleaning nozzle to a target position which is located just above the optical sensor head.

Description

CROSS REFERENCE TO RELATED APPLICATION

This document claims priority to Japanese Patent Application No. 2022-056134 filed Mar. 30, 2022, the entire contents of which are hereby incorporated by reference.

BACKGROUND

In a manufacturing process of a semiconductor device, various materials are repeatedly formed in film shapes on a silicon wafer to form a multilayer structure. In order to form such multilayer structure, a technique of planarizing a surface of an uppermost layer of the multilayer structure is becoming important. Chemical mechanical polishing (CMP) is used as such planarizing technique.

The chemical mechanical polishing (CMP) is performed by a polishing apparatus. This type of polishing apparatus generally includes a polishing table that supports a polishing pad, a polishing head configured to hold a workpiece (for example, a wafer having a film), and a polishing-liquid supply nozzle configured to supply a polishing liquid (for example, slurry) onto the polishing pad. When a workpiece is polished, the surface of the workpiece is pressed against the polishing pad by the polishing head while the polishing liquid is supplied onto the polishing pad from the polishing-liquid supply nozzle. The polishing head and the polishing table are rotated to move the workpiece and the polishing pad relative to each other, thereby polishing a film forming the surface of the workpiece.

In order to measure a thickness of a non-metal film, such as a dielectric film or a silicon layer, the polishing apparatus generally includes an optical film-thickness measuring device. This optical film-thickness measuring device is configured to direct light, emitted by a light source, to the surface of the workpiece and analyze a spectrum of reflected light from the workpiece to determine a film thickness of the workpiece.

However, the spectrum obtained during polishing of the workpiece is likely to be affected by the polishing liquid present on the polishing pad. For example, under polishing conditions where a flow rate of the polishing liquid is increased or where a more concentrated polishing liquid is used, the intensity of the reflected light from the workpiece may decrease, and as a result, the film thickness calculated from the spectrum of the reflected light may differ significantly from an actual film thickness.

SUMMARY

Therefore, the present invention provides a polishing method and a polishing apparatus that can reduce influence of polishing liquid (e.g., slurry) on measuring of a film thickness of a workpiece and can achieve accurate measuring of the film thickness.

The present invention relates to a technique of polishing a workpiece, such as wafer, substrate, or panel, used in manufacture of semiconductor devices, and in particular to a technique for reducing an effect of polishing liquid (e.g., slurry) on measuring of a film thickness of the workpiece.

In an embodiment, there is provided a polishing method for a workpiece, comprising: supplying polishing liquid onto a polishing pad while rotating a polishing table supporting the polishing pad; pressing the workpiece against the polishing pad by a polishing head while the polishing liquid is present on the polishing pad to polish the workpiece; during polishing of the workpiece, directing light from an optical sensor head onto the workpiece and receiving reflected light from the workpiece by the optical sensor head, the optical sensor head being disposed in the polishing table; determining a film thickness of the workpiece based on a spectrum of the reflected light; and during polishing of the workpiece, supplying cleaning liquid from a cleaning nozzle to a target position which is located just above the optical sensor head, the cleaning nozzle being located above the polishing pad and located upstream of the polishing head in a rotating direction of the polishing table.

In an embodiment, supplying of the cleaning liquid from the cleaning nozzle is started when the target position is upstream of the polishing head.

In an embodiment, supplying of the cleaning liquid from the cleaning nozzle is stopped before the target position is moved under the polishing head.

In an embodiment, the cleaning liquid is intermittently supplied from the cleaning nozzle to the target position in synchronization with rotation of the polishing table.

In an embodiment, a supply time of the cleaning liquid per one rotation of the polishing table is less than half a time of one rotation of the polishing table.

In an embodiment, the polishing method further comprises: supplying gas from a gas nozzle to the target position during polishing of the workpiece, the gas nozzle being located above the polishing pad and located upstream of the cleaning nozzle in the rotating direction of the polishing table.

In an embodiment, the gas and the cleaning liquid are alternately supplied to the target position from the gas nozzle and the cleaning nozzle during one rotation of the polishing table.

In an embodiment, there is provided a polishing apparatus for a workpiece, comprising: a polishing table configured to support a polishing pad; a table motor configured to rotate the polishing table; a polishing-liquid supply nozzle configured to supply polishing liquid onto the polishing pad; a polishing head configured to press the workpiece against the polishing pad to polish the workpiece while the polishing liquid is present on the polishing pad; an optical sensor head arranged to direct light to the workpiece and receive reflected light from the workpiece during polishing of the workpiece, the optical sensor head being disposed in the polishing table; a spectrum processing device configured to determine a film thickness of the workpiece based on a spectrum of the reflected light; a cleaning nozzle configured to supply cleaning liquid to a target position which is located just above the optical sensor head, the cleaning nozzle being located above the polishing pad and located upstream of the polishing head in a rotating direction of the polishing table; a cleaning-liquid supply valve coupled to the cleaning nozzle; and a fluid supply controller configured to instruct the cleaning-liquid supply valve to supply the cleaning liquid from the cleaning nozzle to the target position during polishing of the workpiece.

In an embodiment, the fluid supply controller 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 an embodiment, the fluid supply controller is configured to instruct 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 an embodiment, the fluid supply controller is configured to instruct 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.

In an embodiment, a supply time of the cleaning liquid per one rotation of the polishing table is less than half a time of one rotation of the polishing table.

In an embodiment, the polishing apparatus further comprises a gas nozzle configured to supply gas to the target position, the gas nozzle being located above the polishing pad and located upstream of the cleaning nozzle in the rotating direction of the polishing table; and a gas supply valve coupled to the gas nozzle, the fluid supply controller being configured to control operation of the gas supply valve.

In an embodiment, the fluid supply controller is configured to instruct 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 an embodiment, the polishing apparatus further comprises a flow-rate regulating valve configured to regulate a flow rate of the cleaning liquid supplied from the cleaning nozzle to the target position.

According to the embodiments described above, the cleaning liquid is supplied to the target position from above the polishing pad to remove the polishing liquid (e.g., slurry) from the target position. Therefore, the reflected light from the workpiece incident on the optical sensor head is less affected by the polishing liquid. As a result, an accurate film thickness of the workpiece can be determined during polishing of the workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an embodiment of a polishing apparatus;

FIG. 2 shows an example of a spectrum;

FIG. 3 shows a top view for illustrating an example of a positional relationship between a cleaning nozzle and a polishing head;

FIG. 4 shows a cross-sectional view of a polishing apparatus;

FIG. 5 is a schematic diagram showing another embodiment of the polishing apparatus; and

FIG. 6 is a schematic diagram showing yet another embodiment of the polishing apparatus.

DESCRIPTION OF EMBODIMENTS

Embodiments will be described below with reference to the drawings.

FIG. 1 is schematic view showing an embodiment of a polishing apparatus. As shown in FIG. 1, the polishing apparatus includes a polishing table 3 configured to support a polishing pad 2, a polishing head 1 configured to press a workpiece W (e.g., wafer, substrate, or panel used in manufacturing of semiconductor devices) against the polishing pad 2, a table motor 6 configured to rotate the polishing table 3, a polishing-liquid supply nozzle 5 configured to supply polishing liquid, such as slurry, onto the polishing pad 2, and a cleaning nozzle 8 configured to supply cleaning liquid onto the polishing pad 2. The polishing pad 2 has an upper surface constituting a polishing surface 2a for polishing the workpiece W. The workpiece W to be polished in this embodiment is a circular wafer, while the workpiece W may have other shape, such as rectangular, square, or polygonal shape.

The polishing head 1 is coupled to a head shaft 10, which is coupled to a polishing-head motor (now shown). The polishing-head motor is configured to rotate the polishing head 1 together with the head shaft 10 in a direction indicated by an arrow. The polishing table 3 is coupled to the table motor 6, which is configured to rotate the polishing table 3 and the polishing pad 2 in a direction indicated by an arrow.

Polishing of the workpiece W is performed as follows. The polishing-liquid supply nozzle 5 supplies the polishing liquid onto the polishing surface 2a of the polishing pad 2 on the polishing table 3, while the polishing table 3 and the polishing head 1 are rotated in directions indicated by the arrows in FIG. 1. While the workpiece W is being rotated by the polishing head 1, the workpiece W is pressed by the polishing head 1 against the polishing surface 2a of the polishing pad 2 in the presence of the polishing liquid on the polishing pad 2. The surface of the workpiece W is polished by a chemical action of the polishing liquid and a mechanical action of 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 configured to press the workpiece W, with its surface to be polished facing downward, against the polishing surface 2a of the polishing pad 2.

The polishing apparatus includes an optical film-thickness measuring device 20 configured to measure a film thickness of the workpiece W during polishing of the workpiece W. The optical film-thickness measuring device 20 has a light source 22 configured to emit light, an optical sensor head 7 configured to direct the light from the light source 22 to the workpiece W and receive reflected light from the workpiece W, a spectrometer 24 configured to measure intensity of the reflected light from the workpiece W, and a spectrum processing device 27 configured to determine the film thickness of the workpiece W based on intensity measurement data of the reflected light from the workpiece W. The light source 22 and the spectrometer 24 are coupled to the optical sensor head 7. The light source 22, the spectrometer 24, and the optical sensor head 7 are mounted to the polishing table 3 and rotate together with the polishing table 3.

The polishing pad 2 has a through-hole 30 for passing the light therethrough. Each time the polishing table 3 makes one rotation, the 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-hole 30 to the surface of the workpiece W. The light is reflected off the surface of the workpiece W. The reflected light from the surface of the workpiece W travels through the through-hole 30 and is received by the optical sensor head 7. The reflected light is transmitted from the optical sensor head 7 to the spectrometer 24. The spectrometer 24 decomposes the reflected light according to wavelength over a predetermined wavelength range and measures the intensity of the reflected light at each of the wavelengths to generate intensity measurement data of the reflected light. The intensity measurement data of the reflected light is sent from the spectrometer 24 to the spectrum processing device 27.

The spectrum processing device 27 is configured to generate a spectrum of the reflected light of the workpiece W from the intensity measurement data of the reflected light. This spectrum of the reflected light is expressed as a line graph (i.e., a spectral waveform) indicating a relationship between the wavelength and the intensity of the reflected light. The intensity of the reflected light can also be represented by a relative value, such as a reflectance or a relative reflectance.

The spectrum processing device 27 is configured to determine the film thickness of the workpiece W based on the spectrum of the reflected light. A known technique may be used to determine the film thickness of the workpiece W based on the spectrum. For example, the spectrum processing device 27 determines, from a reference spectrum library, a reference spectrum that is closest in shape to the spectrum of the reflected light and determines a film thickness associated with the 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 a resulting frequency spectrum.

FIG. 2 shows an example of a spectrum generated by the spectrum processing device 27. The spectrum is represented as a line graph (i.e., a spectral waveform) showing the relationship between wavelength and intensity of light. In FIG. 2, horizontal axis represents wavelength of the light reflected from the workpiece, and vertical axis represents relative reflectance derived from the intensity of the reflected light. The relative reflectance is an index value that represents the intensity of the reflected light. Specifically, the relative reflectance is a ratio of the intensity of the light to a predetermined reference intensity. By dividing the intensity of the light (i.e., the actually measured intensity) at each wavelength by a predetermined reference intensity, unwanted noises, such as a variation in the intensity inherent in an optical system or the light source of the apparatus, are removed from the actually measured intensity.

In the example shown in FIG. 2, the spectrum of the reflected light is a spectral waveform showing the relationship between the relative reflectance and the wavelength of the reflected light. The spectrum of the reflected light may be a spectral waveform showing a relationship between the intensity itself of the reflected light and the wavelength of the reflected light.

As shown in FIG. 1, the spectrum processing device 27 is coupled to a polishing controller 9 for controlling polishing operation for the workpiece W. The polishing controller 9 is configured to control the polishing operation for the workpiece W based on the film thickness of the workpiece W determined by the spectrum processing device 27. For example, the polishing controller 9 is configured to determine a polishing end point at which the film thickness of the workpiece W reaches a target film thickness, or change polishing conditions for the workpiece W when the film thickness of the workpiece W reaches a predetermined value.

The spectrum processing device 27 has a memory 27a storing programs therein and an arithmetic device 27b configured to perform arithmetic operations according to instructions contained in the programs. The spectrum processing device 27 is composed of at least one computer. The memory 27a includes a main memory, such as random access memory (RAM), and an auxiliary memory, 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 (graphic processing unit). However, the specific configurations of the spectrum processing device 27 are not limited to these examples.

As shown in FIG. 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 a path HP of the optical sensor head 7 rotating with the polishing table 3. The cleaning nozzle 8 faces the path HP. The cleaning nozzle 8 is located upstream of the polishing head 1 in a rotating direction of the polishing table 3 and the polishing pad 2.

The cleaning nozzle 8 is arranged to supply cleaning liquid from above the polishing pad 2 onto the polishing pad 2. More specifically, the cleaning nozzle 8 supplies the cleaning liquid to a target position TP located just above the optical sensor head 7. An example of the cleaning liquid is pure water. The target position TP lies in the polishing surface 2a of the polishing pad 2. Specifically, the target position TP is a position of the through-hole 30 formed in the polishing pad 2. In one embodiment, the cleaning liquid may be supplied to an arcuate area including the target position TP just above the optical sensor head 7. The arcuate area is an area along the path HP of the optical sensor head 7.

The polishing apparatus has a cleaning-liquid supply line 35 coupled to the cleaning nozzle 8, a cleaning-liquid supply valve 36 attached to the cleaning-liquid supply line 35, and a fluid supply controller 39 configured to control operation of the cleaning-liquid supply valve 36. The cleaning-liquid supply line 35 is coupled to a cleaning-liquid supply source (not shown) and supplies the cleaning liquid (e.g., pure water) to the cleaning nozzle 8. The cleaning-liquid supply valve 36 is an actuator-driven valve, such as a motor-driven valve, solenoid valve, or air-operated valve. In one embodiment, the cleaning-liquid supply valve 36 may be directly coupled to the cleaning nozzle 8.

The fluid supply controller 39 is configured to instruct the cleaning-liquid supply valve 36 to supply the cleaning liquid from the cleaning nozzle 8 onto the target position TP during polishing of the workpiece W. The cleaning liquid released from the cleaning nozzle 8 can remove the polishing liquid from the target position TP. Therefore, the reflected light from the workpiece W incident on the optical sensor head 7 is less affected by the polishing liquid, and as a result, the spectrum processing device 27 can accurately determine the film thickness of the workpiece W during polishing of the workpiece W.

The polishing apparatus further includes a flow-rate regulating valve 37 attached to the cleaning-liquid supply line 35. The flow-rate regulating valve 37 is located upstream of the cleaning-liquid supply valve 36 and is configured to regulate a flow rate of the cleaning liquid to be supplied from the cleaning nozzle 8. The flow-rate regulating valve 37 is coupled to the fluid supply controller 39, and operation of the flow-rate regulating valve 37 is controlled by the fluid supply controller 39. The operation of the flow-rate regulating valve 37, i.e., the flow rate of the cleaning liquid to be supplied from the cleaning nozzle 8 to the target position TP, is set based on rotational speed of the polishing table 3, type of the polishing pad 2, type and/or concentration of the cleaning liquid, and structure of the polishing pad 2 (e.g., with or without a transparent window, as described below).

During polishing of the workpiece W, both the polishing liquid and the cleaning liquid are supplied onto the polishing pad 2. Specifically, 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 in the polishing pad 2. In order to prevent the cleaning liquid once supplied to the target position TP from being replaced with the polishing liquid, it is preferable to supply the cleaning liquid from the cleaning nozzle 8 to the target position TP when the target position TP approaches the polishing head 1.

Thus, the fluid supply controller 39 is configured to instruct the cleaning-liquid supply valve 36 to start supplying of the cleaning liquid from the cleaning nozzle 8 when the target position TP is upstream of the polishing head 1 during polishing of the workpiece W. In one embodiment, the fluid supply controller 39 is configured to instruct the cleaning-liquid supply valve 36 during polishing of the workpiece W to stop supplying of the cleaning liquid from the cleaning nozzle 8 before the target position TP moves under the polishing head 1. Such cleaning liquid supply operations make it possible to prevent the polishing liquid from being diluted with the cleaning liquid and to thereby prevent a decrease in polishing rate (which may be referred to as removal rate) of the workpiece W.

In this embodiment, the fluid supply controller 39 is configured to instruct 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. More specifically, each time the polishing table 3 makes one rotation, the supply of the cleaning liquid is started and stopped. Each time the polishing table 3 makes one rotation, the supply of the gas may be started and stopped multiple times to remove the polishing liquid from the target position TP by the pressure of the cleaning liquid. A supply time of the cleaning liquid per one rotation of the polishing table 3 is shorter than half a time of one rotation of the polishing table 3. In one embodiment, from a viewpoint of preventing dilution of the polishing liquid, the supply time of the cleaning liquid per one rotation of the polishing table 3 is shorter than one-third of the time of one rotation of the polishing table 3.

The fluid supply controller 39 has a memory 39a storing programs therein and an arithmetic device 39b configured to perform arithmetic operations according to instructions contained in the programs. The fluid supply controller 39 is composed of at least one computer. The memory 39a includes a main memory, such as random access memory (RAM), and an auxiliary memory, such as a hard disk drive (HDD) or a solid state drive (SSD). Examples of the arithmetic device 39b include a CPU (central processing unit) and a GPU (graphic processing unit). However, the specific configurations of the fluid supply controller 39 are not limited to these examples.

FIG. 3 shows a top view for illustrating an example of a positional relationship between the cleaning nozzle 8 and the polishing head 1. Where a straight line extending from a center of rotation CP of the polishing table 3 to an upstream end surface of the polishing head 1 is denoted by L1, and a straight line extending from the center of rotation CP of the polishing table 3 to an outlet of the cleaning nozzle 8 is denoted by L2, an angle α between the straight line L1 and the straight line L2 is in a range of 0 to 120 degrees, preferably 20 to 90 degrees, more preferably 30 to 60 degrees. The cleaning nozzle 8 in such a position can emit the cleaning liquid onto the target position TP just before the target position TP moves under the polishing head 1. As a result, the cleaning liquid once supplied to the target position TP is prevented from being replaced with the polishing liquid.

Details of the optical film-thickness measuring device 20 are now described with reference to FIG. 4. The spectrometer 24 has a light detector 25. In one embodiment, the light detector 25 comprises a photodiode, CCD, or CMOS. The optical sensor head 7 is optically coupled to the light source 22 and the light detector 25. The light detector 25 is electrically coupled to the spectrum processing device 27.

The optical film-thickness measuring device 20 includes a light-emitting optical fiber cable 41 arranged to direct the light, emitted by the light source 22, to the surface of the workpiece W, and a light-receiving optical fiber cable 42 arranged to receive the reflected light from the workpiece W and transmit the reflected light to the spectrometer 24. A distal end of the light-emitting optical fiber cable 41 and a distal end of the light-receiving optical fiber cable 42 are located in the polishing table 3.

The distal end of the light-emitting optical fiber cable 41 and the distal end of the light-receiving optical fiber cable 42 constitute the optical sensor head 7 that directs the light to the surface of the workpiece W and receives the reflected light from the workpiece W. The other end of the light-emitting optical fiber cable 41 is coupled to the light source 22, and the other end of the light-receiving optical fiber cable 42 is coupled to the spectrometer 24. The spectrometer 24 is configured to decompose the reflected light from the workpiece W according to wavelength and measure intensities of the reflected light over a predetermined wavelength range.

The polishing table 3 has a first hole 50A and a second hole 50B which are open in an upper surface of the polishing table 3. The polishing pad 2 has the through-hole 30 formed at a position corresponding to these holes 50A, 50B. The holes 50A, 50B communicate with the through-hole 30, and the through-hole 30 is open in the polishing surface 2a. The first hole 50A is coupled to a liquid supply line 54, and the second hole 50B is coupled to a drain line 55. The optical sensor head 7, which is constituted of the distal end of the light-emitting optical fiber cable 41 and the distal end of the light-receiving optical fiber cable 42, is located in the first hole 50A and below the through-hole 30.

During polishing of the workpiece W, pure water is supplied as a rinsing liquid to the first hole 50A through the liquid supply line 54, and is further supplied through the first hole 50A to the through-hole 30. The pure water fills a 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 ensuring an optical path.

The light emitted from the optical sensor head 7 travels through the through-hole 30 onto the workpiece W, and the reflected light 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 the target position TP where the cleaning liquid is to be 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, both 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 existing over the optical sensor head 7.

The light-emitting optical fiber cable 41 is a light-transmitting element that directs the light, emitted by the light source 22, to the surface of the workpiece W. The distal ends of the light-emitting optical fiber cable 41 and the light-receiving optical fiber cable 42 are located in the first hole 50A and located near the surface, to be polished, of the workpiece W. The optical sensor head 7, which is constituted of the distal ends of the light-emitting optical fiber cable 41 and the light-receiving optical fiber cable 42, is arranged so as to face the workpiece W held on the polishing head 1. Each time the polishing table 3 makes one rotation, the light is emitted onto predetermined measurement point(s) on the workpiece W. In this embodiment, only one optical sensor head 7 is provided in the polishing table 3, while a plurality of optical sensor heads 7 may be provided in the polishing table 3. For example, two optical sensor heads 7 may be provided so as to sweep across a center and an edge of the workpiece W, respectively.

FIG. 5 is a schematic diagram of another embodiment of the polishing apparatus. Configurations and operations of this embodiment, which will not be described particularly, are the same as those of the embodiments described with reference to FIGS. 1 through 4, and redundant descriptions thereof are omitted. In the embodiment shown in FIG. 5, the polishing apparatus further includes a gas nozzle 61 configured to supply gas to the target position TP, a gas supply line 62 coupled 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 inert gas (e.g., nitrogen gas).

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

The gas nozzle 61 is located above the polishing table 3 and the polishing pad 2. More specifically, the gas nozzle 61 is located above the path HP of the optical sensor head 7 that rotates together with the polishing table 3. The gas nozzle 61 faces the path HP. The gas nozzle 61 is located upstream of the cleaning nozzle 8 in the rotating direction of the polishing table 3 and the polishing pad 2. The gas nozzle 61 is arranged to supply the gas from above the polishing pad 2 onto the polishing pad 2. More specifically, the gas nozzle 61 supplies the gas to the target position TP which is located just above the optical sensor head 7.

The fluid supply controller 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 controller 39 is configured to instruct the gas supply valve 63 to supply the gas from the gas nozzle 61 to the target position TP during polishing of the workpiece W. More specifically, the fluid supply controller 39 is configured to instruct the cleaning-liquid supply valve 36 and the gas supply valve 63 to alternately supply the gas and the 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.

During one rotation of the polishing table 3, the gas is first supplied to the target position TP, and the cleaning liquid is then supplied to the target position TP. Jet of the gas can remove the polishing liquid present at the target position TP. The cleaning liquid can not only remove the residual polishing liquid at the target position TP, but can also return a dried portion of the polishing pad 2 as a result of being exposed to the jet of the gas to a wet state.

The gas, as well as the cleaning liquid, can remove the polishing liquid from the target position TP, but on the other hand, the supply of the gas may dry the polishing pad 2. The 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 the wet state by the cleaning liquid, so that a dried state of the polishing pad 2 can be prevented.

In one embodiment, the fluid supply controller 39 is configured to instruct the gas supply valve 63 to stop the emission of the gas from the gas nozzle 61 during polishing of the workpiece W before the target position TP moves under the polishing head 1. Such gas supply operation can reduce the amount of gas supplied for removing the polishing liquid.

In this embodiment, the fluid supply controller 39 is configured to instruct the gas supply valve 63 and the cleaning-liquid supply valve 36 to alternately and intermittently supply the gas and the cleaning 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. More specifically, each time the polishing table 3 makes one rotation, the supply of the gas is started and stopped, and the supply of the cleaning liquid is started and stopped. A supply time of the gas per one rotation of the polishing table 3 is shorter than half a time of one rotation of the polishing table 3. From the viewpoint of preventing the polishing pad 2 from being dried, the supply time of the gas per one rotation of the polishing table 3 is shorter than one-third of the time of one rotation of the polishing table 3. Each time the polishing table 3 makes one rotation, the supply of the gas may be started and stopped multiple times to remove the polishing liquid from the target position TP by the pressure of the jet of the gas.

FIG. 6 is a schematic diagram showing another embodiment of the polishing apparatus. Configurations and operations of this embodiment, which will not be described particularly, are the same as those of the embodiments described with reference to FIGS. 1 through 4, and redundant descriptions thereof are omitted. In the embodiment shown in FIG. 6, the polishing apparatus has 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 the through-hole 30 formed in the polishing pad 2. The transparent window 70 completely closes the through-hole 30 of the polishing pad 2, so that the transparent window 70 can prevent the polishing liquid and polishing debris from coming into contact with the optical sensor head 7.

The transparent window 70 is located just above the optical sensor head 7. Therefore, the optical sensor head 7 emits the light through the transparent window 70 onto the workpiece W and receives the reflected light from the workpiece W that has passed through the transparent window 70. The transparent window 70 is composed of a material that can transmit the light therethrough. The material of the transparent window 70 is not limited, but for example, it is composed of a transparent resin.

In this embodiment, the target position TP to which the cleaning liquid should be supplied is a position of an upper surface of the transparent window 70. As well as the embodiments described with reference to FIGS. 1 to 4, the cleaning nozzle 8 supplies the cleaning liquid onto the target position TP, i.e., onto the upper surface of the transparent window 70, 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, i.e., the upper surface of the transparent window 70. Therefore, the reflected light from the workpiece W incident on the optical sensor head 7 is less affected by the polishing liquid, and as a result, the spectrum processing device 27 can accurately determine the film thickness of the workpiece W during polishing of the workpiece W.

The embodiment of the transparent window 70 shown in FIG. 6 is applicable to the embodiments having both the gas nozzle 61 and the cleaning nozzle 8 described with reference to FIG. 5. The arrangement of the gas nozzle 61 and cleaning nozzle 8 and the supply timing of gas and liquid are the same as in the embodiments described with reference to FIG. 5, and their redundant descriptions are omitted.

The previous description of embodiments is provided to enable a person skilled in the art to make and use the present invention. Moreover, various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles and specific examples defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the embodiments described herein but is to be accorded the widest scope as defined by limitation of the claims.

Claims

1. A polishing method for a workpiece, comprising:

supplying polishing liquid onto a polishing pad while rotating a polishing table supporting the polishing pad;

pressing the workpiece against the polishing pad by a polishing head while the polishing liquid is present on the polishing pad to polish the workpiece;

during polishing of the workpiece, directing light from an optical sensor head onto the workpiece and receiving reflected light from the workpiece by the optical sensor head, the optical sensor head being disposed in the polishing table;

determining a film thickness of the workpiece based on a spectrum of the reflected light; and

during polishing of the workpiece, supplying cleaning liquid from a cleaning nozzle to a target position which is located just above the optical sensor head, the cleaning nozzle being located above the polishing pad and located upstream of the polishing head in a rotating direction of the polishing table.

2. The polishing method according to claim 1, wherein supplying of the cleaning liquid from the cleaning nozzle is started when the target position is upstream of the polishing head.

3. The polishing method according to claim 2, wherein supplying of the cleaning liquid from the cleaning nozzle is stopped before the target position is moved under the polishing head.

4. 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.

5. The polishing method according to claim 4, wherein a supply time of the cleaning liquid per one rotation of the polishing table is less than half a time of one rotation of the polishing table.

6. The polishing method according to claim 1, further comprising:

supplying gas from a gas nozzle to the target position during polishing of the workpiece, the gas nozzle being located above the polishing pad and located upstream of the cleaning nozzle in the rotating direction of the polishing table.

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

8. A polishing apparatus for a workpiece, comprising:

a polishing table configured to support a polishing pad;

a table motor configured to rotate the polishing table;

a polishing-liquid supply nozzle configured to supply polishing liquid onto the polishing pad;

a polishing head configured to press the workpiece against the polishing pad to polish the workpiece while the polishing liquid is present on the polishing pad;

an optical sensor head arranged to direct light to the workpiece and receive reflected light from the workpiece during polishing of the workpiece, the optical sensor head being disposed in the polishing table;

a spectrum processing device configured to determine a film thickness of the workpiece based on a spectrum of the reflected light;

a cleaning nozzle configured to supply cleaning liquid to a target position which is located just above the optical sensor head, the cleaning nozzle being located above the polishing pad and located upstream of the polishing head in a rotating direction of the polishing table;

a cleaning-liquid supply valve coupled to the cleaning nozzle; and

a fluid supply controller configured to instruct the cleaning-liquid supply valve to supply the cleaning liquid from the cleaning nozzle to the target position during polishing of the workpiece.

9. The polishing apparatus according to claim 8, wherein the fluid supply controller 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.

10. The polishing apparatus according to claim 9, wherein the fluid supply controller is configured to instruct the cleaning-liquid supply valve to stop supplying the cleaning liquid from the cleaning nozzle before the target position moves under the polishing head.

11. The polishing apparatus according to claim 8, wherein the fluid supply controller is configured to instruct 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.

12. The polishing apparatus according to claim 11, wherein a supply time of the cleaning liquid per one rotation of the polishing table is less than half a time of one rotation of the polishing table.

13. The polishing apparatus according to claim 8, further comprising:

a gas nozzle configured to supply gas to the target position, the gas nozzle being located above the polishing pad and located upstream of the cleaning nozzle in the rotating direction of the polishing table; and

a gas supply valve coupled to the gas nozzle, the fluid supply controller being configured to control operation of the gas supply valve.

14. The polishing apparatus according to claim 13, wherein the fluid supply controller is configured to instruct 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.

15. The polishing apparatus according to claim 8, further comprising a flow-rate regulating valve configured to regulate a flow rate of the cleaning liquid supplied from the cleaning nozzle to the target position.