Film thickness measuring method and film thickness measuring device

Abstract

To provide a film thickness measurement method that substantially widens a wavelength range of reflected light spectrum from a work-piece, and can measure an accurate film thickness.SOLUTION: According to a film thickness measurement method, a work-piece W is pressed against an abrasive pad 2 and is polished while rotating a polishing table 3 which supports the abrasive pad 2, light is guided to the work-piece W from a liquid seal sensor 25 and a transparent window sensor 31 which are located on the polishing table 3 during polishing of the work-piece W, reflected light from the work-piece W is received by the liquid seal sensor 25 and the transparent window sensor 31, and a film thickness of the work-piece W is determined on the basis of reflected light spectrum from the work-piece W.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a technique for measuring the film thickness of a workpiece used in the manufacture of semiconductor devices such as wafers, substrates, and panels while polishing the workpiece, and more particularly to a technique for determining the film thickness of the workpiece based on optical information contained in reflected light from the workpiece. [Background technology]

[0002] In the manufacturing process of semiconductor devices, various materials are repeatedly formed in the form of films on a silicon wafer to form a layered structure. In order to form this layered structure, technology for flattening the surface of the top layer is important. Chemical mechanical polishing (CMP) is used as one method of such flattening.

[0003] 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 that holds a wafer having a film, and a polishing liquid supply nozzle that supplies a polishing liquid (e.g., slurry) onto the polishing pad. The polishing apparatus supplies the polishing liquid onto the polishing pad from the polishing liquid supply nozzle while rotating the polishing head and the polishing table. The polishing head presses the surface of the wafer against the polishing pad, thereby polishing the film that forms the surface of the wafer with the polishing liquid present between the wafer and the polishing pad.

[0004] In order to measure the thickness of a film such as an insulating film or a silicon layer (hereinafter simply referred to as film thickness), a polishing apparatus generally includes an optical film thickness measuring device. This optical film thickness measuring device is configured to guide light emitted from a light source to the surface of the wafer from a sensor head, receive the light reflected from the wafer by the sensor head, and determine the film thickness of the wafer by analyzing the spectrum of the reflected light. The polishing apparatus can end the polishing of the wafer based on the determined film thickness, or change the polishing conditions of the wafer.

[0005] During wafer polishing, polishing fluid and polishing debris are present on the polishing pad. If the polishing fluid or polishing debris adheres to the sensor head, the intensity of the light irradiated to the wafer and the intensity of the light reflected from the wafer decrease, making it impossible to measure the film thickness accurately. To address this issue, there are techniques for forming a water flow between the sensor head and the wafer, or for arranging a transparent window between the sensor head and the wafer. These techniques prevent the polishing fluid and polishing debris from coming into contact with the sensor head, ensuring a good optical path. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2017-220683 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, water has a wavelength band where it absorbs light. Also, transparent windows made of resin have wavelength bands where light is difficult to transmit. For this reason, the wavelength range that generates the spectrum of reflected light for measuring the film thickness is limited, and it was sometimes impossible to measure the film thickness accurately depending on the type of film.

[0008] Therefore, the present invention provides a film thickness measurement method and apparatus that can substantially widen the wavelength range of the spectrum of light reflected from a workpiece and accurately measure film thickness. [Means for solving the problem]

[0009] In one aspect, a film thickness measurement method is provided, which includes polishing a workpiece by pressing the workpiece against a polishing pad while rotating a polishing table supporting a polishing pad, and while polishing the workpiece, guiding light to the workpiece from a liquid-sealed sensor and a transparent window sensor arranged on the polishing table, and receiving reflected light from the workpiece by the liquid-sealed sensor and the transparent window sensor, and determining a film thickness of the workpiece based on a spectrum of the reflected light from the workpiece, wherein the liquid-sealed sensor has a liquid flow path through which liquid flows and a first optical sensor head arranged in the liquid flow path, and the transparent window sensor has a second optical sensor head and a transparent window arranged above the second optical sensor head.

[0010] In one embodiment, the liquid-sealed sensor and the transparent window sensor are arranged on a circumference having the same center as the center of rotation of the polishing table. In one embodiment, during a first polishing period, the film thickness of the workpiece is determined based on the spectrum of reflected light from the workpiece sent from one of the liquid-sealed sensor and the transparent window sensor, and during a second polishing period, the film thickness of the workpiece is determined based on the spectrum of reflected light from the workpiece sent from the other of the liquid-sealed sensor and the transparent window sensor. In one embodiment, a spectrum of reflected light from the workpiece sent from the liquid-sealed sensor and a spectrum of reflected light from the workpiece sent from the transparent window sensor are combined to generate a synthetic spectrum, and the film thickness of the workpiece is determined based on the synthetic spectrum. In one embodiment, the wavelength range of the spectrum of the reflected light from the liquid seal sensor is different from the wavelength range of the spectrum of the reflected light from the transparent window sensor. In one aspect, the liquid seal sensor and the transparent window sensor are a plurality of liquid seal sensors and a plurality of transparent window sensors. In one embodiment, the liquid-sealed sensor and the transparent window sensor are arranged on each of a plurality of concentric circles having the same center as the center of rotation of the polishing table.

[0011] In one aspect, a film thickness measurement device is provided, comprising a liquid seal sensor and a transparent window sensor arranged on a rotatable polishing table for supporting a polishing pad for polishing a workpiece, and a spectral processing device for determining a film thickness of the workpiece based on the spectrum of reflected light from the workpiece sent from the liquid seal sensor and the transparent window sensor, wherein the liquid seal sensor has a liquid flow path for flowing liquid and a first optical sensor head arranged in the liquid flow path, and the transparent window sensor has a second optical sensor head and a transparent window arranged above the second optical sensor head.

[0012] In one embodiment, the liquid-sealed sensor and the transparent window sensor are arranged on a circumference having the same center as the center of rotation of the polishing table. In one embodiment, the spectral processing device is configured to determine a film thickness of the workpiece during a first polishing period based on a spectrum of reflected light from the workpiece sent from one of the liquid-sealed sensor and the transparent window sensor, and to determine a film thickness of the workpiece during a second polishing period based on a spectrum of reflected light from the workpiece sent from the other of the liquid-sealed sensor and the transparent window sensor. In one aspect, the spectral processing device is configured to combine a spectrum of reflected light from the workpiece sent from the liquid seal sensor and a spectrum of reflected light from the workpiece sent from the transparent window sensor to generate a composite spectrum, and to determine a film thickness of the workpiece based on the composite spectrum. In one embodiment, the film thickness measurement device further includes a first spectrometer coupled to the liquid-sealed sensor and a second spectrometer coupled to the transparent window sensor, the first spectrometer configured to measure an intensity of light reflected from the workpiece in a first wavelength range to generate first intensity measurement data, and the second spectrometer configured to measure an intensity of light reflected from the workpiece in a second wavelength range to generate second intensity measurement data, the first wavelength range being different from the second wavelength range. In one aspect, the liquid seal sensor and the transparent window sensor are a plurality of liquid seal sensors and a plurality of transparent window sensors. In one embodiment, the liquid-sealed sensor and the transparent window sensor are arranged on each of a plurality of concentric circles having the same center as the center of rotation of the polishing table. Effect of the Invention

[0013] The liquid seal sensor and the transparent window sensor transmit and receive light through different media, i.e., liquid and a transparent window. The reflected light spectrum obtained through these different types of sensors shows good intensity of reflected light in different wavelength ranges. According to the present invention, the reflected light spectrum obtained through both the liquid seal sensor and the transparent window sensor is used during polishing of the workpiece, so that the wavelength range of reflected light used for film thickness measurement is substantially expanded. As a result, the thickness of various types of films can be accurately measured. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram illustrating an embodiment of a polishing apparatus. [Diagram 2] FIG. 2 is a diagram showing an example of a spectrum generated by a spectrum processing device. [Diagram 3] FIG. 1 is a top view showing the arrangement of a liquid seal sensor and a transparent window sensor. [Figure 4] FIG. 2 is a diagram showing a spectrum of light reflected from a workpiece by a liquid seal sensor and a spectrum of light reflected from a workpiece by a transparent window sensor. [Diagram 5] FIG. 10 is a diagram illustrating a process of generating a synthetic spectrum. [Figure 6] FIG. 13 is a schematic diagram showing another embodiment of a film thickness measuring device. [Figure 7] FIG. 2 is a diagram showing a spectrum generated from first intensity measurement data generated by a first spectrometer, and a spectrum generated from second intensity measurement data generated by a second spectrometer. [Figure 8] FIG. 13 is a schematic diagram showing still another embodiment of a film thickness measuring device. [Figure 9] FIG. 1 is a plan view showing an embodiment of a film thickness measurement device having one liquid seal sensor and two transparent window sensors. [Figure 10] FIG. 1 is a schematic diagram showing an embodiment of a film thickness measurement device having one liquid seal sensor and two transparent window sensors. [Figure 11] FIG. 13 is a schematic diagram showing still another embodiment of a film thickness measuring device. [Figure 12] FIG. 1 is a schematic diagram showing an embodiment of a film thickness measuring device having a plurality of liquid-sealed sensors and a plurality of transparent window sensors arranged on the same circumference. [Figure 13] FIG. 1 is a schematic diagram showing an embodiment of a film thickness measuring device having a plurality of liquid-sealed sensors and a plurality of transparent window sensors arranged on the same circumference. [Figure 14] FIG. 1 is a schematic diagram showing an embodiment of a film thickness measurement device having a plurality of liquid-sealed sensors and a plurality of transparent window sensors arranged on concentric circles. [Figure 15] FIG. 1 is a schematic diagram showing an embodiment of a film thickness measurement device having a plurality of liquid-sealed sensors and a plurality of transparent window sensors arranged on concentric circles. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] 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, a substrate, or a panel used in the manufacture of semiconductor devices, against the polishing pad 2, a table motor 6 that rotates the polishing table 3, and a polishing liquid supply nozzle 5 that supplies a polishing liquid, such as a slurry, onto the polishing pad 2. The upper surface of the polishing pad 2 constitutes a polishing surface 2a that polishes the workpiece W.

[0016] The polishing head 1 is connected to a head shaft 10, and the head shaft 10 is connected to a polishing head motor 18 via a connecting device 17. The configuration of the connecting device 17 is not particularly limited, but it is composed of a combination of a pulley and a belt, a combination of gears, or a combination of a sprocket and a chain. The polishing head motor 18 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, and the table motor 6 is configured to rotate the polishing table 3 and the polishing pad 2 in the direction indicated by the arrow.

[0017] The workpiece W is polished as follows. While the polishing table 3 and polishing head 1 are rotated in the direction shown by the arrow in Fig. 1, a polishing liquid is supplied from a polishing liquid supply nozzle 5 to the polishing surface 2a of the polishing pad 2 on the polishing table 3. While the workpiece W is rotated by the polishing head 1, the workpiece W is pressed against the polishing surface 2a of the polishing pad 2 by the polishing head 1 with the polishing liquid present on the polishing pad 2. The surface of the workpiece W is polished by the chemical action of the polishing liquid and the mechanical action of the abrasive grains contained in the polishing liquid and / or the polishing pad 2.

[0018] The polishing apparatus is equipped with a film thickness measuring device 20 for measuring the film thickness of the workpiece W. The film thickness measuring device 20 is equipped with a light source 22 that emits light, a liquid seal type sensor 25 and a transparent window type sensor 31 that irradiate the workpiece W with the light from the light source 22 and receive reflected light from the workpiece W, a spectrometer 40 connected to the liquid seal type sensor 25 and the transparent window type sensor 31, and a spectrum processing device 45 that determines the film thickness of the workpiece W based on measurement data of the intensity of the reflected light from the workpiece W. The liquid seal type sensor 25 and the transparent window type sensor 31 are attached to the polishing table 3 and rotate together with the polishing table 3.

[0019] With each rotation of the polishing table 3, the light emitted from the light source 22 is alternately transmitted to the liquid seal sensor 25 and the transparent window sensor 31, and alternately guided from the liquid seal sensor 25 and the transparent window sensor 31 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 alternately received by the liquid seal sensor 25 and the transparent window sensor 31 and sent to the spectrometer 40. The spectrometer 40 resolves the reflected light according to wavelength over a predetermined wavelength range, and generates reflected light intensity measurement data by measuring the intensity of the reflected light at each wavelength. The reflected light intensity measurement data is sent from the spectrometer 40 to a spectrum processing device 45.

[0020] The spectrum processor 45 is configured to generate a spectrum of the reflected light of 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.

[0021] The spectrum processing device 45 includes a storage device 45a in which a program is stored, and an arithmetic device 45b that executes calculations according to instructions included in the program. The spectrum processing device 45 is composed of at least one computer. The storage device 45a includes a main storage device such as a random access memory (RAM) and an auxiliary storage device such as a hard disk drive (HDD) and a solid state drive (SSD). Examples of the arithmetic device 45b include a CPU (Central Processing Unit) and a GPU (Graphics Processing Unit). However, the specific configuration of the spectrum processing device 45 is not limited to these examples.

[0022] FIG. 2 is a diagram showing an example of a spectrum generated by the spectrum processing device 45. The spectrum is expressed as a line graph (i.e., a spectral waveform) showing the relationship between the wavelength and intensity of light. 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. The 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 (actual intensity) at each wavelength by the predetermined reference intensity, unnecessary noise such as the optical system of the device or the intensity variation inherent to the light source can be removed from the actual intensity.

[0023] In the example shown in FIG. 2, the spectrum of the reflected light is a spectral waveform that indicates the relationship between the relative reflectance and the wavelength of the reflected light, but the spectrum of the reflected light may also be a spectral waveform that indicates the relationship between the intensity of the reflected light itself and the wavelength of the reflected light.

[0024] The spectrum processing device 45 receives intensity measurement data of the reflected light from the workpiece W while the polishing table 3 makes one rotation, and generates a spectrum of the reflected light from the intensity measurement data. The spectrum processing device 45 is configured to determine the film thickness of the workpiece W from the spectrum of the reflected light. A known technique is used as a method for determining the film thickness of the workpiece W based on the spectrum. For example, the spectrum processing device 45 determines a reference spectrum from a reference spectrum library that has a shape closest to the spectrum of the reflected light, and determines the film thickness associated with the determined reference spectrum. In another example, the spectrum processing device 45 performs a Fourier transform on the spectrum of the reflected light, and determines the film thickness from the obtained frequency spectrum.

[0025] The film thickness measuring device 20 will be described in detail with reference to Fig. 1. The spectrometer 40 includes a photodetector 41. In one embodiment, the photodetector 41 is composed of a photodiode, a CCD, a CMOS, or the like. The liquid-sealed sensor 25 and the transparent window sensor 31 are optically coupled to the light source 22 and the photodetector 41. The photodetector 41 is electrically connected to a spectrum processing device 45.

[0026] The film thickness measuring device 20 includes a first light projecting optical fiber cable 51 and a second light projecting optical fiber cable 52 that guide the light emitted from the light source 22 to the surface of the workpiece W, and a first light receiving optical fiber cable 56 and a second light receiving optical fiber cable 57 that receive the light reflected from the workpiece W and send the reflected light to the spectroscope 40. The tip of the first light projecting optical fiber cable 51 and the tip of the first light receiving optical fiber cable 56 are positioned within the polishing table 3. Similarly, the tip of the second light projecting optical fiber cable 52 and the tip of the second light receiving optical fiber cable 57 are positioned within the polishing table 3.

[0027] The liquid seal sensor 25 includes a liquid flow path 26 through which pure water flows as a rinsing liquid, and a first optical sensor head 27 disposed within the liquid flow path 26. The first optical sensor head 27 is composed of a tip of a first light projecting optical fiber cable 51 and a tip of a first light receiving optical fiber cable 56. The first optical sensor head 27 emits light to the workpiece W through the pure water flowing within the liquid flow path 26, and receives reflected light from the workpiece W that has passed through the pure water flowing within the liquid flow path 26.

[0028] The liquid flow path 26 is formed in the polishing table 3 and opens on the upper surface of the polishing table 3. The polishing table 3 has a drain hole 60 that opens on its upper surface. The drain hole 60 is adjacent to the liquid flow path 26. The polishing pad 2 has a first through hole 61 formed at a position corresponding to the liquid flow path 26 and the drain hole 60. The liquid flow path 26 and the drain hole 60 communicate with the first through hole 61, and the first through hole 61 opens on the polishing surface 2a. The liquid flow path 26 is connected to a liquid supply line 63, and the drain hole 60 is connected to a drain line 64. The liquid seal sensor 25 is located below the first through hole 61.

[0029] During polishing of the workpiece W, pure water is supplied to the liquid flow path 26 via the liquid supply line 63 as a transparent rinsing liquid, and is further supplied to the first through hole 61 through the liquid flow path 26. A flow of pure water is formed between the surface (surface to be polished) of the workpiece W and the first optical sensor head 27. The pure water flows into the drain hole 60 and is discharged through the drain line 64. The pure water flowing through the liquid flow path 26 and the first through hole 61 prevents the polishing liquid and polishing debris from contacting the first optical sensor head 27, thereby ensuring the optical path.

[0030] The light source 22 transmits light to the liquid-sealed sensor 25 through the first light-emitting fiber optic cable 51, and the liquid-sealed sensor 25 transmits light toward the workpiece W through the pure water in the liquid flow path 26 and the first through hole 61. The reflected light from the workpiece W passes through the pure water and is received by the liquid-sealed sensor 25, and is sent to the spectrometer 40 through the first light-receiving fiber optic cable 56. The spectrometer 40 resolves the reflected light according to its wavelength, and measures the intensity of the reflected light at each wavelength over a predetermined wavelength range. The spectrometer 40 transmits the reflected light intensity measurement data to the spectrum processing device 45. The spectrum processing device 45 generates a spectrum of the reflected light from the reflected light intensity measurement data, and determines the film thickness of the workpiece W based on the spectrum of the reflected light.

[0031] The transparent window type sensor 31 includes a second optical sensor head 32 and a transparent window 33 arranged above the second optical sensor head 32. The second optical sensor head 32 is composed of an end of a second light-emitting optical fiber cable 52 and an end of a second light-receiving optical fiber cable 57. The second optical sensor head 32 is installed in the polishing table 3, and the transparent window 33 is arranged in a second through hole 34 formed in the polishing pad 2. The transparent window 33 completely closes the second through hole 34 of the polishing pad 2, thereby preventing the polishing liquid and polishing debris from coming into contact with the second optical sensor head 32.

[0032] The second optical sensor head 32 emits light to the workpiece W through the transparent window 33, and receives the reflected light from the workpiece W that has passed through the transparent window 33. The transparent window 33 is a window made of a material that transmits light. The material of the transparent window 33 is not particularly limited, but it is made of a transparent resin, for example.

[0033] The light source 22 transmits light through the second light-emitting fiber optic cable 52 to the transparent window sensor 31, which transmits the light through the transparent window 33 toward the workpiece W. The light reflected from the workpiece W is received by the transparent window sensor 31 and transmitted through the second light-receiving fiber optic cable 57 to the spectrometer 40. The spectrometer 40 resolves the reflected light according to its wavelength and measures the intensity of the reflected light at each wavelength over a predetermined wavelength range. The spectrometer 40 transmits the reflected light intensity measurement data to a spectral processor 45. The spectral processor 45 generates a spectrum of the reflected light from the reflected light intensity measurement data and determines the film thickness of the workpiece W based on the spectrum of the reflected light.

[0034] The first light-projecting fiber optic cable 51 and the second light-projecting fiber optic cable 52 are connected to a first optical path switching device 71, and are coupled to the light source 22 via the first optical path switching device 71. The first optical path switching device 71 has an optical switch, a shutter, or the like, and is configured to optically couple the light source 22 to either the first light-projecting fiber optic cable 51 or the second light-projecting fiber optic cable 52. Therefore, the light emitted from the light source 22 is sent to either the liquid-sealed sensor 25 or the transparent window sensor 31 by the first optical path switching device 71.

[0035] The first light-receiving optical fiber cable 56 and the second light-receiving optical fiber cable 57 are connected to a second optical path switching device 72, and are coupled to the spectrometer 40 via the second optical path switching device 72. The second optical path switching device 72 has an optical switch, a shutter, or the like, and is configured to optically couple the spectrometer 40 to either the first light-receiving optical fiber cable 56 or the second light-receiving optical fiber cable 57. Therefore, the spectrometer 40 is optically coupled to either the liquid-sealed sensor 25 or the transparent window sensor 31 by the second optical path switching device 72.

[0036] The first optical path switching device 71 and the second optical path switching device 72 operate every time the polishing table 3 rotates once to optically connect the light source 22 and the spectroscope 40 to either the liquid-sealed sensor 25 or the transparent window sensor 31. More specifically, when the liquid-sealed sensor 25 is positioned below the workpiece W held by the polishing head 1, the first optical path switching device 71 and the second optical path switching device 72 connect the light source 22 and the spectroscope 40 to the liquid-sealed sensor 25, and when the transparent window sensor 31 is positioned below the workpiece W held by the polishing head 1, the first optical path switching device 71 and the second optical path switching device 72 connect the light source 22 and the spectroscope 40 to the transparent window sensor 31. In this way, the common light source 22 can alternately transmit light to the liquid-sealed sensor 25 and the transparent window sensor 31, and the common spectroscope 40 can alternately receive reflected light from the workpiece W through the liquid-sealed sensor 25 and the transparent window sensor 31.

[0037] FIG. 3 is a top view showing the arrangement of the liquid seal sensor 25 and the transparent window sensor 31. As shown in FIG. 3, the liquid seal sensor 25 and the transparent window sensor 31 are arranged on a circumference CE having the same center as the rotation center CP of the polishing table 3. The liquid seal sensor 25 and the transparent window sensor 31 are arranged at equal intervals around the rotation center CP of the polishing table 3. The liquid seal sensor 25 and the transparent window sensor 31 rotate together with the polishing table 3 while tracing the same trajectory. In the example shown in FIG. 3, the liquid seal sensor 25 and the transparent window sensor 31 are arranged at positions where they alternately pass the center of the workpiece W every time the polishing table 3 rotates once. The circumference CE is an imaginary circle that represents the movement trajectory of the liquid seal sensor 25 and the transparent window sensor 31. In one embodiment, the liquid seal sensor 25 and the transparent window sensor 31 may be arranged on different circumferences having the same center as the rotation center CP of the polishing table 3.

[0038] The liquid seal sensor 25 and the transparent window sensor 31 emit and receive light through different media, i.e., pure water, and a transparent window 33. The spectra of reflected light obtained through these different types of sensors 25, 31 show good intensities of reflected light in different wavelength ranges. According to this embodiment, the spectra of reflected light obtained through both the liquid seal sensor 25 and the transparent window sensor 31 are used during polishing of the workpiece W, so that the wavelength range of reflected light used for film thickness measurement is substantially expanded. As a result, the thicknesses of various types of films can be accurately measured.

[0039] The spectrum processing device 45 determines the film thickness of the workpiece W based on the spectrum of the reflected light of the workpiece W alternately sent from the liquid seal sensor 25 and the transparent window sensor 31. In the embodiment shown in Fig. 3, while the polishing table 3 makes one rotation, the spectrum processing device 45 determines the film thickness of the workpiece W based on the spectrum of the reflected light sent from the liquid seal sensor 25, and determines the film thickness of the workpiece W based on the spectrum of the reflected light sent from the transparent window sensor 31.

[0040] Depending on the type of film on the workpiece W and / or the surface structure of the workpiece W, the shape of the spectrum in the short wavelength range may not change significantly in the early stage of polishing the workpiece W, but the shape of the spectrum in the long wavelength range may change significantly. In contrast, in the later stage of polishing the workpiece W, the shape of the spectrum in the long wavelength range may not change significantly, but the shape of the spectrum in the short wavelength range may change significantly. Since the film thickness of the workpiece W decreases with polishing time, a spectrum that does not change in shape does not accurately reflect the change in film thickness. Pure water has the property of transmitting light in a short wavelength band but absorbing light in a long wavelength band. On the other hand, the transparent window 33 made of resin has the property of transmitting light in a long wavelength band but not easily transmitting light in a short wavelength band.

[0041] Therefore, in one embodiment, the spectrum processing device 45 is configured to determine the film thickness of the workpiece W based on the spectrum of the reflected light from the workpiece W sent from the transparent window sensor 31 during a first polishing period during polishing of the workpiece W, and to determine the film thickness of the workpiece W based on the spectrum of the reflected light from the workpiece W sent from the liquid seal sensor 25 during a second polishing period during polishing of the workpiece W. The first polishing period and the second polishing period are different polishing periods set in advance. For example, the first polishing period is a polishing period from the initial point of polishing to a predetermined intermediate point of polishing, and the second polishing period is a polishing period from the predetermined intermediate point of polishing to the end point of polishing, but is not limited thereto. According to such an operation, the spectrum processing device 45 can determine the film thickness of the workpiece W based on a spectrum that correctly reflects the change in the film thickness of the workpiece W throughout the entire polishing of the workpiece W.

[0042] Depending on the type of film on the workpiece W and / or the surface structure of the workpiece W, the shape of the spectrum in the long wavelength range may not change significantly in the early stage of polishing the workpiece W, while the shape of the spectrum in the short wavelength range may change significantly. Therefore, in one embodiment, the spectrum processing device 45 may determine the film thickness of the workpiece W based on the spectrum of the reflected light from the workpiece W sent from the liquid seal sensor 25 during a first polishing period during polishing the workpiece W, and may determine the film thickness of the workpiece W based on the spectrum of the reflected light from the workpiece W sent from the transparent window sensor 31 during a second polishing period during polishing the workpiece W.

[0043] In one embodiment, in addition to the first polishing period and the second polishing period, a plurality of polishing periods including at least one further polishing period may be provided. The spectrum processing device 45 may determine the film thickness of the workpiece W based on the spectrum of the reflected light from the workpiece W sent from the liquid seal sensor 25 or the transparent window sensor 31 during each polishing period while alternately switching between the liquid seal sensor 25 and the transparent window sensor 31 during polishing of the workpiece W.

[0044] In one embodiment, the spectrum processing device 45 may be configured to generate a composite spectrum by combining the spectrum of the reflected light from the workpiece W sent from the liquid seal sensor 25 and the spectrum of the reflected light from the workpiece W sent from the transparent window sensor 31, and to determine the film thickness of the workpiece W based on the composite spectrum. This embodiment will be described below with reference to Figures 4 and 5.

[0045] 4 is a diagram showing a spectrum SP1 of the light reflected from the workpiece W sent from the liquid seal sensor 25, and a spectrum SP2 of the light reflected from the workpiece W sent from the transparent window sensor 31. The spectra SP1 and SP2 are generated based on the intensity measurement data generated from the same spectrometer 40, so they have the same wavelength range but different amplitudes.

[0046] 5 is a diagram for explaining a state in which a composite spectrum is generated by combining a spectrum SP1 of the light reflected from the workpiece W sent from the liquid seal sensor 25 with a spectrum SP2 of the light reflected from the workpiece W sent from the transparent window sensor 31. The spectrum processing device 45 generates a composite spectrum by combining a portion PN1 of the spectrum SP1 from a first wavelength (e.g., a lower limit wavelength) LL to a predetermined intermediate wavelength MP and a portion PN2 of the spectrum SP2 from the predetermined intermediate wavelength MP to a second wavelength (e.g., an upper limit wavelength) UL. In order to smoothly combine the spectrum SP1 and the spectrum SP2, the spectrum processing device 45 may expand, contract, or move either or both of the spectrum SP1 and the spectrum SP2 along the light intensity (along the relative reflectance).

[0047] The composite spectrum includes the intensity of reflected light reflecting the film thickness of the workpiece W in a wide wavelength range from a first wavelength (e.g., a lower limit wavelength) LL to a second wavelength (e.g., an upper limit wavelength) UL. Therefore, the spectrum processing device 45 can accurately determine the film thickness of the workpiece W based on the composite spectrum. In particular, the spectrum processing device 45 can accurately determine the thicknesses of various types of films.

[0048] FIG. 6 is a schematic diagram showing another embodiment of the film thickness measuring device 20. The configuration and operation of this embodiment that are not particularly described are the same as those of the embodiment described with reference to FIG. 1 to FIG. 5, so that the overlapping description will be omitted. In the embodiment shown in FIG. 6, the film thickness measuring device 20 includes a first spectrometer 40A and a second spectrometer 40B connected to the liquid-sealed sensor 25 and the transparent window sensor 31, respectively. The second optical path switching device 72 is not provided. The first spectrometer 40A is connected to the liquid-sealed sensor 25 via the first light-receiving optical fiber cable 56, and the second spectrometer 40B is connected to the transparent window sensor 31 via the second light-receiving optical fiber cable 57.

[0049] The first spectrometer 40A and the second spectrometer 40B are configured to measure the intensity of reflected light from the workpiece W at different wavelength ranges. More specifically, the first spectrometer 40A is configured to measure the intensity of the reflected light at a first wavelength range to generate first intensity measurement data, and the second spectrometer 40B is configured to measure the intensity of the reflected light at a second wavelength range to generate second intensity measurement data. The first wavelength range is different from the second wavelength range.

[0050] 7 is a diagram showing a spectrum SP3 generated from the first intensity measurement data generated by the first spectrometer 40A and a spectrum SP4 generated from the second intensity measurement data generated by the second spectrometer 40B. The spectrum processing device 45 generates the spectrum SP3 from the first intensity measurement data and determines the film thickness of the workpiece W based on the spectrum SP3. Similarly, the spectrum processing device 45 generates a spectrum SP4 from the second intensity measurement data and determines the film thickness of the workpiece W based on the spectrum SP4.

[0051] 7, the first wavelength range R1 of the spectrum SP3 is different from the second wavelength range R2 of the spectrum SP4, but the first wavelength range R1 and the second wavelength range R2 partially overlap. In one example, the first wavelength range R1 is 200 nm to 1100 nm, and the second wavelength range R2 is 900 nm to 1700 nm.

[0052] Spectrum SP3 having a first wavelength range R1 on the short wavelength side is the spectrum of the reflected light sent from the liquid seal sensor 25. The wavelength band of light absorbed by water is not included in the first wavelength range R1 of spectrum SP3. Therefore, the spectrum processing device 45 can accurately determine the film thickness of the workpiece W from spectrum SP3.

[0053] Spectrum SP4 having a second wavelength range R2 on the longer wavelength side is the spectrum of the reflected light sent from the transparent window sensor 31. The wavelength band of light that is difficult to pass through the transparent window 33 is not included in the second wavelength range R2 of spectrum SP4. Therefore, the spectrum processing device 45 can accurately determine the film thickness of the workpiece W from the spectrum SP4.

[0054] In one embodiment, as described with reference to FIG. 5, the spectral processing device 45 may be configured to combine the spectrum SP3 of the reflected light from the workpiece W sent from the liquid-sealed sensor 25 and the spectrum SP4 of the reflected light from the workpiece W sent from the transparent window sensor 31 to generate a composite spectrum, and to determine the film thickness of the workpiece W based on the composite spectrum.

[0055] In one embodiment, as shown in Fig. 8, the film thickness measuring device 20 may include a first light source 22A and a second light source 22B connected to the liquid-sealed sensor 25 and the transparent window type sensor 31, respectively. The first optical path switching device 71 is not provided. The first light source 22A is connected to the liquid-sealed sensor 25 via a first light-projecting optical fiber cable 51, and the second light source 22B is connected to the transparent window type sensor 31 via a second light-projecting optical fiber cable 52. Other configurations and operations of this embodiment that are not particularly described are the same as those of the embodiment described with reference to Fig. 6, so that duplicated descriptions will be omitted.

[0056] The number and arrangement of the liquid-sealed sensors 25 and the transparent window sensors 31 are not limited to those in the above-mentioned embodiment. In one embodiment, as shown in Fig. 9 and Fig. 10, the film thickness measuring device 20 may include one liquid-sealed sensor 25 and two transparent window sensors 31. In the embodiment shown in Fig. 9 and Fig. 10, the liquid-sealed sensor 25 is connected to the common light source 22 by the first light-projecting optical fiber cable 51 via the first optical path switching device 71, and is further connected to the common spectrometer 40 by the first light-receiving optical fiber cable 56 via the second optical path switching device 72. The two transparent window sensors 31 are connected to the common light source 22 by the second light-projecting optical fiber cable 52 and the third light-projecting optical fiber cable 53 via the first optical path switching device 71, and are further connected to the common spectrometer 40 by the second light-receiving optical fiber cable 57 and the third light-receiving optical fiber cable 58 via the second optical path switching device 72.

[0057] The first optical path switching device 71 and the second optical path switching device 72 operate every time the polishing table 3 rotates once, and optically connect the light source 22 and the spectroscope 40 to the liquid-sealed sensor 25 and one of the two transparent window sensors 31. More specifically, when the liquid-sealed sensor 25 is located below the workpiece W held by the polishing head 1, the first optical path switching device 71 and the second optical path switching device 72 connect the light source 22 and the spectroscope 40 to the liquid-sealed sensor 25. When one of the two transparent window sensors 31 is located below the workpiece W held by the polishing head 1, the first optical path switching device 71 and the second optical path switching device 72 connect the light source 22 and the spectroscope 40 to that transparent window sensor 31. When the other transparent window sensor 31 is positioned below the workpiece W held by the polishing head 1, the first optical path switching device 71 and the second optical path switching device 72 connect the light source 22 and the spectrometer 40 to that transparent window sensor 31.

[0058] 5, in this embodiment, the spectrum processing device 45 may be configured to generate a composite spectrum by combining the spectrum of the reflected light from the workpiece W sent from the liquid-sealed sensor 25 with the spectrum of the reflected light from the workpiece W sent from the two transparent window sensors 31, and determine the film thickness of the workpiece W based on the composite spectrum. More specifically, the spectrum processing device 45 generates an average spectrum of the spectra of the reflected light sent from the two transparent window sensors 31, combines the average spectrum with the spectrum of the reflected light sent from the liquid-sealed sensor 25 to generate a composite spectrum, and determines the film thickness of the workpiece W based on the composite spectrum.

[0059] In one embodiment, as shown in FIG. 11, the film thickness measurement device 20 includes a first spectrometer 40A connected to the liquid-sealed sensor 25 by a first light-receiving optical fiber cable 56, and a second spectrometer 40B connected to two transparent window sensors 31. Light reception For fiber optic cable 57 and the third Light reception For fiber optic cable 58 The second spectrometer 40B may be connected to the first spectrometer 40A via a second optical path switching device 72. The two transparent window type sensors 31 are connected to the second spectrometer 40B via a second optical path switching device 72, and the liquid seal type sensor 25 is connected to the first spectrometer 40A without via the second optical path switching device 72. The configurations and operations of the first spectrometer 40A and the second spectrometer 40B are the same as those in the embodiment shown in Figs. 6 and 7, and therefore repeated explanations will be omitted.

[0060] 12 to 15, the film thickness measurement device 20 may include a plurality of liquid-sealed sensors 25 and a plurality of transparent window-type sensors 31. In the embodiment shown in Fig. 12 and Fig. 13, the plurality of liquid-sealed sensors 25 and the plurality of transparent window-type sensors 31 are arranged on the same circumference CE.

[0061] In the embodiment shown in FIG. 14, the liquid-sealed sensor 25 and the transparent window sensor 31 are arranged on each of a plurality of concentric circles CF having the same center as the rotation center CP of the polishing table 3. The plurality of concentric circles CF represent the movement trajectories of the liquid-sealed sensor 25 and the transparent window sensor 31. One of the plurality of concentric circles CF passes through the center of the workpiece W held by the polishing head 1, and the other of the plurality of concentric circles CF passes through the edge portion of the workpiece W held by the polishing head 1. As shown in FIG. 15, the plurality of liquid-sealed sensors 25 and the plurality of transparent window sensors 31 may be arranged on each of the plurality of concentric circles CF. In the embodiment shown in FIG. 14, two concentric circles CF are set, but three or more concentric circles may be set.

[0062] The number and arrangement of the liquid seal type sensors 25 and the transparent window type sensors 31 are not limited to those in the illustrated embodiment, and various numbers and arrangements can be applied.

[0063] The above-described embodiments have been described for the purpose of enabling a person having ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments are naturally possible for a person skilled in the art, and the technical idea of ​​the present invention can be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope according to the technical idea defined by the claims. [Explanation of symbols]

[0064] W Workpiece 1 Polishing head 2 Polishing Pads 2a Polished surface 3 Polishing table 5 Polishing fluid supply nozzle 6 Table Motor 10 Head shaft 17 Coupling device 18 Polishing head motor 20 Film thickness measuring device 22 Light source 22A 1st light source 22B 2nd light source 25 Liquid seal sensor 26 Liquid flow path 27 First optical sensor head 31 Transparent window type sensor 32 Second optical sensor head 33 Transparent Window 34 2nd hole 40 spectrometer 40A 1st spectrometer 40B 2nd spectrometer 41 Photodetector 45 Spectral Processing Device 45a Storage device 45b Arithmetic unit 51 First light projection optical fiber cable 52 Second light projection optical fiber cable 53 Third light projection optical fiber cable 56 First receiving optical fiber cable 57 Second receiving optical fiber cable 58 3rd receiving optical fiber cable 60 Drain hole 61 1st hole 63 Liquid Supply Line 64 Drain Line 71 First optical path switching device 72 Second optical path switching device

Claims

1. a polishing table supporting a polishing pad is rotated while pressing the workpiece against the polishing pad to polish the workpiece; During polishing of the workpiece, light is guided to the workpiece from a liquid-sealed sensor and a transparent window sensor disposed on the polishing table, and reflected light from the workpiece is received by the liquid-sealed sensor and the transparent window sensor; generating a composite spectrum by combining a spectrum of the light reflected from the workpiece from the liquid seal sensor and a spectrum of the light reflected from the workpiece from the transparent window sensor; determining a film thickness of the workpiece based on the composite spectrum; The liquid seal sensor has a liquid flow path through which a liquid flows, and a first optical sensor head disposed in the liquid flow path, The transparent window type sensor has a second optical sensor head and a transparent window disposed above the second optical sensor head.

2. 2. The film thickness measuring method according to claim 1, wherein the liquid seal type sensor and the transparent window type sensor are arranged on a circumference having the same center as a rotation center of the polishing table.

3. A method for polishing a workpiece by pressing the workpiece against a polishing pad while rotating a polishing table supporting the polishing pad; During polishing of the workpiece, light is guided to the workpiece from a liquid-sealed sensor and a transparent window sensor disposed on the polishing table, and reflected light from the workpiece is received by the liquid-sealed sensor and the transparent window sensor; determining a film thickness of the workpiece based on a spectrum of reflected light from the workpiece; The liquid seal sensor has a liquid flow path through which a liquid flows, and a first optical sensor head disposed in the liquid flow path, the transparent window type sensor has a second optical sensor head and a transparent window disposed above the second optical sensor head; A method for measuring a film thickness, wherein a wavelength range of the spectrum of the reflected light sent from the liquid seal sensor is different from a wavelength range of the spectrum of the reflected light sent from the transparent window sensor.

4. The film thickness measuring method according to claim 1 , wherein the liquid-sealed sensor and the transparent window sensor are a plurality of liquid-sealed sensors and a plurality of transparent window sensors.

5. A method for polishing a workpiece by pressing the workpiece against a polishing pad while rotating a polishing table supporting the polishing pad; During polishing of the workpiece, light is guided to the workpiece from a liquid-sealed sensor and a transparent window sensor disposed on the polishing table, and reflected light from the workpiece is received by the liquid-sealed sensor and the transparent window sensor; determining a film thickness of the workpiece based on a spectrum of reflected light from the workpiece; The liquid seal sensor has a liquid flow path through which a liquid flows, and a first optical sensor head disposed in the liquid flow path, the transparent window type sensor has a second optical sensor head and a transparent window disposed above the second optical sensor head; The film thickness measuring method, wherein the liquid-sealed sensor and the transparent window sensor are arranged on each of a plurality of concentric circles having the same center as the center of rotation of the polishing table.

6. a liquid seal sensor and a transparent window sensor disposed on a rotatable polishing table for supporting a polishing pad for polishing a workpiece; a spectral processing device for determining a film thickness of the workpiece based on a spectrum of light reflected from the workpiece and transmitted by the liquid seal sensor and the transparent window sensor; The liquid seal sensor has a liquid flow path for flowing a liquid, and a first optical sensor head disposed in the liquid flow path, the transparent window type sensor has a second optical sensor head and a transparent window disposed above the second optical sensor head; The spectrum processing device includes: generating a composite spectrum by combining a spectrum of the light reflected from the workpiece from the liquid seal sensor and a spectrum of the light reflected from the workpiece from the transparent window sensor; A film thickness measurement device configured to determine a film thickness of the workpiece based on the composite spectrum.

7. 7. The film thickness measuring device according to claim 6, wherein the liquid-sealed sensor and the transparent window sensor are arranged on a circumference having the same center as a rotation center of the polishing table.

8. A liquid-sealed sensor and a transparent window sensor disposed on a rotatable polishing table for supporting a polishing pad for polishing a workpiece; a spectral processing device for determining a thickness of the workpiece based on a spectrum of light reflected from the workpiece by the liquid seal sensor and the transparent window sensor; a first spectrometer coupled to the liquid seal sensor; a second spectrometer coupled to the transparent window sensor; The liquid seal sensor has a liquid flow path for flowing a liquid, and a first optical sensor head disposed in the liquid flow path, the transparent window type sensor has a second optical sensor head and a transparent window disposed above the second optical sensor head; the first spectrometer is configured to measure an intensity of light reflected from the workpiece over a first wavelength range to generate first intensity measurement data; the second spectrometer is configured to measure an intensity of the reflected light from the workpiece in a second wavelength range to generate second intensity measurement data; The first wavelength range is different from the second wavelength range.

9. 9. The film thickness measuring device according to claim 6, wherein the liquid-sealed sensor and the transparent window sensor are a plurality of liquid-sealed sensors and a plurality of transparent window sensors.

10. A liquid sealed sensor and a transparent window sensor disposed on a rotatable polishing table for supporting a polishing pad for polishing a workpiece; a spectral processing device for determining a film thickness of the workpiece based on a spectrum of light reflected from the workpiece and transmitted by the liquid seal sensor and the transparent window sensor; The liquid seal sensor has a liquid flow path for flowing a liquid, and a first optical sensor head disposed in the liquid flow path, the transparent window type sensor has a second optical sensor head and a transparent window disposed above the second optical sensor head; The film thickness measuring device, wherein the liquid-sealed sensor and the transparent window sensor are arranged on each of a plurality of concentric circles having the same center as the center of rotation of the polishing table.

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