Polishing end point detection apparatus and method, and CMP apparatus

Abstract

[Problem] To provide a polishing end point detection device and method, and a CMP device capable of accurately detecting a polishing end point when polishing a workpiece having a thin film thickness. [Solution] A polishing end point detection device (70) is provided with: a measurement unit (71) that, during polishing of a workpiece (W), radiates measurement light onto the workpiece (W), disperses reflected light from the workpiece (W), and acquires a spectral waveform indicating the relationship between the wavelength and reflectance of the reflected light; the reflectivity is the ratio of the intensity of the reflected light to the reference intensity of each wavelength component obtained in advance; and a detection unit (72) that calculates the film thickness of the thermal oxide film by applying Fourier analysis to the spectral waveform. The reference intensity is calculated by bringing a sample workpiece having substantially the same reflectance characteristic as a substrate of a workpiece (W) into contact with a polishing pad (5) in a state where a CMP slurry is interposed between the polishing pad (5) and the sample workpiece, and irradiating the sample workpiece with measurement light through an observation window (80) of the polishing pad (5) by a measurement unit (71). And the reflected light from the sample workpiece is split.

Description

Technical Field

[0001] The present invention relates to a polishing endpoint detection device and method and a CMP device, and in particular to a polishing endpoint detection device and a CMP device for detecting the polishing endpoint when a workpiece is polished using a chemical mechanical polishing method (CMP). Background Art

[0002] A known workpiece polishing device is a CMP polishing device for polishing a silicon dioxide film or the like formed on the surface of a substrate. CMP polishing is performed by rotating a polishing pad attached to a platen and the workpiece while simultaneously pressing the workpiece against the polishing pad at a predetermined pressure and supplying an abrasive material (slurry) between the polishing pad and the workpiece.

[0003] In such CMP apparatuses, a method is known in which a reflectance spectrum generated based on reflected light from a wafer is extracted using Fast Fourier Transform (FFT) and its intensity, and the wafer film thickness is estimated from the obtained frequency components (see, for example, Patent Document 1).

[0004] [Prior art literature]

[0005] [Patent Document]

[0006] Patent Document 1: Japanese Patent Application Publication No. 2019-30934 Summary of the Invention

[0007] [Problems to be solved by the invention]

[0008] However, the CMP apparatus described in Patent Document 1 has the following problem: A reference spectrum must be acquired in advance using a lens in the presence of water. During the wafer polishing process, a reflectance spectrum is generated that represents the relationship between the wavelength of light reflected from the wafer and the ratio of the reflected light intensity to the reference intensity (relative reflectance). For thin workpieces with a thickness of 500 nm or less, for example, the reflectance spectrum contains as few as one or two peaks, making it impossible to calculate the wafer film thickness.

[0009] Furthermore, it is widely known that when the difference in refractive index between the substrate and the polished layer is small, the amplitude of the reflectance spectrum is small and is particularly susceptible to the influence of slurry thickness and rotation during CMP polishing.

[0010] Therefore, when grinding thin workpieces, in order to accurately detect the grinding end point, a technical problem that needs to be solved arises, and the present invention is aimed at solving this problem.

[0011] [Solutions to solve the problem]

[0012] In order to achieve the above-mentioned purpose, the polishing endpoint detection device according to the present invention is a polishing endpoint detection device that detects the polishing endpoint when the workpiece is brought into contact with the polishing pad and the polished layer of the workpiece is subjected to CMP polishing, wherein the polishing endpoint detection device comprises: a measuring unit that irradiates the workpiece with measuring light during the polishing process of the workpiece, and spectrally separates the reflected light from the workpiece to obtain a spectral waveform representing the relationship between the wavelength and reflectivity of the reflected light, wherein the reflectivity is the ratio of the intensity of the reflected light to a reference intensity of each wavelength component obtained in advance; and a detecting unit that calculates the film thickness of the polished layer based on the spectral waveform, wherein the reference intensity is calculated in the following manner: a sample workpiece having substantially the same reflectivity characteristics as the workpiece is brought into contact with the polishing pad while slurry is interposed between the rotating polishing pad and the sample workpiece, the measuring unit irradiates the sample workpiece with measuring light through the observation window of the polishing pad, and spectrally separates the reflected light from the sample workpiece.

[0013] Furthermore, the CMP apparatus according to the present invention has the above-mentioned polishing endpoint detection device.

[0014] In order to achieve the above-mentioned purpose, the polishing endpoint detection method according to the present invention is a polishing endpoint detection method, which detects the polishing endpoint when a workpiece is brought into contact with a polishing pad and a polished layer of the workpiece is subjected to CMP polishing, wherein the polishing endpoint detection method has the following steps: during the polishing process of the workpiece, irradiating the workpiece with measuring light, and spectroscopically analyzing the reflected light from the workpiece to obtain a spectral waveform representing the relationship between the wavelength and reflectivity of the reflected light, wherein the reflectivity is the ratio of the intensity of the reflected light to a reference intensity of each wavelength component obtained in advance; and calculating the film thickness of the polished layer based on the spectral waveform, wherein the reference intensity is calculated in the following manner: in a state where slurry is interposed between the rotating polishing pad and the sample workpiece, a sample workpiece having substantially the same reflectivity characteristics as the workpiece is brought into contact with the polishing pad, irradiating the sample workpiece with measuring light through an observation window of the polishing pad, and spectroscopically analyzing the reflected light from the sample workpiece.

[0015] [Effects of the Invention]

[0016] The present invention uses a sample workpiece having roughly the same reflectivity characteristics as the workpiece, and unifies the reference measurement conditions (whether the slurry contains abrasive, whether the pressure plate is rotating or stationary, etc.) with the grinding conditions of CMP grinding to calculate the baseline strength of the sample workpiece, thereby being able to accurately detect the grinding end point of a thin workpiece. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] [ Figure 1 ] is a three-dimensional diagram schematically showing a CMP device according to an embodiment of the present invention.

[0018] [ Figure 2 ] is a longitudinal cross-sectional view schematically showing the main parts of the grinding head.

[0019] [ Figure 3 ] is a schematic diagram schematically showing the situation of observing the state of the workpiece during the processing.

[0020] [ Figure 4 ] is a flow chart showing the procedure for detecting the grinding end point of a workpiece.

[0021] [ Figure 5 ] is a spectral waveform showing the relationship between the wavelength of the reflected light and the reflectivity that changes as the polishing progresses.

[0022] [ Figure 6 ] is to indicate Figure 5 The frequency spectrum of the relationship between the film thickness of the thermal oxide film and the intensity of the frequency component is obtained after Fourier analysis of the spectral waveform.

[0023] [ Figure 7 ] is a graph showing the trend of change in the film thickness of the polished layer.

[0024] [ Figure 8 ] for Figure 7 The chart is processed by the optimization method.

[0025] [ Figure 9 ] is the spectral waveform obtained in an embodiment of the present invention and its modified example.

[0026] [ Figure 10 ] for the reason Figure 9 The frequency spectrum obtained from the spectroscopic waveform.

[0027] [ Figure 11 ] is a graph showing the trend of change in the film thickness of the polished layer obtained in the modification example.

[0028] [ Figure 12 ] is the spectral waveform obtained in Comparative Example 1 that changes as the polishing progresses.

[0029] [ Figure 13 ] for the reason Figure 12 The frequency spectrum obtained from the spectroscopic waveform.

[0030] [ Figure 14 ] is a graph showing the trend of change in the film thickness of the polished layer in Comparative Example 1.

[0031] [ Figure 15 ] for Figure 14 The chart is processed by the optimization method.

[0032] [ Figure 16 ] is a spectral waveform obtained in an embodiment of the present invention and Comparative Example 2.

[0033] [ Figure 17 ] for the reason Figure 16 The frequency spectrum obtained from the spectroscopic waveform.

[0034] [ Figure 18 ] is a spectral waveform obtained in an embodiment of the present invention and Comparative Example 3. DETAILED DESCRIPTION

[0035] An embodiment of the present invention will be described with reference to the accompanying drawings. Hereinafter, when reference is made to the number, value, amount, range, etc. of constituent elements, unless otherwise specified or clearly limited to a specific number in principle, the reference is not limited to the specific number and may be greater than or less than the specific number.

[0036] Furthermore, when referring to the shape or positional relationship of components, etc., it includes cases where the shape or positional relationship is substantially similar or similar to the shape or position, except for cases where it is specifically stated or where it is considered to be obviously not so in principle.

[0037] In addition, the drawings may be exaggerated by enlarging features to make them easier to understand, and the dimensional ratios of components may not necessarily be the same as in reality. In addition, in cross-sectional views, hatching of some components may be omitted to make the cross-sectional structure of the components easier to understand.

[0038] CMP equipment

[0039] Figure 1 1 is a perspective view schematically showing a CMP apparatus 1 according to an embodiment of the present invention. The CMP apparatus 1 includes a platen 2 and a polishing head 10 .

[0040] The pressing plate 2 is formed into a disk shape and is connected to a rotating shaft 3 arranged below the pressing plate 2. The rotating shaft 3 is rotated by the driving of the motor 4, thereby the pressing plate 2 is moved to the Figure 1 A polishing pad 5 is attached to the upper surface of the platen 2 , and a CMP slurry containing a polishing agent and chemicals is supplied from a nozzle 6 onto the polishing pad 5 .

[0041] The grinding head 10 is formed into a disk shape with a diameter smaller than that of the pressing plate 2 and is connected to a rotating shaft 10a arranged above the grinding head 10. The rotating shaft 10a is rotated by a motor (not shown), thereby the grinding head 10 moves to the Figure 1The polishing head 10 is rotated in the direction of the arrow D2 in FIG. The polishing head 10 is freely raised and lowered in the vertical direction V by a lifting device not shown in the figure.

[0042] The operation of the CMP apparatus 1 is controlled by a controller 7. The controller 7 controls each component of the CMP apparatus 1. The controller 7 is, for example, a computer and includes a CPU, memory, etc. The functions of the controller 7 can be implemented by software control or by hardware components.

[0043] Secondly, according to Figure 2 、 Figure 3 、 Figure 4 The structure of the grinding head 10 will be described. Figure 2 As shown, the lapping head 10 includes a head body 20 , a carrier 30 , a retaining ring 40 , a diaphragm 50 , and a backing film 60 .

[0044] The head body 20 is connected to the rotating shaft 10a and rotates together with the rotating shaft 10a. The head body 20 is connected to the carrier 30 disposed below the head body 20 through the rotating part 21, and the head body 20 and the carrier 30 rotate in conjunction with each other.

[0045] A carrier pressing mechanism 31 is provided between the head body 20 and the carrier 30. The carrier pressing mechanism 31 is, for example, an air bag inflated by air supplied from an unillustrated air supply source. The pressure of the air supplied from the air supply source is adjusted by a regulator (not shown). The carrier pressing mechanism 31 presses the workpiece W against the polishing pad 5 via the carrier 30 based on the supplied air pressure.

[0046] The carrier 30 is provided with air pipes 32 spaced evenly around its periphery. The lower ends of the air pipes 32 open into the air chamber A formed between the bottom surface 30a of the carrier 30 and the diaphragm 50. The air pipes 32 are connected to an air supply source (not shown), serving as an air supply mechanism, and air is introduced into the air chamber A through the air pipes 32. The pressure of the air supplied to the air pipes 32 is regulated by a regulator (not shown). The air supplied from the air pipes 32 to the air chamber A forms an air pressure layer within the air chamber A that offsets the pressure transmitted to the carrier 30 by the carrier pressing mechanism 31. The air releases excess pressure to the atmosphere, thereby pressing the workpiece W with a uniform pressure distribution.

[0047] The bottom surface 30a of the carrier 30 is provided with multiple coaxially arranged elastic pressing members (not shown). Furthermore, the multiple pressing members are formed into annular rings with different diameters. The elastic pressing members are bolted to the bottom surface 30a of the carrier 30 via brackets (not shown). The elastic pressing members are coaxially arranged with the rotation axis 10a of the polishing head 10 and define the air chamber A.

[0048] The holding ring 40 is arranged so as to surround the circumference of the carrier 30. The holding ring 40 has a frame 41, and a membrane 50 and a backing film 60 are provided on the upper surface of the frame.

[0049] The frame 41 is formed into a circular ring and has a storage pocket 41a in the center for storing the workpiece W. The frame 41 is mounted on the holding and pressing member 43 via a snap ring 42. A holding and pressing mechanism 44 is provided between the head body 20 and the holding and pressing member 43. Indicated at 45 is a cover plate that covers the top of the snap ring 42.

[0050] The holding and pressing mechanism 44 is an air bag or the like that is inflated by air supplied from an air supply source (not shown). The pressure of the air supplied from the air supply source is adjusted by a regulator (not shown). The holding and pressing mechanism 44 presses the retaining ring 40 against the polishing pad 5 according to the pressure of the supplied air.

[0051] The diaphragm 50 is made of a resin such as tetrafluoroethylene perfluoroalkoxy vinyl ether copolymer (PFA) or polyethylene terephthalate (PET). The diaphragm 50 is bonded to the upper surface of the backing film 60. When compressed air is introduced into the air chamber A, the diaphragm 50 elastically deforms toward the storage pocket 41a due to the air pressure.

[0052] The backing film 60 is, for example, a suede film and is attached to the frame 41 to cover the storage pocket 41 a. When compressed air is introduced into the air chamber A, the backing film 60 elastically deforms along with the elastic deformation of the diaphragm 50 , thereby pressurizing the workpiece W.

[0053] <Polishing endpoint detection device>

[0054] like Figure 3 As shown, the CMP apparatus 1 is equipped with a polishing end point detection device 70 for detecting the polishing end point of the workpiece W during the polishing process. The polishing end point detection device 70 includes a measuring unit 71 and a detecting unit 72. Figure 3 A part of the structure of the CMP apparatus 1 is omitted.

[0055] The measuring unit 71 is constructed by, for example, bundling a plurality of optical fibers 74 and 75 connected to a lens 73. The optical fiber 74 is connected to a light source unit 76. The light source unit 76 is, for example, a halogen light source that emits white light with a wavelength of 400 to 800 nm, but is not limited thereto. The optical fiber 75 is connected to a spectrometer 77.

[0056] The lens 73 is disposed opposite to a transparent observation window 80 provided on the platen 2 and the polishing pad 5. The lens 73 is not limited to irradiating light perpendicularly to the observation window 80; the light path may be refracted by a reflective member, etc. The observation window 80 is made of, for example, acrylic.

[0057] The measuring light emitted from the light source unit 76 passes through the optical fiber 74 and the lens 73 , and is transmitted through the observation window 80 to irradiate the polishing layer of the workpiece W. Furthermore, the reflected light reflected from the workpiece W and received by the lens 73 is guided to the spectrometer 77 via the optical fiber 75 .

[0058] The reflected light from the surface of the polished layer of the workpiece W and the back surface of the polished layer (the interface between the polished layer and the substrate) interferes with each other, and the interference pattern varies depending on the film thickness (optical path length) of the polished layer. The spectrometer 77 decomposes the reflected light from the workpiece W by wavelength, generating a spectroscopic waveform that shows the relationship between wavelength and reflectivity. The reflectivity is the value obtained by dividing the intensity of the reflected light by the reference intensity described below.

[0059] The detection unit 72 calculates the thickness of the polished layer in the polishing workpiece W based on the spectral waveform generated by the spectrometer 77. As a method of calculating the thickness of the polished layer based on the spectral waveform, for example, Fourier analysis can be used.

[0060] Specifically, the frequency component and its intensity are extracted from the Fourier series obtained from the spectral waveform, and the obtained frequency component is converted into the film thickness of the polished layer using a predetermined relationship. The predetermined relationship is obtained by considering the attenuation rate of the refractive index of the polished layer.

[0061] <Polishing endpoint detection method>

[0062] Next, a procedure for detecting the grinding end point of the workpiece W using the grinding end point detection device 70 will be described. Figure 4 This is a flowchart showing the procedure for detecting the polishing endpoint of the workpiece W. The following description uses as an example a case where a silicon substrate is used as the workpiece W, and a silicon dioxide film (hereinafter referred to as a "thermally oxidized film") is formed on the surface of the silicon substrate as the polishing layer. However, the types of substrates and films of the workpiece W are not limited thereto.

[0063] (Reference measurement)

[0064] First, a reference intensity is calculated using a sample workpiece whose optical constants such as the refractive index and attenuation rate are known (step S1 ).

[0065] Specifically, CMP slurry is supplied from the nozzle 6 to the polishing pad 5, while the platen 2 is rotated, and the polishing head 10 holding the sample workpiece is lowered toward the rotating polishing pad 5, so that the sample workpiece and the polishing pad 5 come into contact. Furthermore, when the sample workpiece and the polishing pad 5 are brought into contact, the polishing head 10 may be in either a rotating state or a stationary (non-rotating) state. However, the reference measurement conditions that can be arbitrarily set for calculating the reference strength of the sample workpiece, such as the rotation speed of the platen 2 and the supply amount of CMP slurry, are preferably consistent with the polishing conditions for the workpiece W described later.

[0066] Then, the sample workpiece is irradiated with measurement light from the lens 73 via the observation window 80 . The reflected light from the sample workpiece enters the lens 73 via the observation window 80 . The spectrometer 77 calculates the reference intensity of each wavelength component based on the reflected light from the sample workpiece and the optical constants of the sample workpiece.

[0067] The sample workpiece should be made of a material having approximately the same reflectivity characteristics as the workpiece W. Furthermore, "reflectivity characteristics" are characteristics related to the reflected light possessed by the sample workpiece, and are suitable for comparison with the workpiece W, taking into account the reflectivity of the polishing layer and substrate of the workpiece W, the reflected light form caused by the structure of the workpiece W, and other factors. Therefore, the sample workpiece is not limited to being made of the same material as the substrate of the workpiece W and having no film formed thereon, as in this embodiment.

[0068] For example, when the workpiece W has a structure in which a polysilicon film is formed between a silicon substrate and a thermal oxide film, since the refractive indices of silicon and polysilicon are sufficiently close, the sample workpiece can use a silicon substrate or a silicon substrate with a polysilicon film formed thereon.

[0069] In addition, when the workpiece W is a structure in which a titanium layer of about 100 nm is formed between the silicon substrate and the thermal oxide film, since light can hardly pass through the titanium film to the silicon substrate side, if the sample workpiece adopts a structure in which the titanium film is formed on the upper surface, the material of the substrate is not limited to silicon, and materials such as glass can also be used.

[0070] In addition, for example, when the refractive indexes of the substrate and the polished layer formed on the substrate are similar, such as in the case of a workpiece W having a silicon dioxide film formed on a sapphire substrate, the sample workpiece may be a substrate without a film formed thereon or a substrate with a polished layer formed thereon.

[0071] (CMP polishing)

[0072] Next, the controller 7 activates the CMP apparatus 1 and begins CMP polishing the sample workpiece W, thereby flattening the thermal oxide film formed on one side of the sample workpiece W mounted on the bottom surface of the polishing head 10 (step S2). The CMP polishing of the sample workpiece W is performed while the CMP slurry is supplied to the polishing pad 5, while the platen 2 and the polishing head 10 are rotating, and the silicon dioxide film on the sample workpiece W contacts the polishing pad 5.

[0073] (Spectral waveform generation)

[0074] Next, during the grinding process of the workpiece W, the light source unit 76 irradiates the measuring light, and the spectrometer 77 generates a spectroscopic waveform based on the reflected light from the workpiece W (step S3 ).

[0075] Figure 5The spectral waveform shown is a graph in which the horizontal axis is the number of data (equivalent to the wavelength of the reflected light, hereinafter referred to as "wavelength"), and the vertical axis is the reflectivity. The reflectivity is calculated by dividing the intensity of the reflected light from the workpiece W by the reference intensity of the sample workpiece calculated in step S1. Figure 5 (a) shows the spectral waveform when the thermal oxide film thickness is 1.5μm. Figure 5 (b) shows the spectral waveform when the thermal oxide film thickness is 1.0 μm. Figure 5 (c) shows the spectral waveform when the thermal oxide film thickness is 0.6μm. Figure 5 (d) shows the spectral waveform when the thickness of the thermal oxide film is 0.2 μm.

[0076] (Film thickness calculation)

[0077] Next, the detection unit 72 calculates the film thickness of the thermal oxide film on the workpiece W being ground at predetermined intervals (step S4 ).

[0078] Specifically, the detection unit 72 calculates the film thickness of the thermal oxide film during the polishing process by performing Fourier analysis on the spectral waveform generated by the spectrometer 77. Figure 5 The spectral waveforms shown in (a) to (d) are frequency spectra obtained by Fourier analysis to show the relationship between the film thickness of the thermal oxide film and the intensity of the frequency component. Figure 6 As shown in (a) to (d), the trend of continuous change of the thickness of the thermal oxide film decreases as the polishing process progresses. Figure 7 In addition, Figure 8 This is a graph showing the trend of thermal oxide film thickness change. Figure 7 The graph is obtained by curve fitting the theoretical waveform based on the optimization method when the film thickness is less than 1.0μm.

[0079] Next, the detection unit 72 determines whether the thickness of the thermal oxide film of the workpiece W during the grinding process calculated in step S4 has reached a predetermined threshold value (step S5 ).

[0080] Specifically, when a signal peak in the frequency spectrum of the thermal oxide film thickness exceeds a predetermined threshold, the detection unit 72 estimates the thermal oxide film thickness corresponding to the signal peak as the thermal oxide film thickness on the workpiece W during the grinding process. Furthermore, to facilitate film thickness detection, the detection unit 72 may also supplementarily estimate the film thickness of the workpiece W during the grinding process based on a changing trend of the thermal oxide film thickness.

[0081] When the film thickness of the thermal oxide film on the workpiece W during the grinding process is smaller than the predetermined threshold value (No in step S5 ), the process returns to step S4 , and the detection unit 72 recalculates the film thickness of the thermal oxide film on the workpiece W during the grinding process.

[0082] (Grinding endpoint detection)

[0083] When the thickness of the thermal oxide film in the workpiece W during the grinding process reaches a predetermined threshold (step S5 is yes), the detection unit 72 determines that the thickness of the thermal oxide film has reached the target thickness and reached the grinding end point, and outputs a stop signal of the CMP device 1 to the controller 7, ending the CMP grinding of the workpiece W (step S6).

[0084] Furthermore, this embodiment describes a case where the refractive index difference between the substrate (silicon substrate) of the workpiece W and the layer being polished (thermally oxidized film) is relatively large. However, this embodiment is also applicable when the refractive index difference between the substrate (silicon substrate) and the layer being polished is relatively small. The following description uses the case of polishing a sapphire substrate with a thermally oxidized film (a modified example) as an example. Furthermore, at a wavelength of 632.8 nm, the refractive indices of the thermally oxidized film, the silicon substrate, and the sapphire substrate are 1.457, 3.882, and 1.770, respectively.

[0085] In this modification, a sapphire substrate without a thermal oxide film is used for the sample workpiece, while a sapphire substrate with a thermal oxide film is used for the workpiece W. In addition, in this modification, except for the above-mentioned points, the reference measurement conditions for calculating the reference strength and the polishing conditions of the workpiece W are set to be the same as those in the above-mentioned embodiment.

[0086] Figure 9 (a) shows the spectroscopic waveform according to this modification, Figure 9 (b) shows the spectral waveform according to the above embodiment. Figure 9 As can be seen from (a) and (b), the spectral waveform corresponding to the workpiece W with a relatively small reflectivity difference between the substrate and the thermal oxidation film has a smaller reflectivity amplitude than that of the workpiece W with a relatively large reflectivity difference between the substrate and the thermal oxidation film.

[0087] In addition, Figure 10 The frequency spectra obtained by Fourier analysis of the spectral waveforms shown in (a) to (b) are as follows: Figure 9 As shown in (a) to (b). Figure 9As can be seen from (a) to (b), the frequency spectrum corresponding to the workpiece W having a relatively small difference in reflectivity between the substrate and the thermal oxide film contains more noise than the frequency spectrum corresponding to the workpiece W having a relatively large difference in reflectivity between the substrate and the thermal oxide film, or the width of the signal peak is also wider, so there is a tendency for analysis to become difficult. When there is a tilt in the vibration center of the reflectivity of the spectral waveform, this tendency is more pronounced for the workpiece W with a smaller refractive index difference between the substrate and the thermal oxide film. Therefore, as shown in Comparative Example 1, when the refractive index difference between the substrate and the thermal oxide film is small and the film thickness calculation is greatly affected by external interference, the reference intensity is calculated by using a sample workpiece having the same refractive index characteristics as the workpiece W, and the tilt of the vibration center of the reflectivity of the spectral waveform is eliminated, as shown in Comparative Example 1. Figure 11 As shown in FIG, a graph showing the trend of change in the thickness of the thermal oxide film which decreases as the polishing progresses can be accurately obtained. Figure 11 For film thickness up to 1.5μm, only Fourier analysis is applied. For film thickness below 1.5μm, an optimization algorithm is added based on Fourier analysis.

[0088] Next, the characteristics of each of the steps of the reference measurement (step S1 ), the spectral waveform generation (step S3 ), and the film thickness calculation (step S4 ) will be described in detail by comparison with various comparative examples.

[0089] <Influence of sample workpiece reflectivity characteristics on film thickness calculation>

[0090] As shown in the above embodiment, when obtaining the spectral waveform related to the reflected light of a silicon substrate formed with a thermal oxide film, the spectral waveform, frequency spectrum and film thickness analysis results are compared for two cases: one in which the reference intensity is calculated using a silicon substrate as a sample workpiece and the other in which the reference intensity is calculated using a lens (Comparison Example 1).

[0091] In Comparative Example 1, a lens was used in place of the sample workpiece. The non-rotating lens was positioned above the observation window 80 of the CMP apparatus 1. Measurement light was directed from below the non-rotating platen 2 through the observation window 80 toward the lens. Based on the light reflected from the lens, the spectrometer 77 calculated the reference intensity of the lens. Furthermore, during the reference measurement, no CMP slurry was supplied to the polishing pad 5. In Comparative Example 1, except for the above, the reference measurement conditions for calculating the reference intensity and the polishing conditions of the workpiece W (a silicon substrate with a thermally oxidized film formed thereon) were identical to those of the aforementioned embodiment.

[0092] Figure 12 The horizontal axis represents the wavelength of the light reflected from the workpiece W, and the vertical axis represents the reflectivity obtained by dividing the intensity of the light reflected from the workpiece W by a reference intensity calculated based on the reflected light from the mirror surface. Figure 12 (a) shows the spectral waveform when the thickness of the thermal oxide film is 1.5 μm. Figure 12 (b) shows the spectral waveform when the thickness of the thermal oxide film is 1.0 μm. Figure 12 (c) shows the spectral waveform when the thickness of the thermal oxide film is 0.8 μm. Figure 12 (d) shows the spectral waveform when the thickness of the thermal oxide film is 0.6 μm. Figure 12 As can be seen from (a) to (d), a specific peak exists near a wavelength of approximately 100 nm, and the center of the spectral waveform exhibits a tilted state, with the reflectivity decreasing as the wavelength increases. This is likely due to the fact that the reference intensity calculated using the lens is affected by factors such as the reflectivity characteristics of the workpiece W material, the waviness of the workpiece W, vibration caused by the rotation of the polishing pad 5, uneven film thickness on the observation window 80, and the presence or absence of CMP slurry.

[0093] also, Figure 13 (a) to (d) represent the frequency spectrum, which represents Figure 12 The spectral waveforms shown in (a) to (d) are the relationships between the film thickness of the thermal oxide film and the intensity of the frequency component obtained by applying Fourier analysis. Figure 13 As shown in Figures (a) to (d), at film thicknesses of 1.5μm and 1.0μm, a more pronounced peak appears on the thin film side (around 0.5μm thick), compared to the peak corresponding to film thickness. Meanwhile, at film thicknesses of 0.8μm and 0.6μm, the peak corresponding to film thickness merges with the pronounced peak on the thin film side, increasing the peak width. These phenomena are believed to be due to differences in the reflectivity characteristics of the sample workpiece and workpiece W.

[0094] also, Figure 14 A graph showing the trend of the thickness of the thermal oxide film decreasing as polishing progresses. Figure 14 It is known that the film thickness cannot be stably measured below about 1μm. Figure 15 It is aimed at Figure 14 The frequency spectrum shown is a graph showing the thickness variation trend of the thermal oxide film obtained by applying the optimization method and curve fitting the theoretical waveform when the film thickness is less than 1.5μm. Figure 15 It is clear that the film thickness cannot be stably measured below approximately 0.5 μm. This is believed to be due to the presence of a signal peak near the film thickness of 0.5 μm as shown in the frequency spectrum above.

[0095] On the other hand, in this embodiment, according to Figure 5 As can be seen from (a) to (d), the spectral waveform does not contain any special peaks, and the vibration center of the spectral waveform (reflectivity of about 0.9) is approximately flat. Figure 6 From (a) to (d), we can see that there is only one significant signal peak corresponding to the film thickness in the frequency spectrum. Figure 7 It can be seen that the thickness of the thermal oxide film decreases with the progress of polishing, and the thickness can be stably measured up to about 0.5μm. Figure 8 It can be seen that the variation trend of the film thickness of the thermal oxide film is regular, and the film thickness up to about 0.11 μm can be measured.

[0096] <The influence of abrasives contained in slurry on film thickness calculation>

[0097] The results of spectral waveforms, frequency spectra, and film thickness analysis were compared between the cases of using CMP slurry as a polishing medium and using ultrapure water (DIW) containing no abrasive as a polishing medium (Comparative Example 2).

[0098] In Comparative Example 2, a silicon substrate was used as a sample workpiece. Ultrapure water was supplied while the stationary (non-rotating) sample workpiece was brought into contact with the stationary (non-rotating) polishing pad 5, and the baseline strength of the sample workpiece was measured. In Comparative Example 2, except for the above-mentioned points, the reference measurement conditions used to calculate the baseline strength and the polishing conditions of the workpiece W were the same as those in the above-mentioned embodiment.

[0099] Figure 16 (a) shows the spectral waveform of Comparative Example 2. Figure 16 (b) shows the spectroscopic waveform according to the above embodiment. Figure 16 (a) shows that the vibration center of the reflectivity is independent of the wavelength and is stable near the reflectivity of 1. On the other hand, according to Figure 16 As can be seen in (b), the reflectivity vibration center shows an inclination, with the reflectivity increasing as the wavelength increases. This inclination is believed to be caused by the inclusion of abrasives in the slurry. Although it is only about 0.05 over the entire wavelength range, it inevitably affects the film thickness calculation in workpieces W with a relatively small reflectivity difference between the substrate and the polished layer, such as in Comparative Example 1.

[0100] also, Figure 17 (a) and (b) are obtained by Figure 16 The frequency spectrum obtained by Fourier analysis of the spectral waveforms shown in (a) and (b). Figure 18 It is through Figure 17 The frequency spectrum shown in (a) is the frequency spectrum obtained by Fourier analysis. Figure 17 (a) and (b) are different from other frequency spectra described in this manual in that their vertical axes are not normalized by the maximum signal peak. Figure 17 (a) and (b), Figure 17The presence of a specific signal peak near a film thickness of approximately 0.5 μm in (b) is believed to interfere with film thickness calculation. Therefore, using an abrasive-free slurry for benchmark strength measurement and an abrasive-containing slurry for polishing will inevitably affect film thickness calculation. Therefore, even when measuring benchmark strength, it is preferable to use the same abrasive-containing slurry used for polishing.

[0101] <Regarding the influence of platen rotation on film thickness calculation>

[0102] As in the above embodiment, the spectral waveforms averaged 30 times were compared between the cases where the press plate 2 was rotated during the reference measurement and the case where the press plate 2 was not rotated during the reference measurement (Comparative Example 3).

[0103] In Comparative Example 3, a silicon substrate was used as a sample workpiece. While CMP slurry was being supplied, the rotating sample workpiece was brought into contact with a stationary (non-rotating) polishing pad 5, and the baseline strength of the sample workpiece was measured. In Comparative Example 3, except for the above-mentioned points, the reference measurement conditions for calculating the baseline strength and the polishing conditions of the workpiece W were the same as those in the above-mentioned embodiment.

[0104] Figure 18 (a) shows the spectroscopic waveform according to Comparative Example 3, Figure 18 (b) shows the spectroscopic waveform according to the above embodiment. Figure 18 (a) shows that the vibration center of the reflectivity remains stable near the reflectivity of 0.995. Figure 18 As shown in (b), the center of vibration of the reflectivity is located near a reflectivity of 0.96, and below a wavelength of 400 nm, the reflectivity exhibits an inclination, increasing as the frequency decreases. This inclination is believed to be caused by the approximately 3 mm diameter of the measurement light spot, while the inner diameter of the observation window 80 is approximately 2.5 mm. Therefore, when the polishing pad 5 is stationary, both the measurement light and the reflected light pass through a circle with a diameter of 2.5 mm corresponding to the observation window 80. In contrast, when the polishing pad 5 rotates, when the rotation radius of the observation window 80 is 165 mm and the exposure time of the light source unit 76 is 5 milliseconds, the observation window 80 also rotates integrally with the polishing pad 5, moving approximately 5.2 mm in the circumferential direction. This is believed to be due to the fact that the measurement light and reflected light pass through a range approximately 4.3 times wider than that in Comparative Example 3. Furthermore, the inclination of the center of vibration of the reflectivity in the low-wavelength region is believed to be caused by the difference in slurry thickness on the rotating polishing pad 5 compared to the stationary polishing pad 5.

[0105] The polishing endpoint detection device 70 according to the present embodiment is constructed as follows. The polishing endpoint detection device 70 detects the polishing endpoint when the workpiece W is brought into contact with the polishing pad 5 and the thermal oxide film of the workpiece W is subjected to CMP polishing. The polishing endpoint detection device 70 includes: a measuring unit 71, which irradiates the workpiece W with measuring light during the polishing process of the workpiece W, and spectrally separates the reflected light from the workpiece W to obtain a spectral waveform indicating the relationship between the wavelength and reflectivity of the reflected light. The rate is the ratio of the intensity of the reflected light to the reference intensity of each wavelength component obtained in advance; and a detection unit 72, which applies Fourier analysis to the spectral waveform to calculate the film thickness of the thermal oxide film, and the reference intensity is calculated in the following manner: in a state where CMP slurry is inserted between the rotating polishing pad 5 and the sample workpiece, a sample workpiece having a reflectivity characteristic substantially the same as that of the substrate of the workpiece W is brought into contact with the polishing pad 5, and the measuring unit 71 irradiates the sample workpiece with measuring light through the observation window 80 of the polishing pad 5, and spectrally separates the reflected light from the sample workpiece.

[0106] Through this structure, a sample workpiece having approximately the same reflectivity as the workpiece W is used, and the reference measurement conditions such as the presence or absence of abrasive contained in the slurry that may affect the calculation of the film thickness, the rotation or stillness of the pressure plate 2, etc. are unified with the grinding conditions when grinding the workpiece W, and then the baseline strength of the sample workpiece is calculated, thereby accurately detecting the film thickness of the thin workpiece W.

[0107] Furthermore, the CMP apparatus 1 according to this embodiment is configured to include a polishing end point detection device 70 .

[0108] With this configuration, the grinding end point of the thin workpiece W can be detected with high accuracy.

[0109] Furthermore, the configuration is as follows: the grinding endpoint detection method according to the above-mentioned present embodiment is a grinding endpoint detection method that detects the grinding endpoint when the workpiece W is brought into contact with the grinding pad 5 and the thermal oxide film of the workpiece W is subjected to CMP grinding, wherein the grinding endpoint detection method has the following steps: during the grinding of the workpiece W, irradiating the workpiece W with measuring light, and spectroscopically analyzing the reflected light from the workpiece W to obtain a spectral waveform representing the relationship between the wavelength and reflectivity of the reflected light, wherein the reflectivity is the ratio of the intensity of the reflected light to the reference intensity of each wavelength component obtained in advance; and applying Fourier analysis to the spectral waveform to calculate the film thickness of the thermal oxide film, wherein the reference intensity is calculated in the following manner: in a state where slurry is interposed between the rotating grinding pad and the sample workpiece, bringing the sample workpiece grinding pad 5 having substantially the same reflectivity characteristics as the workpiece W into contact, irradiating the sample workpiece with measuring light through the observation window 80 of the grinding pad 5, and spectroscopically analyzing the reflected light from the sample workpiece.

[0110] Through this structure, a sample workpiece having approximately the same reflectivity as the workpiece W is used, and the reference measurement conditions such as the presence or absence of abrasive contained in the slurry that may affect the calculation of the film thickness, and the rotation or stillness of the pressure plate 2 are unified with the grinding conditions when grinding the workpiece W, and then the baseline strength of the sample workpiece is calculated, thereby accurately detecting the film thickness of the thin workpiece W.

[0111] Furthermore, the present invention can be modified in various ways without departing from the spirit of the present invention, and the present invention is of course also applicable to the modified versions.

[0112] In the embodiment described above, the thickness of the polishing layer is calculated by applying Fourier analysis to the spectral waveform. However, this is not limiting. For example, a fast Fourier transform (FFT) or curve fitting to a theoretical waveform may also be applied. When curve fitting to a theoretical waveform is applied, a theoretical waveform of the spectral waveform must be prepared in advance through experiments, etc., and then the theoretical waveform that best matches the spectral waveform obtained by the measuring unit 71 is determined and converted into the thickness of the polishing layer.

[0113] Furthermore, the present invention is also applicable to workpieces W made of materials other than those exemplified in the present embodiment, such as workpieces W made of silicon carbide (silicon carbide: SiC) or gallium nitride (GaN). Sample workpieces corresponding to these materials should use materials having substantially the same reflectivity characteristics as these workpieces W.

[0114] [Explanation of Symbols]

[0115] 1...CMP device

[0116] 2...pressure plate

[0117] 3...Rotation axis

[0118] 4...Motor

[0119] 5. Abrasive pad

[0120] 6...Nozzle

[0121] 7...Controller

[0122] 10...Grinding head

[0123] 10a...rotation axis

[0124] 20...head body

[0125] 21...rotating part

[0126] 30...Carrier

[0127] 30a…Bottom

[0128] 31...air line

[0129] 32...Carrier pressing mechanism

[0130] 40...Retaining ring

[0131] 41...Retaining ring retainer

[0132] 41a……Storage pocket (storage section)

[0133] 42... snap ring

[0134] 43...Retainer pressing part

[0135] 44...Retainer pressing mechanism

[0136] 50...diaphragm

[0137] 60... Backing film

[0138] 70...Grinding endpoint detection device

[0139] 71……Measurement Department

[0140] 72……Detection Department

[0141] 73...Lens

[0142] 74, 75... optical fiber

[0143] 76... Light source unit

[0144] 77...Spectrum Splitter

[0145] 80...Observation window

[0146] A...air chamber

[0147] W...workpiece.

Claims

1. A polishing endpoint detection device for detecting a polishing endpoint when a workpiece is brought into contact with a polishing pad and a polishing layer of the workpiece is subjected to CMP polishing, wherein: The above-mentioned grinding endpoint detection device has: a measuring unit that irradiates the workpiece with measuring light during the polishing process and spectrally separates the reflected light from the workpiece to obtain a spectral waveform representing a relationship between a wavelength of the reflected light and a reflectivity, the reflectivity being a ratio of an intensity of the reflected light to a previously obtained reference intensity of each wavelength component; as well as a detection unit that calculates the thickness of the layer to be polished based on the spectral waveform; The above-mentioned reference intensity is calculated in the following manner: while slurry is interposed between the rotating polishing pad and the sample workpiece, a sample workpiece having reflectivity characteristics substantially the same as those of the above-mentioned workpiece is brought into contact with the above-mentioned polishing pad, the above-mentioned measuring unit irradiates the above-mentioned sample workpiece with measuring light through the observation window of the above-mentioned polishing pad, and splits the reflected light from the above-mentioned sample workpiece.

2. The grinding endpoint detection device according to claim 1, characterized in that: The detection unit calculates the film thickness of the layer to be polished by applying Fourier analysis to the spectral waveform.

3. The grinding endpoint detection device according to claim 1, wherein: The detection unit calculates the thickness of the layer to be polished by applying curve fitting to the spectral waveform with respect to a theoretical waveform of the spectral waveform.

4. A CMP device, characterized in that: This CMP apparatus comprises the polishing endpoint detection device according to any one of claims 1 to 3.

5. A polishing endpoint detection method for detecting a polishing endpoint when a workpiece is brought into contact with a polishing pad and a polishing layer of the workpiece is subjected to CMP polishing, wherein: The above-mentioned grinding endpoint detection method has the following steps: During the polishing process of the workpiece, a step of irradiating the workpiece with measuring light and spectroscopically analyzing reflected light from the workpiece to obtain a spectroscopic waveform representing a relationship between a wavelength of the reflected light and a reflectivity, the reflectivity being a ratio of an intensity of the reflected light to a previously obtained reference intensity of each wavelength component; and the step of calculating the film thickness of the polishing layer based on the spectral waveform; The reference intensity is calculated by placing a sample workpiece having substantially the same reflectivity characteristics as the workpiece in contact with the polishing pad while slurry is interposed between the rotating polishing pad and the sample workpiece, irradiating the sample workpiece with measuring light through the observation window of the polishing pad, and performing spectroscopic analysis on the reflected light from the sample workpiece.

Images