Temperature measurement system and temperature measurement method

Abstract

The present disclosure relates to a temperature measurement system and a temperature measurement method. The system measures the temperature of an object to be measured having a first main surface and a second main surface facing the first main surface, and comprises: a light source unit that generates output light, the output light including first and second wavelength ranges, the output light transmitting through the object to be measured; a measurement unit that measures the spectra of reflected light from the first and second main surfaces; an optical path ratio calculation unit that calculates an optical path ratio by Fourier transforming the spectra, the optical path ratio being the ratio of the optical path of the output light in the first wavelength range to the optical path of the output light in the second wavelength range; and a temperature calculation unit that calculates the temperature of the object to be measured based on the relationship between the optical path ratio and a previously acquired refractive index ratio, the refractive index ratio being the refractive index of the output light in the first wavelength range to the refractive index of the output light in the second wavelength range, and the temperature of the object to be measured.

Description

Technical Field

[0001] Embodiments of the present disclosure relate to a temperature measurement system and a temperature measurement method. Background Art

[0002] Patent Document 1 describes a temperature measurement system that uses optical interference to measure the temperature of an object. The system includes a light source, an optical circulator, a collimator, a spectrometer, an optical path calculation unit, and a temperature calculation unit. Measurement light from the light source is reflected by the two end faces of the object, passing through the collimator and the optical circulator before reaching the spectrometer. The spectrometer measures the intensity distribution of the reflected light, or the interference intensity distribution. The optical path calculation unit performs a Fourier transform on the interference intensity distribution to calculate the optical path corresponding to the thickness of the object. The temperature calculation unit calculates the temperature of the object based on temperature correction data that represents the relationship between temperature and optical path, pre-measured for each object.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2012-109472 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] The present disclosure provides a temperature measurement system and a temperature measurement method capable of measuring the temperature of a measurement object with high accuracy.

[0008] Solutions for solving problems

[0009] A temperature measurement system according to one embodiment of the present invention is used to measure the temperature of a measurement object having a first main surface and a second main surface opposite to the first main surface, the temperature measurement system comprising: a light source unit for generating output light, the output light including a first wavelength range and a second wavelength range different from the first wavelength range, the output light passing through the measurement object; at least one optical element for emitting the output light from the light source unit toward the first main surface of the measurement object, and reflected light from the first main surface and the second main surface is incident on the at least one optical element; a measuring unit connected to the at least one optical element for measuring the wavelength-dependent temperature from the measurement object. a spectrum of reflected light from the first main surface and the second main surface; an optical path ratio calculation unit, which calculates the optical path ratio by performing Fourier transform on the spectrum measured by the measurement unit, wherein the optical path ratio is the ratio of the optical path of the output light with respect to the first wavelength range, i.e., the first optical path, to the optical path of the output light with respect to the second wavelength range, i.e., the second optical path; and a temperature calculation unit, which calculates the temperature of the measurement object based on the relationship between the optical path ratio and a pre-acquired refractive index ratio, which is the ratio of the refractive index of the output light with respect to the first wavelength range at the measurement object, i.e., the first refractive index, to the refractive index of the output light with respect to the second wavelength range at the measurement object, i.e., the second refractive index.

[0010] Effects of the Invention

[0011] According to the present disclosure, it is possible to provide a temperature measurement system and a temperature measurement method capable of measuring the temperature of a measurement object with high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a diagram schematically showing a temperature measurement system according to one embodiment.

[0013] Figure 2 This is a functional block diagram of the optical splitter and computing device.

[0014] Figure 3 This is a schematic diagram illustrating the incident light spectrum and the reflected light spectrum.

[0015] Figure 4 This is a schematic diagram illustrating the Fourier transform of the reflected light spectrum.

[0016] Figure 5 This is an example of temperature correction data showing the relationship between the refractive index ratio and the temperature of the measurement object.

[0017] Figure 6 This is a flowchart illustrating a temperature measurement method according to one embodiment.

[0018] Figure 7Graphs illustrating a temperature measurement method according to one embodiment. (a) shows a light source spectrum indicating the intensity distribution as a function of wavelength. (b) shows a reflected light spectrum indicating the intensity distribution as a function of wavelength. (c) shows a reflected light spectrum indicating the intensity distribution as a function of the inverse of wavelength.

[0019] Figure 8 These graphs illustrate a temperature measurement method according to one embodiment. (a) is a linearly interpolated spectrum of a reflected light spectrum showing an intensity distribution dependent on the inverse of wavelength. (b) is a fast Fourier transformed spectrum of the reflected light spectrum in (a). (c) is a partially enlarged view of (b).

[0020] Figure 9 This is an example of a substrate processing apparatus according to an embodiment.

[0021] Figure 10 This is a diagram schematically showing a temperature measurement system according to a modification.

[0022] Figure 11 This is a diagram schematically showing a temperature measurement system according to a modification.

[0023] Figure 12 This is a diagram schematically showing a temperature measurement system according to a modification.

[0024] Figure 13 This is a diagram schematically showing a temperature measurement system according to a modification.

[0025] Description of Reference Numerals

[0026] 1: Temperature measurement system; 5: Measurement object; 5a: First main surface; 5b: Second main surface; 10: Light source unit; 11: First light source; 12: Second light source; 20: Combiner; 25: Optical circulator; 27: Optical switch; 30: Optical element; 40: Measurement unit; 41: Wave splitter; 42: First spectrometer; 44: Second spectrometer; 50: Operation unit; 51: Optical path ratio calculation unit; 55: Temperature calculation unit; 56: Temperature correction data; 141, 141a, 141b: Light dispersion element; 142, 142a, 142b: Light receiving unit; 300: Substrate processing device; 310: Processing chamber. DETAILED DESCRIPTION

[0027] Various exemplary embodiments are described below.

[0028] In the method described in Patent Document 1, if the thickness of the object being measured decreases due to wear, for example, the optical path length corresponding to the thickness of the object being measured becomes shorter, and thus the temperature calculation unit cannot accurately calculate the temperature of the object being measured. Therefore, there is a need for a temperature measurement system and temperature measurement method that can accurately measure the temperature of the object being measured.

[0029] The present disclosure provides a temperature measurement system and a temperature measurement method capable of measuring the temperature of a measurement object with high accuracy.

[0030] A temperature measurement system according to one embodiment of the present invention is used to measure the temperature of a measurement object having a first main surface and a second main surface opposite to the first main surface, the temperature measurement system comprising: a light source unit for generating output light, the output light including a first wavelength range and a second wavelength range different from the first wavelength range, the output light passing through the measurement object; at least one optical element for emitting the output light from the light source unit toward the first main surface of the measurement object, and for causing reflected light from the first main surface and the second main surface to enter the at least one optical element; a measuring unit connected to the at least one optical element for measuring the wavelength-dependent temperature of the first main surface. a spectrum of reflected light from the main surface and the second main surface; an optical path ratio calculation unit that calculates the optical path ratio by performing Fourier transform on the spectrum measured by the measurement unit, wherein the optical path ratio is the ratio of the optical path of the output light with respect to the first wavelength range, i.e., the first optical path, to the optical path of the output light with respect to the second wavelength range, i.e., the second optical path; and a temperature calculation unit that calculates the temperature of the measurement object based on the relationship between the optical path ratio and a pre-acquired refractive index ratio, and the temperature of the measurement object, wherein the refractive index ratio is the ratio of the refractive index of the output light with respect to the first wavelength range at the measurement object, i.e., the first refractive index, to the refractive index of the output light with respect to the second wavelength range at the measurement object, i.e., the second refractive index.

[0031] According to this temperature measurement system, the optical path ratio is calculated based on the first optical path of the output light with respect to the first wavelength range and the second optical path of the output light with respect to the second wavelength range. The optical path of the output light is represented by the product of the refractive index of the measured object with respect to the output light and the thickness of the measured object. The thickness of the measured object depends on a reference value determined by the physical properties (Japanese: physical properties) of the measured object and a rate of change relative to the reference value caused by temperature, and does not depend on the wavelength of the output light. When calculating the ratio of the first optical path to the second optical path, i.e., the optical path ratio, the terms of the reference value and the rate of change included in the first optical path and the second optical path are eliminated. Therefore, the optical path ratio of the first optical path to the second optical path is represented by the refractive index ratio, i.e., the ratio of the refractive index of the output light with respect to the first wavelength range in the measured object to the refractive index of the output light with respect to the second wavelength range. The refractive index depends on the wavelength range of the output light and the temperature of the measured object. The relationship between the refractive index ratio and the temperature is obtained in advance. The relationship between the refractive index ratio and the temperature obtained in advance represents the relationship between the optical path ratio and the temperature. The temperature measurement system can calculate the temperature of the object being measured based on the relationship between the refractive index ratio and temperature and the calculated optical path ratio. In this temperature measurement system, even if the thickness of the object being measured decreases due to wear and tear, the change in thickness will not affect the optical path ratio. Therefore, the temperature calculation unit can calculate the temperature of the object being measured with high accuracy. In addition, if the relationship between the optical path ratio and temperature is known, the temperature measurement system does not need to calibrate the relationship between the temperature and the optical path at that temperature for each object being measured before temperature measurement, as is conventionally done. As a result, the temperature measurement system can simplify the measurement process compared to a system that calibrates the relationship between the temperature and the optical path at that temperature for each object being measured.

[0032] In one embodiment, the light source unit may include a first light source that emits light in a first wavelength range, a second light source that emits light in a second wavelength range, and a combiner that transmits output light obtained by combining the light in the first wavelength range and the light in the second wavelength range. In this case, the temperature measurement system can allocate a light source for each wavelength range to be measured in the output light.

[0033] In one embodiment, the measurement unit may include a first spectrometer for measuring the spectrum of first reflected light, which is light reflected from the first and second main surfaces by output light in a first wavelength range; and a second spectrometer for measuring the spectrum of second reflected light, which is light reflected from the first and second main surfaces by output light in a second wavelength range. In this case, the first spectrometer can narrow the distribution measurement range to a wavelength range suitable for measuring the first reflected light, and the second spectrometer can narrow the distribution measurement range to a wavelength range suitable for measuring the second reflected light. Therefore, the temperature measurement system can improve the resolution of each of the first and second spectrometers, enabling high-precision spectrum measurement.

[0034] In one embodiment, at least one optical element may include a plurality of optical elements. In this case, the temperature measurement system includes a plurality of optical elements, thereby enabling multi-point measurement.

[0035] In one embodiment, the object to be measured may be composed of silicon, with the first wavelength range being between 1200 nm and 1300 nm, and the second wavelength range being between 1500 nm and 1600 nm. In this case, the temperature measurement system can suppress silicon's absorption of the output light in the first and second wavelength ranges. Furthermore, if the object to be measured, which is part of the chamber's internal components, is made of a material that does not attenuate the measurement light, it is not limited to silicon and may also be made of quartz, sapphire, silicon carbide, and the like.

[0036] In one embodiment, at least one optical element may be provided in a substrate processing apparatus that accommodates a measurement target object, and the measurement target object may be at least one of a substrate, a focus ring, and an upper electrode. In this case, the temperature measurement system can measure the temperature of at least one of the substrate, the focus ring, and the upper electrode with high precision.

[0037] Another embodiment of the present disclosure relates to a temperature measurement method for measuring the temperature of an object to be measured having a first main surface and a second main surface opposite the first main surface. The temperature measurement method includes the following steps: irradiating the object with output light, the output light including a first wavelength range and a second wavelength range different from the first wavelength range, the output light transmitting through the object to be measured; measuring spectra of light reflected from the first and second main surfaces of the object to be measured; calculating an optical path ratio by Fourier transforming the spectra, the optical path ratio being the ratio of a first optical path length of the output light in the first wavelength range to a second optical path length of the output light in the second wavelength range; and calculating the temperature of the object to be measured based on the relationship between the optical path ratio and a previously acquired refractive index ratio, the refractive index ratio being the ratio of a first refractive index of the output light in the first wavelength range to a second refractive index of the output light in the second wavelength range, and the temperature of the object to be measured.

[0038] According to this temperature measurement method, the optical path ratio is calculated based on a first optical path of output light within a first wavelength range and a second optical path of output light within a second wavelength range. The optical path ratio of the output light is the product of the refractive index of the object being measured with respect to the output light and the thickness of the object being measured. The thickness of the object being measured depends on a reference value determined by the physical properties of the object being measured and a temperature-dependent rate of change relative to the reference value, and is independent of the wavelength of the output light. When calculating the optical path ratio, i.e., the ratio of the first optical path to the second optical path, the reference value and rate of change terms included in the first and second optical paths are eliminated. Therefore, the optical path ratio of the first optical path to the second optical path is represented by the refractive index ratio, i.e., the ratio of the refractive index of the output light within the first wavelength range at the object being measured to the refractive index of the output light within the second wavelength range. The refractive index depends on the wavelength range of the output light and the temperature of the object being measured. The relationship between the refractive index ratio and temperature is acquired in advance. The acquired relationship between the refractive index ratio and temperature represents the relationship between the optical path ratio and temperature. About the temperature measurement method, in the step of calculating temperature, the temperature of the object to be measured can be calculated based on the relationship between the refractive index ratio and the temperature and the calculated optical path ratio. In this temperature measurement method, even if, for example, the thickness of the object to be measured decreases due to consumption, the change in thickness will not affect the optical path ratio, and therefore, the temperature of the object to be measured can be calculated with high accuracy. In addition, if the relationship between the optical path ratio and the temperature is known, then this temperature measurement method does not need to correct the relationship between the temperature and the optical path at the temperature for each object to be measured before temperature measurement as in the past. Thus, compared to the situation where the relationship between the temperature and the optical path at the temperature is corrected for each object to be measured, this temperature measurement method can simplify the measurement process.

[0039] The following describes the embodiments in detail with reference to the accompanying drawings. In the following description and the drawings, identical or corresponding elements are denoted by the same reference numerals, and descriptions thereof will not be repeated. The dimensional ratios in the drawings are not necessarily the same as those in the description. The terms "upper," "lower," "left," and "right" are used for convenience, based on the conditions shown in the drawings.

[0040] Figure 1 This is a configuration diagram showing an example of a temperature measurement system according to one embodiment. Figure 1 The temperature measurement system 1 shown measures the temperature of an object 5. The temperature measurement system 1 utilizes optical interference to measure temperature. The temperature measurement system 1 includes a light source 10, an optical element 30 that emits light into space, a measurement unit 40, and a computing device 50. The temperature measurement system 1 may also include an optical circulator 25 and an optical switch 27. The light source 10, optical circulator 25, optical switch 27, optical element 30, and measurement unit 40 are connected using optical fiber cables.

[0041] The object 5 to be measured is, for example, in the shape of a plate and has a first main surface 5a and a second main surface 5b facing the first main surface 5a. Hereinafter, the first main surface 5a will be referred to as the front surface 5a, and the second main surface 5b will be referred to as the back surface 5b, as appropriate. The object 5 to be measured is, for example, made of at least one of Si (silicon), SiO2 (quartz), Al2O3 (sapphire), and SiC (silicon carbide).

[0042] The light source unit 10 generates output light including a first wavelength range and a second wavelength range different from the first wavelength range, and transmits the measurement target 5. The light source unit 10 includes, for example, a first light source 11, a second light source 12, and a combiner 20.

[0043] The first light source 11 generates light having a wavelength that transmits the measurement object 5. The first light source 11 generates light in a first wavelength range. The first wavelength range is, for example, 1200 nm to 1300 nm. For example, an SLD (Super Luminescent Diode) is used as the first light source 11.

[0044] The second light source 12 generates light having a wavelength that transmits the measurement object 5. The first light source 11 generates light in a second wavelength range, which is different from the first wavelength range. The second wavelength range is, for example, from 1500 nm to 1600 nm. For example, an SLD is used as the second light source 12.

[0045] The combiner 20 transmits output light obtained by combining the light in the first wavelength range output from the first light source 11 and the light in the second wavelength range output from the second light source 12. The combiner 20 outputs the combined output light to the optical circulator 25.

[0046] The optical circulator 25 is connected to the multiplexer 20, the optical switch 27, and the measuring unit 40. The optical circulator 25 propagates the output light generated by the multiplexer 20 to the optical element 30 via the optical switch 27.

[0047] The optical switch 27 is connected to the optical circulator 25 and the optical element 30. The optical switch 27 transmits the output light from the multiplexer 20 through the optical circulator 25 to the optical element 30. When a plurality of optical elements 30 are provided, the optical switch 27 transmits the multiplexed light to each optical element 30.

[0048] The optical element 30 emits output light toward the surface 5a of the object 5 to be measured. The optical element 30 emits output light adjusted to parallel light toward the object 5 to be measured. Furthermore, reflected light from the object 5 to be measured enters the optical element 30. The reflected light includes not only light reflected from the surface 5a but also light reflected from the back surface 5b. The optical element 30 propagates the reflected light toward the optical switch 27. The optical switch 27 propagates the reflected light toward the measuring unit 40 via the optical circulator 25. The temperature measurement system 1 includes at least one optical element 30. The temperature measurement system 1 may also include multiple optical elements 30. The optical element 30 is, for example, a collimator or a focuser.

[0049] The measuring unit 40 measures the spectrum of the reflected light obtained from the optical circulator 25. The reflected light spectrum indicates the intensity distribution depending on the wavelength or frequency of the reflected light. Figure 2 4 is a functional block diagram of the measuring unit 40 and the computing device 50. Figure 2 As shown, the measuring unit 40 includes, for example, a light dispersing element 141 and a light receiving unit 142. The light dispersing element 141 is, for example, a diffraction grating, and is an element that disperses light according to a predetermined dispersion angle according to wavelength. The light receiving unit 142 is used to obtain the light dispersed by the light dispersing element 141. As the light receiving unit 142, a CCD (Charge Coupled Device) is used in which a plurality of light receiving elements are arranged in a grid. The number of light receiving elements is the number of samples. In addition, the wavelength span is specified based on the dispersion angle of the light dispersing element 141 and the distance between the light dispersing element 141 and the light receiving element. As a result, the reflected light is dispersed according to wavelength or frequency, and the intensity of the reflected light is obtained according to wavelength or frequency. The measuring unit 40 outputs the reflected light spectrum to the computing device 50.

[0050] The measuring unit 40 may include a splitter 41, a first beam splitter 42, and a second beam splitter 44. The splitter 41 is connected to the optical circulator 25, the first beam splitter 42, and the second beam splitter 44. When the measuring unit 40 includes a plurality of beam splitters, the splitter 41 transmits the reflected light obtained from the optical circulator 25 to each beam splitter.

[0051] The first spectrometer 42 is used to measure the reflected light spectrum of the first reflected light, which is the light reflected from the front surface 5a and the back surface 5b by the output light in the first wavelength range. The first spectrometer 42 outputs the reflected light spectrum to the computing device 50. The second spectrometer 44 is used to measure the reflected light spectrum of the second reflected light, which is the light reflected from the front surface 5a and the back surface 5b by the output light in the second wavelength range. The second spectrometer 44 outputs the reflected light spectrum to the computing device 50. The first spectrometer 42 and the second spectrometer 44 have the same structure as the measuring unit 40. Specifically, the first spectrometer 42 includes, for example, a light dispersing element 141a and a light receiving unit 142a, and the second spectrometer 44 includes, for example, a light dispersing element 141b and a light receiving unit 142b.

[0052] The computing device 50 measures the temperature of the measurement object 5 based on the reflected light spectrum. The computing device 50 includes an optical path ratio calculation unit 51, a temperature calculation unit 55, and temperature correction data 56. The optical path ratio calculation unit 51 performs a Fourier transform on the reflected light spectrum by means of a fast Fourier transform (FFT). For example, if it is a Fourier transform in the time domain, the reflected light spectrum representing the intensity distribution that depends on the frequency (the number of vibrations per unit time) is transformed into a reflected light spectrum representing the intensity distribution that depends on time. In addition, for example, if it is a Fourier transform in the spatial domain, the reflected light spectrum representing the intensity distribution that depends on the spatial frequency (the number of vibrations per unit length) is transformed into a reflected light spectrum representing the intensity distribution that depends on the position. The optical path ratio calculation unit 51 interpolates the data points within a range including a specified peak value of the reflected light spectrum after the Fourier transform. The optical path ratio calculation unit 51 calculates the centroid position of the specified peak value of the reflected light spectrum after the Fourier transform.

[0053] The optical path ratio calculation unit 51 calculates the optical path ratio, which is the ratio of the optical path length of the output light in the first wavelength range, i.e., the first optical path length, to the optical path length of the output light in the second wavelength range, i.e., the second optical path length. First, the optical path ratio calculation unit 51 calculates the first optical path length and the second optical path length based on, for example, the center of gravity position. Next, the optical path ratio calculation unit 51 calculates the value obtained by dividing the first optical path length by the second optical path length as the optical path ratio.

[0054] The temperature calculation unit 55 calculates the temperature of the object 5 based on the optical path ratio and the relationship between the previously acquired refractive index ratio and the temperature of the object 5. The refractive index ratio is the ratio of the first refractive index, which is the refractive index of the object 5 for output light in the first wavelength range, to the second refractive index, which is the refractive index of the object 5 for output light in the second wavelength range. For example, the temperature calculation unit 55 uses the value obtained by dividing the first refractive index by the second refractive index as the refractive index ratio. The temperature correction data 56 includes the previously acquired relationship between the refractive index ratio and the temperature of the object 5. The temperature calculation unit 55 calculates the temperature of the object 5 based on the temperature correction data 56 and the optical path ratio.

[0055] The temperature measurement system 1 having the above-described structure measures the temperature by utilizing optical interference between the front surface 5a and the back surface 5b of the measurement object 5 (FFT frequency domain method). Figure 3 is a schematic diagram illustrating the incident light spectrum and the reflected light spectrum. Figure 3 In this example, the measurement light of wavelength λ from a certain light source is set as the incident light. The intensity S(k) of the incident light spectrum depends on the spatial frequency 1 / λ (the number of vibrations per unit length). The wave number k is 2π / λ. The thickness of the measured object 5 is set to d, the refractive index is set to n, and the reflectivity is set to R. The reflected light E is light with multiple reflection components superimposed. For example, E1 is the reflection component at the surface 5a. E2 is the reflection component at the back surface 5b. E3 is the reflection component reflected once on the surface 5a and twice on the back surface 5b. In addition, the reflection components after E4 are omitted. Multiple components are superimposed to obtain the intensity I(k) of the reflected light spectrum. The intensity I(k) of the reflected light spectrum and the intensity S(k) of the incident light spectrum have a relationship expressed by the following formula.

[0056]

Number 1

[0057] I(k)∝{2R(1-R)-2R(1-2R)cos(2nkd)-2R 2 cos(4nkd)}S(k)…(1)

[0058] In the above formula 1, the second term is the term of surface-back interference. The third term is the term of surface-back multiple interference. When formula 1 is Fourier transformed, a position-dependent reflected light spectrum can be obtained.

[0059] Figure 4 This is a schematic diagram illustrating the Fourier transform of the reflected light spectrum. Figure 4 As shown, the spatial frequency 1 / λ is transformed to position x by spatial Fourier transform. By Fourier transforming Equation 1, the intensity I(x) of the reflected light spectrum at position x is transformed as shown below.

[0060]

Number 2

[0061] I(x)=2R(1-R)·S(x)-R(1-2R)·{S(x+2nd)+S(x-2nd)}-R 2 {S(x+4nd)+S(x-4nd)}…(2)

[0062] As shown in Equation 2 above, a peak occurs every 2nd. 2nd is the optical path length difference between the reflected light from the front and the reflected light from the back. That is, nd is the optical path length between the front and back of the measurement object 5. While the spatial domain Fourier transform is used in the above description, the time domain Fourier transform can also be used.

[0063] Here, the optical path length nd is described in detail. The refractive index n of the measurement object 5 depends on the wavelength λ of the incident measurement light and the temperature T of the measurement object 5. Furthermore, the thickness d of the measurement object 5 depends on a reference value d0 determined by the physical properties of the measurement object 5 and a temperature-dependent rate of change α relative to the reference value, but is independent of the wavelength λ of the measurement light. Therefore, the optical path length nd is expressed as shown in the following equation 3.

[0064]

Number 3

[0065] nd=n(λ,T)·d0·α(T)...(3)

[0066] When the output light of wavelength λ1 from the first light source 11 (an example of the output light in the first wavelength range) is incident on the measurement object 5, the refractive index of the measurement object 5 is n1. The first optical path length n1d is expressed by the following formula 4.

[0067]

Number 4

[0068] n1d=n(λ1,T)·d0·α(T)...(4)

[0069] When the output light of wavelength λ2 from the second light source 12 (an example of the output light in the second wavelength range) is incident on the measurement object 5, the refractive index of the measurement object 5 is n2. The second optical path length n2d is expressed by the following formula 5.

[0070]

Number 5

[0071] n2d=n(λ2,T)·d0·α(T)…(5)

[0072] The optical path ratio calculation unit 51 calculates the optical path ratio, which is the ratio of the first optical path to the second optical path, using Equation 5 and Equation 6. The optical path ratio calculation unit 51 uses, for example, the following Equation 6.

[0073]

Number 6

[0074]

[0075] As described above, in the process of calculating the optical path ratio at the same temperature T, the term of the reference value d0 and the term of the rate of change α included in the first and second optical paths are eliminated. Therefore, changes in the thickness of the object 5 to be measured have no effect on the optical path ratio. Therefore, at the same temperature T, the ratio of the first and second optical paths, or the optical path ratio, is expressed by the ratio of the first and second refractive indices, or the refractive index ratio.

[0076] Next, the relationship between the refractive index ratio and the temperature of the measurement object 5 will be described. Figure 5 This is an example of temperature correction data showing the relationship between the refractive index ratio and the temperature of the measurement object. Figure 5 The horizontal axis is temperature, and the vertical axis is refractive index ratio. Temperature correction data 56 is acquired in advance. The temperature correction data 56 can be acquired by a temperature calibrator. The temperature T and the refractive index ratio at temperature T of a sample having the same material as the measurement object 5 are measured simultaneously to serve as the temperature correction data 56. The temperature T is measured using a platinum resistance thermometer, for example. According to Formula 6, the optical path ratio at the same temperature T is expressed by the refractive index ratio. Therefore, based on the relationship between the refractive index ratio and temperature shown in the temperature correction data 56, the relationship between the optical path ratio and temperature is derived. Thus, the temperature calculation unit 55 calculates the temperature of the measurement object 5 based on the relationship between the refractive index ratio and temperature and the optical path ratio.

[0077] Next, the temperature measurement operation of the temperature measurement system 1 , that is, the temperature measurement method, will be described. Figure 6 This is a flow chart showing a temperature measurement method according to one embodiment. For example, the first light source 11, the second light source 12, and the computing device 50 are repeatedly executed at predetermined intervals from the moment the first light source 11, the second light source 12, and the computing device 50 are powered on. Figure 6 The temperature measurement method shown is MT.

[0078] like Figure 6 As shown, the process starts with inputting the reflected light spectrum (S10). The first light source 11 generates light of a first wavelength range. The second light source 12 generates light of a second wavelength range. For example, the light of the second wavelength range is Figure 7 The spectrum shown in (a) of FIG. The combiner 20 combines the light in the first wavelength range with the light in the second wavelength range, and irradiates the output light to the measurement object 5 through the optical circulator 25 and the optical element 30 (step of irradiating the output light to the measurement object). The first spectrometer 42 and the second spectrometer 44 included in the measuring unit 40 obtain the spectrum of the reflected light reflected from the surface 5a and the back surface 5b of the measurement object 5 (step of measuring). For example, the second spectrometer 44 obtains Figure 7The optical path ratio calculation unit 51 inputs the spectrum of the first reflected light and the spectrum of the second reflected light from the measurement unit 40. When the process of S10 is completed, the process moves to the coordinate conversion process (S12).

[0079] In the process of S12, the optical path ratio calculation unit 51 converts the coordinate axis of the spectrum obtained by the process of S10 from the wavelength λ to the spatial frequency (1 / λ). Figure 7 When the process of S12 is completed, the process proceeds to the first data interpolation process (S14).

[0080] In the process of S14, the optical path ratio calculation unit 51 performs data interpolation on the spectrum obtained by the process of S12. For example, the number of sampling points is set to N s , and set the arrangement of spatial frequencies to (x0, x1, x2, ..., x N-1 ), set the arrangement of intensities to (y0, y1, y2, ..., y N-1 ), as the spectrum data. First, the optical path ratio calculation unit 51 rearranges the arrangement of the spatial frequencies at equal intervals. For example, when the spatial frequencies included in the arrangement of the rearranged spatial frequencies are set to X i When , use the following formula 7 to rearrange.

[0081]

Number 7

[0082]

[0083] Next, the optical path ratio calculation unit 51 calculates the rearranged spatial frequency X by, for example, linear interpolation. i When the intensity at this time is set to Y i , use the following formula 8 to calculate.

[0084]

Number 8

[0085]

[0086] Among them, j is the i >x j Thus, for example, Figure 8 The spectrum shown in (a) can also be calculated by polynomial interpolation to obtain the rearranged spatial frequency X. i When the processing of S14 is completed, transfer to FFT processing (S16).

[0087] In the process of S16, the optical path ratio calculation unit 51 performs Fourier transform on the spectrum interpolated by the process of S14 (Fourier transform step). Figure 8As shown in (b), it becomes a spectrum with the vertical axis being the amplitude and the horizontal axis being the phase. When the processing of S16 ends, it transfers to the filtering process (S18).

[0088] In the processing of S18, the optical path ratio calculation unit 51 filters out the peak at X = 0 from the spectrum obtained through the processing of S16. For example, it substitutes 0 for the intensity data Y in the range from X = 0 to X = Z (prescribed value). When the processing of S18 ends, it transfers to the extraction process (S20).

[0089] In the processing of S20, the optical path ratio calculation unit 51 extracts the peak at X = 2nd from the spectrum obtained through the processing of S18. For example, when the maximum value of the peak is set to Y i in the case, it extracts 20 data points from Y i-10 This is to extract the data from the center to the tail (in Japanese: 裾) of the peak. For example, when the maximum value of the peak is set to 1, it extracts in a way that includes the range from the maximum value to 0.5. For example, it extracts the spectrum shown in (c) of Figure 8 When the processing of S20 ends, it transfers to the second data interpolation process (S22).

[0090] In the processing of S22, the optical path ratio calculation unit 51 interpolates the data of the 2nd peak obtained through the processing of S20 (data interpolation process). The optical path ratio calculation unit 51, for example, performs linear interpolation at equal intervals between data points with the interpolation number N. The interpolation number N is, for example, preset based on the required temperature accuracy. For example, the following equation 9 is used for data interpolation.

[0091]

Equation 9

[0092]

[0093] Here, j is an index for the arrangement of intensities. The optical path ratio calculation unit 51 executes the above equation 9 within the range of i = 0 to N - 1. That is, it calculates taking all the intervals of the 20 points obtained through the processing of S20 as the objects. In this way, it divides the data interval after Fourier transform with the required number of divisions (interpolation number N), and performs linear interpolation of the corresponding number of data according to the number of divisions. When the processing of S22 ends, it transfers to the extraction process (S24).

[0094] In the processing of S24, the optical path ratio calculation unit 51 extracts only the data range for the calculation of the center of gravity from the data interpolated through the processing of S22. For example, the optical path ratio calculation unit 51 sets the threshold for the calculation of the center of gravity to A%, and substitutes 0 for the intensity data Y that is Y MAX ×A or less of the maximum intensity Y of the peak. When the processing of S24 ends, it transfers to the center of gravity calculation process (S26).

[0095] In the process of S26 , the optical path ratio calculation unit 51 calculates the weighted centroid based on the data interpolated in the process of S24 (weighted centroid calculation step). For example, the following formula 10 is used.

[0096]

Number 10

[0097]

[0098] In addition, N is the number of data points after the centroid range is extracted. The optical path length nd can be calculated using Equation 10. Thus, the first optical path length n1d of the output light in the first wavelength range is calculated, and the second optical path length n2d of the output light in the second wavelength range is calculated. When the process of S26 is completed, the process moves to the optical path length ratio calculation process (S28).

[0099] In the process of S28, the optical path ratio calculation unit 51 uses the first optical path n1d and the second optical path n2d obtained by the process of S26 to calculate the optical path ratio (step of calculating the optical path ratio). The optical path ratio calculation unit 51 calculates the optical path ratio using, for example, Formula 6. Thus, the optical path ratio calculation unit 51 can express the optical path ratio by the refractive index ratio. When the process of S28 is completed, the process transfers to the temperature calculation process (S30).

[0100] In the process of S30, the temperature calculation unit 55 calculates the temperature of the measurement object 5 based on the relationship between the refractive index ratio and the temperature of the measurement object 5 and the optical path ratio obtained by the process of S28 (step of calculating temperature). The temperature calculation unit 55 uses, for example, Figure 5 The temperature correction data 56 shown is used as the relationship between the refractive index ratio and the temperature of the measurement object 5. The temperature calculation unit 55 obtains the refractive index ratio based on the optical path ratio obtained by the process of S28, and calculates the temperature corresponding to the refractive index ratio in the temperature correction data 56. When the process of S30 is completed, the process ends. Figure 6 The temperature measurement method shown is MT.

[0101] Next, the effects of the temperature measurement system 1 and temperature measurement method MT according to one embodiment will be summarized. Below, for comparison with one embodiment, a conventional temperature measurement system and temperature measurement method will be described. First, calibration data representing the relationship between the normalized optical path length and temperature is obtained in advance for a calibration sample made of the same material as the object to be measured 5. Initially, the optical path length of the calibration sample is measured by an interferometer for each temperature controlled by a temperature calibrator, and the temperature of the calibration sample is measured by a thermometer. Next, the measured optical path length of the calibration sample is normalized by the optical path length of the calibration sample measured at a predetermined temperature (40°C, for example). This results in calibration data representing the relationship between temperature and the normalized optical path length. The normalized optical path length represents the rate of change of the optical path length relative to temperature fluctuations based on the predetermined temperature and is data that is independent of the thickness of the calibration sample. Next, the optical path length of the object to be measured 5 is measured, and the temperature of the object to be measured 5 is measured by another method. This results in measurement data representing the measured optical path length relative to the measured temperature. Next, the calibration data is transformed so that the relationship between the temperature and the normalized optical path length indicated by the calibration data also matches the measured data. This allows the relationship between the temperature of the object 5 and any optical path length to be determined. The temperature of the object 5 is then calculated based on the relationship between the temperature of the object 5 and any optical path length and the measured optical path length of the object 5.

[0102] As described above, conventional temperature measurement systems and methods require measuring the optical path length for each object 5 to be measured, while also measuring the temperature of the object 5 using other methods. However, depending on the measurement environment, it may be difficult to set up a thermometer, making it impossible to measure the temperature of the object 5 using other methods. Alternatively, one approach might be to predict the temperature of the object 5 based on the ambient temperature of the object 5 and use the predicted temperature as the measured data. However, the predicted temperature includes errors, which can affect the temperature measurement of the object 5. Thus, conventional temperature measurement systems and methods sometimes fail to accurately measure the temperature of the object 5.

[0103] In contrast, in the temperature measurement system 1 and temperature measurement method MT according to one embodiment, only the temperature correction data 56 (the relationship between the optical path ratio (refractive index ratio) and temperature) is known, eliminating the need to previously acquire actual measurement data of the optical path and temperature for each measurement object 5, as is conventionally required. In other words, in the temperature measurement system 1 and temperature measurement method MT according to one embodiment, there is no need to calibrate the calibration data (the relationship between temperature and the normalized optical path at that temperature) for each measurement object before temperature measurement, as is conventionally required. Consequently, compared to conventional temperature measurement systems and temperature measurement methods that acquire actual measurement data for each measurement object 5 and then calibrate the calibration data for each measurement object 5 before temperature measurement, this temperature measurement system 1 and temperature measurement method MT can simplify the measurement process.

[0104] The temperature measurement system 1 and the temperature measurement method MT enable highly accurate measurement of the temperature of the object 5. Even if the thickness of the object 5 decreases due to wear and tear, the change in thickness does not affect the optical path ratio, allowing the temperature calculation unit 55 to accurately calculate the temperature of the object 5.

[0105] According to the temperature measurement system 1 and the temperature measurement method MT, the first spectrometer 42 can narrow the distribution measurement range to a wavelength range suitable for measuring the first reflected light, and the second spectrometer 44 can narrow the distribution measurement range to a wavelength range suitable for measuring the second reflected light. Therefore, the resolution of each spectrometer can be improved, enabling high-precision measurement of the reflected light spectrum.

[0106] According to the temperature measurement system 1 and the temperature measurement method MT, the inclusion of multiple optical elements 30 enables multi-point measurement. According to the temperature measurement system 1 and the temperature measurement method MT, a measurement target 5 composed of at least one of silicon, quartz, and sapphire is irradiated with light having a wavelength of 1200 nm to 1300 nm and light having a wavelength of 1500 nm to 1600 nm. This suppresses absorption of the output light by the measurement target 5.

[0107] The above-described embodiment is intended to illustrate an example of the temperature measurement system 1 and the temperature measurement method MT, and the device and method according to the embodiment may be modified or applied to other devices.

[0108] For example, the temperature measurement system 1 described in one embodiment may be mounted on the substrate processing apparatus 300 . Figure 9It is an example of a substrate processing device. Here, as an example of the measurement object 5 in a substrate processing device such as a plasma etching device, the case of applying it to the temperature measurement of a wafer Tw is described. In addition, the measurement object 5 can be any object accommodated in the substrate processing device 300. The object accommodated in the substrate processing device 300 can also be, for example, at least one of a substrate, a focus ring, and an upper electrode. In the case where the object accommodated in the processing chamber is made of a material that is transparent to light in the first wavelength range and the second wavelength range, the temperature can be measured as the measurement object 5. In this case, silicon, quartz, sapphire, etc. are used as the material of the measurement object 5.

[0109] Light transmitted through and reflected from both end surfaces S1 and S2 of the wafer Tw being measured is used as the first and second light sources 11 and 12. For example, since the wafer Tw is made of silicon, light sources capable of emitting light with a wavelength of 1.2 to 2.5 μm, which is permeable to silicon materials such as silicon and silicon oxide films, are used as the first and second light sources 11 and 12.

[0110] like Figure 9 As shown, the substrate processing device 300 includes a processing chamber 310 for performing predetermined processing such as etching processing and film forming processing on the wafer Tw. That is, the wafer Tw is accommodated in the processing chamber 310. The processing chamber 310 is configured to be connected to an exhaust pump not shown in the figure so as to be able to perform vacuum exhaust. An upper electrode 350 and a lower electrode 340 facing the upper electrode 350 are provided inside the processing chamber 310. The lower electrode 340 also serves as a loading table for loading the wafer Tw. An electrostatic chuck (not shown) for electrostatically adsorbing the wafer Tw is provided on the upper part of the lower electrode 340, for example. In addition, a cooling unit is provided on the lower electrode 340. The cooling unit circulates a refrigerant, for example, in a refrigerant flow path 342 formed in a roughly annular shape on the lower electrode 340 to control the temperature of the lower electrode 340. Thus, the temperature of the wafer Tw is controlled. Wafer Tw is loaded into processing chamber 310 through a gate valve (not shown) provided on the side of processing chamber 310. Lower electrode 340 and upper electrode 350 are connected to high frequency power supplies 320 and 330 for applying predetermined high frequency power, respectively.

[0111] The upper electrode 350 is configured to support an electrode plate 351 located at the bottom via an electrode support 352. The electrode plate 351 is formed, for example, of a silicon material (silicon, silicate, etc.), and the electrode support 352 is formed, for example, of an aluminum material. An inlet pipe (not shown) for introducing a predetermined process gas is provided above the upper electrode 350. A large number of ejection holes (not shown) are formed through the electrode plate 351 to uniformly eject the process gas introduced through the inlet pipe toward the wafer Tw placed on the lower electrode 340.

[0112] The upper electrode 350 is provided with a cooling unit. This cooling unit, for example, circulates a refrigerant in a refrigerant flow path formed in the electrode support 352 of the upper electrode 350, thereby controlling the temperature of the upper electrode 350. The refrigerant flow path is formed in a substantially annular shape, and the refrigerant flow path is formed, for example, into two systems, an outer refrigerant flow path 353 for cooling the outer side of the surface of the upper electrode 350 and an inner refrigerant flow path 354 for cooling the inner side. Figure 9 As shown by the arrows in the figure, the outer refrigerant flow path 353 and the inner refrigerant flow path 354 are respectively configured to be supplied with refrigerant by the supply pipe, so that the refrigerant circulates through each refrigerant flow path 353, 354 and is discharged from the discharge pipe and returned to the external refrigerator (not shown) to circulate. The same refrigerant can be circulated in the refrigerant flow paths of the two systems, and different refrigerants can also be circulated. In addition, the cooling unit of the upper electrode 350 is not limited to Figure 9 The unit having two refrigerant flow paths shown may be a unit having only one refrigerant flow path, or may be a unit having a refrigerant flow path branched into two in one system.

[0113] A low heat transfer layer 356 is provided between the outer portion of the electrode support 352, where the outer refrigerant flow path 353 is provided, and the inner portion, where the inner refrigerant flow path 354 is provided. Due to the low heat transfer layer 356, heat is not easily transferred between the outer and inner portions of the electrode support 352. Therefore, the outer and inner portions can be controlled to different temperatures by controlling the refrigerant in the outer and inner refrigerant flow paths 353 and 354. This allows for efficient and accurate control of the in-plane temperature of the upper electrode 350.

[0114] In such a substrate processing apparatus 300, a wafer Tw is loaded via a gate valve, for example, using a transfer arm. The wafer Tw loaded into the processing chamber 310 is placed on the lower electrode 340. High-frequency power is applied to the upper electrode 350 and the lower electrode 340, and a predetermined processing gas is introduced into the processing chamber 310 from the upper electrode 350. The processing gas introduced from the upper electrode 350 is thereby converted into plasma, and an etching process, for example, is performed on the surface of the wafer Tw.

[0115] The output light of the temperature measurement system 1 is irradiated from the lower electrode 340 to the wafer Tw as the measurement object via the optical element 30. Specifically, the optical element 30 is arranged so as to irradiate the output light to the wafer Tw via a through hole 344 formed in, for example, the central portion of the lower electrode 340. In addition, the position where the optical fiber F is arranged in the in-plane direction of the wafer Tw can be any position as long as it is a position where the output light is irradiated to the wafer Tw, and it does not need to be a position where the output light is irradiated to the wafer Tw. Figure 9For example, the optical fiber F may be arranged so as to irradiate the output light toward the end portion of the wafer Tw.

[0116] As described above, by installing the temperature measurement system 1 in the substrate processing apparatus 300, the temperature of at least one of the substrate, the focus ring, and the upper electrode can be measured with high precision. Furthermore, the temperature of the wafer Tw, which is the measurement object, can be measured during etching.

[0117] Next, a modification of the temperature measurement system 1 will be described. Figure 10 This is a diagram schematically showing a temperature measurement system according to a modification. Figure 10 The temperature measurement system 1A shown is Figure 1 Compared with the temperature measurement system 1 shown in FIG, the structure of the light source portion is different, and other than that, the temperature measurement system 1 is the same. Figure 10 As shown, the light source unit 10A of the temperature measurement system 1A does not include the second light source 12 and the combiner 20 , and is composed only of the first light source 11A.

[0118] The first light source 11A is used to generate output light that transmits the measurement object 5 and has wavelengths within a first wavelength range and a second wavelength range. The output light has a wide wavelength range, for example, from 1200 nm to 1600 nm. The wavelength splitter 41 transmits the reflected light obtained by the optical circulator 25 with a wavelength range of from 1200 nm to 1300 nm to the first spectrometer 42, and transmits the reflected light with a wavelength range of from 1500 nm to 1600 nm to the second spectrometer 44. The principle of temperature measurement is the same as that of the temperature measurement system 1. In this way, the temperature measurement system 1A can use a single light source to generate output light to measure the temperature of the measurement object 5.

[0119] Figure 11 This is a diagram schematically showing a temperature measurement system according to a modification. Figure 11 The temperature measurement system 1B shown is Figure 1 Compared with the temperature measurement system 1 shown in FIG, the structure of the light source unit and the measurement unit are different, but other than that, they are the same. Figure 11 As shown, the light source unit 10B of the temperature measurement system 1B includes a first wavelength-swept light source 11B instead of the first light source 11, and a second wavelength-swept light source 12B instead of the second light source 12. The measurement unit 40B of the temperature measurement system 1B includes a first photodetector 42B instead of the first spectrometer 42, and a second photodetector 44B instead of the second spectrometer 44.

[0120] The first wavelength-swept light source 11B generates light having a wavelength within a first wavelength range that transmits the measurement object 5. The first wavelength-swept light source 11B generates narrowband light having a fixed bandwidth, for example, light that is wavelength-swept within a wavelength range of 1200 nm to 1300 nm.

[0121] The second wavelength-swept light source 12B generates second measurement light having a wavelength within a second wavelength range. The second measurement light transmits through the measurement object 5. The second wavelength-swept light source 12B generates narrowband light having a fixed bandwidth, for example, light that is wavelength-swept within a wavelength range of 1500 nm to 600 nm.

[0122] When the measuring unit 40B includes a plurality of photodetectors as described above, the wavelength splitter 41 transmits the reflected light obtained from the optical circulator 25 to each photodetector.

[0123] The first photodetector 42B measures a reflected light spectrum of first reflected light, which is light reflected from the front surface 5 a and back surface 5 b of the object 5 by the output light obtained by wavelength scanning within the first wavelength range. The second photodetector 44B measures a reflected light spectrum of second reflected light, which is light reflected from the front surface 5 a and back surface 5 b of the object 5 by the output light obtained by wavelength scanning within the second wavelength range.

[0124] The first wavelength-swept light source 11B and the second wavelength-swept light source 12B generate narrowband light. Consequently, the measuring unit 40B can include a first photodetector 42B and a second photodetector 44B, each of which narrows the distribution measurement range to a wavelength range suitable for measuring narrowband reflected light. The principle of temperature measurement is the same as that of the temperature measurement system 1. Thus, the temperature measurement system 1B can measure the temperature of the object 5 by generating output light using the wavelength-swept light source and acquiring the reflected light spectrum using the photodetector.

[0125] Figure 12 This is a diagram schematically showing a temperature measurement system according to a modification. Figure 12 The temperature measurement system 1C shown is Figure 11 Compared with the temperature measurement system 1B shown in FIG, the structure of the light source portion is different, but other than that, the temperature measurement system 1B is the same. Figure 12 As shown, the light source unit 10C of the temperature measurement system 1C includes a first light source 11C instead of the first wavelength-swept light source 11B and the second wavelength-swept light source 12B, and includes a variable wavelength filter 20C instead of the combiner 20B.

[0126] The first light source 11C is identical to the first light source 11A. The variable wavelength filter 20C selectively transmits light from the first light source 11C based on time and wavelength. For example, the variable wavelength filter 20C transmits output light within a specified wavelength range for a specified period of time and transmits the light to the optical circulator 25. The principle of temperature measurement is the same as that of the temperature measurement system 1. Thus, the temperature measurement system 1C can measure the temperature of the object 5 by generating output light using a light source with a wide wavelength range and a variable wavelength filter, and measuring the reflected light using a photodetector.

[0127] Figure 13 This is a diagram schematically showing a temperature measurement system according to a modification. Figure 13 The temperature measurement system 1D shown is Figure 10 Compared with the temperature measurement system 1A shown in FIG. 1 , the structure of the measuring unit and the computing device are different, but other than that, the temperature measurement system 1A is the same. Figure 13 As shown, the measuring unit 40D of the temperature measurement system 1D does not include a wavelength splitter and two optical splitters, but includes a single optical splitter 42D. The temperature measurement system 1D includes an arithmetic unit 50D instead of the arithmetic unit 50.

[0128] The measuring unit 40D measures the reflected light spectrum of light within the wavelength range of 1200 nm to 1600 nm, among the reflected light obtained via the optical circulator 25. The computing device 50D computes the reflected light spectrum of light within the wavelength range of 1200 nm to 1300 nm, and also computes the reflected light spectrum of light within the wavelength range of 1500 nm to 1600 nm. The principle of temperature measurement is the same as that of the temperature measurement system 1. Thus, the temperature measurement system 1D can measure the temperature of the measurement object 5 with high accuracy without including the second light source 12, the combiner 20, the demultiplexer 41, and the second optical splitter 44.

[0129] From the above description, it can be understood that various modifications can be made to the embodiments of the present disclosure without departing from the scope and spirit of the present disclosure. Therefore, the various embodiments disclosed in this specification are not intended to be limiting, and the true scope and spirit are indicated by the appended claims.

Claims

1. A temperature measurement system for measuring the temperature of an object having a first main surface and a second main surface facing the first main surface, characterized in that: The temperature measurement system comprises: a light source unit configured to generate output light, the output light including a first wavelength range and a second wavelength range different from the first wavelength range, the output light transmitting through the object to be measured; at least one optical element that emits the output light from the light source unit toward the first main surface of the measurement object, and on which reflected light from the first main surface and the second main surface is incident; a measuring unit connected to the at least one optical element to measure a spectrum of the reflected light from the first main surface and the second main surface that depends on the wavelength; an optical path ratio calculation unit configured to calculate an optical path ratio by performing Fourier transform on the spectrum measured by the measurement unit, the optical path ratio being a ratio of a first optical path length of the output light in the first wavelength range to a second optical path length of the output light in the second wavelength range; as well as a temperature calculation unit that calculates the temperature of the object to be measured based on the optical path ratio and a relationship between a previously acquired refractive index ratio and the temperature of the object to be measured, wherein the refractive index ratio is a ratio of a first refractive index of the output light in the first wavelength range at the object to be measured to a second refractive index of the output light in the second wavelength range at the object to be measured.

2. The temperature measurement system according to claim 1, characterized in that The light source unit includes a first light source that emits light in the first wavelength range, a second light source that emits light in the second wavelength range, and a multiplexer that transmits output light obtained by multiplexing the light in the first wavelength range and the light in the second wavelength range.

3. The temperature measurement system according to claim 1 or 2, characterized in that: The measuring unit includes: a first spectrometer for measuring the spectrum of first reflected light, which is the reflected light from the first main surface and the second main surface generated by the output light in the first wavelength range; and a second spectrometer for measuring the spectrum of second reflected light, which is the reflected light from the first main surface and the second main surface generated by the output light in the second wavelength range.

4. The temperature measurement system according to claim 1 or 2, characterized in that: The at least one optical element includes a plurality of optical elements.

5. The temperature measurement system according to claim 1 or 2, characterized in that: The object to be measured is composed of silicon, The first wavelength range is greater than or equal to 1200 nm and less than or equal to 1300 nm. The second wavelength range is greater than or equal to 1500 nm and less than or equal to 1600 nm.

6. The temperature measurement system according to claim 1 or 2, characterized in that: The at least one optical element is provided in a substrate processing device that accommodates the object to be measured, The object to be measured is at least one of a substrate, a focus ring, and an upper electrode.

7. A temperature measurement method for measuring the temperature of an object having a first main surface and a second main surface facing the first main surface, characterized in that: The temperature measurement method comprises the following steps: irradiating the object to be measured with output light, the output light including a first wavelength range and a second wavelength range different from the first wavelength range, the output light transmitting through the object to be measured; measuring spectra of reflected light from the first main surface and the second main surface of the measurement object; Calculating an optical path ratio by performing Fourier transform on the spectrum, the optical path ratio being a ratio of an optical path of the output light in the first wavelength range, i.e., a first optical path, to an optical path of the output light in the second wavelength range, i.e., a second optical path; The temperature of the object to be measured is calculated based on the relationship between the optical path ratio and a previously acquired refractive index ratio, which is the ratio of the refractive index of the output light in the first wavelength range at the object to be measured, i.e., the first refractive index, to the refractive index of the output light in the second wavelength range at the object to be measured, i.e., the second refractive index.

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