Temperature measurement device, temperature measurement method, and program

Abstract

A temperature measurement device (1) comprises: a light emission unit (10) that generates coherent, continuous measurement-light; a light detection unit (30) that detects reflected light or transmitted light of the continuous measurement-light which is projected onto a sample (50) to be measured; and an analysis unit (42) that calculates a temperature distribution of the sample (50) to be measured on the basis of the intensity of the reflected light or the transmitted light detected by the light detection unit (30). The analysis unit (42) calculates the optical thickness of the sample (50) to be measured from a temporal change in the intensity of the reflected light or the transmitted light and, by using a refractive index distribution model representing the relationship between the optical thickness and a refractive index distribution in the thickness direction of the sample (50) to be measured at the time of a temperature change, calculates the refractive index distribution from the optical thickness, and calculates the temperature distribution of the sample (50) to be measured by converting the refractive index distribution into the temperature distribution on the basis of the thermo-optical coefficient of the sample (50) to be measured.

Description

Temperature measurement device, temperature measurement method and program

[0001] The present invention relates to a temperature measurement device, a temperature measurement method, and a program.

[0002] 2. Description of the Related Art Conventionally, temperature measurement devices have been developed that irradiate a sample with coherent light such as laser light and measure the temperature distribution of the sample using the light reflected from the sample (see, for example, Patent Document 1).

[0003] Re-table No. 2007-4644

[0004] In Patent Document 1, when solving the heat conduction equation, the most probable temperature distribution is found by manually fitting the measured waveform of the reflected wave using the heat input distribution from the outside and the heat transfer efficiency from the heat source as fitting parameters. However, this method requires a lot of time and effort because fitting is performed on the measured waveform, making it difficult to find the temperature distribution in real time.

[0005] The present invention has been made in view of the above circumstances, and has an object to provide a temperature measurement device, a temperature measurement method, and a program that are capable of measuring the temperature distribution of a sample to be measured in real time.

[0006] In order to achieve the above object, a temperature measuring device according to a first aspect of the present invention comprises: a light emitting unit that generates coherent continuous measurement light; a light detecting unit that detects reflected light or transmitted light of the continuous measurement light irradiated onto a sample to be measured; and an analyzing unit that calculates a temperature distribution of the sample to be measured based on the intensity of the reflected light or transmitted light detected by the light detecting unit, wherein the analyzing unit calculates the optical thickness of the sample to be measured from the change over time in the intensity of the reflected light or transmitted light, and calculates the temperature distribution of the sample to be measured based on the refractive index distribution in the thickness direction of the sample to be measured and the optical thickness when the temperature changes.

[0007] The analysis unit may also calculate the refractive index distribution from the optical thickness using a refractive index distribution model that represents the relationship between the refractive index distribution in the thickness direction of the measured sample when the temperature changes and the optical thickness, and calculate the temperature distribution of the measured sample by converting the refractive index distribution into a temperature distribution based on the thermo-optic coefficient of the measured sample.

[0008] The refractive index distribution model may be derived by converting the change in temperature distribution over time in the thickness direction calculated based on a thermal diffusion model of the sample to the change in refractive index over time based on the thermo-optic coefficient.

[0009] The light emitting unit may also include a light source, a collimator, and an optical fiber connecting the light source and the collimator, wherein the light source generates laser light having a linewidth of 10 MHz or less, and the optical fiber is a single-mode optical fiber or a multi-mode optical fiber having a core diameter of 50 μm or less.

[0010] The light emitting unit may also include a light source, a collimator, and an optical fiber connecting the light source, the light detecting unit, and the collimator, wherein the light source generates laser light having a linewidth of 10 MHz or less, and the optical fiber is a bundle of a single-mode optical fiber or a multi-mode optical fiber having a core diameter of 50 μm or less, and a multi-mode optical fiber.

[0011] In addition, a temperature measurement method according to a second aspect of the present invention includes irradiating a sample to be measured with coherent continuous measurement light, detecting reflected light or transmitted light of the continuous measurement light, calculating the optical thickness of the sample to be measured from the change in intensity of the reflected light or transmitted light over time, and calculating the temperature distribution of the sample to be measured based on the refractive index distribution in the thickness direction of the sample to be measured and the optical thickness when the temperature changes.

[0012] Furthermore, a program according to a third aspect of the present invention causes a computer to operate as an analysis unit that calculates the optical thickness of the sample to be measured from the change over time in the intensity of reflected light or transmitted light of coherent continuous measurement light irradiated onto the sample to be measured, and calculates the temperature distribution of the sample to be measured based on the refractive index distribution in the thickness direction of the sample to be measured and the optical thickness when the temperature changes.

[0013] According to the temperature measurement device, temperature measurement method and program of the present invention, the optical thickness of the sample to be measured is calculated from the fluctuation in reflectance or transmittance caused by the temperature change of the sample to be measured, and the temperature distribution of the sample to be measured is calculated based on the refractive index distribution and optical thickness in the thickness direction of the sample to be measured as the temperature changes, making it possible to measure the temperature quickly and accurately.

[0014] FIG. 1 is a conceptual diagram showing multiple reflections of light within a sample to be measured according to the measurement principle of the present invention. FIG. 2 is a diagram showing a schematic configuration of a temperature measurement device according to a first embodiment. FIG. 3 is a diagram showing a schematic configuration of an experimental device for investigating laser linewidths. FIG. 4 is a diagram showing an example of the relationship between temperature change and intensity change of transmitted light for measurement light with different laser linewidths, where (A) is for a laser linewidth of 100 Hz, (B) is for a laser linewidth of 2 MHz, and (C) is for a laser linewidth of 15 MHz. FIG. 5 is a diagram showing an example of the relationship between temperature change and intensity change of transmitted light for optical fibers with different core diameters, where (A) is for a single-mode optical fiber with a core diameter of 10 μm, and (B) is for a multimode optical fiber with a core diameter of 50 μm. FIG. 6 is a functional block diagram of an analysis unit according to the first embodiment. FIG. 7 is a schematic diagram showing an example of the configuration of a temperature measurement device according to the first embodiment. FIG. 8 is a flowchart showing the flow of temperature measurement according to the first embodiment. FIG. 9 is a diagram showing data conversion related to temperature measurement processing, where (A) is an example of reflectivity, (B) is an optical thickness, (C) is an example of refractive index distribution, and (D) is an example of temperature distribution. FIG. 10 is a diagram showing an example of time change in refractive index distribution calculated based on a refractive index distribution model. 1 is a diagram showing a schematic configuration of a temperature measuring device according to a second embodiment. FIG. 2 is a diagram showing an example of a fiber bundle, where (A) is a bundle of one single-mode fiber and one multi-mode fiber, and (B) is a bundle of single-mode fibers surrounded by multi-mode fibers. FIG. 3 is a schematic diagram showing the configuration of an experimental method for evaluating the light-collection efficiency of a fiber bundle. FIG. 4 is a diagram showing an example of measurement results of the light-collection efficiency of a fiber bundle. FIG. 5 is a graph showing an example of results when temperature measurement is performed using a fiber bundle, where (A) is a graph of reflectivity and (B) is a graph of measured temperature. FIG. 6 is a diagram showing an example of the arrangement of a light emitting unit, a measured sample, and a light detecting unit, where (A) is a case of normal reflection measurement, (B) is a case of normal transmission measurement, (C) is a case of oblique reflection measurement, and (D) is a case of oblique transmission measurement. FIG. 7 is a diagram showing a schematic configuration of a temperature measuring device when measuring temperatures at multiple measurement locations.

[0015] (Measurement principle) First, the temperature measurement principle of the present invention will be explained. As shown in FIG. 1, light incident on the sample to be measured undergoes multiple reflections and interference within the sample. Therefore, the transmittance and reflectance are determined by the phase synthesis of these light beams. The physical thickness of the sample to be measured is defined as d, the temperature as T, and the refractive index as n(T). In general, the refractive index of a substance is temperature dependent. The portion other than the sample to be measured is considered to be air or vacuum, and its refractive index is defined as 1. The angle of incidence of light is defined as θ １ , the refraction and reflection angles within the sample are defined as θ ２ Then, the relationship between these is expressed by the following equation (1).

[0016] The difference in optical path length between each light beam that is multiple-reflected within the sample to be measured and then transmitted and reflected is expressed as follows:

[0017] Therefore, when the wavelength of the measurement light is λ, the phase corresponding to the difference in optical path length is expressed by the following equation (3).

[0018] That is, when the temperature T of the sample to be measured changes over time, the refractive index n(T) changes and the phase also changes. Therefore, temporal oscillations (constructive and destructive interference) occur in the transmittance and reflectance due to changes in interference conditions. Here, when the measurement light is perpendicularly incident on the sample to be measured, cosθ2 = 1. The thermo-optic coefficient (= n(T)), which represents the temperature dependence of the refractive index of the sample to be measured, is obtained in advance by experiment, etc.

[0019] When heat is input to the sample from the outside, the temperature distribution within the sample is calculated based on the heat conduction equation. The temperature distribution can also be converted into a refractive index distribution based on the thermo-optic coefficient. A conventional method (Publication No. 2007-4644) calculates the temperature distribution of the sample by calculating the time change in transmittance or reflectance using an optical simulation that takes multiple reflections and interference into account, and then fitting the waveform of the transmittance or reflectance to the waveform of the actually measured transmittance or reflectance.

[0020] In the temperature measurement method according to the present invention, a change in apparent thickness (optical thickness) is calculated from the measured phase change, and the temperature distribution within the sample is calculated based on the refractive index distribution and optical thickness of the sample in the thickness direction during temperature change.

[0021] A temperature measuring device 1 according to an embodiment of the present invention will be described below with reference to the drawings. In this embodiment, the case of measuring the temperature of a silicon carbide (SiC) wafer, which is a sample 50 to be measured, when the SiC wafer is subjected to heat treatment in an atmospheric pressure plasma device will be described as an example.

[0022] As shown in FIG. 2 , the temperature measuring device 1 according to this embodiment includes a light emitting unit 10, a beam splitter 20, a light detecting unit 30, and an analyzing unit 40. The SiC wafer, which is the sample 50 to be measured, is a flat sample having a front surface and a back surface that are parallel to each other, and the front surface is heated by a micro-plasma jet (μ-TPJ), which is an atmospheric pressure thermal plasma jet (TPJ) with a plasma size densified to less than a millimeter. The temperature measuring device 1 measures the temperature of the sample 50 based on a change in the reflectance of the laser light detected on the back surface of the sample 50.

[0023] The light emitting unit 10 is an optical system device that generates continuous light for measurement, which is coherent collimated light used for measurement, and includes a light source 11, an optical fiber 12, and a collimator 13. The light source 11 is a laser oscillator that generates continuous light for measurement (hereinafter also referred to as measurement light).

[0024] Requirements for the measurement light of the temperature measurement device 1 according to the present invention include a certain level of output power (approximately 10 mW) and optical coherence. Furthermore, to miniaturize the temperature measurement device 1, it is preferable that the light source 11 be small, for example, 100 mm square or less. These conditions generally have a trade-off relationship. For example, miniaturizing the light source 11 reduces the output power and weakens the optical coherence. In this embodiment, the characteristics of the measurement light suitable for measurement will be described based on the laser linewidth. The laser linewidth is the width of the laser spectrum and is expressed as the full width at half maximum. The smaller the laser linewidth, the higher the coherence of the laser light.

[0025] 3 is a schematic diagram of an experimental setup for studying the laser linewidth. While changing the temperature of the sample 50, measurement light emitted from the light emitting unit 10 is irradiated onto the sample 50, and the transmitted measurement light is detected by the light detecting unit 30. This allows measurement of changes in the intensity of the transmitted light caused by changes in the refractive index associated with temperature changes in the sample 50. In this experiment, the laser linewidth of the measurement light was changed by changing the light source 11, and the laser linewidth required for temperature measurement was studied.

[0026] 4A to 4C are graphs showing examples of the relationship between the temperature change of the sample 50 and the intensity change of the transmitted light for measurement light beams with different laser linewidths. FIG. 4A is a graph for a He-Ne laser with a laser linewidth of approximately 100 Hz, FIG. 4B is a graph for a semiconductor laser with a laser linewidth of approximately 2 MHz, and FIG. 4C is a graph for a semiconductor laser with a laser linewidth of approximately 15 MHz. As shown in FIGS. 4A to 4C, the larger the laser linewidth, the smaller the change in the intensity of the measurement light. In the case of a semiconductor laser with a laser linewidth of approximately 1500 GHz, the change was so small that vibrations were not observable (not shown). To measure temperature based on changes in the intensity of the measurement light, as in the present invention, a sufficiently large vibration amplitude is required, specifically, a transmittance fluctuation of 5% or more. Based on the results of this experiment, it is believed that a laser linewidth of 10 MHz or less is preferable for the measurement light to stably observe transmittance fluctuations of 5% or more.

[0027] The optical fiber 12 connects the light source 11 and the collimator 13, and causes the measurement light emitted from the light source 11 to enter the collimator 13. Requirements for the optical fiber 12 include high coupling efficiency with the light source 11, maintaining the coherence of the measurement light, and avoiding instability of the measurement light due to returned light. Using a single-mode optical fiber with a small core diameter makes it possible to maintain the coherence of the measurement light. However, the coupling efficiency with the light source 11 is higher with a multi-mode optical fiber with a large core diameter.

[0028] An experiment to examine the core diameter of the optical fiber 12 was conducted using the experimental apparatus shown in the schematic diagram of Figure 3. While changing the temperature of the sample 50, measurement light emitted from the light emitting unit 10 was irradiated onto the sample 50, and the transmitted measurement light was detected by the light detecting unit 30. This allows the change in intensity of the transmitted light caused by the change in refractive index accompanying the change in temperature of the sample 50 to be measured. In this experiment, optical fibers 12 with different core diameters were used to verify the effect on the change in intensity of the transmitted light. A highly coherent He-Ne laser was used as the light source 11.

[0029] 5A and 5B show examples of the relationship between temperature change and intensity change of transmitted light for optical fibers 12 with different core diameters. FIG. 5A is a graph showing the relationship when a single-mode optical fiber with a core diameter of 10 μm is used, and FIG. 5B is a graph showing the relationship when a multi-mode optical fiber with a core diameter of 50 μm is used. As shown in FIGS. 5A and 5B, the larger the core diameter, the smaller the change in intensity of the measurement light. As shown in FIG. 5B, when a multi-mode optical fiber with a core diameter of 50 μm is used, the amplitude of the change in intensity of the transmitted light is smaller than when the single-mode optical fiber of FIG. 5A is used, but the change in transmittance due to temperature change can be observed. From the results of this experiment, it is considered preferable that the optical fiber 12 be a single-mode optical fiber or a multi-mode optical fiber with a core diameter of 50 μm or less, so as to prevent the coherence of the measurement light from being lost during transmission.

[0030] The collimator 13 converts the incident measurement light into parallel light. The parallel measurement light that has passed through the collimator 13 is emitted to the beam splitter 20. The connector that connects the optical fiber 12 and the collimator 13 is preferably a connector with a PC / APC structure in order to suppress reflected light that occurs at the connection portion.

[0031] The beam splitter 20 is disposed on the optical path of the measurement light emitted from the collimator 13, and separates the incident light from the collimator 13 from the reflected light from the measured sample 50. More specifically, the beam splitter 20 transmits the incident light from the collimator 13 to irradiate the measured sample 50, and separates the reflected light from the measured sample 50 to make it incident on the light detection unit 30.

[0032] 2, the light detection unit 30 includes a photodiode 31 and a voltage output unit 32, and detects reflected light from the measured sample 50. The photodiode 31 receives the reflected light from the measured sample 50 that is incident from the beam splitter 20, and generates a photocurrent.

[0033] The voltage output section 32 has a load resistor and converts the photocurrent generated by the photodiode 31 into a voltage signal. The voltage output section 32 outputs the converted voltage signal to the analysis unit 40.

[0034] The analysis unit 40 is, for example, a computer device, and includes an analog interface 41, an analysis section 42, a storage section 43, a display section 44, and an input section 45, as shown in the functional block diagram of FIG.

[0035] The analog interface 41 converts the voltage signal input from the voltage output unit 32 into a digital signal and transmits it to the analysis unit 42 .

[0036] The analysis unit 42 analyzes the intensity fluctuation of the reflected light from the received digital signal to calculate the change in the refractive index of the measured sample 50 and analyze the temperature distribution of the measured sample 50. The detailed procedure for analyzing the temperature distribution of the measured sample 50 will be described later.

[0037] The analysis unit 42 is composed of a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc. The analysis unit 42 loads various operating programs and data stored in the ROM of the analysis unit 42, the storage unit 43, etc. into the RAM and operates the CPU, thereby realizing each function of the analysis unit 42 shown in Fig. 6. As a result, the analysis unit 42 operates as a phase calculation unit 421, an optical thickness calculation unit 422, and a temperature distribution calculation unit 423, and analyzes the temperature distribution of the measurement sample 50 based on the digital signal received from the analog interface 41.

[0038] The phase calculation unit 421 calculates the phase from the digital signal of the reflected light intensity, which is the vibration signal received from the analog interface 41 .

[0039] The optical thickness calculation unit 422 calculates the optical thickness of the sample 50 to be measured from the phase calculated by the phase calculation unit 421. The optical thickness is calculated based on the above-mentioned measurement principle (Equation (3)).

[0040] The temperature distribution calculation unit 423 calculates the refractive index distribution from the optical thickness using a refractive index distribution model that represents the relationship between the refractive index distribution in the thickness direction of the measured sample 50 during temperature change and the optical thickness. The temperature distribution calculation unit 423 also calculates the temperature distribution of the measured sample 50 by converting the refractive index distribution into a temperature distribution based on the thermo-optic coefficient of the measured sample 50.

[0041] The storage unit 43 is a non-volatile memory such as a hard disk or flash memory, and stores programs relating to phase calculation and optical thickness calculation, thermo-optic coefficients, refractive index distribution models, and the like.

[0042] The display unit 44 is a display device, such as a liquid crystal panel, provided in the analysis unit 40, which is a computer device, and displays the measured reflectance, temperature distribution, and the like.

[0043] The input unit 45 is an input device for inputting instructions to start and end measurement, changes to various measurement conditions, etc. in the temperature measuring device 1. The input unit 45 is a keyboard, a touch panel, a mouse, etc., provided in the analysis unit 40.

[0044] (Temperature Measurement Method) A temperature measurement method using the temperature measurement device 1 will be specifically described below. In this embodiment, the case of measuring the temperature of a silicon wafer in a parallel-plate plasma shown in FIG. 7 will be described. The silicon wafer, which is the sample 50 to be measured, is placed on a lower electrode with a measurement hole (2 mm in diameter). The plasma generator, which is the heating means for heating the sample 50 to be measured, generates plasma by applying a high frequency of 13.56 MHz to the upper electrode. The temperature measurement device 1 can also measure the temperature rise due to ion bombardment by applying a DC bias (negative) to the lower electrode.

[0045] The measurement light (wavelength 1310 nm) emitted from the light emitting unit 10 is irradiated onto the measured sample 50 from below the lower electrode through a quartz window of the vacuum chamber. The measurement light reflected by the measured sample 50 is detected by the light detecting unit 30, and a signal of the detected reflected light is sent to the analyzing unit 40.

[0046] The flow of processing by the analysis section 42 of the analysis unit 40 is shown in the flowchart of Figure 8. Because the voltage signal, which is the reflected light signal (Figure 9A) transmitted from the light detection section 30, contains noise depending on the measurement environment, the phase calculation section 421 removes noise using a Gaussian filter, moving average method, or the like (step S11). The phase calculation section 421 acquires phase information from the temporal change in the reflected light intensity (step S12). If the temperature is rising, the phase advances (the value increases), and if the temperature is falling, the phase returns (the value decreases). When measurement light is perpendicularly incident on the measured sample 50 and perpendicularly reflected light is measured, the phase is expressed by the following equation (4) from the above equation (3).

[0047] Based on the above formula (4), the optical thickness calculation unit 422 obtains the time change in the optical thickness n(T)d of the wafer (FIG. 9B) from the time change in the phase (step S13).

[0048] Next, the amount of change in optical thickness calculated in step S13 is input into a refractive index distribution model to obtain a refractive index distribution (step S14). The temperature distribution calculation unit 423 calculates the refractive index distribution from the optical thickness using the refractive index distribution model stored in the storage unit 43.

[0049] A method for deriving the refractive index distribution model pre-stored in the storage unit 43 will now be described. First, the time change in temperature distribution when heat is input from the outside to the measured sample 50 is calculated based on a thermal diffusion model expressed by a heat conduction equation. In this embodiment, the temperature distribution in the thickness direction of the measured sample 50 is considered. The calculated temperature distribution is converted into a refractive index distribution based on the thermo-optic coefficient of the measured sample 50. This makes it possible to derive a refractive index distribution model that represents the time change in the refractive index distribution when heat is input to the measured sample 50.

[0050] 10 shows an example of the change in refractive index distribution over time (change in refractive index distribution due to temperature change) when the thickness of the measured sample 50 is 525 μm. The graph in FIG. 10 is calculated from a refractive index distribution model and shows the relationship between the optical thickness and the refractive index distribution. Specifically, in the graph in FIG. 10, the area surrounded by the lines indicating the vertical axis, the horizontal axis, and the refractive index value corresponds to the optical thickness. Therefore, the optical thickness calculated in step S13 can be converted into the refractive index distribution (FIG. 9C) using the refractive index distribution model.

[0051] Next, the temperature distribution calculation unit 423 converts the refractive index distribution into a temperature distribution based on the thermo-optic coefficient (FIG. 9D). Here, the temperature change relative to the initial temperature is obtained by the above analysis. Therefore, to measure the actual temperature distribution of the sample 50 to be measured, the initial temperature is added to the calculated temperature change. The initial temperature may be set by measuring it in advance using a thermocouple, a radiation thermometer, or the like. By following the above procedure, the temperature distribution inside the wafer can be obtained (step S15). The response speed of the temperature measurement in this embodiment was 1 ms or less.

[0052] As described above, according to the temperature measurement device and temperature measurement method of this embodiment, the optical thickness of the sample 50 is calculated from the reflectance variation caused by a temperature change of the sample 50, and the refractive index distribution is calculated from the optical thickness using a refractive index distribution model that represents the relationship between the refractive index distribution in the thickness direction of the sample 50 and the optical thickness when the temperature changes. Furthermore, the temperature distribution of the sample 50 is calculated by converting the refractive index distribution into a temperature distribution based on the thermo-optic coefficient of the sample 50. Therefore, the temperature distribution can be calculated at high speed without performing a fitting process for reflectance variation or transmittance variation, making it possible to measure temperature in real time.

[0053] Furthermore, in the temperature measurement device and temperature measurement method according to this embodiment, the temperature distribution can be calculated using a refractive index distribution model, thermo-optic coefficient, etc., which have been derived in advance through measurements, etc., and therefore it is possible to accurately measure the temperature of the sample 50 to be measured, including the surface temperature.

[0054] As described above, the temperature measurement device according to this embodiment calculates the optical thickness of the sample from the time change in the intensity of reflected or transmitted light, and calculates the refractive index distribution from the optical thickness using a refractive index distribution model that represents the relationship between the refractive index distribution in the thickness direction of the sample and the optical thickness as the temperature changes. The temperature measurement device then calculates the temperature distribution of the sample by converting the refractive index distribution into a temperature distribution based on the thermo-optic coefficient of the sample. Generally, the relationship between the optical thickness and the temperature distribution is not uniquely determined for various temperature change states. In contrast, the present invention calculates the thermal diffusion process from the time change in the intensity of reflected or transmitted light, and sequentially converts it into the optical thickness and temperature distribution based on this. Therefore, it is possible to accurately measure the temperature of the sample even when the heating rate and cooling rate vary.

[0055] Furthermore, although the temperature measurement device according to the present embodiment calculates the refractive index distribution from the optical thickness using a refractive index distribution model and converts the refractive index distribution into a temperature distribution based on the thermo-optic coefficient of the sample, the method of deriving the temperature distribution is not limited to this. For example, when heat treatment is performed on samples of the same material and thickness and similar temperature measurements are repeatedly performed, the temperature measurement device may measure the temperature using a function, conversion table, or the like that calculates the temperature distribution of the sample from the relationship between the refractive index distribution in the thickness direction of the sample and the optical thickness as the temperature changes. In this case, the temperature measurement device may measure the temperature of the sample using a function, conversion table, or the like that derives the temperature distribution that is created in advance based on data such as the measured temperature distribution and stored in the memory unit 43.

[0056] Second Embodiment In the first embodiment, the beam splitter 20 is disposed between the collimator 13 and the measured sample 50, and the reflected light is split from the optical path of the measurement light emitted from the collimator 13 and incident on the light detection unit 30. However, the method for separating the incident light on the measured sample 50 from the reflected light is not limited to this. For example, the measurement light and the reflected light may be separated by changing the structure of the optical fiber 12. In the present embodiment, a temperature measurement device 1′ is described in which the optical path of the measurement light and the optical path of the reflected light are separated by using an optical fiber 12′ having a different configuration from the optical fiber 12 according to the first embodiment instead of the beam splitter 20.

[0057] Specifically, as shown in FIG. 11 , light emitted from the light source 11 is coupled into an optical fiber 12′, passes through a collimator 13 near the sample 50, and is converted into roughly parallel light, which is then irradiated onto the sample 50. The reflected light is coupled back into the optical fiber 12′ via the collimator 13 and separated from the light from the light source 11. The reflected light separated by the optical fiber 12′ is incident on a photodiode 31 of the light detection unit 30. A photocurrent generated in the photodiode 31 is converted into a voltage signal by a voltage output unit 32. The voltage signal is converted into a digital signal by an analog interface 41 of the analysis unit 40 and transmitted to an analysis unit 42 for analysis. This allows the temperature measurement device 1′ to calculate temperature information of the sample 50 in real time.

[0058] Possible methods for emitting and collecting measurement light using the optical fiber 12' include a method using a three-port single-mode fiber circulator, a method using a double-clad fiber, etc. In both the method using a three-port single-mode fiber circulator and the method using a double-clad fiber, the optical fiber 12' is expensive, and therefore these methods are not very versatile.

[0059] In this embodiment, a fiber bundle made up of multiple optical fibers is used. This allows for more inexpensive emission and collection of measurement light. More specifically, the fiber bundle is made up of a single-mode fiber or a multi-mode fiber with a diameter of 50 μm or less that transmits incident light from the light source 11 to the measured sample 50, and a multi-mode fiber that transmits reflected light from the measured sample 50 (FIG. 12A). Alternatively, a fiber bundle having a structure in which a single-mode fiber or a multi-mode fiber with a diameter of 50 μm or less is at the center and is surrounded by multi-mode fibers may be used as the optical fiber 12' (FIG. 12B).

[0060] The optical fiber 12' into which the measurement light from the light source 11 is coupled is a single-mode or multimode fiber with a diameter of 50 μm or less, and the coherence of the measurement light is maintained. The measurement light emitted from the end of the optical fiber 12' is collimated by the collimator 13 and irradiated onto the sample 50 under measurement. The light reflected from the sample 50 under measurement is again incident on the collimator 13 and focused at the end of the optical fiber 12'. Since the reflected light does not need to be coherent, it can be guided to the light detection unit 30 by a multimode fiber with a large core diameter.

[0061] To evaluate the level of signal that can be collected using the above-described fiber bundle, the light intensity at each point shown in Fig. 13 was measured using a power meter. More specifically, an infrared laser light source was coupled with a single-mode fiber SM, and the light intensity of the light emitted from the collimator and reflected by an aluminum mirror was measured at measurement point P1 in Fig. 13. In addition, the light intensity of the reflected light collected by the multimode fiber MM via the collimator was measured at measurement point P2. The light collection efficiency of the reflected light by the fiber bundle can be evaluated based on the ratio of the light intensity at measurement point P2 to the light intensity at measurement point P1.

[0062] Fig. 14 shows the measurement results of the light collection efficiency in fiber bundles with different arrangements of single-mode fibers SM and multimode fibers MM. The Rate (%) on the vertical axis of Fig. 14 is the light intensity ratio obtained by dividing the light intensity at measurement point P2 by the light intensity at measurement point P1. As shown in Fig. 14, even if there is a misalignment in the arrangement of the single-mode fibers SM and multimode fibers MM in the fiber bundle, it is possible to obtain a light collection efficiency of approximately 60%, and it is clear that sufficient light intensity can be obtained for temperature measurement.

[0063] Figure 15 is a graph showing an example of the results of temperature measurement using the fiber bundle of this example. More specifically, a silicon wafer was placed in the position of the aluminum mirror in Figure 13, and reflectivity measurements and temperature analysis were performed while heating with a halogen lamp. As shown in Figure 15(A), it can be seen that a clear reflectivity signal was obtained that oscillated with changes in the temperature of the silicon wafer. Furthermore, as shown in Figure 15(B), it can be seen that real-time temperature measurement is possible using the fiber bundle of this example.

[0064] As described above, the temperature measuring device 1' according to this embodiment can be configured so that the collimator 13 that emits measurement light to the sample 50 under test and the light detecting unit 30 are separated and connected by the optical fiber 12'. This allows the head unit placed near the sample 50 under test to be configured only with the collimator 13 and the connected end of the optical fiber 12', making it possible to reduce the size. This allows for greater flexibility in the measurement target, measurement location, etc.

[0065] (Modification) In the first embodiment described above, as shown in Fig. 16(A), the measurement light is irradiated perpendicularly onto one surface of the sample 50 under measurement, and the temperature is measured from the change in intensity of the reflected light. However, this is not limited to this. For example, as shown in Fig. 16(B), the temperature may be measured from the change in intensity of the transmitted light. Furthermore, as shown in Figs. 16(C) and 16(D), the measurement light may be irradiated obliquely onto one surface of the sample 50 under measurement, and the temperature may be measured from the change in intensity of the reflected light or the transmitted light. This increases the degree of freedom in the arrangement of the light emitting unit 10 and the light detecting unit 30.

[0066] Furthermore, although the second embodiment has been described with respect to a single measurement location, this is not limiting. As shown in Fig. 17, the configuration of the fiber bundle may be changed to emit multiple measurement beams. In the temperature measuring device 1' according to the second embodiment, the head unit can be made smaller, making it possible to easily measure the temperature at multiple measurement locations.

[0067] The temperature measurement method according to each of the above embodiments can be realized using a normal computer system. For example, a computer program for executing the above temperature measurement operations can be distributed via a network and installed on a computer, causing the computer to function as an analysis unit for the above temperature measurement device.

[0068] This invention allows various embodiments and modifications without departing from the broad spirit and scope of this invention. Furthermore, the above-described embodiments are intended to explain this invention and do not limit the scope of this invention. That is, the scope of this invention is defined by the claims, not the embodiments. Various modifications made within the scope of the claims and the meaning of the invention equivalent thereto are considered to be within the scope of this invention.

[0069] The present invention is suitable for a temperature measurement device that measures the temperature distribution of a sample at high speed, and is particularly suitable for measuring temperature changes during heat treatment of a semiconductor wafer, where the temperature changes occur rapidly in a short period of time.

[0070] 1, 1' temperature measuring device, 10 light emitting section, 11 light source, 12, 12' optical fiber, 13 collimator, 20 beam splitter, 30 light detecting section, 31 photodiode, 32 voltage output section, 40 analysis unit, 41 analog interface, 42 analysis section, 421 phase calculation section, 422 optical thickness calculation section, 423 temperature distribution calculation section, 43 memory section, 44 display section, 45 input section, 50 measured sample

Claims

1. A temperature measurement device comprising: a light emitting unit that generates coherent continuous measurement light; a light detecting unit that detects reflected light or transmitted light of the continuous measurement light irradiated onto a sample to be measured; and an analyzing unit that calculates a temperature distribution of the sample to be measured based on the intensity of the reflected light or transmitted light detected by the light detecting unit, wherein the analyzing unit calculates the optical thickness of the sample to be measured from the change over time in the intensity of the reflected light or transmitted light, and calculates the temperature distribution of the sample to be measured based on the refractive index distribution in the thickness direction of the sample to be measured and the optical thickness as the temperature changes.

2. The temperature measuring device according to claim 1, characterized in that the analysis unit calculates the refractive index distribution from the optical thickness using a refractive index distribution model that represents the relationship between the refractive index distribution in the thickness direction of the measured sample when the temperature changes and the optical thickness, and calculates the temperature distribution of the measured sample by converting the refractive index distribution into a temperature distribution based on the thermo-optic coefficient of the measured sample.

3. The temperature measuring device according to claim 2, characterized in that the refractive index distribution model is derived by converting the change in temperature distribution over time in the thickness direction calculated based on a thermal diffusion model of the sample to the change in refractive index over time based on the thermo-optic coefficient.

4. A temperature measuring device according to any one of claims 1 to 3, characterized in that the light emitting unit comprises a light source, a collimator, and an optical fiber connecting the light source and the collimator, the light source generating laser light with a linewidth of 10 MHz or less, and the optical fiber being a single-mode optical fiber or a multi-mode optical fiber with a core diameter of 50 μm or less.

5. A temperature measuring device according to any one of claims 1 to 3, characterized in that the light emitting unit comprises a light source, a collimator, and an optical fiber connecting the light source, the light detecting unit and the collimator, the light source generating laser light with a linewidth of 10 MHz or less, and the optical fiber being a bundle of a single mode optical fiber or a multimode optical fiber with a core diameter of 50 μm or less and a multimode optical fiber.

6. A temperature measurement method comprising: irradiating a sample to be measured with continuous coherent measurement light; detecting reflected or transmitted light of the continuous measurement light; calculating the optical thickness of the sample to be measured from the change over time in the intensity of the reflected or transmitted light; and calculating the temperature distribution of the sample to be measured based on the refractive index distribution in the thickness direction of the sample to be measured and the optical thickness when the temperature changes.

7. A program that causes a computer to operate as an analysis unit that calculates the optical thickness of a sample to be measured from the change over time in the intensity of reflected light or transmitted light of continuous coherent measurement light irradiated onto the sample, and calculates the temperature distribution of the sample to be measured based on the refractive index distribution in the thickness direction of the sample to be measured and the optical thickness when the temperature changes.

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