A high-precision thermal expansion coefficient measuring device and method

Abstract

This invention provides a high-precision thermal expansion coefficient measuring device and method, relating to the field of thermal expansion coefficient measurement technology. It includes a vacuum chamber, a thermostat disposed within the vacuum chamber for placing the sample to be tested, and a distance acquisition mechanism disposed within the vacuum chamber for collecting the distance between the two ends of the sample. The distance acquisition mechanism is located outside the thermostat. It also includes a total length measuring component for measuring the distance between the two acquisition points of the distance acquisition mechanism. Based on the technical solution of this invention, multiple laser interferometers are used to measure the length change of the sample to be tested in a vacuum environment. The vacuum environment effectively avoids interference from environmental factors. Through reasonable structural design, processing accuracy requirements, and assembly requirements, multiple errors can be effectively eliminated, thereby improving measurement accuracy.

Description

Technical Field

[0001] This invention relates to the field of thermal expansion coefficient measurement technology, and in particular to a high-precision thermal expansion coefficient measuring device and method. Background Art

[0002] In advanced lithography equipment, such as deep ultraviolet lithography (DUVL) and extreme ultraviolet lithography (EUVL), achieving extremely high etching precision requires exceptionally high thermal stability from key components. These components must be designed to minimize temperature-related effects within a specific temperature range (5–35°C), especially lenses and mirrors. During exposure, the laser irradiation on these lenses inevitably generates heat, which can cause changes in the lens surface shape due to thermal expansion and contraction, leading to phase differences. This directly affects the quality of the laser spot irradiated onto the silicon wafer surface, thus impacting etching precision. Therefore, materials with extremely low coefficients of thermal expansion are typically used to manufacture these components, such as Corning's ULE series ultra-low thermal expansion glass, OHARA's CLEARCERAM glass, and Schott's ZERODUR microcrystalline glass. The development of materials with extremely low coefficients of thermal expansion relies heavily on the development of high-precision methods for measuring the coefficient of thermal expansion. Laser interferometry offers very high measurement accuracy and is well-suited for measuring extremely low coefficients of thermal expansion. Since the measurement principle of laser interferometers is related to the wavelength of the laser, the more stable the wavelength, the smaller the measurement error. The wavelength is related to the refractive index of the medium through which light passes. The refractive index of air is affected by factors such as temperature, air pressure, humidity, and airflow disturbances. Therefore, to eliminate these influencing factors, the measurement process is usually conducted in a vacuum environment. It is generally believed that when the air pressure reaches 10... -3 At the Pa level, gas flow disturbances and convective heat exchange can be ignored. The operating temperature range of components such as lenses in a lithography machine is approximately between 20°C and 50°C; therefore, the measurement range for the thermal expansion coefficient of these materials only needs to cover this temperature range. In a thermal expansion coefficient measurement device, the thermostat, which controls the temperature of the sample under test, is one of its core components. Two requirements apply to the thermostat: first, the temperature control zone must be wide enough to ensure uniform temperature across all parts of the sample; second, it must have very high temperature control accuracy.

[0003] A common laser interferometry method involves fixing one end of the sample and using an interferometer to measure the displacement of the other end. However, this method is susceptible to many factors affecting the fixed end, resulting in limited accuracy. Meanwhile, common approaches use electric heating to change the sample temperature. While electric heating is well-suited for higher temperature ranges, temperature control near room temperature is difficult because stabilizing the temperature requires a balance between heating and cooling. Near room temperature in a vacuum, passive natural heat dissipation is inefficient, making it difficult to achieve thermal equilibrium without active cooling.

[0004] Overcoming these interfering factors is a direction that those skilled in the art should strive to achieve. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned technical problems existing in the prior art. This invention proposes a high-precision thermal expansion coefficient measuring device.

[0006] To achieve the above objectives, the present invention proposes the following technical solution:

[0007] A high-precision thermal expansion coefficient measuring device includes a vacuum chamber, a thermostat, a distance acquisition mechanism, and a total length measuring assembly; the thermostat is disposed inside the vacuum chamber and is used to place the sample to be tested.

[0008] The distance acquisition mechanism includes two distance acquisition devices, which are slidably disposed inside the vacuum chamber. The distance between the two distance acquisition devices is adjustable, and the two distance acquisition devices are located on opposite sides of the outside of the thermostat. The total length measuring component is used to measure the distance between the two distance acquisition devices.

[0009] In one embodiment, the two distance acquisition devices are respectively a first distance measuring component and a second distance measuring component disposed on both sides of the thermostat.

[0010] In one embodiment, the thermostat, the first ranging component, and the second ranging component are all mounted on the same base, which is located inside the vacuum cavity. The base is made of a material with a low coefficient of thermal expansion, such as Invar or microcrystalline glass, to minimize system errors. The base is provided with a mounting bracket for supporting the thermostat.

[0011] In one embodiment, the first ranging component includes a first mounting bracket and a first interferometer;

[0012] The first interferometer is mounted on the first mounting bracket and is used to measure the distance from it to one end of the sample to be tested.

[0013] The second ranging component includes a second mounting bracket and a second interferometer:

[0014] The second interferometer is mounted on the second mounting bracket and is used to measure the distance from it to the other end of the sample to be tested.

[0015] The first mounting bracket and the second mounting bracket are both slidably mounted on the base and are located on the outer sides of the thermostat, respectively.

[0016] In one embodiment, the total length measuring component includes a third interferometer and a reflector; the third interferometer is mounted on the corresponding side of the first mounting bracket or the second mounting bracket, and its optical axis is located above the sample to be measured; the reflector is mounted on the second mounting bracket or the first mounting bracket and cooperates with the third interferometer.

[0017] In one embodiment, the optical axes of the first interferometer, the second interferometer, the third interferometer, and the sample under test are parallel to each other. Maintaining parallelism among the four components reduces cosine error.

[0018] In one embodiment, the thermostat is symmetrically provided with measurement through holes on both sides for the optical axes of the first interferometer, the second interferometer, and the third interferometer to pass through.

[0019] In addition, it is preferred to set the two through holes symmetrically so that the optical axes of the three interferometers can pass through them. The two through holes can also be set symmetrically, as long as the optical axis of the third interferometer passes through the two through holes from the surface of the sample to be tested, the optical axis of the first interferometer contacts one end of the sample to be tested through one of the measurement through holes, and the optical axis of the second interferometer contacts the other end of the sample to be tested through the other measurement through hole.

[0020] In one embodiment, both the first and second mounting brackets are equipped with a water-cooling structure to keep the corresponding interferometer at a constant temperature. This ensures the interferometer remains at a constant temperature, preventing thermal drift caused by temperature fluctuations.

[0021] In one embodiment, thermal shielding structures are provided between the first mounting bracket and the thermostat, and between the second mounting bracket and the thermostat, to prevent temperature changes in the thermostat from affecting the measurement values ​​of the corresponding interferometer.

[0022] In one embodiment, the thermostat has a sandwich structure, and a temperature control medium is provided inside the thermostat. The thermostat is provided with a medium inlet pipe and a medium outlet pipe communicating with its interior. Both the medium inlet pipe and the medium outlet pipe are connected to a temperature controller located outside the vacuum chamber.

[0023] Specifically, water at a certain temperature flows into the jacket from the medium inlet pipe in the temperature controller and circulates inside the thermostat, making the temperature of the inner wall of the thermostat uniform and stable. Then, the temperature of the sample to be tested is controlled by the thermal radiation of the inner wall of the thermostat.

[0024] This embodiment uses a water circulation method to change the temperature of the sample under test. Depending on the required temperature range for measuring the coefficient of thermal expansion, different temperature methods can be selected, such as oil, liquid nitrogen, liquid helium, resistance heating, or radiation heating.

[0025] In one embodiment, the sample to be tested is placed inside the thermostat via a bracket, and a temperature sensor for detecting the temperature of the sample to be tested is disposed on the surface of the sample to be tested, and the temperature sensor is electrically connected to the temperature controller.

[0026] A high-precision method for measuring the coefficient of thermal expansion, using the aforementioned high-precision coefficient of thermal expansion measuring device, includes the following steps:

[0027] S1. Place the sample to be tested inside the thermostat;

[0028] S2. Set the measurement temperature to t (K), and measure various distance parameters at this temperature: measure the distance L1 from the third interferometer to the reflector, measure the distance L2 from the first interferometer to one end face of the sample to be tested, and measure the distance L3 from the second interferometer to the right end face of the sample to be tested. The following relationship can be obtained:

[0029] L1+σ1=L2+L+L3 (1);

[0030] In the formula, L is the original length of the sample to be tested; σ1 is the systematic error, which comes from design tolerances, machining errors, and installation errors, and will not change during the measurement process.

[0031] S3, when the temperature of the sample to be tested changes by d t (K), the length of the sample to be tested becomes L+dL, and various distance parameters are measured at this temperature: the distance L1' from the third interferometer to the reflector is measured, the distance L2' from the first interferometer to one end face of the sample to be tested is measured, and the distance L3' from the second interferometer to the other end face of the sample to be tested is measured. The relationship becomes:

[0032] L1'+σ1=L2'+(L+dL)+L3' (2);

[0033] In the formula, dL is the change in length of the sample to be tested; ideally, L1 and L1' are equal, but in reality they may not be equal.

[0034] S4. Calculate the thermal expansion coefficient:

[0035] Subtracting relation (1) from relation (2) yields the temperature change d of the sample. t At that time, the change in the length of the sample to be tested is:

[0036] dL=(L1'-L1)-(L2'-L2)-(L3'-L3) (3);

[0037] The average linear thermal expansion coefficient α of the sample material can be obtained, and the formula for calculating α is as follows:

[0038] α=dL / (L*dt )=[(L1'-L1)-(L2'-L2)-(L3'-L3)] / (L*d t (4).

[0039] The above-mentioned technical features can be combined in various suitable ways or replaced by equivalent technical features, as long as the purpose of the present invention can be achieved.

[0040] The high-precision thermal expansion coefficient measuring device provided by this invention has at least the following advantages compared with the prior art:

[0041] 1. The thermal expansion coefficient measuring device disclosed in this invention uses multiple laser interferometers to measure the length change of the sample under test in a vacuum environment. The vacuum environment effectively avoids interference from environmental factors. Through reasonable structural design, processing accuracy requirements and assembly requirements, multiple errors can be effectively eliminated, thereby improving the measurement accuracy.

[0042] 2. The base is made of a material with a low coefficient of thermal expansion to minimize system errors, such as Invar steel or microcrystalline glass.

[0043] 3. All interferometers and reflectors are mounted on mounting brackets outside the thermostat to prevent temperature changes in the thermostat from affecting the interferometer's measurement values. If necessary, a heat shield structure should be added between the mounting bracket and the thermostat, and a water-cooling structure should be designed inside the mounting bracket to ensure that the interferometer is kept at a constant temperature and to avoid thermal drift caused by temperature fluctuations. Attached Figure Description

[0044] The invention will now be described in more detail with reference to embodiments and the accompanying drawings.

[0045] Figure 1 This is a schematic diagram of a high-precision method for measuring the coefficient of thermal expansion.

[0046] Figure 2 This is a structural diagram of a high-precision thermal expansion coefficient measuring device.

[0047] In the accompanying drawings, the same parts use the same reference numerals. The drawings are not to scale.

[0048] Figure label:

[0049] 11. Third interferometer; 12. First interferometer; 13. First mounting bracket; 14. Second mounting bracket; 15. Second interferometer; 16. Reflector; 17. Sample to be tested; 201. Thermostat; 202. Bracket; 203. Mounting support; 204. Base; 205. Vacuum chamber; 206. Temperature control medium; 207. Medium inlet pipe; 208. Temperature sensor; 209. Medium outlet pipe; 210. Thermal shielding shell; 211. Temperature controller. Detailed Implementation

[0050] The invention will now be further described with reference to the accompanying drawings.

[0051] like Figure 2 As shown, an embodiment of the present invention provides a high-precision thermal expansion coefficient measuring device, including a vacuum chamber 205, a thermostat 201 disposed within the vacuum chamber 205 for placing a sample 17 to be tested, and a distance acquisition mechanism disposed within the vacuum chamber 205 for collecting the distance between the two ends of the sample 17 to be tested. The distance acquisition mechanism is located outside the thermostat 201 and includes two distance acquisition devices. The two distance acquisition devices are slidably disposed within the vacuum chamber 205, and the distance between the two distance acquisition devices is adjustable. The two distance acquisition devices are respectively located on both sides outside the thermostat. A total length measuring component is used to measure the distance between the two distance acquisition devices.

[0052] Specifically, vacuum chamber 205 is a vacuum chamber that provides a vacuum environment with a vacuum level of up to 10⁻³ Pa and provides interfaces for temperature control media, electricity, and signals.

[0053] In one embodiment, the two distance acquisition devices are a first distance measuring component and a second distance measuring component disposed on both sides of the thermostat 201.

[0054] In one embodiment, the thermostat 201, the first ranging component, and the second ranging component are all mounted on the same base 204, which is located inside the vacuum chamber 205. The base 204 is made of a material with a low coefficient of thermal expansion, such as Invar steel or microcrystalline glass, in order to minimize system errors. The base 204 is provided with a mounting bracket 203 for supporting the thermostat 201.

[0055] In one embodiment, the first ranging component includes a first mounting bracket 13 and a first interferometer 12 disposed on the first mounting bracket 13 for measuring the distance to one end of the sample 17 to be tested; the second ranging component includes a second mounting bracket 14 and a second interferometer 15 disposed on the second mounting bracket 14 for measuring the distance to the other end of the sample 17 to be tested; both the first mounting bracket 13 and the second mounting bracket 14 are slidably disposed on the base 204, and are respectively located on both sides outside the thermostat 201.

[0056] In one embodiment, the total length measuring component includes a third interferometer 11 mounted on the first mounting bracket 13 and a reflector 16 mounted on the corresponding side of the second mounting bracket 14; or in another embodiment, the total length measuring component includes a third interferometer 11 mounted on the second mounting bracket 14 and a reflector 16 mounted on the corresponding side of the first mounting bracket 13; in both embodiments, the reflector 16 and the third interferometer 11 cooperate to measure the distance between them, and the optical axis of the third interferometer 11 is located above the sample 17 to be measured.

[0057] Specifically, this embodiment uses a three-interferometer expansion coefficient measurement device consisting of a first interferometer 12, a second interferometer 15, and a third interferometer 11. In addition, multiple first interferometers 12, second interferometers 15, and third interferometers 11 can be set, and their respective distances can be calculated by averaging. This method can reduce errors.

[0058] In one embodiment, the optical axes of the first interferometer 12, the second interferometer 15, the third interferometer 11, and the sample 17 to be tested are placed parallel to each other. Maintaining parallelism among the four components reduces cosine error.

[0059] In one embodiment, the thermostat 201 is symmetrically provided with measurement through holes on both sides for the optical axes of the first interferometer 12, the second interferometer 15, and the third interferometer 11 to pass through.

[0060] In addition, it is preferred to set the two through holes symmetrically so that the optical axes of the three interferometers can pass through them. The two through holes can also be set symmetrically, as long as the optical axis of the third interferometer 11 passes through the two through holes from the surface of the sample 17 to be tested, the optical axis of the first interferometer 12 contacts one end of the sample 17 to be tested through one of the measurement through holes, and the optical axis of the second interferometer 15 contacts the other end of the sample 17 to be tested through the other measurement through hole.

[0061] In one embodiment, either the first mounting bracket 13 or the second mounting bracket 14 is equipped with a water-cooling structure to keep the corresponding interferometer at a constant temperature. This ensures that the interferometer remains at a constant temperature, preventing thermal drift caused by temperature fluctuations.

[0062] Specifically, to facilitate the installation of the water-cooling structure, both the first mounting bracket 13 and the second mounting bracket 14 are square plates with a certain thickness. The specific thickness can be selected according to the actual situation. The water-cooling structure of both the first mounting bracket 13 and the second mounting bracket 14 is a circulating cooling chamber. In addition, a water storage tank can be installed in the base 204. The bottom of the circulating cooling chamber of the first mounting bracket 13 or the second mounting bracket 14 is connected to the water storage tank through an inlet hose and an outlet hose. In order to achieve the same temperature as the thermostat 201, the water storage tank is connected to the thermostat 201 through inlet and outlet pipes.

[0063] Since both the first mounting bracket 13 and the second mounting bracket 14 are slidably mounted on the base 204, in order to ensure the sealing performance of the cooling structure during movement, the lengths of the inlet hoses and outlet hoses connected to each circulating cooling chamber have a certain adjustment space (a preferred method is that the inlet hoses and outlet hoses are connected in a spiral state between the circulating cooling chamber and the water tank, which facilitates the stretching and compression of the corresponding inlet hoses and outlet hoses during the movement of the first mounting bracket 13 and the second mounting bracket 14, thereby achieving the adjustment of the distance between the first mounting bracket 13 and the second mounting bracket 14 while ensuring the cooling function).

[0064] In one embodiment, heat shielding structures are provided between the first mounting bracket 13 and the thermostat 201, and between the second mounting bracket 14 and the thermostat 201. This prevents temperature changes in the thermostat 201 from affecting the measurement values ​​of the corresponding interferometer.

[0065] In one embodiment, the thermostat 201 has a sandwich structure, and a temperature control medium 206 is provided inside the thermostat 201. A medium inlet pipe 207 and a medium outlet pipe 209 communicating with the interior are provided on the thermostat 201. Both the medium inlet pipe 207 and the medium outlet pipe 209 are connected to a temperature controller 211 located outside the vacuum chamber 205.

[0066] In one embodiment, to prevent temperature changes in the thermostat 201 from affecting the base 204, a heat shield shell 210 is wrapped around the thermostat 201.

[0067] Specifically, water at a certain temperature in the temperature controller 211 flows into the jacket through the medium inlet pipe 207 and circulates within the thermostat 201, ensuring a uniform and stable temperature on the inner wall of the thermostat 201. The temperature of the sample 17 under test is then controlled by thermal radiation from the inner wall of the thermostat 201. Water is typically chosen as the temperature control medium 206, and the water bath structure within the thermostat 201 must be appropriately designed to ensure temperature uniformity within the space containing the sample.

[0068] In this embodiment, a water circulation method is used to change the temperature of the sample 17 to be tested. Depending on the required temperature range for measuring the coefficient of thermal expansion, different temperature methods such as oil, liquid nitrogen, liquid helium, resistance heating, and radiation heating can be selected.

[0069] In one embodiment, the sample 17 to be tested is placed in the thermostat 201 via a bracket 202, and a temperature sensor 208 for detecting the temperature of the sample 17 is provided on the surface of the sample 17. The temperature sensor 208 is electrically connected to the temperature controller 211.

[0070] like Figure 1As shown, an embodiment of the present invention also provides a high-precision method for measuring the coefficient of thermal expansion, using the aforementioned high-precision coefficient of thermal expansion measuring device. Since this device consists of three interferometers, this embodiment provides a three-interferometer method for measuring the coefficient of thermal expansion, comprising the following steps:

[0071] S1. Place the sample to be tested 17 inside the thermostat 201;

[0072] S2. Set the measurement temperature to t (K), and measure various distance parameters at this temperature: measure the distance L1 from the third interferometer 11 to the reflector 16, measure the distance L2 from the first interferometer 12 to one end face of the sample 17 to be tested, and measure the distance L3 from the second interferometer 15 to the right end face of the sample 17 to be tested. The following relationship can be obtained:

[0073] L1+σ1=L2+L+L3 (1);

[0074] In the formula, L is the original length of the sample 17 to be tested; σ1 is the systematic error, which comes from design tolerance, machining error and installation error, and will not change during the measurement process;

[0075] S3, when the temperature of the sample to be tested changes by d t (K), the length of the sample 17 to be tested becomes L+dL, and various distance parameters are measured at this temperature: the distance L1' from the third interferometer 11 to the reflector 16 is measured, the distance L2' from the first interferometer 12 to one end face of the sample 17 to be tested is measured, and the distance L3' from the second interferometer 15 to the other end face of the sample 17 to be tested is measured. The relationship becomes:

[0076] L1'+σ1=L2'+(L+dL)+L3' (2);

[0077] In the formula, dL is the change in length of the sample 17 to be tested; ideally, L1 and L1' are equal, but in reality they may not be equal.

[0078] S4. Calculate the thermal expansion coefficient:

[0079] Subtracting relation (1) from relation (2) yields the temperature change d of the sample. t At that time, the change in the length of the sample to be tested is:

[0080] dL=(L1'-L1)-(L2'-L2)-(L3'-L3) (3);

[0081] The average linear thermal expansion coefficient α of the material of the sample 17 to be tested can be obtained. The formula for calculating α is as follows:

[0082] α=dL / (L*d t)=[(L1'-L1)-(L2'-L2)-(L3'-L3)] / (L*d t (4).

[0083] Error analysis of measuring devices and methods:

[0084] Errors caused by environmental factors: Since the measurement principle of laser interferometers is related to the wavelength of the laser, the more stable the wavelength, the smaller the measurement error. The wavelength is related to the refractive index of the medium through which light passes. If the interferometer operates in an atmospheric environment, the refractive index of the air is affected by factors such as temperature, air pressure, humidity, and airflow disturbances, thus increasing the measurement error. To obtain a high-precision coefficient of thermal expansion, the measurement process of the method disclosed in this embodiment is completed in a vacuum environment. It is generally considered that when the air pressure reaches the order of 10⁻³ Pa, gas flow disturbances and convective heat exchange can be ignored.

[0085] Systematic error: The systematic error σ1 is introduced by design tolerance, machining error, and installation error, which causes the length value obtained by the third interferometer to be unequal to the sum of the length values ​​of the first interferometer, the second interferometer, and the length of the sample to be measured. The systematic error is considered to be unchanged after the measuring device is assembled, and from the measurement principle, the systematic error will not affect the measurement result and has been eliminated.

[0086] Cosine error: Cosine error originates from the non-parallelism between the interferometer's optical axis and the axis of the sample under test. Assuming the included angle is θ, this causes a deviation related to cosθ between the measured value and the actual value after the sample length changes. Cosine error cannot be completely eliminated, but it can be minimized by improving machining and assembly accuracy.

[0087] Dead path error: Dead path error also originates from environmental factors and refers to the error caused by the influence of environmental factors on the wavelength outside the calibration length of the interferometer. This error has also been eliminated.

[0088] Abbe error: This device can eliminate Abbe error to the greatest extent by adjusting the positions of the second and third interferometers so that their laser optical axis is as close as possible to the axis of the sample to be measured.

[0089] Inherent error of laser interferometer: This error can be minimized by selecting a laser interferometer with extremely high measurement accuracy.

[0090] In summary, the thermal expansion coefficient measuring device and method use multiple laser interferometers to measure the length change of the sample under test in a vacuum environment. The vacuum environment effectively avoids interference from environmental factors. Through reasonable structural design, processing accuracy requirements and assembly requirements, multiple errors can be effectively eliminated, thereby improving the measurement accuracy.

[0091] In the description of this invention, it should be understood that the terms "upper", "lower", "bottom", "top", "front", "rear", "inner", "outer", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0092] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A high-precision thermal expansion coefficient measuring device, characterized in that, include: Vacuum cavity; A thermostat, which is located inside the vacuum chamber, is used to place the sample to be tested; The distance acquisition mechanism includes two distance acquisition devices, which are slidably disposed in the vacuum chamber. The distance between the two distance acquisition devices is adjustable, and the two distance acquisition devices are respectively located on both sides of the outside of the thermostat. as well as A total length measuring component, used to measure the distance between the two distance acquisition devices; The two distance acquisition devices are a first distance measuring component and a second distance measuring component respectively disposed on both sides of the thermostat; the thermostat, the first distance measuring component and the second distance measuring component are all disposed on the same base, and the base is located inside the vacuum cavity; The first ranging component includes a first mounting bracket and a first interferometer, which is mounted on the first mounting bracket and used to measure the distance to one end of the sample to be tested; the second ranging component includes a second mounting bracket and a second interferometer, which is mounted on the second mounting bracket and used to measure the distance to the other end of the sample to be tested; wherein the first mounting bracket and the second mounting bracket are both slidably mounted on the base and are respectively located on both sides of the outside of the thermostat; The total length measuring component includes: A third interferometer is mounted on either the first or second mounting bracket, with its optical axis positioned above the sample under test. A reflector is mounted on the corresponding side of the second mounting bracket or the first mounting bracket and cooperates with the third interferometer; The reflector, in conjunction with the third interferometer, is used to measure the distance between the first mounting bracket and the second mounting bracket; The optical axes of the first interferometer, the second interferometer, the third interferometer, and the sample to be tested are parallel to each other.

2. The high-precision thermal expansion coefficient measuring device according to claim 1, characterized in that, The thermostat is symmetrically provided with measurement through holes on both sides for the optical axes of the first interferometer, the second interferometer, and the third interferometer to pass through.

3. The high-precision thermal expansion coefficient measuring device according to claim 1, characterized in that, Both the first mounting bracket and the second mounting bracket are equipped with a water-cooling structure to keep the corresponding interferometer at a constant temperature.

4. The high-precision thermal expansion coefficient measuring device according to claim 1, characterized in that, A heat shield structure is provided between the first mounting bracket and the thermostat, and between the second mounting bracket and the thermostat.

5. The high-precision thermal expansion coefficient measuring device according to claim 1 or 2, characterized in that, The thermostat has a sandwich structure and contains a temperature control medium. The thermostat is equipped with a medium inlet pipe and a medium outlet pipe that communicate with its interior. Both the medium inlet pipe and the medium outlet pipe are connected to a temperature controller located outside the vacuum chamber.

6. The high-precision thermal expansion coefficient measuring device according to claim 1 or 2, characterized in that, The sample to be tested is placed inside the thermostat via a bracket. A temperature sensor for detecting the temperature of the sample to be tested is provided on the surface of the sample, and the temperature sensor is electrically connected to the thermostat.

7. A high-precision method for measuring the coefficient of thermal expansion, using the high-precision coefficient of thermal expansion measuring device as described in claim 1, characterized in that, Includes the following steps: S1. Place the sample to be tested inside the thermostat; S2. Set the measurement temperature to t (K), and measure various distance parameters at this temperature: measure the distance from the third interferometer to the reflector. Measure the distance from the first interferometer to one end face of the sample to be tested. The distance from the second interferometer to the right end face of the sample under test is measured. We can obtain the following relationship: （1）； In the formula, The original length of the sample to be tested; This is a systematic error, originating from design tolerances, machining errors, and installation errors, and it will not change during the measurement process; S3. When the temperature of the sample to be tested changes (K), the length of the sample to be tested becomes Measure various distance parameters at this temperature: measure the distance from the third interferometer to the mirror. Measure the distance from the first interferometer to one end face of the sample to be tested. Measure the distance from the second interferometer to the right end face of the sample. The relation becomes: （2）； In the formula, The change in length of the sample to be tested; S4. Calculate the thermal expansion coefficient: Subtracting equation (1) from equation (2) yields the temperature change of the sample. At that time, the change in the length of the sample to be tested is: （3）； The average linear thermal expansion coefficient of the sample material can be obtained. , The calculation formula is as follows: （4）。

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