Method and device for measuring zero crossing point temperature of thermal expansion coefficient of quartz glass

Abstract

The invention relates to a measuring method and device, in particular to a method and device for measuring the temperature of a thermal expansion coefficient at a zero crossing point of quartz glass. According to the method, a stress temperature curve is obtained through stress measurement under the temperature gradient, so that the zero crossing point temperature is obtained. According to the method, measurement can be carried out through an independent sample to be measured, so that the measurement cost can be effectively reduced. The measurement process is easy to implement, all measurement and data arrangement can be completed within three hours, the measurement accuracy can be effectively improved through mutual verification of multiple groups of data, calibration is not dependent on experience, and the measurement efficiency can be effectively improved under the condition that the measurement accuracy is guaranteed. The problems that an existing testing method depends on calibration, testing is complex, the testing period is long, efficiency is low, or testing errors are large are solved.

Description

Technical Field

[0001] The invention relates to a measuring method and a device, and in particular to a method and a device for measuring the zero-crossing temperature of the thermal expansion coefficient of quartz glass. Background Art

[0002] The zero crossover temperature (Tzc) of the thermal expansion coefficient of quartz glass is an important indicator for measuring the thermal performance of quartz glass. In the past, the zero crossover temperature was obtained by measuring the thermal expansion coefficient of the material. For example, the patent application disclosed in German patent DE102011085358, "Optical arrangement ie projection lens, for use in extreme UV lithography system, has substrates, where increase of coefficients of one of substrates and / or another increase of coefficients of other substrate includes negative sign", requires the zero crossover temperature of the thermal expansion coefficient of quartz glass in the optical system of EUV lithography. The zero crossover temperature measurement methods of the thermal expansion coefficient of quartz glass mainly include the ejector expansion method, the ultrasonic method, the absolute expansion method (such as Fizeau interferometry, Fabry-Perot interferometry, etc.), the photoelastic differential analysis method, etc.

[0003] The push rod expansion method is a non-absolute measurement method that requires further calibration. In addition, the method is a contact measurement method, and the mechanical stress between the rod and the sample will affect the accuracy of the test results, resulting in relatively low test accuracy.

[0004] The ultrasonic method can quickly and non-destructively measure the thermal expansion coefficient of the sample, and has low requirements for the measurement environment. However, it requires a large amount of data accumulation on the relationship between the absolute thermal expansion coefficient of the sample and the ultrasonic propagation velocity measured at its corresponding position. The measurement of different materials requires calibration according to the specific relationship of the material, otherwise the test error will be large.

[0005] The absolute expansion method is relatively mature, and has developed methods such as Fizeau interferometry, Fabry-Perot interferometry, double-pass Michelson interferometry, dual-path optical heterodyne interferometry, and modified Michelson interferometry to calculate the thermal expansion coefficient by measuring the length change of the sample. However, these optical paths all have a common problem: zero drift effect. Since the thermal expansion coefficient measurement needs to be measured over a large temperature range, the temperature control of the entire process takes a long time. During this period, the optical path difference in the interference optical path will drift due to non-sample factors. This is caused by factors such as mechanical stability, changes in the temperature of mechanical components and lenses, and airflow disturbances, which will bring difficult-to-eliminate measurement errors to the measurement results. In addition, the preparation and measurement of samples during the measurement process is very time-consuming (about two weeks), and the equipment is expensive and has high requirements for operators.

[0006] The photoelastic differential analysis method measures the optical delay of the middle sealing layer to deduce the difference in thermal expansion coefficient between the middle sealing layer glass and the two end sealing layer glasses, and then combines it with standard parts with known thermal expansion coefficients to achieve absolute measurement of the thermal expansion coefficient of the sample. The equipment used is much simpler and faster than that required for absolute expansion measurement. However, the pretreatment of the sample to be tested requires heating it to a temperature higher than the softening point of the glass and then melting and bonding it with two standard parts with known thermal expansion coefficients. After sealing, it needs to be carefully annealed to prevent residual stress due to thermal gradients, so as to ensure that the only residual stress in the finished seal is caused by the expansion difference between the two glasses. The pretreatment process of making the sample and the standard parts into a sandwich seal is costly and inefficient, and other residual stresses during the sample pretreatment process may also affect the experimental results. Therefore, it is necessary to design a method and device for measuring the zero-crossing temperature of the thermal expansion coefficient of quartz glass to solve the above problems. Summary of the invention

[0007] The purpose of the present invention is to provide a method and device for measuring the zero-crossing temperature of the thermal expansion coefficient of quartz glass, which is convenient to test, has a short process, can effectively improve the test efficiency, does not rely on any empirical calibration parameters, effectively improves the accuracy, and reduces the test error, so as to solve the problems that the existing test method relies on calibration, the test is complicated, and the test cycle is long, the efficiency is low, or the test error is large.

[0008] The technical solution of the present invention is: A device for measuring the zero-crossing temperature of the thermal expansion coefficient of quartz glass comprises a vacuum box, a heating plate, a cooling plate, a polarized light source and a stress detection probe, and is characterized in that: the heating plate and the cooling plate are arranged in parallel in the vacuum box, a polarized light source is arranged at the top of the vacuum box between the heating plate and the cooling plate, and a stress detection probe is arranged at the bottom of the vacuum box between the heating plate and the cooling plate. A method for measuring the zero-crossing temperature of the thermal expansion coefficient of quartz glass, characterized in that it comprises the following steps: 1) Fixing the sample to be tested between the heating plate and the cooling plate of the device for measuring the zero-crossing temperature of the thermal expansion coefficient of quartz glass, and placing the heating plate and the cooling plate close to the end surface of the sample to be tested respectively; 2) Evacuate the vacuum box to isolate heat transfer and make the top and bottom end surfaces of the sample to be tested form insulating surfaces; 3) Using a polarized light source and a stress detection probe to measure the stress of the sample to be tested, and obtaining initial stress distribution data of the sample to be tested; 4) The end surface of one side of the sample to be tested is heated by the heating plate, and the end surface of the other side of the sample to be tested is cooled by the cooling plate, so that a stable temperature gradient is formed from the heating plate to the cooling plate of the sample to be tested; 5) Using a polarized light source and a stress detection probe to measure stress of the sample to be tested again, and obtaining heating stress distribution data of the sample to be tested under a temperature gradient; 6) Subtract the initial stress distribution data from the stress distribution data after heating to obtain the stress change distribution data; 7) A stress-temperature diagram of the relationship between stress and temperature is obtained from the relationship between temperature and position and the stress change distribution data; the stress-temperature diagram is calculated and fitted to obtain a temperature-stress curve. In the temperature-stress curve, the temperature at the point where the stress change is the maximum is the zero-crossing temperature Tzc of the thermal expansion coefficient; 8) Repeat steps 1)-7) multiple times to obtain multiple sets of stress-temperature curves. By cross-checking the multiple sets of stress-temperature data, an accurate zero-crossing temperature Tzc of the thermal expansion coefficient can be obtained.

[0009] The principle of the present invention is that a temperature gradient is applied to the sample to be tested, resulting in different degrees of deformation of the sample to be tested on different temperature planes. However, due to the mutual constraints between the planes, thermal stress is generated between the different temperature planes. The modeling is carried out by partial microelement research. Due to the application of different temperature gradients, the model can be simplified into two rods with different thermal expansion coefficients (rod 1 and rod 2, see Figure 2 ) are connected together, and rod 1 and rod 2 are of equal length. Assume that the two rods cannot move relative to each other and do not bend. Their initial temperatures are the same, t0, and the final temperatures of rod 1 and rod 2 are t1 and t2 respectively. Assuming that temperature t1>t2, the thermal expansion coefficients of rod 1 and rod 2 are α1>α2. When the two rods are not restrained by each other, they expand freely. At this time, there is no thermal stress, and their strains are: Δl1=α1(t1-t0)l (1) Δl2=α2(t2-t0)l (2) Where Δl1 represents the strain of rod 1, Δl2 represents the strain of rod 2, and l represents the initial length of the rod.

[0010] Comparing equation 1 and equation 2, we know that Δl1>Δl2, but when the two rods are connected and constrained, their elongation is always the same. Therefore, the actual expansion value of rod 1 is less than the free expansion value of rod 1, and rod 1 is subject to compressive stress. The actual expansion value of rod 2 is greater than the free expansion value of rod 2, and rod 2 is subject to tensile stress. The corresponding strain and elongation are: In the formula: ε is the strain of the rod, ε1 is the strain of rod 1, and ε2 is the strain of rod 2; σ is the stress on the rod, σ1 is the stress on rod 1, and σ2 is the stress on rod 2; E is the tensile and compressive elastic modulus, E1 is the tensile and compressive elastic modulus of rod 1, and E2 is the tensile and compressive elastic modulus of rod 2.

[0011] The final elongation of rod 1 and rod 2 is: Since the two rods are always the same length, the final extension of rod 1 is equal to the final extension of rod 2: In the absence of other external forces, the compressive force on rod 1 is equal to the tensile force on rod 2: σ1A1=-σ2A2 (8) Where A1 and A2 are the cross-sectional areas of rod 1 and rod 2.

[0012] Since it is actually the same sample, taking the same length of microelement, it can be regarded as A1 = A2, E1 = E2 Solving (7) and (8) together, we can obtain: σ2=kα1E(t1-t0) (10) in: When at Tzc, α1 and α2 are positive and negative respectively. At this moment, the k value is the largest, and thus the stress is the largest. Therefore, the temperature at the point where the stress is maximum is the zero-crossing temperature of the thermal expansion coefficient.

[0013] The beneficial effects of the present invention are: The method for measuring the zero-point temperature of the thermal expansion coefficient of quartz glass uses a simple device, is easy to operate, and has low operating difficulty. Since it can be measured through an independent piece of sample to be tested, the measurement cost can be effectively reduced. The measurement process is easy to implement, and all measurements and data collation can be completed within 5 hours. Moreover, through the mutual verification of multiple groups of data, the measurement accuracy can be effectively improved, and it does not rely on empirical calibration, and can effectively improve the measurement efficiency while ensuring the measurement accuracy. The problem that the existing test method relies on calibration, the test is complicated, resulting in a long test cycle, low efficiency, or large test errors is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the structure of the measuring device of the present invention; Figure 2 It is a calculation schematic diagram of the modeling of the present invention; Figure 3 is the initial stress distribution diagram of the present invention; Figure 4 It is the heating stress distribution diagram under the temperature gradient of 0-40°C of the present invention; Figure 5 It is a stress variation distribution diagram under a temperature gradient of 0-40°C of the present invention; Figure 6 Schematic diagram of the stress-temperature curve fitting of the present invention; Figure 7 is the stress position curve of the sample to be tested under different temperature gradients of the present invention; Figure 8 is the stress-temperature curve of the sample to be tested under different temperature gradients of the present invention; Fig. 9 It is the stress-temperature curve of the sample to be tested obtained using the absolute expansion method. In the figure: 1. vacuum box, 2. heating plate, 3. cooling plate, 4. polarized light source, 5. stress detection probe, 6. sample to be tested. DETAILED DESCRIPTION

[0015] The method for measuring the zero-crossing temperature of the thermal expansion coefficient of quartz glass comprises the following steps: Select a suitable sample to be tested. The sample to be tested must have a certain length, width and height ratio, preferably a length-width-height ratio of 2:2:1 (under this ratio, the error caused by the limited length-width ratio is very small and basically does not affect the shape of the stress distribution).

[0016] The sample to be tested is fixed between the heating plate 2 and the cooling plate 3 of the device for measuring the zero-crossing temperature of the thermal expansion coefficient of quartz glass, and the heating plate 2 and the cooling plate 3 are respectively closely attached to the end surfaces of the sample to be tested.

[0017] The device for measuring the zero-point temperature of the thermal expansion coefficient of quartz glass comprises a vacuum box 1, a heating plate 2, a cooling plate 3, a polarized light source 4 and a stress detection probe 5. The heating plate 2 and the cooling plate 3 are arranged in parallel in the vacuum box 1, so that the sample to be measured is heated by the heating plate 2, and the sample to be measured is cooled by the cooling plate 3. The function of the vacuum box 1 is to form a vacuum insulation environment through the vacuum box 1 to avoid the influence of external temperature on the measurement process, thereby ensuring that the measurement is accurate and reliable. A polarized light source 4 is arranged on the top of the vacuum box 1 between the heating plate 2 and the cooling plate 3, and a stress detection probe 5 is arranged on the bottom of the vacuum box 1 between the heating plate 2 and the cooling plate 3. The function of the polarized light source 4 is to detect the change of the polarization state of the light beam passing through the isothermal surface in the sample through the polarized light source 4 in cooperation with the stress detection probe 5, and then detect the stress of the isothermal surface of the sample.

[0018] The vacuum box 1 is evacuated to isolate heat transfer and form insulating surfaces on the top and bottom end faces of the sample to be tested. The method can also be carried out in air or other atmospheres (such as inert gas). However, when this method is carried out in air or atmosphere, heat will be conducted through the air, resulting in an uneven temperature gradient distribution, which will increase the error. Therefore, when carried out in a vacuum chamber, the method is more accurate, which avoids heat leakage into the environment. When using the vacuum box 1, the pressure is 10-30 mmHg. The stress of the sample to be tested is measured by the polarized light source 4 and the stress detection probe 5 to obtain the initial stress distribution data of the sample to be tested (see Figure 3 ).

[0019] The end face of one side of the sample to be tested is heated by the heating plate 2, and the end face of the other side of the sample to be tested is cooled by the cooling plate 3, so that a stable temperature gradient is formed from the heating plate 2 to the cooling plate 3 for the sample to be tested. Since the end face of one side of the sample to be tested is heated and the other side is cooled, and the heating and cooling are continuous processes, during the heating and cooling process, the temperature of one side of the sample to be tested is high and the temperature of the other side is low, and the temperature of the sample to be tested gradually decreases from the heating plate 2 to the cooling plate 3, that is, a temperature gradient from the heating plate 2 to the cooling plate 3 is formed in the sample to be tested. The temperature distribution inside the sample to be tested changes linearly along the horizontal direction under heating and cooling conditions, and the temperature is constant in the vertical direction, forming an isothermal surface. The selection of the heating temperature and the cooling temperature makes it inevitable that a plane inside the sample to be tested obtains an isothermal surface equal to the zero-crossing temperature Tzc of the sample to be tested. Since a uniform temperature gradient needs to be established, a smaller sample is required. The smaller sample requirement also increases the flexibility of selection and makes the measuring device smaller and more economical.

[0020] The stress of the sample to be tested is measured again by using the polarized light source 4 and the stress detection probe 5 to obtain the heating stress distribution data of the sample to be tested under the temperature gradient (see Figure 4 , Figure 4This is a diagram showing the relationship between stress and position after heating measured under a temperature gradient of 0-40°C).

[0021] Subtract the initial stress distribution data from the heating stress distribution data to obtain the stress change distribution data (see Figure 5 ). For example: Figure 4 The initial stress at 5mm is 0.0128Mpa. Figure 3 The heating stress at 5mm is 0.0132Mpa, and the stress change is 0.0128-0.0132=-0.0004Mpa. The stress measurement depends entirely on the position of the stress change in the sample to be measured, rather than the intensity of the strain itself. Therefore, the stress measurement will not be affected by measurement errors caused by factors such as stress optical coefficients or sample finite size elastic corrections.

[0022] The stress-temperature diagram of the relationship between stress and temperature is obtained from the relationship between temperature and position and the distribution data of stress change. Due to the linear change of heat flow and the fact that the thermal conductivity of glass is almost constant in a relatively narrow range near room temperature, the temperature change is linearly related to the position. Therefore, the geometric position of the measured stress can be uniquely associated with the temperature, and the measured value of stress can be expressed at the temperature. The temperature-stress curve is obtained by calculating and fitting the stress-temperature diagram. In the temperature-stress curve, the temperature at the point where the stress change is the maximum is the zero-crossing temperature Tzc of the thermal expansion coefficient (see Figure 6 , Figure 6 The figure is the relationship between the thermal stress generated under the temperature gradient of 0-40℃ and the temperature. The dotted line part is the thermal stress relationship obtained by actual measurement, and the solid line part is the relationship curve between thermal stress and temperature obtained by calculation and fitting. From the solid line fitting part of the figure, it can be seen that the temperature at the maximum thermal stress is 22.32℃, so the zero-crossing temperature Tzc of the sample to be tested is 22.32℃).

[0023] Repeat the above steps many times to obtain multiple sets of stress-temperature curves. By verifying multiple sets of stress-temperature data, the accurate zero-crossing temperature Tzc of the thermal expansion coefficient can be obtained (see Figure 7 , Figure 8 , Fig. 9 , Figure 7 It is the stress position curve measured by the sample under different temperature gradients. The solid line is the stress distribution curve measured when the temperature gradient is 0℃-40℃, the long dashed line is the stress distribution curve measured when the temperature gradient is 5℃-35℃, and the short dashed line is the stress distribution curve measured when the temperature gradient is 10℃-30℃; Figure 8The solid line is the stress-temperature curve measured at a temperature gradient of 0°C-40°C, the long dashed line is the stress-temperature curve measured at a temperature gradient of 5°C-35°C, and the short dashed line is the stress-temperature curve measured at a temperature gradient of 10°C-30°C. The zero-point temperatures Tzc of the samples under different temperature gradients are 22.32°C, 22.69°C, and 22.83°C, respectively, with an error within ±1°C. Fig. 9 The zero-crossing temperature Tzc of the sample to be tested obtained by the absolute expansion method is 22.95°C, which is consistent with Figure 8 The zero-crossing temperature Tzc of the sample to be tested obtained is close to ).

[0024] The method for measuring the zero-point temperature of the thermal expansion coefficient of quartz glass uses a simple device, is easy to operate, and has low operating difficulty. Since it can be measured through an independent piece of sample to be tested, the measurement cost can be effectively reduced. The measurement process is easy to implement, and all measurements and data collation can be completed within 5 hours. Moreover, through the mutual verification of multiple groups of data, the measurement accuracy can be effectively improved, and it does not rely on empirical calibration, and can effectively improve the measurement efficiency while ensuring the measurement accuracy. The problem that the existing test method relies on calibration, the test is complicated, resulting in a long test cycle, low efficiency, or large test errors is solved.

Claims

1. A method for measuring the zero-crossing temperature of the thermal expansion coefficient of quartz glass, characterized in that: The following steps are involved: 1) fixing the sample to be tested between the heating plate (2) and the cooling plate (3) of the device for measuring the zero-crossing temperature of the thermal expansion coefficient of quartz glass, and placing the heating plate (2) and the cooling plate (3) in close contact with the end surface of the sample to be tested respectively; 2) evacuating the vacuum box (1) to isolate heat transfer so that the top and bottom end surfaces of the sample to be tested form heat-insulating surfaces; 3) measuring the stress of the sample to be tested by using a polarized light source (4) and a stress detection probe (5) to obtain initial stress distribution data of the sample to be tested; 4) heating one end surface of the sample to be tested by the heating plate (2) and cooling the other end surface of the sample to be tested by the cooling plate (3), so that a stable temperature gradient is formed from the heating plate (2) to the cooling plate (3) of the sample to be tested; 5) performing stress measurement on the sample to be tested again by using the polarized light source (4) and the stress detection probe (5) to obtain heating stress distribution data of the sample to be tested under the temperature gradient; 6) Subtract the initial stress distribution data from the heating stress distribution data to obtain the stress change distribution data; 7) A stress-temperature diagram of the relationship between stress and temperature is obtained from the relationship between temperature and position and the stress change distribution data; the stress-temperature diagram is calculated and fitted to obtain a temperature-stress curve. In the temperature-stress curve, the temperature at the point where the stress change is the maximum is the zero-crossing temperature Tzc of the thermal expansion coefficient; 8) Repeat steps 1)-7) multiple times to obtain multiple sets of stress-temperature curves. By verifying the multiple sets of stress-temperature data, an accurate zero-crossing temperature Tzc of the thermal expansion coefficient can be obtained.

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