A method and system for simulating thermal stress under epitaxial conditions

Abstract

This invention relates to the field of thermal stress testing technology for materials, and discloses a method and system for simulating thermal stress testing under epitaxial conditions. The method includes: selecting a graphite substrate with a SiC coating deposited on its surface as the test piece; detecting the warpage, coating crack density, and defect distribution before thermal cycling; and delineating a central test area, an intermediate test area, and an edge test area; placing the test piece in a high-temperature test chamber purged with H2 or an inert gas, and simulating epitaxial conditions through radiation heating and rotational bearing; controlling the test piece to undergo 100-1000 thermal cycles at 1200-1650℃, 5-50 rpm, and a radial temperature difference of 10-60℃; and evaluating the thermal stress level, stress distribution uniformity, and thermal fatigue performance by combining temperature changes, changes in partition height, temperature gradient strain, changes in warpage, and changes in coating crack density. This invention improves the correspondence between the thermal stress test results of the SiC-coated graphite substrate and the actual epitaxial service condition.

Description

Technical Field

[0001] This invention relates to the field of thermal stress testing technology for materials, and more specifically, to a method and system for simulating thermal stress under epitaxial conditions. Background Technology

[0002] In SiC epitaxial equipment, the graphite substrate typically needs to support the wafer and participate in heat transfer in a high-temperature atmosphere. To improve the high-temperature resistance and surface stability of the graphite substrate, a CVD SiC coating is usually applied to the surface of the graphite substrate.

[0003] However, there is a difference in thermal expansion characteristics between the SiC coating and the graphite substrate. During the high-temperature operation of the epitaxial equipment, the substrate is simultaneously subjected to radiative heating, atmospheric flow, rotational motion, and radial temperature gradient, which can easily lead to thermal stress concentration between the coating and the graphite substrate, further causing coating cracks, localized coating peeling, substrate warping, or thermal fatigue damage.

[0004] Existing water-cooled thermal shock tests can usually only reflect the surface crack resistance of materials under low-temperature thermal shock conditions, while conventional high-temperature annealing tests can usually only reflect the stability of materials under overall constant-temperature thermal exposure conditions. It is difficult to simultaneously simulate the radiation heating state, atmosphere flow state, base rotation state, and radial temperature gradient from the center to the edge in the epitaxial furnace, resulting in deviations between the test results and the failure performance under actual epitaxial conditions.

[0005] Therefore, it is necessary to propose a method and system for simulating thermal stress testing under epitaxial operating conditions. By constructing a test environment that closely resembles the operating state of an epitaxial furnace, and combining temperature gradient loading, thermal cycling loading, and multi-index evaluation, quantitative testing of the thermal stress performance of SiC-coated graphite substrates can be achieved. Summary of the Invention

[0006] The purpose of this invention is to provide a method and system for simulating thermal stress under epitaxial conditions to solve the above-mentioned technical problems.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] On one hand, the present invention provides a method for simulating thermal stress under epitaxial conditions, comprising the following steps:

[0009] A graphite substrate with a SiC coating deposited on its surface was selected as the test piece. Before thermal cycling, the warpage of the test piece was measured, the crack density of the SiC coating was checked, and the defect distribution of the SiC coating was checked. The central test area, the middle test area, and the edge test area were delineated on the bearing surface of the test piece.

[0010] The test specimen is placed on a rotating support platform inside a high-temperature test chamber. H2 or inert gas is introduced into the high-temperature test chamber. The rotating support platform is started to rotate the test specimen at 5 rpm to 50 rpm, and the test specimen is heated by a radiation heater.

[0011] While the test piece is rotating, after the test piece is heated to 1200℃ to 1650℃, the temperatures of the central test area, the middle test area, and the edge test area are measured simultaneously. The heating power of the radiation heater at different radial positions is adjusted to maintain the radial temperature difference between the test areas between 10℃ and 60℃.

[0012] The test piece was subjected to 100 to 1000 thermal cycles under the condition that the radial temperature difference was maintained between 10°C and 60°C. Each thermal cycle included heating, holding and cooling.

[0013] During the thermal cycling process, the temperature changes, the duration of the radial temperature difference, and the height changes of each measurement area were recorded, and the temperature gradient strain was determined based on the radial temperature difference and the height changes of each measurement area.

[0014] After the thermal cycling was completed, the warpage of the test piece was measured again, and the crack density and defect distribution of the SiC coating in the center, middle and edge test areas were checked respectively.

[0015] The thermal stress level, stress distribution uniformity, and thermal fatigue performance of the test specimen were obtained based on the changes in warpage before and after thermal cycling, the changes in crack density of the SiC coating, the radial temperature difference, and the temperature gradient strain.

[0016] Preferably, the central testing area is located at the center of the test piece's bearing surface, the intermediate testing area is located between the central testing area and the edge testing area, and the edge testing area is located near the outer periphery of the test piece;

[0017] The boundaries of the central test area, intermediate test area, and edge test area are defined according to the effective bearing capacity of the test piece's bearing surface and the outer diameter of the test piece.

[0018] Preferably, at least three temperature measurement points are provided in the central measurement area, the intermediate measurement area, and the edge measurement area;

[0019] The temperatures of the central measuring area, the middle measuring area, and the edge measuring area are the average values ​​of the temperatures at each measuring point within their respective measuring areas. The radial temperature difference is the difference between the highest and lowest values ​​among the central measuring area temperature, the middle measuring area temperature, and the edge measuring area temperature.

[0020] Preferably, the radial temperature difference control range is 10°C to 60°C;

[0021] When the measured radial temperature difference is less than 10℃, increase the heating power difference between the heating area corresponding to the highest temperature measurement area and the heating area corresponding to the lowest temperature measurement area.

[0022] When the measured radial temperature difference is greater than 60℃, reduce the heating power difference between the heating area corresponding to the highest temperature measurement area and the heating area corresponding to the lowest temperature measurement area.

[0023] Preferably, in a single thermal cycle, the test piece is heated to the target test temperature while rotating, and then enters the heat preservation stage;

[0024] During the heat preservation stage, maintain an H2 or inert gas environment, rotate the test piece, and maintain a radial temperature difference of 10°C to 60°C.

[0025] After the heat preservation is completed, the test piece is cooled to the starting temperature of the next thermal cycle in an H2 or inert gas environment and under rotation, with a cooling rate of 10℃ / min to 30℃ / min.

[0026] Preferably, the height change in each measurement area includes the height change in the central measurement area, the height change in the middle measurement area, and the height change in the edge measurement area;

[0027] The temperature gradient strain is determined based on the radial temperature difference, the duration of the radial temperature difference, the height change of the central measuring area, the height change of the middle measuring area, and the height change of the edge measuring area. Among them, the maximum temperature gradient strain is the maximum value of the ratio of the difference in height change between adjacent measuring areas to the distance between the representative radii of adjacent measuring areas.

[0028] Preferably, warpage detection and coating crack detection are performed on the test specimen before and after thermal cycling;

[0029] The difference between the warpage after thermal cycling and the warpage before thermal cycling is taken as the warpage change.

[0030] The difference between the coating crack density after thermal cycling and the coating crack density before thermal cycling is taken as the coating crack density change.

[0031] Preferably, the thermal stress level is evaluated based on radial temperature difference and temperature gradient strain;

[0032] The uniformity of stress distribution is evaluated based on the differences in temperature gradient strain and coating crack density among the central, intermediate, and edge test areas.

[0033] Thermal fatigue performance is evaluated based on the number of thermal cycles, changes in warpage, and changes in coating crack density.

[0034] Preferably, the test specimens are classified into superior, medium or lower thermal stress resistance performance levels according to the evaluation limits determined by the historical test results of qualified bases of the same specification and the operating conditions of the target epitaxial furnace;

[0035] The thermal stress resistance rating is used to characterize the service stability of the test piece under target epitaxial furnace conditions.

[0036] On the other hand, the present invention also provides an epitaxial operating condition simulation thermal stress testing system for implementing the above-mentioned epitaxial operating condition simulation thermal stress testing method, comprising:

[0037] The high-temperature test chamber has an internal test space for placing a graphite substrate with a SiC coating on its surface.

[0038] A rotating support platform, set inside the high-temperature testing chamber, is used to support and drive the graphite base to rotate;

[0039] A radiation heater is installed at the top of the high-temperature test chamber and has heating areas corresponding to the central test area, the middle test area, and the edge test area respectively.

[0040] An atmosphere supply pipeline is connected to a high-temperature test chamber and is used to introduce H2 or inert gas into the high-temperature test chamber.

[0041] The exhaust pipe is connected to the high-temperature test chamber and is used to exhaust the test gas inside the high-temperature test chamber.

[0042] Multiple temperature measuring elements are arranged facing the central measuring area, middle measuring area and edge measuring area of ​​the graphite base respectively;

[0043] Warpage detection piece, used to measure the warpage of a graphite base before and after thermal cycling, as well as the height change of each measurement area during thermal cycling;

[0044] Crack detection component, used to check the crack density of SiC coating before and after thermal cycling of graphite substrate;

[0045] The evaluation process receives test results from multi-point temperature measuring devices, warpage detection devices, and crack detection devices, and outputs the thermal stress level, stress distribution uniformity, thermal fatigue performance, and thermal stress resistance level of the graphite base.

[0046] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0047] This invention creates a testing environment that closely resembles the operating conditions of an epitaxial furnace by combining radiation heating, high-temperature atmosphere, and rotational load-bearing. This makes the thermal stress testing conditions of the SiC-coated graphite substrate more closely resemble the target epitaxial working conditions, thereby improving the correspondence between the test results and the actual service conditions.

[0048] By measuring the temperature in the central, intermediate, and edge test areas and maintaining the radial temperature difference between 10°C and 60°C, the test process can reflect the strain differences and crack distribution differences of the SiC-coated graphite substrate under a radially non-uniform thermal field, thereby evaluating the stress distribution uniformity of the substrate. Attached Figure Description

[0049] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 An epitaxial working condition simulation thermal stress testing system is provided for embodiments of the present invention.

[0051] In the figure, 1. High-temperature test chamber; 2. Rotary bearing stage; 3. Graphite base test piece; 31. Graphite substrate; 32. SiC coating; 4. Radiant heater; 41. Central heating area; 42. Intermediate heating area; 43. Edge heating area; 5. Atmosphere supply pipeline; 6. Exhaust pipeline; 7. Multi-point temperature measuring element; 8. Warpage detection element; 9. Crack detection element; 10. Evaluation and treatment element. Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0054] In the embodiments, the SiC-coated graphite substrates used were all disk-shaped graphite substrates for supporting 8-inch wafer epitaxy, with a CVD SiC coating deposited on the substrate surface. Crack density was calculated based on the total crack length per unit area, in mm / mm. 2 The warping amount is the height difference between the highest and lowest points of the bearing surface after fitting to the reference plane.

[0055] See Figure 1The diagram shows the epitaxial working condition simulation thermal stress testing system provided by this invention. The high-temperature test chamber 1 forms a high-temperature sealed test space. A rotating support platform 2 is located at the center of the bottom of the high-temperature test chamber 1. The graphite base test piece 3 is placed on the support surface of the rotating support platform 2 and is supported and rotated by the rotating support platform 2. A radiation heater 4 is disposed above the graphite base test piece 3. The radiation heater 4 includes a central heating region 41, an intermediate heating region 42, and an edge heating region 43. The three heating regions radiate heat towards the central, intermediate, and edge test regions of the graphite base test piece 3, respectively. An atmosphere supply pipeline 5 is connected to one side of the high-temperature test chamber 1 to introduce H2 or inert gas into the high-temperature test chamber 1; an exhaust pipeline 6 is connected to the other side of the high-temperature test chamber 1 to exhaust the test gas. Multi-point temperature measuring element 7 is positioned corresponding to the high-temperature test chamber 1 and measures the temperature in the center, middle, and edge measuring areas of the graphite base test piece 3. Warpage detection element 8 performs height scanning on the bearing surface of the graphite base test piece 3. Crack detection element 9 captures images of cracks on the SiC coating surface. Evaluation processing element 10 is located outside the high-temperature test chamber 1 and is connected to the multi-point temperature measuring element 7, warpage detection element 8, and crack detection element 9 via data cable or communication interface. After receiving data, it generates thermal stress evaluation results.

[0056] It should be noted that the heating power difference at different radial positions refers to the power difference between the heating areas corresponding to the central, intermediate, and edge measuring zones in the radiant heater. The temperature distribution relationships of the central, intermediate, and edge measuring zones differ, and the adjustment direction of the heating power difference differs accordingly. When it is necessary to increase the radial temperature difference, the power difference between the heating areas corresponding to the highest and lowest temperatures is increased; conversely, when it is necessary to decrease the radial temperature difference, the power difference between the heating areas corresponding to the highest and lowest temperatures is decreased. This maintains the radial temperature difference between the three measuring zones within the target control range.

[0057] In addition, the starting temperature of the next thermal cycle is lower than the target test temperature and corresponds to the temperature drop in the target epitaxial furnace condition. When simulating temperature fluctuations in continuous epitaxial production, the starting temperature of the next thermal cycle can be selected from 500℃ to 800℃; when used for accelerated thermal fatigue evaluation, the starting temperature of the next thermal cycle can be selected from room temperature to 500℃. When comparing test pieces from the same batch, the starting temperature of the next thermal cycle remains consistent.

[0058] In this embodiment of the invention, the thermal stress level, stress distribution uniformity, and thermal fatigue performance are evaluated as follows.

[0059] The level of thermal stress is characterized by both radial temperature difference and temperature gradient strain. Under the target test temperature and the same number of thermal cycles, a larger radial temperature difference and a larger temperature gradient strain indicate a higher level of thermal stress between the center and edge of the test piece. If the maximum temperature gradient strain does not exceed 2.0 × 10⁻⁶, the stress level is considered to be within acceptable limits. -4 If the maximum temperature gradient strain is greater than 2.0 × 10⁻⁶, then the thermal stress level falls into the lower range; if the maximum temperature gradient strain is greater than 2.0 × 10⁻⁶, then the thermal stress level falls into the lower range. -4 And not greater than 5.0 × 10 -4 If the thermal stress level is within the medium range, then the maximum temperature gradient strain is greater than 5.0 × 10⁻⁶. -4 If the thermal stress level falls into the higher range, then the thermal stress level will be classified as higher.

[0060] Stress distribution uniformity is characterized by the differences in temperature gradient strain and coating crack density among the three test zones. The smaller the difference in crack density among the central, intermediate, and edge test zones, the more uniform the stress distribution. If the crack density variation in the edge or intermediate test zone is significantly higher than in other test zones, then that zone is considered a thermal stress concentration area. The difference in crack density variation is the difference between the maximum and minimum crack density variations among the three test zones.

[0061] Thermal fatigue performance is characterized by the number of thermal cycles, changes in warpage, and changes in coating crack density. Under the same number of thermal cycles, smaller changes in warpage and coating crack density indicate better thermal fatigue performance of the test specimen; maintaining low changes in warpage and coating crack density even after reaching higher numbers of thermal cycles indicates that the test specimen has higher thermal fatigue stability.

[0062] The thermal stress resistance grade is determined comprehensively based on the thermal stress level, stress distribution uniformity, and thermal fatigue performance. The test piece is deemed suitable if the warpage variation is no greater than 30 μm and the crack density variation in any test area is no greater than 0.10 mm / mm². 2 And the maximum temperature gradient strain is no greater than 2.0 × 10⁻⁶. -4 If the warpage of the test specimen is greater than 30 μm but not greater than 80 μm, or the crack density change in any test area is greater than 0.10 mm / mm, then it is classified as a superior thermal stress resistance performance level; 2 And not greater than 0.30 mm / mm 2 Or the maximum temperature gradient strain is greater than 2.0 × 10⁻⁶. -4 And not greater than 5.0 × 10 -4 If the warpage of the test specimen is greater than 80 μm, or the crack density change in any test area is greater than 0.30 mm / mm, then it is classified as a medium thermal stress resistance performance level; 2 Or the maximum temperature gradient strain is greater than 5.0 × 10⁻⁶. -4 If so, it will be classified as a lower thermal stress resistance performance level.

[0063] The above evaluation limits are used to illustrate the grading method in this embodiment. For SiC-coated graphite substrates of different specifications, the evaluation limits can be adjusted based on the historical test results of qualified substrates of the same specifications, the operating conditions of the target epitaxial furnace, and the allowable service life; when comparing test pieces from the same batch, the same evaluation limits are used.

[0064] Example 1

[0065] In this embodiment, a SiC-coated graphite substrate was selected as test piece 1. Test piece 1 has an outer diameter of 260.0 mm, a thickness of 12.0 mm, an effective bearing diameter of 205.0 mm, and a CVD SiC coating thickness of 108 μm.

[0066] Before testing, the surface of the substrate was wiped twice with a lint-free cloth soaked in isopropyl alcohol, then purged with 99.999% nitrogen for 120 seconds, and dried in an oven at 120℃ for 30 minutes. After drying, the warpage of the substrate surface was measured using a laser profilometer. During measurement, the surface was scanned along four radial directions: 0°, 45°, 90°, and 135°. At least 200 height points were collected along each scan line, and the height difference between the highest and lowest points after fitting the reference plane was taken as the warpage. The warpage of test piece 1 before thermal cycling was 38 μm.

[0067] The test piece was divided into a central testing area, an intermediate testing area, and an edge testing area. The central testing area was a circular region with a radius of 0 mm to 30 mm; the intermediate testing area was an annular region with a radius of 30 mm to 75 mm; and the edge testing area was an annular region with a radius of 75 mm to 101.5 mm. Six microscopic inspection fields were selected for each testing area, each with an area of ​​3 mm × 3 mm. Images were taken using a 100x optical microscope, and the total crack length was counted. Before thermal cycling, the crack density in the central testing area of ​​test piece 1 was 0.06 mm / mm². 2 The crack density in the intermediate test zone is 0.07 mm / mm. 2 The crack density in the edge test area is 0.08 mm / mm. 2 The results of the coating defect distribution inspection were as follows: no peeling was observed in the central test area, two pinholes were found in the middle test area, and one shallow scratch with a length of about 0.4 mm was found in the edge test area.

[0068] Test piece 1 was placed on a rotating support platform inside the high-temperature testing chamber, with the support surface facing the radiant heater. The high-temperature testing chamber was first purged with argon gas for 20 minutes at a flow rate of 15 L / min. After purging, H2 was introduced at a flow rate of 12 L / min, maintaining a slight positive pressure of 50 Pa within the chamber. The rotating support platform initially rotated test piece 1 at 20 rpm. The radiant heater then began heating from 400°C at a rate of 20°C / min, reaching 1500°C and holding for 8 minutes. During the cooling phase, the H2 atmosphere and 20 rpm rotation were maintained, with a cooling rate of 20°C / min.

[0069] Temperature measurements were taken using dual-wavelength infrared thermometers in the central, intermediate, and edge measurement zones, with three measurement points in each zone. The temperature of a single zone was calculated as the average of the three measurement points. During the heat preservation phase, the average temperature in the central zone was 1503℃, the average temperature in the intermediate zone was 1489℃, and the average temperature in the edge zone was 1474℃, with an average radial temperature difference of 29℃. During the heat preservation process, the radial temperature difference was controlled between 25℃ and 35℃. When the radial temperature difference was below 25℃, the power difference between the corresponding heating areas in the central and edge zones was increased; when the radial temperature difference was above 35℃, the power difference between the corresponding heating areas in the central and edge zones was decreased.

[0070] Test piece 1 underwent 300 thermal cycles. A single thermal cycle consisted of heating from 400℃ to 1500℃, holding at 1500℃ for 8 minutes, and then cooling back to 400℃. Every 50 thermal cycles, the height changes in the central, intermediate, and edge test areas were recorded. At the end of the 300th thermal cycle, the height change in the central test area was 21 μm, in the intermediate test area 37 μm, and in the edge test area 58 μm. Based on the radial temperature difference, the duration of the radial temperature difference, and the height changes in the three test areas, the maximum temperature gradient strain was determined to be 3.2 × 10⁻⁶. -4 .

[0071] The maximum temperature gradient strain is the maximum strain value obtained by comparing the difference in height variation among the measurement zones with the radial spacing between the zones. The representative radius of each measurement zone is the median value of its corresponding radius range, and the radial spacing between adjacent measurement zones is the distance between the representative radii of two adjacent measurement zones.

[0072] After the thermal cycling was completed, test piece 1 was cooled to room temperature, and the warpage and crack density were measured using the same testing method as before the thermal cycling. The results are shown in Table 1.

[0073] Table 1

[0074]

[0075] After 300 thermal cycles, the warpage of test piece 1 increased by 44 μm. The crack density increase in the edge test area was greater than that in the center and middle test areas, indicating that the edge test area was the main thermal stress concentration area under the conditions of this embodiment. Based on the radial temperature difference, temperature gradient strain, warpage change, and crack density change, test piece 1 was classified as a medium thermal stress resistance performance level.

[0076] Example 2

[0077] In this embodiment, test piece 2 is selected. Test piece 2 has an outer diameter of 260.0 mm, a thickness of 12.0 mm, an effective bearing diameter of 203.0 mm, and a CVD SiC coating thickness of 105 μm. The cleaning, test area division, warpage detection, and crack density statistics methods before testing are the same as in Example 1.

[0078] The warpage of test piece 2 before thermal cycling was 35 μm; the crack density in the central test area was 0.05 mm / mm. 2 The crack density in the intermediate test zone is 0.06 mm / mm. 2 The crack density in the edge test area is 0.06 mm / mm. 2 .

[0079] This embodiment uses an argon atmosphere with an argon flow rate of 18 L / min. The rotating platform initially rotates the test piece 2 at 10 rpm, and the radiant heater heats the test piece 2 from 500°C to 1300°C at a rate of 15°C / min. After holding at this temperature for 10 minutes, the temperature is lowered to 500°C. During the cooling phase, the argon atmosphere and 10 rpm rotation are maintained, with a cooling rate of 15°C / min. The average temperature of the central test area is 1301°C, the average temperature of the middle test area is 1292°C, and the average temperature of the edge test areas is 1281°C. The average radial temperature difference is 20°C. The radial temperature difference is controlled within the range of 17°C to 23°C. The test piece 2 completes 150 thermal cycles.

[0080] At the end of the 150th thermal cycle, the height change in the central measurement area was 9 μm, the height change in the middle measurement area was 14 μm, and the height change in the edge measurement area was 21 μm. The maximum temperature gradient strain was 1.4 × 10⁻⁶. -4 The test results after thermal cycling are shown in Table 2.

[0081] Table 2

[0082]

[0083] Test piece 2 showed a warpage increase of 16 μm under conditions of 1300℃, a radial temperature difference of 20℃, and 150 thermal cycles. The crack density growth in all three test areas was less than 0.08 mm / mm. 2 The stress distribution difference is less than that in Example 1. Test specimen 2 is classified as having a better thermal stress resistance performance level.

[0084] Example 3

[0085] In this embodiment, test piece 3 is selected. Test piece 3 has an outer diameter of 260.0 mm, a thickness of 12.0 mm, an effective bearing diameter of 205.0 mm, and a CVD SiC coating thickness of 115 μm. The cleaning, test area division, warpage detection, and crack density statistics methods before testing are the same as in Example 1.

[0086] The warpage of test piece 3 before thermal cycling was 41 μm; the crack density in the central test area was 0.07 mm / mm. 2 The crack density in the intermediate test zone is 0.08 mm / mm. 2 The crack density in the edge test area is 0.09 mm / mm. 2 .

[0087] In this embodiment, an H2 atmosphere was used with a flow rate of 15 L / min. The rotating platform initially rotated the test piece 3 at 45 rpm, while the radiant heater heated the test piece 3 from 400°C to 1600°C at a rate of 25°C / min. After holding at this temperature for 6 minutes, the temperature was lowered back to 400°C. The rotating platform speed was 45 rpm. The average temperature of the central testing area was 1602°C, the average temperature of the middle testing area was 1575°C, and the average temperature of the edge testing areas was 1548°C. The average radial temperature difference was 54°C. The radial temperature difference was controlled within the range of 50°C to 60°C. The test piece 3 underwent 800 thermal cycles.

[0088] At the end of the 800th thermal cycle, the height change in the central measurement area was 61 μm, the height change in the middle measurement area was 96 μm, and the height change in the edge measurement area was 148 μm. The maximum temperature gradient strain was 7.8 × 10⁻⁶. -4 The test results after thermal cycling are shown in Table 3.

[0089] Table 3

[0090]

[0091] Test piece 3 showed an increase in warpage of 127 μm under radial temperature differences of 54 °C and 800 thermal cycles, with a crack density increase of 0.73 mm / mm in the edge test area. 2 The performance was significantly higher than that of the central and intermediate test areas. Test piece 3 was classified as having a lower thermal stress resistance performance level.

[0092] Comparative Example 1

[0093] Test piece 4 was selected for this comparative example. The specifications, SiC coating thickness, cleaning method, and testing aperture of test piece 4 were the same as those in Example 1. The difference was that this comparative example did not control the radial temperature difference between the central test area, the middle test area, and the edge test area; it only performed an overall high-temperature thermal cycle.

[0094] Test piece 4 was heated from 400℃ to 1500℃ in an H2 atmosphere, held at that temperature for 8 minutes, and then cooled back to 400℃. The rotating platform was rotated at 20 rpm, and the number of thermal cycles was 300. During the test, the temperature difference between the three test areas was controlled within 5℃.

[0095] The test results are shown in Table 4.

[0096] Table 4

[0097]

[0098] The crack density variations in the three test zones of test piece 4 were similar. Compared with Example 1, this comparative example can reflect the crack growth caused by overall high-temperature cycling, but the differences in crack growth between zones are not significant, making it impossible to effectively distinguish the degree of stress concentration and difficult to evaluate the uniformity of stress distribution of the graphite substrate under epitaxial radial temperature difference conditions.

[0099] Comparative Example 2

[0100] Test piece 5 was selected for this comparative example. The specifications and testing aperture of test piece 5 are the same as those in Example 1. Test piece 5 was tested using a water-cooled thermal shock method: test piece 5 was first heated to 360°C and held at that temperature for 10 minutes, and then transferred to 25°C deionized water to cool, completing one water-cooled thermal shock cycle; this was repeated 100 times.

[0101] The test results are shown in Table 5.

[0102] Table 5

[0103]

[0104] Test piece 5 did not show significant coating peeling after 100 water-cooled thermal shocks, and the crack density growth was lower than that in Example 1. This result indicates that the water-cooled thermal shock conditions differ from the combined effects of the high-temperature atmosphere of the epitaxial furnace, rotational load, and radial temperature gradient, and cannot fully reflect the thermal stress response of the SiC-coated graphite substrate under epitaxial conditions.

[0105] Results Analysis

[0106] Examples 1 to 3 simulate three epitaxial operating conditions: mild, moderate, and high load, respectively. Different combinations of test temperature, radial temperature difference, and number of thermal cycles resulted in distinguishable differences in the corresponding changes in warpage, coating crack density, and temperature gradient strain. The edge test area exhibited greater crack density growth under a larger radial temperature difference, indicating that this invention can reveal stress concentration regions in SiC-coated graphite substrates within a radially non-uniform thermal field.

[0107] Compared to Comparative Example 1, Example 1, under the same target temperature, same H2 atmosphere, same rotation speed, and same number of thermal cycles, achieved the difference in crack density variation among the three test zones by adding a radial temperature difference control of 10°C to 60°C. Compared to Comparative Example 2, Example 1's test conditions included a high-temperature atmosphere, rotational load, and radial temperature gradient, which more closely approximates the operating conditions of an epitaxial furnace. Therefore, this invention can improve the correlation between the thermal stress test results of SiC-coated graphite substrates and the actual epitaxial service conditions.

[0108] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the present invention.

Claims

1. An epitaxial process simulation thermal stress test method, characterized in that, Includes the following steps: A graphite substrate with a SiC coating deposited on its surface was selected as the test piece. Before thermal cycling, the warpage of the test piece was measured, the crack density of the SiC coating was checked, and the defect distribution of the SiC coating was checked. The central test area, the middle test area, and the edge test area were delineated on the bearing surface of the test piece. The test specimen is placed on a rotating support platform inside a high-temperature test chamber. H2 or inert gas is introduced into the high-temperature test chamber. The rotating support platform is started to rotate the test specimen at 5 rpm to 50 rpm, and the test specimen is heated by a radiation heater. While the test piece is rotating, after the test piece is heated to 1200℃ to 1650℃, the temperatures of the central test area, the middle test area, and the edge test area are measured simultaneously. The heating power of the radiation heater at different radial positions is adjusted to maintain the radial temperature difference between the test areas between 10℃ and 60℃. The test piece was subjected to 100 to 1000 thermal cycles under the condition that the radial temperature difference was maintained between 10°C and 60°C. Each thermal cycle included heating, holding and cooling. During the thermal cycling process, the temperature changes, the duration of the radial temperature difference, and the height changes of each measurement area were recorded, and the temperature gradient strain was determined based on the radial temperature difference and the height changes of each measurement area. After the thermal cycling was completed, the warpage of the test piece was measured again, and the crack density and defect distribution of the SiC coating in the center test area, middle test area and edge test area were checked respectively. The thermal stress level, stress distribution uniformity, and thermal fatigue performance of the test specimen were obtained based on the changes in warpage before and after thermal cycling, the changes in crack density of the SiC coating, the radial temperature difference, and the temperature gradient strain.

2. The epitaxial process simulation thermal stress test method of claim 1, wherein, The central testing area is located at the center of the test piece's bearing surface; the intermediate testing area is located between the central testing area and the edge testing area; and the edge testing area is located near the outer periphery of the test piece. The boundaries of the central test area, intermediate test area, and edge test area are defined according to the effective bearing capacity of the test piece's bearing surface and the outer diameter of the test piece.

3. The method for simulating thermal stress under epitaxial conditions according to claim 1, characterized in that, At least three temperature measurement points are set up in the central measurement area, the middle measurement area, and the edge measurement area; The temperatures of the central measuring area, the middle measuring area, and the edge measuring area are the average values ​​of the temperatures at each measuring point within their respective measuring areas. The radial temperature difference is the difference between the highest and lowest values ​​among the central measuring area temperature, the middle measuring area temperature, and the edge measuring area temperature.

4. The method for simulating thermal stress under epitaxial conditions according to claim 1, characterized in that, The radial temperature difference control range is set at 10℃ to 60℃. When the measured radial temperature difference is less than 10℃, increase the heating power difference between the heating area corresponding to the highest temperature measurement area and the heating area corresponding to the lowest temperature measurement area. When the measured radial temperature difference is greater than 60℃, reduce the heating power difference between the heating area corresponding to the highest temperature measurement area and the heating area corresponding to the lowest temperature measurement area.

5. The method for simulating thermal stress under epitaxial conditions according to claim 1, characterized in that, In a single thermal cycle, the test piece is heated to the target test temperature while rotating, and then enters the heat preservation stage; During the heat preservation stage, maintain an H2 or inert gas environment, rotate the test piece, and maintain a radial temperature difference of 10°C to 60°C. After the heat preservation is completed, the test piece is cooled to the starting temperature of the next thermal cycle in an H2 or inert gas environment and under rotation, with a cooling rate of 10℃ / min to 30℃ / min.

6. The method for simulating thermal stress under epitaxial conditions according to claim 1, characterized in that, The height changes in each measurement area include the height changes in the central measurement area, the height changes in the middle measurement area, and the height changes in the edge measurement areas; The temperature gradient strain is determined based on the radial temperature difference, the duration of the radial temperature difference, the height change of the central measuring area, the height change of the middle measuring area, and the height change of the edge measuring area. Among them, the maximum temperature gradient strain is the maximum value of the ratio of the difference in height change between adjacent measuring areas to the distance between the representative radii of adjacent measuring areas.

7. The method for simulating thermal stress under epitaxial conditions according to claim 1, characterized in that, Warpage and coating crack detection were performed on the test specimens before and after thermal cycling. The difference between the warpage after thermal cycling and the warpage before thermal cycling is taken as the warpage change. The difference between the coating crack density after thermal cycling and the coating crack density before thermal cycling is taken as the coating crack density change.

8. The method for simulating thermal stress under epitaxial conditions according to claim 1, characterized in that, The level of thermal stress is evaluated based on radial temperature difference and temperature gradient strain. The uniformity of stress distribution is evaluated based on the differences in temperature gradient strain and coating crack density among the central, intermediate, and edge test areas. Thermal fatigue performance is evaluated based on the number of thermal cycles, changes in warpage, and changes in coating crack density.

9. The method for simulating thermal stress under epitaxial conditions according to claim 8, characterized in that, Based on the historical test results of qualified bases of the same specification and the evaluation limits determined by the target epitaxial furnace usage conditions, the test pieces are classified into superior, medium or lower thermal stress resistance performance levels. The thermal stress resistance rating is used to characterize the service stability of the test piece under target epitaxial furnace conditions.

10. A system for simulating thermal stress under epitaxial conditions, used to implement the method for simulating thermal stress under epitaxial conditions as described in any one of claims 1-9, characterized in that, include: The high-temperature test chamber has an internal test space for placing a graphite substrate with a SiC coating on its surface. A rotating support platform, set inside the high-temperature testing chamber, is used to support and drive the graphite base to rotate; A radiation heater is installed at the top of the high-temperature test chamber and has heating areas corresponding to the central test area, the middle test area, and the edge test area respectively. An atmosphere supply pipeline is connected to a high-temperature test chamber and is used to introduce H2 or inert gas into the high-temperature test chamber. The exhaust pipe is connected to the high-temperature test chamber and is used to exhaust the test gas inside the high-temperature test chamber. Multiple temperature measuring elements are arranged facing the central measuring area, middle measuring area and edge measuring area of ​​the graphite base, respectively; Warpage detection piece, used to measure the warpage of a graphite base before and after thermal cycling, as well as the height change of each measurement area during thermal cycling; Crack detection component, used to check the crack density of SiC coating before and after thermal cycling of graphite substrate; The evaluation process receives test results from multi-point temperature measuring devices, warpage detection devices, and crack detection devices, and outputs the thermal stress level, stress distribution uniformity, thermal fatigue performance, and thermal stress resistance level of the graphite base.

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