Evaluation method for stress distribution uniformity of silicon carbide crystal bar

Abstract

The invention discloses a silicon carbide crystal bar stress distribution uniformity evaluation method, and belongs to the technical field of silicon carbide crystal bar characterization. The evaluation method comprises the following steps that (1) 1-N silicon carbide substrates are prepared from a silicon carbide crystal bar, N is a positive integer and represents the serial number of the silicon carbide substrates, a head piece and a tail piece are selected for polarized light testing, the head piece is a first silicon carbide substrate containing a first end face, the serial number is 1, and the tail piece is a second silicon carbide substrate containing a second end face; the tail piece is the last silicon carbide substrate comprising a second end face, and the serial number is N; and (2) calculating polarized light test results of the head piece and the tail piece, and if the optical path difference value of the head piece and the tail piece is in a range of-5-5nm, determining that the stress of the silicon carbide crystal bar is uniform in the axial direction. According to the method, the stress distribution uniformity in the axial direction of the silicon carbide crystal bar can be accurately and rapidly evaluated by adopting the difference value of the optical path difference of the head piece and the tail piece, the feedback efficiency is improved while the detection cost is reduced, and the production process of the silicon carbide crystal bar can be adjusted in time.

Description

Technical Field

[0001] The present application relates to a method for evaluating the uniformity of stress distribution of a silicon carbide crystal rod, and belongs to the technical field of silicon carbide crystal rod characterization. Background Art

[0002] At present, the technical methods available on the market for preparing silicon carbide single crystals include physical vapor deposition (PVT), solution method, high temperature chemical vapor deposition (HTCVD) and other methods to grow SiC ingots. Then, they are rolled into standard-sized crystal rods, followed by multiple wafer processing steps such as crystal rod cutting, grinding, and polishing to obtain SiC substrates.

[0003] Due to the presence of axial and radial temperature gradients during the growth process, it is necessary to characterize the stress distribution in the grown crystal rod, so as to evaluate the overall crystal rod and provide feedback to the production process, so as to control the quality of the SiC crystal rod through production process adjustments. If the SiC crystal rod is cut and the stress distribution of the SiC crystal rod is measured and counted separately during each characterization, a lot of time will be consumed in the cutting, grinding, polishing and testing process, resulting in increased testing costs, and the feedback cycle for the production process is long, making it difficult to achieve a rapid improvement in the quality of the SiC crystal rod in a short period of time. Summary of the invention

[0004] In order to solve the above problems, a method for evaluating the uniformity of stress distribution of silicon carbide crystal rods is provided. Based on the characteristics of silicon carbide crystal rods, the method uses the difference in optical path difference between the head piece and the tail piece to accurately and quickly evaluate the uniformity of stress distribution in the axial direction of the silicon carbide crystal rod, thereby reducing the detection cost and improving the feedback efficiency, and the production process of the silicon carbide crystal rod can be adjusted in time.

[0005] The present application provides a method for evaluating the uniformity of stress distribution of a silicon carbide crystal rod, comprising the following steps:

[0006] (1) 1 to N silicon carbide substrates prepared from a silicon carbide crystal rod, where N is a positive integer representing the serial number of the silicon carbide substrate, and a head piece and a tail piece are selected for polarized light testing, wherein the head piece is the first silicon carbide substrate including the first end face, and the serial number is 1, and the tail piece is the last silicon carbide substrate including the second end face, and the serial number is N;

[0007] (2) Calculate the polarized light test results of the head piece and the tail piece. If the optical path difference between the head piece and the tail piece is within the range of -5 to 5 nm, the stress of the silicon carbide crystal rod is uniform in the axial direction.

[0008] This evaluation method does not require the entire silicon carbide crystal rod to be cut and processed into a substrate. It only needs to cut, grind and polish the head and tail pieces of the silicon carbide crystal rod into wafers with light-transmitting surfaces, and use polarized birefringence detection to obtain the optical path difference of the head and tail pieces. The optical path difference of the head and tail pieces can be used to evaluate the optical path difference of the entire crystal rod, thereby obtaining the uniformity of stress distribution of the silicon carbide crystal rod, improving the detection efficiency and the accuracy of the detection results, and can be fed back to the production process in a timely manner for process adjustment to obtain silicon carbide crystal rods with stable quality.

[0009] The above naming of the silicon carbide substrate as 1 to N refers to the naming of the silicon carbide substrate prepared from a single silicon carbide crystal rod. The naming between different silicon carbide crystal rods is not continuous, and each silicon carbide crystal rod is named from serial number 1 until it is named to serial number N. In addition, the above effect explains that this evaluation method does not need to test all the cuts of the silicon carbide crystal rod, only the head piece and the tail piece need to be tested. The serial number of the head piece is always 1, and the specific value of the serial number N of the tail piece is calculated based on the thickness of the silicon carbide crystal rod and the thickness of each cut piece. Therefore, it is not necessary to cut all of them, and the specific serial number N of the tail piece in a silicon carbide crystal rod can be obtained.

[0010] Optionally, the optical path difference between the head piece and the tail piece is an optical path difference calculated for the entire area, and the overall optical path difference between the head piece and the tail piece is <10 nm.

[0011] Optionally, the head piece and the tail piece both include an annular area and a central area surrounded by the annular area, the annular area is an area with a width of 3 mm extending inward from the edge, the optical path difference between the head piece and the tail piece is the optical path difference in the central area, and the optical path difference in the central area of ​​the head piece and the tail piece is both <6 nm.

[0012] The optical path difference difference between the head piece and the tail piece in the above step (2) can be either the difference in the overall optical path difference of the piece or the difference in the optical path difference of the central area of ​​the piece. The above two evaluation indicators can both realize efficient and accurate evaluation of the stress distribution of the silicon carbide crystal rod, so as to control the quality of the SiC crystal rod and control the optical path difference range of the SiC crystal rod.

[0013] Optionally, if the head piece and the tail piece follow the following formula, it means that the stress of the silicon carbide crystal rod is uniform as a whole:

[0014] |σ1-σ2|<3nm, σ1 represents the standard deviation of the optical path difference of the head piece, and σ2 represents the standard deviation of the optical path difference of the tail piece.

[0015] The standard deviation of the optical path difference of the head piece can reflect the difference in the optical path difference distribution of the head piece, and the standard deviation of the optical path difference of the tail piece can reflect the uniformity of the optical path difference distribution of the tail piece. The difference between the standard deviations of the optical path difference of the head piece and the tail piece |σ1-σ2| is used as an evaluation index. Combined with the axial evaluation method (the difference in optical path difference between the head piece and the tail piece), it is possible to evaluate the uniformity of the axial and radial distribution of the silicon carbide crystal rod from the head to the tail, and to achieve accurate evaluation while improving detection efficiency.

[0016] Optionally, the method further includes the step of performing polarized light detection on the remaining silicon carbide substrates except the head piece and the tail piece. If the head piece, the tail piece and the remaining silicon carbide substrates follow the following formula, it means that the stress of the silicon carbide crystal rod is uniform in both the axial direction and the in-plane direction:

[0017] Said The value range is 0.8~1.2, The value range is 0.8~1.2, It represents the average value of the standard deviation of the optical path difference of all SiC substrates obtained by cutting the silicon carbide ingot.

[0018] In this way, the above-mentioned evaluation method of axial and radial distribution uniformity can be verified. If this condition is met, it means that the method of using the difference in optical path difference between the head piece and the tail piece to evaluate the axial uniformity of the crystal rod and the method of using the difference in standard deviation of the optical path difference between the head piece and the tail piece to evaluate the in-plane uniformity of the crystal rod are reliable and accurate.

[0019] Although this method improves the evaluation accuracy, it requires the detection of all silicon carbide substrates, which reduces the detection efficiency of this evaluation method. However, this application uses polarized light to detect the optical path difference to evaluate the stress of silicon carbide crystal rods, which has higher detection efficiency than Raman and XRD methods. Therefore, even if the optical path difference of all substrates is detected, the detection efficiency of this evaluation method can still be improved.

[0020] Optionally, σ1 is the standard deviation of the overall optical path difference of the head piece, σ2 is the standard deviation of the overall optical path difference of the tail piece, σ is the average value of the standard deviation of the overall optical path difference of the SiC substrate, and the standard deviation of the overall optical path difference of the head piece and the tail piece are both <6nm.

[0021] Optionally, the head piece and the tail piece each include an annular area and a central area surrounded by the annular area, wherein the annular area is an area extending inward from the edge and having a width of 3 mm.

[0022] σ1 is the standard deviation of the optical path difference in the central area of ​​the head piece, σ2 is the standard deviation of the optical path difference in the central area of ​​the tail piece, and σ is the average value of the standard deviation of the optical path difference in the central area of ​​the SiC substrate. The standard deviation of the optical path difference in the central area of ​​the head piece and the tail piece are both <3nm.

[0023] Similarly, the standard deviation of the optical path difference of the head film and the tail film can be the standard deviation of the optical path difference of the entire film or the standard deviation of the optical path difference of the central area of ​​the film. The above two evaluation indicators can also be verified with each other to improve the accuracy of this evaluation method.

[0024] Optionally, if the head piece and the tail piece follow the following formula, it means that the stress of the silicon carbide crystal rod is uniform as a whole:

[0025] On any horizontal line, σ4 / σ5<1.9, σ4 represents the standard deviation of the optical path difference in the annular area, and σ5 represents the standard deviation of the optical path difference in the central area.

[0026] Optionally, for the head piece and the tail piece, on any horizontal line, the standard deviation of the optical path difference in the annular area is <4nm, and the standard deviation of the optical path difference in the central area is <2nm.

[0027] Optionally, if the optical path difference between the head piece and the tail piece satisfies the following formula:

[0028] △=a(N-1)+b, where △ represents the optical path difference, the unit is nm, the value range of a is -1 to 1, and the value of b is 0.5 to 10.5, the unit is nm, then the stress of the silicon carbide crystal rod is uniform in the axial direction.

[0029] In the above evaluation method, the serial number of the head piece is 1, and the optical path difference value of the head piece is related to b, and the serial number of the tail piece is N, and the optical path difference value of the tail piece is related to both a and b. The above formula is used in this evaluation method to verify the uniformity of the silicon carbide crystal rod, which can further improve the evaluation accuracy and evaluation efficiency.

[0030] Optionally, the value range of a is -0.004 to -0.4 or 0.004 to 0.4.

[0031] Optionally, the surface roughness Ra of the silicon carbide substrate after polishing is not greater than 10 nm.

[0032] The beneficial effects of this application include but are not limited to:

[0033] 1. The method for evaluating the uniformity of stress distribution of a silicon carbide crystal rod of the present application takes two silicon carbide substrates, a head piece and a tail piece, as detection objects. The difference in the optical path difference between the two can be used to evaluate the difference in the axial optical path difference of the crystal rod from the head to the tail. This difference is the stress distribution difference of the crystal rod, thereby accurately knowing the uniformity of stress distribution in the axial direction of the crystal rod.

[0034] 2. The evaluation method for the uniformity of stress distribution of silicon carbide crystal rods of the present application adopts the overall optical path difference difference between the head piece and the tail piece or the optical path difference difference in the central area as the evaluation index of axial uniformity, which can fit the stress distribution characteristics of the silicon carbide crystal rod and improve the accuracy and consistency of the evaluation. In addition, the two evaluation indicators of the overall optical path difference difference and the optical path difference difference in the central area can also be checked against each other to verify the accuracy of the evaluation method.

[0035] 3. The method for evaluating the uniformity of stress distribution of silicon carbide crystal rods in the present application adopts the standard deviation difference of the overall optical path difference of the head piece and the tail piece or the standard deviation difference of the optical path difference in the central area as the evaluation index of radial uniformity. It can be used to know the radial distribution difference of the silicon carbide crystal rod from the head to the tail, and can also achieve accurate and efficient evaluation.

[0036] 4. In the evaluation method of the uniformity of stress distribution of silicon carbide crystal rods of the present application, the two evaluation indicators of the standard deviation difference of the overall optical path difference between the head piece and the tail piece and the standard deviation difference of the optical path difference in the central area of ​​the head piece and the tail piece can also be checked against each other to improve the accuracy of the evaluation method. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0038] Figure 1 This is a schematic diagram of the structure of the induction furnace with precise positioning and installation involved in Example 1 of the present application;

[0039] List of parts and reference numerals:

[0040] 1-furnace chamber; 2-upper flange; 3-lower flange; 4-crucible body; 5-transition crucible cover; 6-crucible holder; 7-external insulation; 8-lower insulation; 9-movable support rod; 10-movable laser positioner; 11-transverse slide rail; 12-transverse rail; 13-graphitized carbon fiber cloth; 14-transverse moving part; 15-longitudinal moving part; 16-lifting assembly; 17-rotating assembly; 18-temperature measuring hole; 19-induction coil. DETAILED DESCRIPTION

[0041] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0042] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0043] Unless otherwise specified, the methods used in the embodiments of the present application are conventional methods in the prior art.

[0044] Example 1

[0045] like Figure 1 As shown, this embodiment provides an induction crystal growth furnace, including a furnace chamber 1 and an upper flange 2 on the top of the furnace chamber 1, and a lower flange 3 on the bottom of the furnace chamber 1. A crucible, an external insulation 7 and a lower insulation 8 are arranged in the furnace chamber 1. The external insulation 7 and the lower insulation 8 form an insulation layer. The crucible is arranged inside the insulation layer. A movable support rod 9 is fixed to the bottom of the lower insulation 8. A moving mechanism is arranged on the top of the lower flange 3. The moving mechanism includes a planar moving component. The planar moving component can drive the movable support rod 9 to drive the insulation layer to move. A closeable slide rail is arranged on the top of the furnace chamber 1, and a movable laser locator 10 is arranged on the closeable slide rail.

[0046] The movable laser locator 10 can move along the enclosed slide rail. The laser locator can determine the outer edge of the crucible and the inner edge of the outer insulation 7 by measuring the round-trip time and combining the distance relationship and then comparing the changing trend of the round-trip time, wherein the outer insulation 7 is the insulation felt, thereby determining the cavity width between the outer insulation 7 and the crucible, and then controlling the planar moving component in the motion mechanism according to the determined cavity width. The planar moving component can control the movable support rod 9 to drive the insulation layer to move, thereby driving the outer insulation 7 to move, and then the width of the cavity between the inner edge of the outer insulation 7 and the outer edge of the crucible can be adjusted to be similar, thereby ensuring the uniformity of the temperature field, reducing the influence of the temperature field disturbance on the growth of SiC, and thus ensuring the quality of SiC products.

[0047] The present application does not limit the implementation method of the plane moving assembly, as long as it can drive the movable support rod 9 to move and adjust within the plane. For example, as an implementation method, the plane moving assembly includes a transverse moving part 14 and a longitudinal moving part 15; the longitudinal moving part 15 is used to control the longitudinal movement of the movable support rod 9; the transverse moving part 14 is used to control the transverse movement of the movable support rod 9.

[0048] It should be noted that the closable slide rail in the present application is a closable type and can be used to protect the movable laser locator 10 and the slide rail. It is opened before crystal growth to allow the movable laser locator 10 to work, and is closed during the crystal growth process, thereby protecting the movable laser locator 10 and the slide rail and preventing them from being affected by the Si atmosphere or SiC atmosphere during the crystal growth process and affecting their subsequent normal operation.

[0049] As a specific implementation, the lower flange 3 is provided with a longitudinal track, and the longitudinal moving part 15 can move longitudinally along the longitudinal track provided on the lower flange 3 under the action of the driving mechanism. Further, the longitudinal moving part 15 is provided with a transverse track 12, and the transverse moving part 14 can move transversely along the transverse track 12 provided on the longitudinal moving part 15 under the action of the driving mechanism, and then drive the movable support rod 9 to move. Through the cooperation of the transverse moving part 14 and the longitudinal moving part 15, the movable support rod 9 can be moved in a plane, thereby driving the movement of the outer insulation 7 to adjust the relative position with the crucible. In addition, the skilled and technical personnel can understand that the order of setting the longitudinal moving part 15 and the transverse moving part 14 can be exchanged. It is only necessary to set the transverse track 12 corresponding to the lower flange 3, and the transverse moving part 14 moves on this transverse track 12, and then set the longitudinal track on the transverse moving part 14, and the longitudinal moving part 15 moves on this longitudinal track, so as to achieve the same function.

[0050] As an implementation mode, the motion mechanism further includes a rotating assembly 17 and a lifting assembly 16; the rotating assembly 17 is used to control the rotation of the movable support rod 9; and the lifting assembly 16 is used to control the movable support rod 9 to rise or fall.

[0051] By setting the rotating component 17, the movable support rod 9 can be rotated, thereby driving the rotation of the external insulation 7. Since the external insulation 7 is easily corroded by the Si atmosphere, its inner edge may change, thereby affecting the cavity distance between the inner edge of the external insulation 7 and the outer edge of the crucible. After the external insulation 7 is set to be rotatable, the movable laser positioner 10 can measure and adjust more radial directions of the external insulation 7, thereby ensuring that the uniformity of the cavity distance between the inner edge of the external insulation 7 and the outer edge of the crucible is more accurate, thereby further improving the uniformity of the temperature field.

[0052] By providing the lifting assembly 16 , the rise or fall of the thermal insulation layer can be controlled, thereby meeting different requirements for the thermal insulation layer during the SiC crystal growth process.

[0053] The present application does not impose any specific limitation on the implementation method of the rotating assembly 17 and the lifting assembly 16, which can be conventionally selected by those skilled in the art. There is no specific limitation on the connection method between the rotating assembly 17, the lifting assembly 16 and the planar moving assembly. For example, the planar moving assembly is arranged at the bottom, the lifting assembly 16 is arranged in the middle, and the rotating assembly 17 is arranged at the top, or the structural order of the three is swapped as long as the effect required by the present application can be normally met. Those skilled in the art can perform conventional implementation or make adjustments and solutions based on some problems that arise.

[0054] As an implementation mode, the closable slide rail includes a transverse slide rail 11 and a longitudinal slide rail, and a movable laser locator 10 is disposed on both the transverse slide rail 11 and the longitudinal slide rail.

[0055] By setting two slide rails, the number of movable laser locators 10 thereon can be increased, thereby improving the efficiency of determining the outer edge of the crucible and the inner edge of the outer insulation 7. At the same time, several movable laser locators 10 work at the same time, which can significantly improve the efficiency of adjusting the cavity distance between the outer edge of the crucible and the inner edge of the outer insulation 7.

[0056] As an implementation mode, a crucible holder 6 is fixed to the bottom of the upper flange 2, and the crucible includes a transitional crucible cover 5 and a crucible body 4;

[0057] The transitional crucible cover 5 is located between the crucible holder 6 and the crucible body 4 , and is respectively connected to the crucible holder 6 and the crucible body 4 through threads.

[0058] As a specific implementation manner, the bottom of the crucible holder 6 is provided with an internal thread, the top of the transitional crucible cover 5 is provided with an external thread that cooperates with the internal thread at the bottom of the crucible holder 6, the bottom of the transitional crucible cover 5 is provided with an internal thread, and the top of the crucible body 4 is provided with an external thread that cooperates with the internal thread at the bottom of the transitional crucible cover 5.

[0059] As another specific embodiment, the bottom of the crucible holder 6 is provided with an external thread, the top of the transition crucible cover 5 is provided with an internal thread that cooperates with the external thread at the bottom of the crucible holder 6, the bottom of the transition crucible cover 5 is provided with an external thread, and the top of the crucible body 4 is provided with an internal thread that cooperates with the external thread at the bottom of the transition crucible cover 5.

[0060] The skilled person and technicians know that since the intermediate transition crucible cover 5 is respectively connected to the upper and lower crucible holders 6 and the crucible body 4 by threads, there are other different implementation methods, and the skilled person and technicians can design them according to needs.

[0061] It should be noted that the skilled and technical personnel can adjust the shapes of the transition crucible cover 5, the crucible holder 6 and the crucible body 4 according to the situation to meet the technical effect to be achieved by the present application. For example, since the movable laser locator 10 needs to meet the positioning of the outer edge of the crucible body 4, the outer edges of the transition crucible cover 5 and the crucible holder 6 cannot block the positioning of the outer edge of the crucible body 4 by the movable laser locator 10, so the corresponding threaded connection structure can be designed according to the needs. For example, in the case where the bottom of the transition crucible cover 5 is provided with an internal thread, and the top of the crucible body 4 is provided with an external thread that matches the internal thread at the bottom of the transition crucible cover 5, in order to meet the positioning needs of the above-mentioned movable laser locator 10, a narrowed transition structure can be provided on the top of the crucible body 4, and then the outer edge of the transition crucible cover 5 can be set so that it cannot block the outer edge of the crucible body 4.

[0062] The crucible holder 6 is fixed on the bottom of the upper flange 2, and the crucible body 4 and the crucible holder 6 are respectively connected through the transition crucible cover 5. After the reaction materials are filled into the crucible body 4, the crucible body 4 can be fixed at a fixed position of the upper flange 2, and then the relative position of the external insulation 7 can be adjusted.

[0063] As an embodiment, a graphitized carbon fiber cloth 13 is also arranged between the outer insulation 7 and the crucible. The graphitized carbon fiber cloth 13 includes a matrix and carbon fiber bundles in the matrix. The matrix is ​​tar pitch, and the carbon fiber bundles are graphitized carbon fiber bundles. The graphitized carbon fiber bundles are arranged in parallel in the tar pitch matrix.

[0064] Tar pitch is the binder, and graphitized carbon fiber bundles are the support. Since Si atmosphere is more easily captured by the tar pitch binder, it can effectively reduce the erosion of Si atmosphere on the insulation felt during the preparation of silicon carbide crystals by the PVT method, thereby ensuring the insulation effect of the insulation felt, ensuring the uniformity and stability of the temperature field during the crystal growth process, and reducing the generation of polymorphism. The support is a graphitized carbon fiber bundle, which can significantly improve the tensile strength and high temperature resistance of the carbon fiber cloth, and can meet the use environment of more than 2000°C during the growth of silicon carbide.

[0065] It should be noted that the tar pitch and graphitized carbon fiber bundles used in the present application are commonly used materials, and those skilled in the art can select them according to their needs. In addition, the present application does not limit the preparation process of the graphitized carbon fiber cloth 13, and the commonly used preparation process in the field can be adopted, and the prepreg method can also be adjusted according to needs.

[0066] It should be noted that the present application scheme mainly describes the main invention points. Other structures in the induction furnace can be implemented by referring to the scheme of the induction furnace in the field. This is something that can be routinely determined by those skilled in the art and does not require additional elaboration. For example, those skilled in the art can set the deployment mode of the induction coil 19 as needed, and can also set the temperature measuring hole 18 structure on the upper flange 2 as needed. In addition, those skilled in the art can also adjust and set the position of the closable slide rail and the crucible holder 6 on the upper flange 2 as needed, and adjust the shape of the transition crucible cover 5 as needed, so that the movable laser positioner 10 on the closable slide rail can have sufficient movement space and can detect the outer edge of the crucible body 4 and the inner edge of the outer insulation 7. This is a routine skill of those skilled in the art and does not require additional explanation.

[0067] As an embodiment, the graphitized carbon fiber cloth 13 includes a matrix and carbon fiber bundles in the matrix, wherein the matrix is ​​tar pitch, and the carbon fiber bundles are graphitized carbon fiber bundles, and the graphitized carbon fiber bundles are arranged in parallel in the tar pitch matrix.

[0068] The above-mentioned induction crystal growth furnace is used for crystal growth, and the specific crystal growth method is as follows:

[0069] (1) Place the raw materials in a crystal growth furnace and heat them up to 1450-1500°C, adjust the pressure to 50-55 mabr, maintain for 5 hours, and introduce 300-320 sccm of Ar gas and 30-35 sccm of N2 gas.

[0070] (2) Raise the temperature to 2000-2100°C within 5 hours, reduce the pressure to 30-35 mbar, and maintain for 10-12 hours, during which time introduce Ar gas 100-120 sccm and N2 gas 20-25 sccm

[0071] (3) The temperature was raised to 2200-2250°C within 15 hours, the pressure was reduced to 7-8 mbar, and the temperature was maintained for 150-160 hours for crystal growth. During this period, 50-55 sccm of Ar gas and 10-15 sccm of N2 gas were introduced. After the crystal growth was completed, the temperature was naturally lowered and the furnace was opened to obtain the crystal.

[0072] SiC crystals 1# to 3# are prepared according to the above-mentioned crystal growth method. The specific crystal growth method is as follows:

[0073] SiC crystal 1#

[0074] (1) Place the raw materials in a crystal growth furnace and heat them up to 1450°C, adjust the pressure to 55 mabr, maintain for 5 hours, and introduce 320 sccm of Ar gas and 35 sccm of N2 gas.

[0075] (2) The temperature was raised to 2000°C within 5 hours, and the pressure was reduced to 35 mbar and maintained for 10 hours. During this period, 120 sccm of Ar gas and 25 sccm of N2 gas were introduced.

[0076] (3) The temperature was raised to 2250°C within 15 hours, and the pressure was reduced to 7 mbar, and maintained for 160 hours for crystal growth. During this period, 50 sccm of Ar gas and 10 sccm of N2 gas were introduced. After the crystal growth was completed, the temperature was naturally lowered and the furnace was opened to obtain the crystal.

[0077] SiC crystal 2#

[0078] (1) Place the raw materials in a crystal growth furnace and heat them up to 1500°C, adjust the pressure to 50 mabr, maintain for 5 hours, and introduce 300-sccm Ar gas and 30 sccm N2 gas.

[0079] (2) The temperature was raised to 2100°C within 5 h, and the pressure was reduced to 30 mbar and maintained for 12 h. During this period, 100 sccm of Ar gas and 20 sccm of N2 gas were introduced.

[0080] (3) The temperature was raised to 2200°C within 15 hours, and the pressure was reduced to 8 mbar, and maintained for 150 hours for crystal growth. During this period, 55 sccm of Ar gas and 15 sccm of N2 gas were introduced. After the crystal growth was completed, the temperature was naturally lowered and the furnace was opened to obtain the crystal.

[0081] SiC crystal 3#

[0082] (1) Place the raw materials in a crystal growth furnace and heat them up to 1450°C. Adjust the pressure to 53 mabr and maintain for 5 hours. Then introduce 310 sccm of Ar gas and 35 sccm of N2 gas.

[0083] (2) The temperature was raised to 2050°C within 5 h, and the pressure was reduced to 33 mbar and maintained for 10 h. During this period, 110 sccm of Ar gas and 22 sccm of N2 gas were introduced.

[0084] (3) The temperature was raised to 2230°C within 15 hours, and the pressure was reduced to 7 mbar, and maintained for 150 hours for crystal growth. During this period, 50 sccm of Ar gas and 10 sccm of N2 gas were introduced. After the crystal growth was completed, the temperature was naturally lowered and the furnace was opened to obtain the crystal.

[0085] The parameters obtained by performing polarized light testing on each SiC substrate obtained from each SiC crystal are as follows:

[0086] 1. Convert the light source into polarized light through a polarizer,

[0087] 2. Polarized light is transmitted through a polished and transparent single-crystal SiC substrate through a preset optical path. When there is residual stress in the SiC substrate, the substrate lattice will be distorted, including crystal defects such as dislocations and microtubes, as well as processing damage such as edge collapse and scratches. Lattice distortion causes polarized light to deflect, and the deflection angle causes polarized light to undergo polarization birefringence, presenting polarized light in two directions.

[0088] 3. Then, the polarization camera is used to analyze the interference fringes of the two polarized lights in the optical path, and the polarization stress map can be qualitatively obtained. When the stress in the sample surface reaches equilibrium, the polarized lights in the two directions completely cancel each other out, resulting in black interference fringes; when residual stress exists, the polarized lights in the two directions do not completely cancel each other out, presenting bright colors, thereby achieving the residual stress characterization and analysis of the SiC single crystal substrate;

[0089]

[0090] in,

[0091] Δ: optical path difference between ordinary light (o light) and extraordinary light (e light);

[0092] d: sample thickness;

[0093] Δn: The difference in refractive index between ordinary light (o light) and extraordinary light (e light);

[0094] λ: wavelength.

[0095] One SiC crystal obtains 1 to N SiC substrates, and each SiC substrate obtains an optical path difference value. The values ​​represented in Table 1 with "maximum value" refer to the maximum value obtained by testing among several SiC substrates obtained from the SiC crystal, so the several SiC substrates obtained from the entire SiC crystal are less than or equal to the values ​​in Table 1; similarly, the values ​​with "minimum value" refer to the minimum value obtained by testing among several SiC substrates obtained from the SiC crystal. For example The minimum and The maximum value of the SiC

[0096] Crystalline whole At the same time, the optical path difference of 1 to N silicon carbide substrates is statistically analyzed to determine whether

[0097] Whether it meets △=a(N-1)+b, the test results are shown in Table 1.

[0098] The SiC crystals 1# to 3# prepared above are all 8 inches in size, and the annular region refers to a region extending inward from the edge of the SiC substrate with a width of 3 mm.

[0099] Table 1

[0100]

[0101]

[0102] Example 2

[0103] This embodiment relates to a method for evaluating the uniformity of stress distribution of a silicon carbide crystal rod, comprising the following steps:

[0104] (1) A plurality of silicon carbide substrates are obtained by cutting, grinding and polishing a silicon carbide crystal rod, where N is a positive integer representing the serial number of the silicon carbide substrate, and the surface roughness Ra of the silicon carbide substrate after polishing is not greater than 10 nm, and the thickness is less than 1 mm. A head piece and a tail piece are selected for polarized light testing, where the head piece is the first silicon carbide substrate including the first end face, and the serial number is 1, and the tail piece is the last silicon carbide substrate including the second end face, and the serial number is N;

[0105] (2) Calculate the polarized light test results of the head piece and the tail piece. If the optical path difference between the head piece and the tail piece is within the range of -5 to 5 nm, the stress of the silicon carbide crystal rod is uniform in the axial direction.

[0106] The specific steps of the polarized light test in step (1) are:

[0107] 1. Convert the light source into polarized light through a polarizer,

[0108] 2. Polarized light is transmitted through a polished and transparent single-crystal SiC substrate through a preset optical path. When there is residual stress in the SiC substrate, the substrate lattice will be distorted, including crystal defects such as dislocations and microtubes, as well as processing damage such as edge collapse and scratches. Lattice distortion causes polarized light to deflect, and the deflection angle causes polarized light to undergo polarization birefringence, presenting polarized light in two directions.

[0109] 3. Then, the polarization camera is used to analyze the interference fringes of the two polarized lights in the optical path, and the polarization stress map can be qualitatively obtained. When the stress in the sample surface reaches equilibrium, the polarized lights in the two directions completely cancel each other out, resulting in black interference fringes; when residual stress exists, the polarized lights in the two directions do not completely cancel each other out, presenting bright colors, thereby achieving the residual stress characterization and analysis of the SiC single crystal substrate;

[0110]

[0111] in,

[0112] The phase difference between ordinary light (o light) and extraordinary light (e light);

[0113] d: sample thickness;

[0114] Δn: The difference in refractive index between ordinary light (o light) and extraordinary light (e light);

[0115] λ: wavelength.

[0116] As an implementation manner, the optical path difference between the head piece and the tail piece is the optical path difference calculated for the entire area, and the overall optical path difference between the head piece and the tail piece is <10 nm.

[0117] As an embodiment, the head piece and the tail piece both include an annular area and a central area surrounded by the annular area, the annular area is an area with a width of 3 mm extending inward from the edge, the optical path difference between the head piece and the tail piece is the optical path difference in the central area, and the optical path difference in the central area of ​​the head piece and the tail piece is <6nm.

[0118] As an implementation method, if the head piece and the tail piece follow the following formula, it means that the stress of the silicon carbide crystal rod is uniform as a whole:

[0119] |σ1-σ2|<3nm, σ1 represents the standard deviation of the optical path difference of the head piece, and σ2 represents the standard deviation of the optical path difference of the tail piece.

[0120] As an implementation method, the step of performing polarized light detection on the remaining silicon carbide substrates except the head piece and the tail piece is also included. If the head piece, the tail piece and the remaining silicon carbide substrates follow the following formula, it means that the stress of the silicon carbide crystal rod is uniform in the axial direction and in the plane:

[0121] Said The value range is 0.8~1.2, The value range is 0.8~1.2, It represents the average value of the standard deviation of the optical path difference of all SiC substrates obtained by cutting the silicon carbide ingot.

[0122] As an implementation method, σ1 is the standard deviation of the overall optical path difference of the head piece, σ2 is the standard deviation of the overall optical path difference of the tail piece, is the average value of the standard deviation of the overall optical path difference of the SiC substrate, and the standard deviation of the overall optical path difference of the head piece and the tail piece is <6nm.

[0123] As an embodiment, the head piece and the tail piece each include an annular area and a central area surrounded by the annular area, wherein the annular area is an area extending inward from the edge and having a width of 3 mm.

[0124] σ1 is the standard deviation of the optical path difference in the central area of ​​the head piece, and σ2 is the standard deviation of the optical path difference in the central area of ​​the tail piece. is the average value of the standard deviation of the optical path difference in the central area of ​​the SiC substrate. The standard deviation of the optical path difference in the central area of ​​the head piece and the tail piece is <3nm.

[0125] As an implementation method, if the head piece and the tail piece follow the following formula, it means that the stress of the silicon carbide crystal rod is uniform as a whole:

[0126] On any horizontal line, σ4 / σ5<1.9, σ4 represents the standard deviation of the optical path difference in the annular area, and σ5 represents the standard deviation of the optical path difference in the central area.

[0127] As an implementation mode, for the head piece and the tail piece, on any horizontal line, the standard deviation of the optical path difference in the annular area is <4nm, and the standard deviation of the optical path difference in the central area is <2nm.

[0128] As an implementation method, if the optical path difference between the head piece and the tail piece satisfies the following formula:

[0129] △=a(N-1)+b, where △ represents the optical path difference, in nm, X represents the sheet number of the silicon carbide substrate, the value of the first silicon carbide substrate containing the first end face of the silicon carbide crystal is 1, the value range of a is -1 to 1, the value of b is 0.5 to 10.5, in nm, then the stress of the silicon carbide crystal rod is uniform in the axial direction.

[0130] As a preferred implementation, the value range of a is -0.004 to -0.4 or 0.004 to 0.4.

[0131] The above evaluation method was used to test and evaluate the silicon carbide crystals 1# to 3# of Example 1. Micro Raman was used to test the in-plane peak intensity, half-peak width and peak position shift to reflect the lattice vibration of the silicon carbide substrate prepared by the crystal, and radial and axial statistics were performed to reflect the in-plane stress distribution and the axial distribution of the entire crystal rod. The evaluation method of this application is consistent with the test results of micro Raman. It is proved that the evaluation method has high accuracy, saves more detection time and improves detection efficiency compared to micro Raman.

[0132] The above is only the embodiment of the present application, and the protection scope of the present application is not limited by these specific embodiments, but is determined by the claims of the present application. For those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the technical ideas and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for evaluating the uniformity of stress distribution of a silicon carbide crystal rod, characterized in that: The steps include: (1) 1 to N silicon carbide substrates prepared from a silicon carbide crystal rod, where N is a positive integer representing the serial number of the silicon carbide substrate, and a head piece and a tail piece are selected for polarized light testing, wherein the head piece is the first silicon carbide substrate including the first end face, and the serial number is 1, and the tail piece is the last silicon carbide substrate including the second end face, and the serial number is N; (2) Calculate the polarized light test results of the head piece and the tail piece. If the optical path difference between the head piece and the tail piece is within the range of -5 to 5 nm, the stress of the silicon carbide crystal rod is uniform in the axial direction.

2. The method for evaluating the uniformity of stress distribution of a silicon carbide crystal rod according to claim 1, characterized in that: The optical path difference between the head piece and the tail piece is the optical path difference calculated for the entire area, and the overall optical path difference between the head piece and the tail piece is <10 nm.

3. The method for evaluating the uniformity of stress distribution of a silicon carbide crystal rod according to claim 1, characterized in that: The head piece and the tail piece both include an annular area and a central area surrounded by the annular area. The annular area is an area with a width of 3 mm extending inward from the edge. The optical path difference between the head piece and the tail piece is the optical path difference in the central area. The optical path difference in the central area of ​​the head piece and the tail piece is both <6 nm.

4. The method for evaluating the uniformity of stress distribution of a silicon carbide crystal rod according to claim 1, characterized in that: If the head piece and the tail piece follow the following formula, it means that the stress of the silicon carbide crystal rod is uniform as a whole: |σ1-σ2|<3nm, σ1 represents the standard deviation of the optical path difference of the head piece, and σ2 represents the standard deviation of the optical path difference of the tail piece.

5. The method for evaluating the uniformity of stress distribution of a silicon carbide crystal rod according to claim 4, characterized in that: The method also includes the step of performing polarized light detection on the remaining silicon carbide substrates except the head piece and the tail piece. If the head piece, the tail piece and the remaining silicon carbide substrates follow the following formula, it means that the stress of the silicon carbide crystal rod is uniform in the axial direction and in the plane: Said The value range is 0.8~1.2, The value range is 0.8~1.2, It represents the average value of the standard deviation of the optical path difference of all SiC substrates obtained by cutting the silicon carbide ingot.

6. The method for evaluating the uniformity of stress distribution of a silicon carbide crystal rod according to claim 5, characterized in that: σ1 is the standard deviation of the overall optical path difference of the head piece, σ2 is the standard deviation of the overall optical path difference of the tail piece, is the average value of the standard deviation of the overall optical path difference of the SiC substrate, and the standard deviation of the overall optical path difference of the head piece and the tail piece is <6nm.

7. The method for evaluating the uniformity of stress distribution of a silicon carbide crystal rod according to claim 5, characterized in that: The head piece and the tail piece each include an annular area and a central area surrounded by the annular area, wherein the annular area is an area extending inward from the edge and having a width of 3 mm. σ1 is the standard deviation of the optical path difference in the central area of ​​the head piece, and σ2 is the standard deviation of the optical path difference in the central area of ​​the tail piece. is the average value of the standard deviation of the optical path difference in the central area of ​​the SiC substrate. The standard deviation of the optical path difference in the central area of ​​the head piece and the tail piece is <3nm.

8. The method for evaluating the uniformity of stress distribution of a silicon carbide crystal rod according to claim 1, characterized in that: If the optical path difference between the head piece and the tail piece satisfies the following formula: △=a(N-1)+b, where △ represents the optical path difference, the unit is nm, the value range of a is -1 to 1, and the value of b is 0.5 to 10.5, the unit is nm, then the stress of the silicon carbide crystal rod is uniform in the axial direction.

9. The method for evaluating the uniformity of stress distribution of a silicon carbide crystal rod according to claim 1, characterized in that: The value range of a is -0.004 to -0.4 or 0.004 to 0.

4.

10. The method for evaluating the uniformity of stress distribution of a silicon carbide crystal rod according to claim 1, characterized in that: The surface roughness Ra of the tested silicon carbide substrate is no greater than 10 nm.

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