Low-stress silicon carbide single crystal growth induction furnace and silicon carbide single crystal growth method

Abstract

The invention discloses a low-stress silicon carbide single crystal growth induction furnace and a silicon carbide single crystal growth method, and belongs to the technical field of silicon carbide crystal preparation. The low-stress silicon carbide single crystal growth vacuum induction furnace comprises a supporting cylinder, an induction furnace upper cover and an induction furnace lower cover, the induction furnace upper cover is arranged on the upper portion of the supporting cylinder, and the induction furnace lower cover is arranged on the lower portion of the supporting cylinder. The heat preservation layer is divided into the upper part and the lower part, the position of the upper heat preservation layer is controlled through the lifting mechanism, the plug conveying mechanism is additionally arranged on the upper cover of the growth furnace, and the middle temperature measurement hole is moved to the outer edge of the crucible for temperature measurement, so that the diameter of the temperature measurement hole is minimized, and the radial temperature gradient of the silicon carbide seed crystal is reduced. In the silicon carbide single crystal growth process by adopting the device provided by the invention, the temperature in the growth process is controlled by improving the growth process and adopting the constructed function, so that the temperature of the growth surface of the silicon carbide crystal ingot is accurately controlled, and the stability of the crystal form of the silicon carbide crystal ingot is improved, thereby reducing the stress of the silicon carbide crystal ingot.

Description

Technical Field

[0001] The invention belongs to the technical field of silicon carbide crystal preparation, and in particular relates to a low-stress silicon carbide single crystal growth induction furnace and a silicon carbide single crystal growth method. Background Art

[0002] Silicon carbide (SiC), as one of the third-generation semiconductor materials, has the advantages of high breakdown electric field, high saturation electron velocity, high thermal conductivity, high electron density, and high mobility, and is widely used in high-power power electronic devices and aerospace devices.

[0003] The common method for preparing large-diameter SiC crystals is physical vapor transport, which is based on the principle of heating the closed crucible system by induction or resistance heating, placing the solid mixture as the growth source at the bottom of the crucible with a higher temperature, and fixing the seed crystal at the top of the crucible with a lower temperature. The growth source sublimates and decomposes at low pressure and high temperature to produce gaseous substances. Driven by the pressure gradient formed by the temperature gradient between the growth source and the seed crystal, this gaseous substance is naturally transported to the low-temperature seed crystal position and grows cleanly due to the generation of supersaturation. After the silicon carbide crystal is taken out, it is mechanically cut, ground and polished.

[0004] From the growth process of silicon carbide crystals and the structure of the equipment, it can be seen that there are large temperature gradients in both the axial and radial directions, which inevitably lead to large internal stresses in the grown silicon carbide crystals. Secondly, the seed crystal needs to be bonded to the crucible cover, and the thermal expansion coefficients between the silicon carbide crystal and the crucible cover are quite different, which adds extra stress to the internal part of the silicon carbide crystal. From the growth of the crystal to the application of the wafer, a series of processing processes such as cutting and grinding are required. The existence of internal stress will greatly increase the difficulty of processing, resulting in a low wafer yield, and it is difficult to achieve a good surface shape of the processed wafer, which will inevitably bring difficulties to the subsequent epitaxial process.

[0005] Patent CN 111118598 B discloses a high-quality silicon carbide single crystal, substrate and efficient preparation method thereof, belonging to the field of semiconductor materials. The preparation method includes placing raw materials and seed crystals in a crucible, assembling the crucible and the heat preservation structure and placing them in a crystal growth furnace, setting a heating coil group on the periphery of the side wall of the crystal growth furnace, installing an adjustment mechanism, removing impurities, and growing crystals; wherein the heating coil group includes a first coil group corresponding to the raw material area and a second coil group corresponding to the crystal growth area, and the inner diameter of the second coil group increases along the direction from the raw material to the seed crystal. The preparation method of the silicon carbide single crystal is arranged to form an axial temperature gradient in the growth chamber, and high-quality silicon carbide single crystals can be obtained; the radial temperature gradient in the growth chamber of the growing single crystal is adjusted to improve the crystal growth rate and crystal growth quality; while reducing the radial temperature gradient, a certain axial temperature gradient can be ensured, and high-quality silicon carbide single crystals can be efficiently obtained.

[0006] Patent CN 110284199 B discloses a crystal in-situ carbonization annealing device and method, the crystal in-situ carbonization annealing device comprises: a graphite crucible forming a growth chamber and growing crystals therein; a peripheral insulation layer wrapped around the periphery of the graphite crucible but exposing at least part of the top of the crucible; a growth furnace, a graphite crucible wrapped with a peripheral insulation layer is placed at the lower part of the growth furnace, an induction coil for adjusting the temperature in the growth furnace is arranged at and on the inner periphery of the lower part of the growth furnace, the growth furnace also has a gas charging and discharging interface to selectively connect with a vacuum source or an inert gas source; an upper insulation layer that can be raised and lowered is arranged above the graphite crucible, a silicon powder loading unit is suspended on the upper insulation layer toward one side of the graphite crucible, the upper insulation layer is located at the top of the growth furnace away from the crucible when the crystal grows stably, and when the growth is completed, the upper insulation layer is lowered to cover the graphite crucible and use the annealing temperature to make the silicon powder loading unit release silicon atmosphere into the growth chamber.

[0007] In existing solutions, in order to reduce the internal stress caused by crystal growth, direct annealing is usually performed after the growth is completed, that is, the crystal is annealed for the first time in situ. However, the existing in situ annealing effect is insufficient, and the internal stress of the crystal cannot be effectively removed by in situ annealing alone. Summary of the invention

[0008] In view of the shortcomings of the prior art and to solve the internal stress problem caused by crystal growth, the present invention provides a low-stress silicon carbide single crystal growth vacuum induction furnace, in which the insulation layer is divided into an upper and a lower part, and the position of the upper insulation layer is controlled by a lifting mechanism, so as to realize the controllability of the temperature gradient in the furnace; by moving the middle temperature measuring hole to the outer edge of the crucible for temperature measurement, the diameter of the temperature measuring hole is minimized, and the radial temperature gradient of the silicon carbide seed crystal is reduced; by adding a plugging and transporting mechanism to the upper cover of the growth furnace, the temperature gradient of the silicon carbide crystal is further reduced during the annealing process, thereby reducing the residual stress; by improving the growth process, the crystal ingot is heated up to release the stress when the crystal ingot grows to half the thickness, thereby reducing the expansion of stress and defects during the growth process; by sealing the temperature measuring hole and heating the crystal ingot for annealing after the growth is completed, the temperature gradient inside the crystal is reduced and the stress in the crystal is released during the cooling process, thereby obtaining a low-stress silicon carbide single crystal; by improving the temperature control method, the temperature of the growth surface of the silicon carbide crystal ingot is accurately controlled, the stability of the crystal form of the silicon carbide crystal ingot is improved, thereby reducing the stress of the silicon carbide crystal ingot.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] A low-stress silicon carbide single crystal growth vacuum induction furnace, specifically comprising a support tube, an induction furnace upper cover and an induction furnace lower cover, wherein the induction furnace upper cover is arranged on the upper part of the support tube, and the induction furnace lower cover is arranged on the lower part of the support tube;

[0011] The upper cover of the induction furnace is provided with an upper insulation layer lifting mechanism, a first sealing structure, an upper temperature measuring window, a third sealing structure and a temperature measuring hole plugging movement mechanism, the upper insulation layer lifting mechanism passes through the center of the upper cover of the induction furnace, the first sealing structure is arranged between the upper insulation layer lifting mechanism and the upper cover of the induction furnace, and dynamic sealing is achieved through the first sealing structure, the upper insulation layer lifting mechanism is connected to the upper insulation layer lifting motor, the upper insulation layer lifting motor is arranged at the top of the induction furnace upper cover, the temperature measuring hole plugging movement mechanism passes through the upper cover of the induction furnace and is fixed by the third sealing structure to achieve dynamic sealing, and an upper infrared thermometer is arranged on the top of the upper temperature measuring window;

[0012] The support tube is provided with a temperature measuring hole plug, an upper insulation layer, a crucible cover, a crucible, a lower insulation layer and a crucible fixing mechanism in sequence from top to bottom. The temperature measuring hole plug is connected to the temperature measuring hole plug movement mechanism, the upper insulation layer is connected to the upper insulation layer lifting mechanism, an upper temperature measuring hole is provided on the upper insulation layer, a crucible and a crucible cover are provided inside the lower insulation layer, a lower temperature measuring hole is provided at the bottom center of the lower insulation layer, a crucible fixing mechanism is provided at the lower part of the lower insulation layer, and the crucible cover is provided at the upper part of the crucible; an induction coil and a coil lifting mechanism are provided around the outside of the support tube, the coil lifting mechanism is provided outside the induction coil, and the upper part of the coil lifting mechanism is connected to the coil lifting motor;

[0013] The lower cover of the induction furnace is provided with a crucible rotating shaft and a second sealing structure, the crucible rotating shaft passes through the center of the lower cover of the induction furnace, the second sealing structure is arranged between the crucible rotating shaft and the lower cover of the induction furnace, and dynamic sealing is achieved through the second sealing structure, a second gear and a lower temperature measuring window are arranged on the crucible rotating shaft from top to bottom, a first gear is arranged on one side of the second gear, and is connected to the crucible rotating motor through the first gear, and a lower infrared thermometer is arranged at the bottom of the lower temperature measuring window.

[0014] The support tube is a double-layer structure, and its material is quartz.

[0015] The upper insulation layer lifting mechanism has the function of automatically lifting and lowering the upper insulation layer.

[0016] The central axes of the upper insulation layer and the lower insulation layer coincide with each other.

[0017] The crucible rotating motor can drive the crucible, the crucible cover and the lower insulation layer around the central axis through the transmission of the first gear, the second gear, the crucible rotating shaft and the crucible fixing mechanism.

[0018] The temperature measuring hole plug movement mechanism has the function of moving up and down, controlling the temperature measuring hole plug to enter or move out of the upper temperature measuring hole; the temperature measuring hole plug movement mechanism has a rotational movement function, controlling the temperature measuring hole plug to rotate outside the upper temperature measuring hole; the diameter of the temperature measuring hole plug is 0.5mm to 1mm smaller than the diameter of the upper temperature measuring hole, and the bottom of the temperature measuring hole plug has a chamfer, and the chamfer size is 0.5mm to 1mm.

[0019] The coil lifting motor moves the induction coil up and down through the coil lifting mechanism.

[0020] The crucible cover and the crucible are made of graphite. Silicon carbide seed crystals are bonded to the crucible cover, and silicon carbide powder is contained in the crucible.

[0021] A method for growing silicon carbide crystals is implemented using the above device, and specifically comprises the following steps:

[0022] Step 1. Preparation: Place silicon carbide powder into the crucible cavity, bond the seed crystal to the crucible cover, and then tighten the crucible to seal it to a sealed state, place it in a vacuum induction furnace, seal the vacuum induction furnace and then evacuate it;

[0023] Step 2. First stage growth: grow silicon carbide single crystals using physical vapor transport, move the induction coil to the initial position, fill with inert gas as carrier gas, grow the single crystal at a set growth temperature, and obtain ingot I; the initial position is the first stage growth position, which is lower than the surface of silicon carbide powder; the temperature of silicon carbide powder is higher than the temperature of ingot I.

[0024] Step 3. Primary heat treatment: When the silicon carbide crystal grows to half the thickness of the desired final product, an inert gas is introduced into the reaction chamber, the induction coil is uniformly moved upward from the initial position to the center of the induction coil to the level of the primary heat treatment position, and the power of the induction coil is adjusted to control the temperature increase of the crystal ingot I, and then maintained for a set time; the primary heat treatment position is located between position A and position B, wherein position A is the center position of the crystal ingot I, and position B is the center position between the lower surface of the crystal ingot I and the upper surface of the silicon carbide powder; the reaction chamber is filled with inert gas, the induction coil is moved, and the temperature of the crystal ingot I is increased simultaneously, and it is completed in 4h to 5h;

[0025] Step 4. Second stage growth: reduce the pressure in the reaction chamber, move the induction coil downward at a uniform speed to the initial position, adjust the power of the induction coil to reduce the average temperature of the growth surface of ingot I to the set growth temperature, and the silicon carbide single crystal continues to grow on ingot I, and finally obtains ingot II; during the growth process, the average temperature of the growth surface of ingot II is kept consistent with the set growth temperature; the pressure in the reaction chamber is reduced, the induction coil is moved downward, and the growth surface of ingot I is cooled down simultaneously, and it is completed in 4h to 5h; the temperature of the silicon carbide powder is higher than the temperature of ingot II;

[0026] Step 5. Secondary heat treatment: after the growth of silicon carbide single crystal is completed, inert gas is introduced into the reaction chamber, the upper insulation layer is uniformly lowered until the gap between the upper insulation layer and the lower insulation layer is the smallest, the induction coil is uniformly moved upward from the initial position to the level of the center of the induction coil and the secondary heat treatment position, the power of the induction coil is adjusted to control the temperature increase of the crystal ingot II, the temperature measuring hole plug is placed inside the temperature measuring hole, and the set time is maintained, and then the heating is stopped, and the temperature of the single crystal growth furnace is cooled to room temperature, and the crystal ingot II is taken out to obtain a low-stress silicon carbide crystal ingot; the secondary heat treatment position is located between position C and position D, wherein position C is the center position of the crystal ingot II, and position D is the center position between the lower surface of the crystal ingot II and the upper surface of the silicon carbide powder; the reaction chamber is filled with inert gas, the induction coil is moved, and the temperature of the crystal ingot II is increased simultaneously, and it is completed in 4h to 5h;

[0027] The growth time of the first stage growth and the second stage growth, the average growth surface temperature of ingots I and II, and the reaction chamber pressure are kept consistent; wherein the average growth surface temperature of ingots I and II is the single crystal growth temperature;

[0028] During the primary heat treatment and the secondary heat treatment, the reaction chamber pressure, the holding time, and the temperature of ingots I and II after heating remain consistent; the temperature of ingots I and II after heating is the ingot temperature.

[0029] In the method, the height of the lower insulation layer remains unchanged; the graphite crucible and the lower insulation layer rotate horizontally around the crucible rotation axis all the time.

[0030] In step 1, the silicon carbide powder is of 5N grade;

[0031] In step 2 and step 4, the growth time of the silicon carbide single crystal is ≥ 80 hours, and the pressure in the reaction chamber is 1 kPa to 4 kPa;

[0032] In step 3 and step 5, after the inert gas is filled, the pressure of the reaction chamber is 0.9atm-1.0atm, the temperature of the crystal ingot after heating is 80°C-100°C higher than the single crystal growth temperature, and the holding time is 5h-6h;

[0033] During the first and second growth stages, the temperature function T 控 =T(t) directly controls the temperature of the upper temperature measuring point, and directly controls the height of the upper insulation layer through the upper and lower insulation layer gap function L=L(t); thereby indirectly controlling the silicon carbide growth rate to meet v=v(t) and the average temperature of the ingot growth surface to meet the set growth temperature;

[0034] The upper temperature measuring point is set at the upper temperature measuring hole, and the temperature of the upper temperature measuring point is the temperature of the crucible cover corresponding to the upper temperature measuring hole measured by the upper infrared thermometer; through the pre-constructed function T 控=T(t), adjust the temperature of the upper temperature measuring point so that the temperature of the upper temperature measuring point reaches the temperature T at time t 控 ; The function T 控 =T(t), L=L(t), v=v(t) The construction process is:

[0035] S1. Take the values ​​of the variation range of the ingot thickness h at equal intervals and number them, recorded as h i , the variation range of the gap L between the upper and lower insulation layers is equidistantly selected and numbered, recorded as L j , where i and j are the numbers of the ingot thickness and the gap between the upper and lower insulation layers respectively; a specific value T is selected from the silicon carbide single crystal growth temperature range of 1950℃~2550℃ 生长 As the set growth temperature, the average temperature of the ingot growth surface is controlled to be T 生长 , the control temperature of the upper temperature measuring point is expressed as T 控 , then the temperature difference between the growth surface of the silicon carbide ingot and the upper temperature measurement point is △T = T 生长 -T 控 ; The actual temperature measured at the upper temperature measuring point is T 测 represents, and the growth time is represented by t;

[0036] S2. Through numerical simulation, the induction coil power is adjusted to meet the average temperature of the growth surface of the silicon carbide ingot to be T 生长 ±0.2℃, get h i , L j Temperature difference △T under different combinations ij , growth rate v ij , growth quality P ij ; The temperature difference function △T=f1(h,L), the growth rate function v=f2(h,L), and the growth quality function P=f3(h,L) are obtained by fitting;

[0037] S3. For each h i , from v ij Select a growth rate from the i Indicates that through v i and h i The fitting function v=f4(h) is obtained; the v i Meet the growth rate and growth quality P requirements at the same time;

[0038] S4. Take the seed crystal thickness as the initial ingot thickness h0, assume that the functional relationship between the thickness h and the growth time t is h = h(t), and v = f4(h). By integration or solving the formula The functional relationship h=h(t) can be obtained, which is the control process of the thickness of the silicon carbide ingot;

[0039] S5. Combining the functions v=f4(h) and h=h(t) to obtain v=f4(h(t)), where there is only one independent variable t, further simplified to v=v(t), i.e., the control process of the growth rate of the silicon carbide single crystal;

[0040] S6. Substitute h=h(t) and v=v(t) into the function v=f2(h,L) to obtain L=f2 -1 (v(t), h(t)), simplified to L = L(t), the control process of the distance between the upper and lower insulation layers during the growth of silicon carbide single crystal is obtained;

[0041] S7. Substitute L=L(t) and h=h(t) into the function △T=f1(h,L) to obtain △T=f1(h(t),L(t)). This function has only one independent variable t, which can be further simplified to △T=g(t). According to △T=T in S1, 生长 -T 控 , get T 控 =T 生长 -g(t), simplified to T 控 =T(t), and the temperature control process of the temperature measuring point during the growth of silicon carbide single crystal is obtained;

[0042] S8. The heating power of the induction coil is calculated based on the difference between the temperature control value and the measured value T at the temperature control point. 控 -T 测 And the temperature control function T 控 =T(t) for dynamic adjustment; during the growth of silicon carbide single crystal, the position of the upper insulation layer is dynamically adjusted by the servo motor according to the function L=L(t);

[0043] S9. Establish a silicon carbide single crystal growth database for each furnace, and save the data after each silicon carbide crystal growth in the database, including the corresponding growth process v = v(t), h = h(t), L = L(t), T 控 =T(t), the final thickness data of the ingot and the single crystal growth quality data, and use this database to adjust the parameters of the function v=f2(h,L) to update the growth process.

[0044] The thickness h of the ingot in S1 is determined by taking the initial thickness h0 of the silicon carbide ingot as the minimum thickness, i.e. the seed crystal thickness, and taking the target thickness at the end of growth as the maximum thickness;

[0045] In S1, the gap L between the upper and lower insulation layers satisfies the minimum gap that the upper and lower insulation layers do not interfere with each other, and the maximum gap is the gap value when the bottom of the upper insulation layer is not higher than the top of the lower insulation layer; the minimum gap between the upper insulation layer and the lower insulation layer is 0.5 mm to 1 mm;

[0046] In S1, i and j are independently 15 to 30. If the number size is too large, the simulation workload will be seriously increased, and it should be selected with comprehensive consideration;

[0047] In S3, when the growth rate v is selected as a constant value v0, h=v0t+h0.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] 1. The present invention divides the insulation layer into two parts, an upper part and a lower part, controls the position of the upper insulation layer through a lifting mechanism, increases the temperature gradient by lifting the position of the upper insulation layer to achieve diameter expansion, and reduces the temperature gradient by lowering the position of the insulation layer, thereby achieving controllability of the temperature gradient in the furnace.

[0050] 2. The present invention measures the temperature by moving the middle temperature measuring hole to the outer edge of the crucible, so that the size of the temperature measuring hole can be minimized and the radial temperature gradient of the silicon carbide seed crystal is reduced; by adding a plug transport mechanism to the upper cover of the growth furnace, the temperature gradient of the silicon carbide crystal is further reduced during the annealing process, thereby reducing the residual stress.

[0051] 3. The present invention improves the growth process and performs an operation of heating the ingot to release stress when the ingot grows to half its thickness, thereby reducing the expansion of stress and defects in the subsequent growth process; by sealing the temperature measuring holes and heating and annealing the ingot after the growth is completed, the temperature gradient inside the crystal can be reduced and the stress in the crystal can be released during the cooling process, thereby obtaining a low-stress silicon carbide single crystal.

[0052] 4. The present invention realizes dynamic and precise control of the temperature of the growth surface of the silicon carbide ingot during the growth process by improving the temperature control method, thereby improving the stability of the crystal form of the silicon carbide ingot and reducing the stress of the silicon carbide ingot. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 Schematic diagram of the low-stress silicon carbide single crystal growth vacuum induction furnace of the present invention;

[0054] Among them, 1-upper insulation layer lifting motor, 2-first sealing structure, 3-induction furnace upper cover, 4-upper insulation layer lifting mechanism, 5-upper insulation layer, 6-crucible cover, 7-silicon carbide seed crystal, 8-lower insulation layer, 9-silicon carbide powder, 10-crucible, 11-lower temperature measuring hole, 12-crucible rotating shaft, 13-second sealing structure, 14-first gear, 15-crucible rotating motor; 16-upper infrared thermometer; 17-third sealing structure; 18-upper temperature measuring window; 19-temperature measuring hole plug movement mechanism; 20-temperature measuring hole plug; 21-coil lifting motor; 22-upper temperature measuring hole; 23-induction coil; 24-support cylinder; 25-coil lifting mechanism; 26-crucible fixing mechanism; 27-induction furnace lower cover; 28-second gear; 29-lower temperature measuring window; 30-lower infrared thermometer;

[0055] Figure 2 Schematic diagram of the position of the induction coil during the primary heat treatment in Example 2 of the present invention;

[0056] Figure 3 Schematic diagram of the position of the induction coil during the primary heat treatment in Example 3 of the present invention;

[0057] Figure 4 Schematic diagram of the position of the upper temperature measurement point in an embodiment of the present invention; wherein L is the gap between the upper and lower insulation layers, and h is the thickness of the single crystal. DETAILED DESCRIPTION

[0058] In the embodiment of the present invention, the silicon carbide raw material used is 5N grade.

[0059] Example 1

[0060] A low stress SiC single crystal growth vacuum induction furnace Figure 1 As shown, it specifically includes a support tube 24, an induction furnace upper cover 3 and an induction furnace lower cover 27. The induction furnace upper cover 3 is arranged at the upper part of the support tube 24, and the induction furnace lower cover 27 is arranged at the lower part of the support tube 24; specifically, the support tube 24 is a double-layer structure and is made of quartz.

[0061] The induction furnace upper cover 3 is provided with an upper insulation layer lifting mechanism 4, a first sealing structure 2, an upper temperature measuring window 18, a third sealing structure 17 and a temperature measuring hole plugging movement mechanism 19. The upper insulation layer lifting mechanism 4 passes through the center of the induction furnace upper cover 3. The first sealing structure 2 is arranged between the upper insulation layer lifting mechanism 4 and the induction furnace upper cover 3, and dynamic sealing is achieved through the first sealing structure 2. The upper insulation layer lifting mechanism 4 is connected to the upper insulation layer lifting motor 1, and the upper insulation layer lifting motor 1 is arranged on the top of the induction furnace upper cover 3. The temperature measuring hole plugging movement mechanism 19 passes through the induction furnace upper cover 3 and is fixed by the third sealing structure 17 to achieve dynamic sealing. An upper infrared thermometer 16 is provided on the top of the upper temperature measuring window 18. Specifically, the upper insulation layer lifting mechanism 4 has the function of automatically lifting and lowering the upper insulation layer 5.

[0062] The support tube 24 is provided with a temperature measuring hole plug 20, an upper insulation layer 5, a crucible cover 6, a crucible 10, a lower insulation layer 8 and a crucible fixing mechanism 26 in sequence from top to bottom. The temperature measuring hole plug 20 is connected to the temperature measuring hole plug movement mechanism 19, the upper insulation layer 5 is connected to the upper insulation layer lifting mechanism 4, the upper insulation layer 5 is provided with an upper temperature measuring hole 22, the lower insulation layer 8 is provided with a crucible 10 and a crucible cover 6, the lower insulation layer 8 is provided with a lower temperature measuring hole 11 at the bottom center of the lower insulation layer 8, the lower part of the lower insulation layer 8 is provided with a crucible fixing mechanism 26, and the crucible cover 6 is provided on the upper part of the crucible 10; an induction coil 23 and a coil lifting mechanism 25 are provided around the outside of the support tube 24, and the coil lifting mechanism 2 5 is arranged outside the induction coil 23, and the upper part of the coil lifting mechanism 25 is connected to the coil lifting motor 21; specifically, the temperature measuring hole plug movement mechanism 19 has the function of moving up and down, and controls the temperature measuring hole plug 20 to enter or move out of the upper temperature measuring hole 22; the temperature measuring hole plug movement mechanism 19 has the function of rotating and moving, and can rotate the temperature measuring hole plug 20 to the outside of the upper temperature measuring hole 22; the diameter of the temperature measuring hole plug 20 is 0.75mm smaller than the diameter of the upper temperature measuring hole 22, and the bottom of the temperature measuring hole plug 20 has a chamfer, and the chamfer size is 0.75mm; the crucible cover 6 and the crucible 10 are made of graphite, the crucible cover 6 is bonded with a silicon carbide seed crystal 7, and the crucible 10 contains silicon carbide powder 9.

[0063] The induction furnace lower cover 27 is provided with a crucible rotating shaft 12 and a second sealing structure 13, the crucible rotating shaft 12 passes through the center of the induction furnace lower cover 27, the second sealing structure 13 is arranged between the crucible rotating shaft 12 and the induction furnace lower cover 27, and dynamic sealing is achieved through the second sealing structure 13, the crucible rotating shaft 12 is provided with a second gear 28 and a lower temperature measuring window 29 from top to bottom, a first gear 14 is provided on one side of the second gear 28, and is connected to the crucible rotating motor 15 through the first gear 14, and a lower infrared thermometer 30 is provided at the bottom of the lower temperature measuring window 29;

[0064] The central axes of the upper insulation layer 5 and the lower insulation layer 8 coincide with each other.

[0065] The crucible rotating motor 15 can rotate the crucible 10 , the crucible cover 6 and the lower insulation layer 8 around the central axis through the transmission of the first gear 14 , the second gear 28 , the crucible rotating shaft 12 and the crucible fixing mechanism 26 .

[0066] Example 2

[0067] A method for growing a silicon carbide single crystal is implemented using the silicon carbide single crystal growth vacuum induction furnace in Example 1, and specifically comprises the following steps:

[0068] In this embodiment, an upper temperature measuring point is set at the upper temperature measuring hole (see Figure 4), the upper temperature measuring point temperature is the temperature of the crucible cover corresponding to the upper temperature measuring hole measured by the upper infrared thermometer. Pre-construct the upper temperature measuring point temperature control function T during the growth of silicon carbide single crystal 控 =T(t), and the gap function between the upper and lower insulation layers L = L(t), the specific construction method is realized by the following steps:

[0069] S1: Take the values ​​of the variation range of the ingot thickness h at equal intervals and number them, recorded as h i , i = 1, 2, ..., n, n = 15; the range of the gap L between the upper and lower insulation layers is equidistantly selected and numbered, recorded as L j , j = 1, 2, ..., n, n = 15; control the average temperature of the ingot growth surface to be T 生长 =2200℃, the upper temperature point control temperature is expressed as T 控 , then the temperature difference between the carbide ingot growth surface and the upper temperature measurement point is △T = 2200-T 控 , the actual temperature measured at the upper temperature measuring point is T 测 represents, and the growth time is represented by t;

[0070] The thickness h of the ingot is determined by taking the initial thickness h0 of the ingot as the minimum thickness, i.e. the seed crystal thickness, and taking the target thickness at the end of growth as the maximum thickness;

[0071] The gap L between the upper and lower insulation layers has a minimum gap of 0.5 mm, which satisfies the minimum gap that the upper and lower insulation layers do not touch each other, and a maximum gap that is the gap value when the bottom of the upper insulation layer is not higher than the top of the lower insulation layer;

[0072] S2: Through numerical simulation, the induction coil power is adjusted to ensure that the average temperature of the growth surface of the silicon carbide ingot is within the error range T 生长 ±0.2℃, get the single crystal thickness h i , gap between upper and lower insulation layers L j Temperature difference △T under different combinations ij , growth rate v ij , growth quality P ij , through fitting, we obtain the temperature difference function △T=f1(h,L), the growth rate function v=f2(h,L), and the growth quality function P=f3(h,L);

[0073] S3: For each h i , from v ij Select a growth rate from the i Indicates that the growth rate v i It can simultaneously meet the requirements of growth rate and growth quality P, through v i and h i The function v = f4(h) can be obtained by fitting;

[0074] When the growth rate v i Select v0 as a constant, at any thickness h i (i=1,2...15) cases can satisfy both high growth rate and high growth quality. i =v0, h = v0t + h0;

[0075] S4: Take the initial thickness of the ingot as h0, that is, the seed crystal thickness, and assume that the functional relationship between the thickness h and the growth time t is h = h(t). It is known that v = f4(h). By solving the formula The functional relationship h=h(t) is obtained and used to control the thickness of the silicon carbide ingot;

[0076] S5: Combine functions v=f4(h) and h=h(t) to obtain v=f4(h(t)), which is simplified to v=v(t) for controlling the growth rate of silicon carbide single crystal;

[0077] S6: Substitute h = h(t) and v = v(t) into the function v = f2(h, L), and we get L = f2 -1 (v(t), h(t)), which is simplified to L = L(t), which is used to control the gap between the upper and lower insulation layers during the growth of silicon carbide single crystals;

[0078] S7: Substitute L = L(t) and h = h(t) into the function △T = f1(h, L), and obtain △T = f1(h(t), L(t)), which is simplified to △T = g(t); From step S1, it can be seen that △T = 2200-T 控 , we can further get T 控 =2200-g(t), which is simplified to T 控 =T(t), used to control the temperature of the temperature measuring point during the growth of silicon carbide single crystal;

[0079] S8: The heating power of the induction coil is determined by the difference T between the temperature control value and the measured value at the temperature control point. 控 -T 测 And the temperature control function T 控 =T(t) for dynamic adjustment; during the growth of silicon carbide single crystal, the position of the upper insulation layer is dynamically adjusted by the servo motor according to the function L=L(t);

[0080] S9: Establish a silicon carbide single crystal growth database for the induction furnace, and save the data after each silicon carbide crystal growth in the database, including the corresponding growth process v=v(t), h=h(t), L=L(t), T 控 =T(t), the final thickness data of the ingot and the single crystal growth quality data, and use this database to adjust the parameters of the function v=f2(h,L) to update the growth process.

[0081] Based on the above constructed function T for controlling the temperature of the measuring point during the growth of silicon carbide single crystal 控 =T(t), and controlling the gap L between the upper and lower insulation layers during the growth of the silicon carbide single crystal to be L=L(t). The method for growing the silicon carbide single crystal of this embodiment includes the following steps:

[0082] (1) Preparation: placing high-purity silicon carbide powder into a graphite crucible cavity, bonding a seed crystal to a graphite crucible cover, and tightening the graphite crucible cover and the graphite crucible body to a sealed state; placing the sealed graphite crucible device into a vacuum induction furnace, sealing the vacuum induction furnace, and evacuating the furnace;

[0083] (2) First stage growth: Silicon carbide single crystals are grown using physical vapor transport method. The induction coil is moved to the initial position, which is a growth position below the powder surface. Inert gas is introduced as a carrier gas to maintain the pressure in the reaction chamber between 1 and 4 kPa. The silicon carbide single crystal is grown at a set growth temperature of 1950 to 2550 °C for no less than 80 hours to obtain ingot I. During the growth process, the temperature of the silicon carbide powder is higher than that of ingot I.

[0084] During the growth process, the temperature of the upper temperature measuring point is calculated using the function T 控 =T(t) for control, and the height of the upper insulation layer is controlled by the function L=L(t);

[0085] (3) Primary heat treatment: When the silicon carbide single crystal grows to half the thickness of the final product, inert gas is introduced to a pressure of 0.9 atm, and the induction coil is moved upward at a uniform speed so that the center of the coil is flush with the center of the ingot I (see Figure 2 ), adjust the coil power to control the temperature of ingot I to be 80-100°C higher than the single crystal growth temperature, and maintain it for 5 hours; wherein the reaction chamber is filled with inert gas, the induction coil is moved, and the temperature of ingot I is increased simultaneously, and it is completed in 4h-5h.

[0086] (4) Second growth stage: reduce the pressure in the reaction chamber to between 1 and 4 kPa, move the induction coil downward to the initial position, adjust the power of the induction coil to reduce the average temperature of the growth surface of ingot I to the set single crystal growth temperature (the growth temperature is the same as step (2)), and continue to grow the silicon carbide single crystal on ingot I for no less than 80 hours to finally obtain ingot II; wherein, the pressure in the reaction chamber is reduced, the induction coil is moved downward, and the temperature of ingot I is cooled simultaneously, which needs to be completed within 4 to 5 hours; the temperature of the silicon carbide powder is higher than the temperature of ingot II.

[0087] (5) Secondary heat treatment: After the growth of the silicon carbide single crystal is completed, an inert gas is introduced into the reaction chamber until the pressure reaches 0.9 atm. The upper insulation layer is lowered at a uniform speed to minimize the gap between the upper and lower insulation layers. The coil is moved upward so that the center of the coil is flush with the center of the crystal ingot II. The coil power is adjusted to control the temperature of the crystal ingot II to be 80-100°C higher than the single crystal growth temperature. The temperature measuring hole plug is placed into the upper temperature measuring hole and maintained for 5 hours. Then the heating is stopped. After the temperature of the single crystal growth furnace is cooled to room temperature, the crystal ingot II is taken out to obtain a low stress silicon carbide single crystal.

[0088] During the growth of the silicon carbide single crystal, the height of the lower insulation layer is kept unchanged, and the graphite crucible and the lower insulation layer are always rotated horizontally around the crucible rotation axis.

[0089] In this embodiment, the growth time of the first stage growth and the second stage growth, the average growth surface temperature of ingots I and II, and the reaction chamber pressure are kept consistent; wherein, the average growth surface temperature of ingots I and II is the single crystal growth temperature; during the primary heat treatment and the secondary heat treatment, the reaction chamber pressure, the holding time, and the temperature of ingots I and II after heating are kept consistent.

[0090] Example 3

[0091] The growth method and function construction process of the silicon carbide single crystal in this embodiment are the same as those in Embodiment 2, except that:

[0092] In step (3), the coil is moved upward until the center of the coil is flush with the center of the lower surface of the ingot I and the upper surface of the silicon carbide powder (see Figure 3 );

[0093] In step (5), the coil is moved upward so that the center of the coil is flush with the center of the lower surface of ingot II and the upper surface of the silicon carbide powder.

[0094] Example 4

[0095] The growth method and function construction process of the silicon carbide single crystal provided in this embodiment are the same as those in Embodiment 2, except that:

[0096] In step S1, the average temperature of the single crystal growth surface is controlled to be T 生长 =2000℃.

Claims

1. A low stress silicon carbide single crystal growth induction furnace, characterized in that: Specifically comprises a support tube, an induction furnace upper cover and an induction furnace lower cover, wherein the induction furnace upper cover is arranged at the upper part of the support tube, and the induction furnace lower cover is arranged at the lower part of the support tube; The upper cover of the induction furnace is provided with an upper insulation layer lifting mechanism, a first sealing structure, an upper temperature measuring window, a third sealing structure and a temperature measuring hole plug movement mechanism; the inside of the support tube is provided with a temperature measuring hole plug, an upper insulation layer, a crucible cover, a crucible, a lower insulation layer and a crucible fixing mechanism from top to bottom; the lower cover of the induction furnace is provided with a crucible rotating shaft and a second sealing structure.

2. The low stress silicon carbide single crystal growth induction furnace according to claim 1, characterized in that: The upper insulation layer lifting mechanism passes through the center of the induction furnace upper cover, the first sealing structure is arranged between the upper insulation layer lifting mechanism and the induction furnace upper cover, and dynamic sealing is achieved through the first sealing structure, the upper insulation layer lifting mechanism is connected to the upper insulation layer lifting motor, the upper insulation layer lifting motor is arranged on the top of the induction furnace upper cover, the temperature measuring hole plug movement mechanism passes through the induction furnace upper cover and is fixed by the third sealing structure to achieve dynamic sealing, and an upper infrared thermometer is arranged on the top of the upper temperature measuring window; The upper insulation layer lifting mechanism has the function of automatically lifting and lowering the upper insulation layer; The central axes of the upper insulation layer and the lower insulation layer coincide with each other.

3. The low stress silicon carbide single crystal growth induction furnace according to claim 1, characterized in that: The temperature measuring hole plug is connected to the temperature measuring hole plug movement mechanism, the upper insulation layer is connected to the upper insulation layer lifting mechanism, the upper insulation layer is provided with an upper temperature measuring hole, the lower insulation layer is provided with a crucible and a crucible cover, the bottom center of the lower insulation layer is provided with a lower temperature measuring hole, the lower insulation layer is provided with a crucible fixing mechanism, and the crucible cover is provided on the upper part of the crucible; an induction coil and a coil lifting mechanism are provided around the outside of the support tube, the coil lifting mechanism is provided outside the induction coil, and the upper part of the coil lifting mechanism is connected to the coil lifting motor; the coil lifting motor lifts and lowers the induction coil through the coil lifting mechanism; The support tube is a double-layer structure, and its material is quartz; the temperature measuring hole plug movement mechanism has the function of moving up and down, controlling the temperature measuring hole plug to enter or move out of the upper temperature measuring hole; the temperature measuring hole plug movement mechanism has a rotational movement function, controlling the temperature measuring hole plug to rotate outside the upper temperature measuring hole; the diameter of the temperature measuring hole plug is 0.5mm~1mm smaller than the diameter of the upper temperature measuring hole, and the bottom of the temperature measuring hole plug has a chamfer, and the chamfer size is 0.5mm~1mm.

4. The low stress silicon carbide single crystal growth induction furnace according to claim 1, characterized in that: The crucible rotating shaft passes through the center of the lower cover of the induction furnace, the second sealing structure is arranged between the crucible rotating shaft and the lower cover of the induction furnace, and dynamic sealing is achieved through the second sealing structure; a second gear and a lower temperature measuring window are arranged from top to bottom on the crucible rotating shaft, a first gear is arranged on one side of the second gear, and is connected to the crucible rotating motor through the first gear, and a lower infrared thermometer is arranged at the bottom of the lower temperature measuring window; The crucible rotating motor can drive the crucible, the crucible cover and the lower insulation layer around the central axis through the transmission of the first gear, the second gear, the crucible rotating shaft and the crucible fixing mechanism; The crucible cover and the crucible are made of graphite. Silicon carbide seed crystals are bonded to the crucible cover, and silicon carbide powder is contained in the crucible.

5. A method for growing a low stress silicon carbide single crystal, implemented by using the low stress silicon carbide single crystal growth induction furnace according to any one of claims 1 to 4, characterized in that: The specific steps include: Step 1. Preparation: Place silicon carbide powder into the crucible cavity, bond the seed crystal to the crucible cover, and then tighten the crucible to seal it to a sealed state, place it in a vacuum induction furnace, seal the vacuum induction furnace and then evacuate it; Step 2. First stage growth: grow silicon carbide single crystal by physical vapor transport method, move the induction coil to the initial position, fill with inert gas as carrier gas, grow the single crystal at a set growth temperature, and obtain ingot I; the initial position is the first stage growth position, which is lower than the surface of silicon carbide powder; the temperature of silicon carbide powder is higher than the temperature of ingot I; Step 3. Primary heat treatment: When the silicon carbide crystal grows to half the thickness of the desired final product, an inert gas is introduced into the reaction chamber, the induction coil is uniformly moved upward from the initial position to the center of the induction coil to the level of the primary heat treatment position, and the power of the induction coil is adjusted to control the temperature rise of the crystal ingot I, and then maintained for a set time; the reaction chamber is filled with inert gas, the induction coil is moved, and the temperature rise of the crystal ingot I is carried out simultaneously, and it is completed in 4h to 5h; Step 4. Second stage growth: reduce the pressure in the reaction chamber, move the induction coil downward at a uniform speed to the initial position, adjust the power of the induction coil to reduce the average temperature of the growth surface of ingot I to the set growth temperature, and the silicon carbide single crystal continues to grow on ingot I to finally obtain ingot II; during the growth process, keep the average temperature of the growth surface of ingot II consistent with the set growth temperature; The pressure in the reaction chamber is reduced, the induction coil is moved downward, and the temperature of the growth surface of the crystal ingot I is reduced simultaneously, which is completed in 4h to 5h; the temperature of the silicon carbide powder is higher than that of the crystal ingot II; Step 5. Secondary heat treatment: After the growth of silicon carbide single crystal is completed, inert gas is introduced into the reaction chamber, the upper insulation layer is lowered at a uniform speed until the gap between the upper insulation layer and the lower insulation layer is the smallest, the induction coil is uniformly moved upward from the initial position to the level of the center of the induction coil and the secondary heat treatment position, the power of the induction coil is adjusted to control the temperature increase of the crystal ingot II, the temperature measuring hole plug is placed inside the temperature measuring hole, and the set time is maintained, and then the heating is stopped, and the temperature of the single crystal growth furnace is cooled to room temperature, and the crystal ingot II is taken out to obtain a low-stress silicon carbide crystal ingot; the reaction chamber is filled with inert gas, the induction coil is moved, and the temperature of the crystal ingot II is increased simultaneously, and it is completed in 4h to 5h; The primary heat treatment position is located between position A and position B, wherein position A is the center position of ingot I, and position B is the center position between the lower surface of ingot I and the upper surface of silicon carbide powder; The secondary heat treatment position is located between position C and position D, wherein position C is the center position of ingot II, and position D is the center position between the lower surface of ingot II and the upper surface of silicon carbide powder; The growth time of the first stage growth and the second stage growth, the average growth surface temperature of ingots I and II, and the reaction chamber pressure are kept consistent; wherein the average growth surface temperature of ingots I and II is the single crystal growth temperature; During the primary heat treatment and the secondary heat treatment, the reaction chamber pressure, the holding time, and the temperature of ingots I and II after heating remain consistent; the temperature of ingots I and II after heating is the ingot temperature.

6. The method for growing a low-stress silicon carbide single crystal according to claim 5, characterized in that: During the first and second growth stages, the temperature function T 控 =T(t) directly controls the temperature of the upper temperature measuring point, and directly controls the height of the upper insulation layer through the upper and lower insulation layer gap function L=L(t); thereby indirectly controlling the growth rate of silicon carbide to satisfy v=v(t); The upper temperature measuring point is set at the upper temperature measuring hole, and the temperature of the upper temperature measuring point is the temperature of the crucible cover corresponding to the upper temperature measuring hole measured by the upper infrared thermometer; through the pre-constructed function T 控 =T(t), adjust the temperature of the upper temperature measuring point so that the temperature of the upper temperature measuring point reaches the temperature T at time t 控 .

7. A method for growing a low stress silicon carbide single crystal according to claim 6, characterized in that: The function T 控 =T(t), L=L(t), v=v(t) The construction process is: S1. Take the values ​​of the variation range of the ingot thickness h at equal intervals and number them, denoted as h i , the variation range of the gap L between the upper and lower insulation layers is equidistantly selected and numbered, recorded as L j , where i and j are the numbers of the ingot thickness and the gap between the upper and lower insulation layers respectively; a specific value T is selected from the silicon carbide single crystal growth temperature range of 1950℃~2550℃ 生长 As the set growth temperature, the average temperature of the ingot growth surface is controlled to be T 生长 , the control temperature of the upper temperature measuring point is expressed as T 控 , then the temperature difference between the growth surface of the silicon carbide ingot and the upper temperature measurement point is △T = T 生长 -T 控 ; The actual temperature measured at the upper temperature measuring point is T 测 represents, and the growth time is represented by t; S2. Through numerical simulation, the induction coil power is adjusted to meet the average temperature of the growth surface of the silicon carbide ingot to be T 生长 ±0.2℃, get h i , L j Temperature difference △T under different combinations ij , growth rate v ij , growth quality P ij ; The temperature difference function △T=f1(h,L), the growth rate function v=f2(h,L), and the growth quality function P=f3(h,L) are obtained by fitting; S3. For each h i , from v ij Select a growth rate and use v i Indicates that through v i and h i The fitting function v=f4(h) is obtained; the v i Meet the growth rate and growth quality P requirements at the same time; S4. Take the seed crystal thickness as the initial ingot thickness h0, assume that the functional relationship between the thickness h and the growth time t is h = h(t), and v = f4(h). By integration or solving the formula The functional relationship h=h(t) can be obtained, which is the control process of the thickness of the silicon carbide ingot; S5. Combining the functions v=f4(h) and h=h(t) to obtain v=f4(h(t)), where there is only one independent variable t, further simplified to v=v(t), i.e., the control process of the growth rate of the silicon carbide single crystal; S6. Substitute h=h(t) and v=v(t) into the function v=f2(h,L) to obtain L=f2 -1 (v(t), h(t)), simplified to L = L(t), the control process of the distance between the upper and lower insulation layers during the growth of silicon carbide single crystal is obtained; S7. Substitute L=L(t) and h=h(t) into the function △T=f1(h,L) to obtain △T=f1(h(t),L(t)). This function has only one independent variable t, which can be further simplified to △T=g(t). According to △T=T in S1, 生长 -T 控 , get T 控 =T 生长 -g(t), simplified to T 控 =T(t), and the temperature control process of the temperature measuring point during the growth of silicon carbide single crystal is obtained; S8. The heating power of the induction coil is calculated based on the difference between the temperature control value and the measured value T at the temperature control point. 控 -T 测 And the temperature control function T 控 =T(t) for dynamic adjustment; during the growth of silicon carbide single crystal, the position of the upper insulation layer is dynamically adjusted by the servo motor according to the function L=L(t); S9. Establish a silicon carbide single crystal growth database for each furnace, and save the data after each silicon carbide crystal growth in the database, including the corresponding growth process v = v(t), h = h(t), L = L(t), T 控 =T(t), the final thickness data of the ingot and the single crystal growth quality data, and use this database to adjust the parameters of the function v=f2(h,L) to update the growth process.

8. The method for growing a low-stress silicon carbide single crystal according to claim 7, characterized in that: The thickness h of the ingot in S1 is determined by taking the initial thickness h0 of the silicon carbide ingot as the minimum thickness, i.e. the seed crystal thickness, and taking the target thickness at the end of growth as the maximum thickness; i and j are independently 15 to 30; In S1, the gap L between the upper and lower insulation layers satisfies the minimum gap that the upper and lower insulation layers do not interfere with each other, and the maximum gap is the gap value when the bottom of the upper insulation layer is not higher than the top of the lower insulation layer; the minimum gap between the upper insulation layer and the lower insulation layer is 0.5 mm to 1 mm; In S3, when the growth rate v is selected as a constant value v0, h=v0t+h0.

9. The method for growing a low-stress silicon carbide single crystal according to claim 6, characterized in that: In step 1, the silicon carbide powder is of 5N grade; In step 2 and step 4, the growth time of the silicon carbide single crystal is ≥80h, and the gas pressure in the reaction chamber is 1kPa to 4kPa.

10. The method for growing a low-stress silicon carbide single crystal according to claim 6, characterized in that: In step 3 and step 5, after the inert gas is filled, the pressure of the reaction chamber is 0.9atm~1.0atm, the temperature of the crystal ingot after heating is 80℃~100℃ higher than the single crystal growth temperature, and the insulation time is 5h~6h.

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