High-quality P-type silicon carbide crystal and silicon carbide substrate
By placing protrusions on the inner wall of the crucible and combining rotation and vibration techniques, the problem of difficult suppression of bubbles and holes in the preparation of SiC single crystals by liquid phase is solved, and the growth of high-quality silicon carbide crystals is achieved, which is suitable for large size and long-term growth.
Patent Information
- Application Number
- CN202411758466.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-03
- Publication Date
- 2025-03-14
AI Technical Summary
When the SiC single crystal is prepared by the existing liquid phase method, bubbles and holes are difficult to effectively suppress, resulting in a decrease in crystal quality. Especially during large-size growth and long-term growth, bubble generation is difficult to control.
By placing multiple protrusions on the inner wall of the crucible and combining rotation and vibration mechanisms, the crucible rotates and vibration is driven to promote the precipitation of bubbles at the crucible wall and reduce the probability of bubbles adhering to the crystal surface.
The bubble and cavity density of silicon carbide crystals is significantly reduced, especially within and outside the 2/3 radius area, improving the use and quality of the crystals, suitable for large sizes and long-term growth.
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Figure CN119615370A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to a high-quality P-type silicon carbide crystal and a silicon carbide substrate, and belongs to the technical field of silicon carbide material preparation. Background Art
[0002] In the current liquid phase method for preparing SiC single crystals, a graphite crucible is often used as a reaction container and a source of carbon atoms, and a SiC wafer is used as a seed crystal. Polycrystalline silicon and a solvent are placed in the graphite crucible as growth raw materials. The seed crystal is fixed on the top crystal support shaft and grown by TSSG pulling in an inert gas environment.
[0003] In the above preparation process, the inert gas dissolved in the solution will precipitate from the liquid phase due to temperature or flow fluctuations, forming bubbles attached to the surface of the growing crystal. These bubbles will exist inside the crystal as cavities or solution inclusions in the subsequent growth, which will not only affect the crystal utilization rate, but also cause new microscopic defects (such as TSD, etc.), leading to stress concentration or cracks, thereby further reducing the quality of the crystal.
[0004] At present, the precipitation of bubbles from the solution is often reduced by suppressing the fluctuation of temperature and flow as much as possible, but this also brings new technical problems:
[0005] 1. Limiting the transmission of solutes in the solution: Avoiding stirring the solution as much as possible during liquid phase growth will cause the carbon atoms dissolved on the crucible wall to be unable to be efficiently transported to the crystal growth interface through flow, thereby limiting the high-speed growth of the crystal;
[0006] 2. Limiting the size of the growing crystal: Growing larger crystals requires a larger crucible to hold the solution, and a larger solution size will bring stronger turbulence, further causing temperature and flow fluctuations. Therefore, the existing method alone cannot effectively suppress the generation of bubbles when growing large-sized silicon carbide crystals by liquid phase method;
[0007] 3. It is impossible to effectively suppress the generation of bubbles during long-term growth: During long-term growth, the growth temperature often rises due to changes in the shape of the crucible or the decrease in the solution height. Even if the heating power is adjusted based on experience, the temperature cannot be effectively maintained at a constant level. In addition, changes in the shape of the crucible and the growing crystal will further disrupt the flow of the solution and increase the probability of bubble generation.
[0008] In summary, the existing methods cannot effectively suppress the generation of bubbles during the growth process, and therefore cannot grow high-quality silicon carbide crystals. Summary of the invention
[0009] In order to solve the above problems, a high-quality P-type silicon carbide crystal is provided. The overall bubble and void density of the silicon carbide crystal are lower than those of the existing silicon carbide crystal, and the bubble or void density in the 2 / 3 radius area of the silicon carbide crystal is lower and the diameter is smaller, which can improve the crystal utilization rate and inhibit the formation of micro defects, thereby improving the crystal quality.
[0010] According to one aspect of the present application, a high-quality P-type silicon carbide crystal is provided, wherein the density of bubbles or voids in the 2 / 3 radius area of the silicon carbide crystal is less than 0.1 / cm 2 , and the diameter of a single bubble or cavity is less than 10 μm, and the density of bubbles or cavities outside the 2 / 3 radius area of the silicon carbide crystal is less than 1 / cm 2 , and the diameter of a single bubble or cavity is less than 100μm.
[0011] Optionally, the TSD density within the 2 / 3 radius area of the silicon carbide crystal is less than 100 / cm 2 , BPD density is less than 100 / cm 2 The TSD density outside the 2 / 3 radius area of the silicon carbide crystal is less than 200 / cm 2 , BPD density is less than 500 / cm 2 ;
[0012] Preferably, the BPD density of the direction within the 2 / 3 radius of the silicon carbide crystal with an angle greater than 30° and less than 150° with the [11-20] direction is less than 20 / cm 2 The BPD density of the direction outside the 2 / 3 radius region of the silicon carbide crystal with an angle greater than 30° and less than 150° with the [11-20] direction is less than 400 / cm 2 .
[0013] Optionally, the 2 / 3 radius area of the silicon carbide crystal is divided into a number of square areas with a side length of 5 mm, and the difference in TSD density between adjacent square areas is not greater than 20 / cm 2 , the difference in BPD density is no more than 20 / cm 2 .
[0014] Optionally, T1-T2 < 70 cells / cm 2 , wherein T1 represents the TSD density outside the 2 / 3 radius area of the silicon carbide crystal, and T2 represents the TSD density within the 2 / 3 radius area of the silicon carbide crystal;
[0015] B1-B2<350 pieces / cm 2 , wherein B1 represents the BPD density outside the 2 / 3 radius region of the silicon carbide crystal, and B2 represents the BPD density within the 2 / 3 radius region of the silicon carbide crystal.
[0016] Optionally, the radial in-body absolute stress value in the 2 / 3 radius region of the silicon carbide crystal is -10 to 20 MPa, and the axial in-body absolute stress value is -10 to 20 MPa;
[0017] The absolute stress value in the outer radial direction of the 2 / 3 radius region of the silicon carbide crystal is -20 to 40 MPa, and the absolute stress value in the axial direction is -20 to 40 MPa.
[0018] Optionally, there are 0 microtubes in the silicon carbide crystal.
[0019] Optionally, the resistivity of the silicon carbide crystal at any position is less than 200 mΩ·cm.
[0020] Optionally, on any horizontal plane of the silicon carbide crystal, ρ1-ρ2<20mΩ·cm, ρ3-ρ4<10mΩ·cm, ρ1 represents the maximum resistivity in the entire surface area of the horizontal plane of the silicon carbide crystal, ρ2 represents the minimum resistivity in the entire surface area of the horizontal plane of the silicon carbide crystal, ρ3 represents the maximum resistivity in the 2 / 3 radius area of the horizontal plane of the silicon carbide crystal, and ρ4 represents the minimum resistivity in the 2 / 3 radius area of the horizontal plane of the silicon carbide crystal.
[0021] Optionally, the concentration of Al element in the silicon carbide crystal is 1×10 19 -1.8×10 20 Atom / cm 3 .
[0022] Optionally, the size of the silicon carbide crystal is larger than 4 inches, preferably larger than 6 inches, and more preferably larger than 8 inches.
[0023] Optionally, the concentration of other solvent elements other than Al in the silicon carbide crystal is greater than 1×10 13 Atom / cm 3 and less than 5×10 15 Atom / cm 3 .
[0024] The other co-solvent elements are selected from any one of Ti, Cr, Sc, Ni, Co, Mn, Mg, Ge, As, Dy, Y, Nb, Nd or Fe.
[0025] Since polysilicon and solvent are used as solution raw materials in the liquid phase growth of silicon carbide, the solvent must contain Al element, and one or more other solvent elements are added, for example, when Cr is added, the concentration of Cr in the silicon carbide crystal is greater than 1×10 13 Atom / cm 3 and less than 5×10 15 Atom / cm3 For example, when Ti is added, the concentration of Ti in the silicon carbide crystal is greater than 1×10 13 Atom / cm 3 and less than 5×10 15 Atom / cm 3 For example, when V is added, the concentration of V in the silicon carbide crystal is greater than 1×10 13 Atom / cm 3 and less than 5×10 15 Atom / cm 3 .
[0026] According to another aspect of the present application, a high-quality P-type silicon carbide substrate is provided, wherein the density of bubbles or voids in the 2 / 3 radius area of the silicon carbide substrate is less than 0.1 / cm 2 , and the diameter of a single bubble or cavity is less than 10 μm, the density of bubbles or voids outside the 2 / 3 radius area of the silicon carbide substrate is less than 1 / cm2, and the diameter of a single bubble or cavity is less than 100 μm.
[0027] Optionally, the TSD density within the 2 / 3 radius area of the silicon carbide substrate is less than 100 / cm 2 , BPD density is less than 100 / cm 2 The TSD density outside the 2 / 3 radius area of the silicon carbide substrate is less than 200 / cm 2 , BPD density is less than 500 / cm 2 ;
[0028] Preferably, the BPD density of the direction within the 2 / 3 radius of the silicon carbide substrate with an angle greater than 30° and less than 150° with the [11-20] direction is less than 20 / cm 2 The BPD density of the outer direction of the 2 / 3 radius region of the silicon carbide substrate with an angle greater than 30° and less than 150° with the [11-20] direction is less than 400 / cm 2 .
[0029] Optionally, the 2 / 3 radius area of the silicon carbide substrate is divided into a plurality of square areas with a side length of 5 mm, and the difference in TSD density between adjacent square areas is not greater than 20 / cm 2 , the difference in BPD density is no more than 20 / cm 2 .
[0030] T1-T2<70 cells / cm 2 , wherein T1 represents the TSD density outside the 2 / 3 radius area of the silicon carbide substrate, and T2 represents the TSD density within the 2 / 3 radius area of the silicon carbide substrate;
[0031] B1-B2<350 pieces / cm2 , wherein B1 represents the BPD density outside the 2 / 3 radius area of the silicon carbide substrate, and B2 represents the BPD density within the 2 / 3 radius area of the silicon carbide substrate.
[0032] Optionally, the radial internal absolute stress value in the 2 / 3 radius region of the silicon carbide substrate is -10 to 20 MPa, and the axial internal absolute stress value is -10 to 20 MPa;
[0033] The absolute stress value in the outer radial direction of the 2 / 3 radius region of the silicon carbide substrate is -20 to 40 MPa, and the absolute stress value in the axial direction is -20 to 40 MPa.
[0034] The number of micropipes in the silicon carbide substrate is zero.
[0035] Optionally, the resistivity of the silicon carbide substrate at any position is less than 200 mΩ·cm.
[0036] Optionally, in the silicon carbide substrate, ρ1-ρ2 is less than 20mΩ·cm, ρ3-ρ4 is less than 10mΩ·cm, ρ1 represents the maximum resistivity in the entire surface area of the silicon carbide substrate, ρ2 represents the minimum resistivity in the entire surface area of the silicon carbide substrate, ρ3 represents the maximum resistivity in the 2 / 3 radius area of the silicon carbide substrate, and ρ4 represents the minimum resistivity in the 2 / 3 radius area of the silicon carbide substrate.
[0037] Optionally, the Al concentration in the silicon carbide substrate is 1×10 19 -1.8×10 20 Atom / cm 3 .
[0038] Optionally, the size of the silicon carbide substrate is larger than 4 inches, preferably larger than 6 inches, and more preferably larger than 8 inches.
[0039] Optionally, the silicon carbide substrate contains other solvent elements other than Al in a concentration greater than 1×10 13 Atom / cm 3 and less than 5×10 15 Atom / cm 3 .
[0040] The other co-solvent elements are selected from any one of Ti, Cr, Sc, Ni, Co, Mn, Mg, Ge, As, Dy, Y, Nb, Nd or Fe.
[0041] The above-mentioned P-type silicon carbide substrate is prepared by cutting, grinding and polishing a P-type silicon carbide crystal. In the preparation of the P-type silicon carbide crystal, as long as the bubbles in the raw material solution can be controlled to be more inclined to precipitate toward the inner wall of the crucible, so that the proportion of bubbles reaching the surface of the seed crystal is reduced, the bubbles can be inhibited from entering the crystal, the quality of the crystal can be improved, and the high-quality P-type silicon carbide crystal of the present application can be obtained. The following is an example of a preparation method that can prepare the P-type silicon carbide crystal of the present application, but the preparation method does not constitute a limitation on the P-type silicon carbide crystal and the P-type silicon carbide substrate of the present application, as long as the bubbles can be controlled to precipitate at the crucible wall during the growth of the crystal.
[0042] A method for preparing the above-mentioned high-quality P-type silicon carbide crystal, providing a crucible capable of containing a raw material solution, a crystal support shaft and a rotating mechanism, wherein the inner wall of the crucible is provided with a plurality of protrusions, and the plurality of protrusions are equally spaced from each other in the circumferential direction of the inner wall; the crystal support shaft is used to fix a seed crystal and a crystal grown on the seed crystal; and the rotating mechanism is used to drive the crucible to rotate;
[0043] The crucible is rotated by a rotating mechanism during at least a portion of the growth period of the silicon carbide crystal.
[0044] Preferably, the rotating mechanism drives the crucible to rotate, so that a first period of rotating the crucible at a first rotation speed and a second period of rotating the crucible at a second rotation speed higher than the first rotation speed are performed alternately.
[0045] Optionally, the first rotation speed is lower than 10 rpm, preferably 0-5 rpm.
[0046] Optionally, the second rotation speed is above 10 rpm, preferably above 50 rpm.
[0047] The rotating mechanism can drive the crucible to rotate clockwise and counterclockwise;
[0048] The crystal growth period includes a period of repeating in the order of rotating at a first rotation speed clockwise for a first period, rotating at a second rotation speed clockwise for a second period, rotating at the first rotation speed counterclockwise for a first period, and rotating at the second rotation speed counterclockwise for a second period; or
[0049] The crystal growth period includes a period of repeating the sequence of rotating at a second rotation speed clockwise for a second period, rotating at a first rotation speed clockwise for a first period, rotating at a second rotation speed counterclockwise for a second period, and rotating at the first rotation speed counterclockwise for a first period.
[0050] Also comprising a vibration mechanism, the vibration mechanism drives the crucible to vibrate during at least a portion of the growth period of the semiconductor single crystal;
[0051] Preferably, the vibration amplitude of the vibration mechanism is 50-500 μm, and the vibration frequency is 10-50 KHz.
[0052] The beneficial effects of this application include but are not limited to:
[0053] 1. The high-quality P-type silicon carbide crystal of the present application can significantly remove bubbles or voids in the liquid phase silicon carbide crystal, thereby improving the utilization rate and crystallization quality of the silicon carbide crystal, and improving the reliability and service life of the silicon carbide substrate.
[0054] 2. The high-quality P-type silicon carbide crystal of the present application can prepare silicon carbide crystals with a diameter of more than 8 inches by suppressing the generation of bubbles and the number of bubbles at the center of the seed crystal for a long time during the growth process, thereby improving production efficiency and reducing production costs.
[0055] 3. The crystal quality of the high-quality P-type silicon carbide crystal of the present application is significantly improved compared to the existing P-type silicon carbide crystal. The P-type silicon carbide substrate prepared therefrom is less likely to cause "killer-type" defects in the subsequent epitaxial process, and is less likely to cause increased leakage current and reduced breakdown voltage in the device preparation process, so the overall utilization rate is higher. BRIEF DESCRIPTION OF THE DRAWINGS
[0056] 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:
[0057] Figure 1 is a schematic structural cross-sectional view of the crystal growth system 1;
[0058] Figure 2 is an enlarged cross-sectional view near the crucible 10;
[0059] Figure 3 yes Figure 2 A cross-sectional view taken along line III-III;
[0060] Figure 4 yes Figure 2 A cross-sectional view taken along line IV-IV of FIG.
[0061] Figure 5 is a cross-sectional view showing a conventional crystal growth method;
[0062] Figure 6 is a cross-sectional view illustrating a crystal growth method according to the technology herein;
[0063] Figure 7 yes Figure 6 A cross-sectional view of line VIII-VIII;
[0064] Figure 8 This is the test picture of silicon carbide crystal 2#.
[0065] List of parts and reference numerals:
[0066] 1. Crystal growth system; 2. Control device; 3. Crystal growth device; 5. Chamber; 10. Crucible; 10i. Inner wall; 10p. Protrusion; 12. Crucible axis; 13. Crystal support axis; 14. High-frequency coil; 16. Seed crystal; 17. Solution; 18. Growing crystal; 19. Rotating part; 20. Driving part; 21. Vibration mechanism; 31. Operation control component; 32. Vibration control component; CA, rotating axis; BU, bubble. DETAILED DESCRIPTION
[0067] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.
[0068] Unless otherwise specified, the raw materials in the examples and comparative examples of the present application were purchased through commercial channels.
[0069] Unless otherwise specified, the methods used in the examples and comparative examples of the present application are conventional methods in the prior art.
[0070] Example 1
[0071] This embodiment relates to a crystal growth system
[0072] Figure 1 1 shows a schematic cross-sectional view of the crystal growth system 1. The crystal growth system 1 includes a control device 2 and a crystal growth device 3. The crystal growth device 3 is a device capable of growing various semiconductor single crystals using a liquid phase method. In this embodiment, the growth of a silicon carbide (SiC) single crystal will be described.
[0073] The crystal growth device 3 mainly includes a chamber 5, a crucible 10, a crucible table 11, a crucible shaft 12, a crystal support shaft 13, a high-frequency coil 14, a rotating part 19, a driving part 20, and a vibration mechanism 21. The chamber 5 has an outer surface outside a cylinder, and stores the high-frequency coil 14, the crucible 10, and the crucible table 11. The crucible table 11 is a table for mounting the crucible 10, and the crucible shaft 12 is a shaft that rotatably supports the crucible 10 and the crucible table 11, and the crucible shaft 12 has a rotation axis CA. The rotating part 19 is arranged below the crucible 10, and the rotating part 19 rotates the crucible shaft 12 around the rotation axis CA. The vibration mechanism 21 is arranged on the crucible shaft 12, and the vibration mechanism 21 is a mechanism for applying vibration to the crucible shaft 12, and the vibration mechanism 21 will be described later. The high-frequency coil 14 receives power from a power supply device (not shown) and induction heats the crucible 10.
[0074] A crystal support shaft 13 is disposed above the crucible 10, and a seed crystal 16 and a growth crystal 18 are fixed below the crystal support shaft 13. In this embodiment, the seed crystal 16 and the growth crystal 18 are single crystals of silicon carbide. The bottom of the crystal support shaft 13 extends into the interior of the crucible 10, and the crystal support shaft 13 has a rotation axis CA. The driving unit 20 rotates the crystal support shaft 13 around the rotation axis CA and moves in the vertical direction ( Figure 1 Move in the Z-axis direction).
[0075] The control device 2 includes an operation control component 31 and a vibration control component 32. The operation control component 31 is a component for controlling the operation of the rotating component 19 and the driving component 20, and the vibration control component 32 is a component for controlling the vibration of the vibration mechanism 21. For example, the control device 2 may be a PC having a CPU or a memory.
[0076] Figure 2 An enlarged cross-sectional view of the vicinity of the crucible 10 is shown. The crucible 10 has a cylindrical shape centered on the rotation axis CA, and contains a solution 17 in the crucible 10, which is a silicon-based solution. The crucible 10 is inductively self-heated by a high-frequency coil 14, providing a heat source for the solution 17 during crystal growth. The crucible 10 is made of a carbon material (graphite), so carbon atoms can be supplied from the crucible 10 to the solution 17.
[0077] Figure 3 express Figure 2 The cross-sectional view along line III-III, Figure 4 It also shows Figure 2 The cross-sectional view along line IV-IV, Figure 3 and Figure 4 Each of them is a cross-sectional view through the protrusion 10p. Figure 3 is the upper cross section of the crucible 10, Figure 4 A plurality of protrusions 10p are arranged on the inner wall 10i of the crucible 10, and the shapes of the protrusions 10p can be various, such as cones, pyramids, cylinders, prisms, hemispheres, etc. In this embodiment, the shape of the protrusions 10p is a cone.
[0078] The method of forming the plurality of protrusions 10p may be various. For example, when the crucible 10 is formed, it may be formed integrally with the inner wall 10i. In addition, for example, the protrusions 10p formed to be separated from the crucible 10 may be fixed to the inner wall 10i. In the present embodiment, the plurality of protrusions 10p are formed integrally with the inner wall 10i. Note that the protrusions 10p formed integrally can be formed by a well-known crucible manufacturing method, and therefore a detailed description thereof is omitted.
[0079] like Figure 3 and Figure 4As shown, a plurality of protrusions 10p are arranged at equal intervals from each other in the circumferential direction of the inner wall 10i. Figure 3 As shown in FIG. 1 , the intervals D1 between adjacent protrusions 10p are all the same. Figure 4 As shown, the intervals D2 between adjacent protrusions 10p are all the same. Therefore, the heat capacity of the crucible 10 can be made uniform in the circumferential direction, so that the temperature distribution when the crucible 10 is heated is rotationally symmetric with respect to the rotation axis CA.
[0080] As one embodiment, the interval D1 on the upper side is smaller than the interval D2 on the lower side. That is, the arrangement density of the plurality of protrusions 10p is higher on the upper side than on the lower side. As described later, bubbles BU are more likely to precipitate on the upper side than on the lower side.
[0081] The height H of the plurality of protrusions 10p from the surface of the inner wall 10i may be appropriately determined so as to balance the efficiency of forming the bubbles BU and the efficiency of growing the crystals. That is, if the height H of the protrusions 10p is too low, the effect of forming the bubbles BU is reduced. On the other hand, if the height H of the protrusions 10p is too high, the disturbed area of the solution 17 expands from the inner wall 10i to the center side, and the crystal growth rate may decrease. For example, the height H may be in the range of 0.2 to 2 mm.
[0082] The height H of the plurality of protrusions 10p may vary in the vertical direction of the crucible 10. For example, the height H of the upper side may be higher than that of the lower side. In addition, the height H of the central portion may also be higher than that of the lower side and the upper side.
[0083] The intervals between the plurality of protrusions 10p may be appropriately determined in a manner that balances the efficiency of forming the bubbles BU and the processing cost of the protrusions 10p. That is, if the intervals are too large, the effect of forming the bubbles BU will be reduced. On the other hand, if the intervals are too small, the difficulty of processing the protrusions 10p increases, the manufacturing cost of the crucible 10 increases, or the production yield rate decreases. For example, the intervals may be in the range of 1 to 5 mm.
[0084] Note that the protrusions 10p do not increase the amount of polycrystals precipitated on the inner wall 10i. Since the crucible 10 is heated by the high frequency coil 14, the inner wall 10i is hotter than the center of the solution 17, and polycrystals are less likely to precipitate.
[0085] Example 2
[0086] The difference between this embodiment and the first embodiment is that the present embodiment further uses a vibration mechanism 21. Hereinafter, only the differences from the first embodiment will be described.
[0087] The vibration mechanism 21 is disposed on the crucible shaft 12 . The vibration mechanism 21 is a mechanism for applying vibration to the crucible 10 via the crucible shaft 12 . The vibration mechanism 21 may be of various types, for example, an ultrasonic vibration device.
[0088] The vibration mechanism 21 vibrates the crucible 10 during at least some of the growth cycles of the growing crystal 18, which allows the oscillation to be transmitted to the solution 17 located near the inner wall 10i, further promoting the precipitation of bubbles BU near the inner wall 10i due to the effect of the cavitation phenomenon.
[0089] The period of time during which vibration is applied by the vibration mechanism 21 may be different. For example, vibration may be applied during a portion of the high rotation period or the entire period. Alternatively, vibration may be applied during the entire growth period of the crystal.
[0090] The amplitude or frequency of the vibration generated by the vibration mechanism 21 can be appropriately determined to balance the efficiency of the formation of the bubbles BU and the stability of the crystal growth. That is, if the amplitude is too small, it is difficult for the bubbles BU to precipitate from the vicinity of the inner wall 10i; on the other hand, if the amplitude is too large, the vibration wave will propagate from the inner wall 10i to the crystal growth area on the central side, which may have an adverse effect on the crystal growth. For example, the amplitude of the vibration can be in the range of 50 to 500 μm, and the frequency can be in the range of 10 to 50 kHz.
[0091] Example 3
[0092] The liquid phase growth method of the current prior art includes the following steps:
[0093] Perform the preparation process: polycrystalline silicon and a flux are placed in a crucible 10, and the flux includes, in addition to Al, one or a combination of two or more of Ti, Cr, Sc, Ni, Co, Mn, Mg, Ge, As, Dy, Y, Nb, Nd or Fe. The amount of flux added accounts for 30%-70% of the total molar number in the solution. The crucible 10 is arranged on the crucible table 11, the seed crystal 16 is fixed on the crystal support shaft 13, the seed crystal 16 is arranged at a predetermined position inside the crucible 10, and the chamber 5 is sealed.
[0094] Heating and temperature raising process: the internal atmosphere of the chamber 5 is vacuumed, and then filled with an inert gas (any one of helium, neon or argon), and the temperature in the crucible 10 is heated by the high-frequency coil 14 to reach a predetermined growth temperature. The growth temperature of silicon carbide is generally in the range of 1700 to 2000° C. In this embodiment, the growth temperature is set to 1800° C., which causes the polysilicon and the flux to melt and form a solution 17.
[0095] Seed crystal contact step: Specifically, after reaching the growth temperature, the seed crystal 16 is lowered to contact the solution 17 .
[0096] Growth process: The driving unit 20 lifts the seed crystal 16 upward at a constant speed based on the crystal growth rate to achieve gradual growth of the crystal.
[0097] Determine whether the crystal growth amount reaches the specified amount: If the determination is negative, continue to the growth step to grow the crystal. If the determination is yes, enter the cooling step, after raising the growing crystal 18 and making it leave the liquid surface, turn off the heating component; then perform the furnace opening step: open the chamber 5 and take out the crystal.
[0098] However, in the above-mentioned preparation method, the cross-sectional view of the crystal growth process is shown in FIG. Figure 5 In the liquid phase crystal growth method, due to factors such as temperature fluctuations and turbulence, the inert gas dissolved in the solution 17 sometimes forms bubbles BU. Figure 5 In the figure, bubbles BU are shown as white circles in simulation, and the generated bubbles BU rise upward (in the +z direction) by buoyancy and reach the liquid surface 17s. In the conventional crystal growth method, a part of the bubbles BU reaching the liquid surface 17s sometimes adheres to the surface 18s of the growing crystal 18 (see region RE1), and as a result, the bubbles BU are sometimes wrapped inside the growing crystal 18 (see region RE2). If the bubbles BU are wrapped in the growing crystal 18, cracks, stress concentration, TSD, and voids may occur.
[0099] The present embodiment relates to a method for preparing high-quality P-type silicon carbide crystals, which is carried out using the crystal growth device of Embodiment 1 or 2. In the original growth process, the crucible 10 is driven to rotate by the rotating mechanism 19, so that low-speed rotation periods and high-speed rotation periods come alternately.
[0100] The low-speed rotation period is a period in which the crucible 10 is rotated at a first rotation speed. The high-speed rotation period is a period in which the crucible 10 is rotated at a second rotation speed higher than the first rotation speed. The first rotation speed is lower than 10 rpm, preferably, the first rotation speed is 0 to 5 rpm. The second rotation speed is greater than 10 rpm, preferably, the second rotation speed is greater than 50 rpm. This will be described in detail below.
[0101] The rotating mechanism 19 repeats in this order: a clockwise low-speed rotation period, a clockwise high-speed rotation period, a counterclockwise low-speed rotation period, and a counterclockwise high-speed rotation period. Figure 3 As shown, the clockwise rotation period is the period when the crucible 10 rotates in the clockwise rotation direction R1, and the counterclockwise rotation period is the period when the crucible 10 rotates in the counterclockwise rotation direction R2. The above periods are repeated periodically, and the length and period conditions of each period can be set in various ways according to the crystal growth state.
[0102] A specific example of this embodiment is as follows: in the clockwise low-speed rotation period, the crucible 10 is rotated in the clockwise rotation direction R1 at a first rotation speed, and after a first predetermined time (eg, 0.1 to 1 hour) has passed, the crucible 10 enters the clockwise high-speed rotation period.
[0103] In the clockwise high-speed rotation period, first, the first rotation speed is accelerated to the second rotation speed, and the time required for acceleration can be, for example, 0.1 to 1 minute. Then, the state of rotating in the rotation direction R1 at the second rotation speed is maintained for a second predetermined time (for example, 1 to 5 minutes). After the second predetermined time, the crucible 10 is reversely rotated in the counterclockwise rotation direction R2, thereby decelerating from the second rotation speed to zero speed, and the time required for deceleration can be, for example, 0.1 to 1 minute. When the deceleration is completed, the crucible 10 is transferred to the counterclockwise low-speed rotation period.
[0104] In the counterclockwise low-speed rotation period, crucible 10 is rotated in the counterclockwise rotation direction R2 at a first rotation speed, and proceeds to the counterclockwise high-speed rotation period according to the lapse of a first predetermined time.
[0105] In the counterclockwise high-speed rotation period, the first rotation speed is accelerated to the second rotation speed. Then, the state of rotating in the rotation direction R2 at the second rotation speed is maintained for a second predetermined time. After the second predetermined time, the crucible 10 is reversely rotated in the clockwise rotation direction R1, and decelerated from the second rotation speed to zero speed. When the deceleration is completed, the process is transferred to the step of determining whether the crystal growth amount reaches the specified amount.
[0106] refer to Figure 6 The technical effects of this embodiment are described. Figure 6 is with Figure 5 The same cross-sectional view, Figure 7 yes Figure 6 The technology of the present specification includes a high-speed rotation period in which the crucible 10 is rotated in the clockwise rotation direction R1 at a rotation speed of 10 rpm or more. In the high-speed rotation period, Figure 7 As shown, a rotating flow RF around the rotation axis CA can be generated in the solution 17, and the flow velocity distribution of the rotating flow RF is the largest near the inner wall 10i and the smallest near the rotation axis CA, and since the greater the flow velocity, the lower the hydraulic pressure, bubbles BU can be easily formed. Figure 6 As shown, bubbles BU can be preferentially formed in the peripheral area A2 near the inner wall 10i, compared with the central area A1 near the rotation axis CA, and the central area A1 is an area where the growing crystal 18 is located above it (in the +z direction) and the liquid surface 17s is blocked by the growing crystal 18. On the other hand, the peripheral area A2 is an area where there is no growing crystal 18 above it, and therefore the liquid surface 17s is a free liquid surface, that is, the bubbles BU generated in the peripheral area A2 will discharge the solution 17 from the free liquid surface area of the liquid surface 17S, and will not adhere to the growing crystal surface 18s.
[0107] Therefore, in the technology of the present specification, more bubbles BU can be precipitated in the peripheral area A2 compared with the central area A1, so the ratio of bubbles BU attached to the surface 18s can be reduced, and thus the bubbles BU can be suppressed from being wrapped in the growing crystal 18. In addition, the same effect is obtained when the crucible 10 is rotated in the counterclockwise direction R2 at a rotation speed of 10 rpm or more.
[0108] In the technology of the present specification, the plurality of protrusions 10p arranged on the inner wall 10i can generate local turbulence near the inner wall 10i. Since turbulence can form a low-pressure area, more bubble BU nucleation points (tiny points in the liquid that promote the formation of bubbles BU) can be generated near the inner wall 10i compared to the vicinity of the rotation axis CA. As a result, more bubbles BU can be precipitated in the peripheral area A2 compared to the central area A1, so the proportion of bubbles BU attached to the surface 18s can be reduced.
[0109] During the period when the bubbles BU generated in the peripheral area A2 move to the liquid surface 17s, the bubbles BU move to the central area A1 due to the flow of the solution 17, and sometimes adhere to the surface 18s. The longer the moving distance of the bubbles BU (that is, the lower the position of the bubbles BU), the greater the probability of such a situation. Therefore, in the technology of the present invention, the arrangement density of the protrusions 10p is at the top (see Figure 3 ) is higher than the bottom (see Figure 4 ). As a result, air bubbles BU are more likely to be precipitated on the upper side than on the lower side, so that the probability of air bubbles BU adhering to the surface 18s can be further reduced.
[0110] The rotation of the crucible in the preparation method can remove bubbles in the solution and promote the flow of the solution to increase the crystal growth rate.
[0111] This preparation method is still effective in large-scale growth systems. In fact, the larger the crucible size, the faster the solution flow rate near the crucible wall, which is more conducive to the precipitation of bubbles from the crucible wall, and it is easier to obtain large-sized, high-quality silicon carbide crystals.
[0112] The above preparation method is used to prepare P-type silicon carbide crystal, and the specific differences are as follows:
[0113] Silicon carbide crystal 1#
[0114] (1) placing polycrystalline silicon, 5% Al and 50% Cr in a crucible, and fixing a seed crystal on a crystal support shaft;
[0115] (2) Evacuate the crucible, introduce inert gas, raise the temperature to 1700°C, bring the seed crystal into contact with the solution, pull the seed crystal up by 1 mm, form a curved liquid surface with the solution surface, and start growth;
[0116] (3) The rotating mechanism first rotates clockwise at 0 rpm for 0.1 hour, then increases to 10 rpm within 0.1 minute and rotates clockwise, maintains for 5 minutes, then decelerates to 0 rpm within 0.1 minute; then rotates counterclockwise at 0 rpm for 0.1 hour, then increases to 10 rpm within 0.1 minute and rotates counterclockwise, maintains for 5 minutes, and finally decelerates to 0 rpm within 0.1 minute;
[0117] (4) determining whether the crystal growth amount reaches a specified amount, if it is determined to be yes, proceeding to step (5), if it is determined to be no, continuing to step (3) until it is determined to be yes;
[0118] (5) Pull the crystal away from the liquid surface, cool it down, open the furnace and then take out the crystal.
[0119] Silicon carbide crystal 2#
[0120] (1) placing polycrystalline silicon, 5% Al and 30% Ti in a crucible, and fixing a seed crystal on a crystal support shaft;
[0121] (2) Evacuate the crucible, introduce inert gas, raise the temperature to 2000°C, bring the seed crystal into contact with the solution, pull the seed crystal 5 mm, form a curved liquid surface with the solution surface, and start growth;
[0122] (3) The rotating mechanism first rotates clockwise at 5 rpm for 1 hour, then increases to 50 rpm within 1 minute and rotates clockwise, maintains for 1 minute, then decelerates to 0 rpm within 1 minute; then rotates counterclockwise at 5 rpm for 1 hour, then increases to 50 rpm within 1 minute and rotates counterclockwise, maintains for 1 minute, and finally decelerates to 0 rpm within 1 minute;
[0123] (4) determining whether the crystal growth amount reaches a specified amount, if it is determined to be yes, proceeding to step (5), if it is determined to be no, continuing to step (3) until it is determined to be yes;
[0124] (5) Pull the crystal away from the liquid surface, cool it down, open the furnace and then take out the crystal.
[0125] Silicon carbide crystal 3#
[0126] The difference between the present silicon carbide crystal and silicon carbide crystal 2# is that the vibration mechanism continuously provides vibration in step (3), the vibration amplitude is 50 μm, the vibration frequency is 10 KHz, and the rest is the same as silicon carbide crystal 2#.
[0127] Silicon carbide crystal 4#
[0128] The difference between this silicon carbide crystal and silicon carbide crystal 2# is that the vibration mechanism only provides continuous vibration during the 50 rpm clockwise rotation and 50 rpm counterclockwise rotation periods in step (3), the vibration amplitude is 500 μm, the vibration frequency is 50 KHz, and the rest is the same as silicon carbide crystal 2#.
[0129] Silicon carbide crystal 5#
[0130] The difference between the present silicon carbide crystal and silicon carbide crystal 2# is that, in step (3): the rotating mechanism first increases the speed to 50 rpm within 1 minute and rotates clockwise, maintains for 1 minute, then decreases the speed to 5 rpm within 1 minute and rotates clockwise, maintains for 1 hour, then decelerates to 0 rpm within 0.1 minute; then increases the speed to 50 rpm within 1 minute and rotates counterclockwise for 1 minute, then decreases the speed to 5 rpm within 1 minute and rotates counterclockwise for 1 hour, finally decelerates to 0 rpm within 0.1 minute, and the rest is the same as silicon carbide crystal 2#.
[0131] Test Case
[0132] The silicon carbide crystal prepared in the above Example 3 was cut off at 1 mm at the head and 1 mm at the tail, and then the crystal was cut, ground and polished into several silicon carbide substrates. Several silicon carbide substrates obtained from each crystal were tested, and the test results are shown in Table 1.
[0133] The parameters in Table 1 such as bubble or void density, maximum diameter of bubbles or voids, microtubes, TSD density, BPD density, stress, resistivity, Al concentration and maximum concentration of other co-solvent elements except Al all refer to the maximum values obtained by testing several silicon carbide substrates obtained from the silicon carbide crystal. Therefore, the parameters representing the entire silicon carbide crystal are less than or equal to the values in Table 1. Except for a silicon carbide substrate with the maximum value obtained by testing, the parameters of the remaining silicon carbide substrates are less than or equal to the values in Table 1.
[0134] The maximum difference in TSD density between adjacent square areas within the 2 / 3 radius area in Table 1 (pieces / cm 2 )” and the maximum difference in BPD density of adjacent square areas outside the 2 / 3 radius area (pcs / cm 2 The square area mentioned in the two parameters of " )" refers to a plurality of square areas with a side length of 5 mm divided within a 2 / 3 radius area of the silicon carbide crystal.
[0135] Table 1
[0136]
[0137]
[0138]
[0139] Figure 8 This is the test image of silicon carbide crystal 2#, where Figure 8 (a) is the crystal surface observed under an optical microscope, and no macroscopic defects such as bubbles, voids, and inclusions were observed; Figure 8 (b) shows the crystal micro defects detected by X-ray diffraction morphology technology. No TSD was observed, and only a small amount of BPD existed, proving that the quality of the crystal obtained by the method of the present application is significantly improved. Figure 8 (b) It can be seen that the existing BPDs are all along the [11-20] direction. The BPD in this direction is an inherent defect of the liquid phase growth method. The present application controls the distribution of bubbles to reduce the number of BPDs in other directions, thereby obtaining high-quality silicon carbide crystals.
[0140] Although the above embodiment 3 describes the method of switching alternately between the low-speed rotation period and the high-speed rotation period, the preparation of high-quality P-type silicon carbide crystals in the present application is not limited to this method. For example, the crucible 10 can rotate at a high speed during the entire crystal growth period. And the speed of the crucible rotation can be arbitrarily adjusted in accordance with different growth processes.
[0141] 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 high-quality P-type silicon carbide crystal, characterized in that: The density of bubbles or cavities in the 2 / 3 radius area of the silicon carbide crystal is less than 0.1 / cm 2 , and the diameter of a single bubble or cavity is less than 10 μm, and the density of bubbles or cavities outside the 2 / 3 radius area of the silicon carbide crystal is less than 1 / cm 2 , and the diameter of a single bubble or cavity is less than 100μm.
2. The high-quality P-type silicon carbide crystal according to claim 1, characterized in that: The TSD density within the 2 / 3 radius area of the silicon carbide crystal is less than 100 / cm 2 , the BPD density is less than 100 / cm2, and the TSD density outside the 2 / 3 radius area of the silicon carbide crystal is less than 200 / cm 2 , BPD density is less than 500 / cm 2 ; Preferably, the BPD density of the direction within the 2 / 3 radius of the silicon carbide crystal with an angle greater than 30° and less than 150° with the [11-20] direction is less than 20 / cm 2 The BPD density of the direction outside the 2 / 3 radius region of the silicon carbide crystal with an angle greater than 30° and less than 150° with the [11-20] direction is less than 400 / cm 2 .
3. The high-quality P-type silicon carbide crystal according to claim 2, characterized in that: The 2 / 3 radius area of the silicon carbide crystal is divided into several square areas with a side length of 5 mm, and the difference in TSD density between adjacent square areas is no more than 20 / cm 2 , the difference in BPD density is no more than 20 / cm 2 ; and / or T1-T2<70 cells / cm 2 , wherein T1 represents the TSD density outside the 2 / 3 radius area of the silicon carbide crystal, and T2 represents the TSD density within the 2 / 3 radius area of the silicon carbide crystal; B1-B2<350 pieces / cm 2 , wherein B1 represents the BPD density outside the 2 / 3 radius region of the silicon carbide crystal, and B2 represents the BPD density within the 2 / 3 radius region of the silicon carbide crystal.
4. The high-quality P-type silicon carbide crystal according to claim 1, characterized in that: The radial body absolute stress value in the 2 / 3 radius region of the silicon carbide crystal is -10 to 20 MPa, and the axial body absolute stress value is -10 to 20 MPa; The absolute stress value in the outer radial body of the 2 / 3 radius region of the silicon carbide crystal is -20 to 40 MPa, and the absolute stress value in the axial body is -20 to 40 MPa; and / or The number of microtubes in the silicon carbide crystal is 0.
5. The high-quality P-type silicon carbide crystal according to claim 1, characterized in that: The resistivity of the silicon carbide crystal at any position is less than 200 mΩ·cm; and / or The Al concentration in the silicon carbide crystal is 1×10 19 -1.8×10 20 Atom / cm 3 .
6. A high-quality P-type silicon carbide substrate, characterized in that: The density of bubbles or voids in the 2 / 3 radius area of the silicon carbide substrate is less than 0.1 / cm 2 , and the diameter of a single bubble or cavity is less than 10 μm, and the density of bubbles or cavities outside the 2 / 3 radius area of the silicon carbide substrate is less than 1 / cm 2 , and the diameter of a single bubble or cavity is less than 100μm.
7. The high-quality P-type silicon carbide substrate according to claim 6, characterized in that: The TSD density in the 2 / 3 radius area of the silicon carbide substrate is less than 100 / cm 2 , BPD density is less than 100 / cm 2 The TSD density outside the 2 / 3 radius area of the silicon carbide substrate is less than 200 / cm 2 , BPD density is less than 500 / cm 2 ; Preferably, the BPD density of the direction within the 2 / 3 radius of the silicon carbide substrate with an angle greater than 30° and less than 150° with the [11-20] direction is less than 20 / cm 2 The BPD density of the outer direction of the 2 / 3 radius region of the silicon carbide substrate with an angle greater than 30° and less than 150° with the [11-20] direction is less than 400 / cm 2 .
8. The high-quality P-type silicon carbide substrate according to claim 7, characterized in that: The 2 / 3 radius area of the silicon carbide substrate is divided into a number of square areas with a side length of 5 mm, and the difference in TSD density between adjacent square areas is no more than 20 / cm 2 , the difference in BPD density is no more than 20 / cm 2 ; and / or T1-T2<70 cells / cm 2 , wherein T1 represents the TSD density outside the 2 / 3 radius area of the silicon carbide substrate, and T2 represents the TSD density within the 2 / 3 radius area of the silicon carbide substrate; B1-B2<350 pieces / cm 2 , wherein B1 represents the BPD density outside the 2 / 3 radius area of the silicon carbide substrate, and B2 represents the BPD density within the 2 / 3 radius area of the silicon carbide substrate.
9. The high-quality P-type silicon carbide substrate according to claim 6, characterized in that: The radial internal absolute stress value in the 2 / 3 radius region of the silicon carbide substrate is -10 to 20 MPa, and the axial internal absolute stress value is -10 to 20 MPa; The absolute stress value of the silicon carbide substrate in the outer radial direction of the 2 / 3 radius region is -20 to 40 MPa, and the absolute stress value of the silicon carbide substrate in the axial direction is -20 to 40 MPa; and / or The number of micropipes in the silicon carbide substrate is zero.
10. The high-quality P-type silicon carbide substrate according to claim 6, characterized in that: The resistivity of the silicon carbide substrate at any position is less than 200 mΩ·cm; and / or The Al concentration in the silicon carbide substrate is 1×10 19 -1.8×10 20 Atom / cm 3 .