N-type silicon carbide crystal and liquid phase growth method thereof

Abstract

The invention discloses an n-type silicon carbide crystal and a liquid phase growth method thereof, and belongs to the technical field of semiconductors. By changing the formula of a growth raw material for silicon carbide growth, the growth raw material is configured to be SixCryMz, the molar ratio x of Si to the raw material is 40-76%, the molar ratio y of Cr to the raw material is 20-60%, and the molar ratio z of M to the raw material is 1-4%; m is one or more of Sc, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Y, Zr, Nb, Mo, Ce, La, Tb, Nd, Ta and Pr. According to the method, other elements M are doped on the basis of a Si-Cr system, the liquid growth method is matched to replace an Al element to improve the crystal morphology, meanwhile, evaporation of solution components can be inhibited, and the growth system can be kept stable for a longer time, so that the n-type silicon carbide crystal with more uniform surface steps can be grown.

Description

Technical Field

[0001] This invention relates to the field of semiconductors, and in particular to an n-type silicon carbide crystal and its liquid-phase growth method. Background Technology

[0002] Silicon carbide, as the most representative third-generation wide-bandgap semiconductor material, possesses advantages such as high thermal conductivity, low density, and a large bandgap, making it an ideal substrate material for fabricating high-frequency, high-voltage, and high-power devices. The liquid-phase method is an important method for growing silicon carbide single crystals. Compared to the physical vapor transport (PVT) method, it has a relatively lower growth temperature and is closer to thermodynamic equilibrium, making it a method with the potential to grow high-quality silicon carbide single crystals. Its basic growth principle utilizes a graphite crucible as both the container for the raw materials and the source of carbon. During crystal growth, carbon dissolves at the wall of the graphite crucible (high-temperature region) and is transported through the solution to the silicon carbide seed crystal (low-temperature region), where it combines with silicon to precipitate and form silicon carbide crystals.

[0003] Since the liquid phase method grows silicon carbide crystals from a solution, the properties of the solution have a significant impact on crystal growth. In the liquid phase flux system, Al doping can reduce the aggregation of crystal surface steps and improve the crystal surface morphology. Cr doping can increase the solubility of carbon in the solution, providing sufficient carbon source for crystal growth. Therefore, the systems currently used for growing large-size silicon carbide crystals using the liquid phase method are almost all Cr-Si-Al systems. This method utilizes Al doping to achieve the growth of p-type silicon carbide crystals.

[0004] However, research progress on liquid-phase growth of n-type silicon carbide crystals has been relatively slow. N-type silicon carbide crystals have wide applications in electronic devices, new energy vehicles, and many other fields. Therefore, further exploration is needed for liquid-phase growth of n-type silicon carbide crystals. First, the selection of the flux system must be considered, focusing on the positive impact of doped elements in the flux on suppressing step coalescence, and the effective role of doped elements in suppressing solution component evaporation and maintaining the stability of the growth system for a longer period. Therefore, this invention proposes a liquid-phase growth method for n-type silicon carbide crystals. Summary of the Invention

[0005] The purpose of this invention is to provide an n-type silicon carbide crystal and its liquid-phase growth method to solve the problems in the background art.

[0006] According to a first aspect of this application, the present invention provides an n-type silicon carbide crystal, wherein the resistivity of the n-type silicon carbide crystal is not higher than 21.8 mΩ·cm, the difference in resistivity between any two points is less than 2 mΩ·cm, and the carrier concentration is not lower than 5.0E+18 / cm. -3 .

[0007] Optionally, the Hall coefficient of the n-type silicon carbide crystal is -0.57 to -1.25 cm⁻¹. -3 / C.

[0008] Optionally, the resistivity of the n-type silicon carbide crystal is 21.8 mΩ·cm, and the carrier concentration is 5.0 E18 / cm. -3 Hall coefficient is -1.25cm -3 / C.

[0009] Optionally, the step height of the n-type silicon carbide crystal is less than 3 μm;

[0010] Preferably, the height difference between adjacent steps of the n-type silicon carbide crystal is no greater than 500 nm.

[0011] Optionally, the n-type silicon carbide crystal is obtained by liquid phase growth method, wherein the molar percentage of Si in the growth raw material is 40-76%, the molar percentage of Cr is 20-60%, and the molar percentage of M is 1-4%, wherein M is one or more of Sc, Ti, V, Mn, Fe, Co, Cu, Zn, Y, Zr, Nb, Mo, Ce, La, Tb, Nd, Ta, and Pr. Preferably, the molar ratio of M to Si in the n-type silicon carbide crystal growth raw material is 1:(30-59).

[0012] Optionally, the diameter of the n-type silicon carbide crystal is not less than 4 inches, and the silicon carbide crystal is not polymorphic.

[0013] Preferably, the growth material for the n-type silicon carbide crystal is Si. 0.6 Cr 0.38 Cu 0.02 Si 0.6 Cr 0.38 Nd 0.02 Si 0.58 Cr 0.38 Zn 0.04 More preferably, the growth raw material for the n-type silicon carbide crystal is Si. 0.6 Cr 0.38 Nd 0.02 or Si 0.58 Cr 0.38 Zn 0.04 .

[0014] According to a second aspect of this application, the present invention provides a liquid-phase growth method for n-type silicon carbide crystals, specifically comprising the following steps:

[0015] Step 1: Mix Si, Cr, and dopant element M to obtain a mixture Si. x Cr y M zThe molar percentage of M is 1-4%. The mixture is placed in a graphite crucible, and then the silicon carbide seed crystal is placed on top of the mixture.

[0016] Step 2: After removing impurities, heat the material to process it, while rotating the silicon carbide seed crystal and the graphite crucible in opposite directions.

[0017] Step 3: After melting, lower the silicon carbide seed crystal below the liquid surface and remelt it. After remelting, pull the silicon carbide seed crystal upward to grow silicon carbide crystals. The growth time is 0.5-100 hours.

[0018] Step four: After growth is complete, remove the grown silicon carbide crystal from the liquid surface, stop rotating, and cool it to room temperature to obtain the final product.

[0019] Preferably, the liquid phase growth method for the n-type silicon carbide crystal specifically includes the following steps:

[0020] Step 1: Clean and dry Si, Cr, and dopant element M, and mix them thoroughly to obtain a mixture of Si. x Cr y M z The molar percentage of M is 1-4%. The mixture is placed at the bottom of the graphite crucible as the growth material. Then, the graphite crucible is wrapped with insulation material and placed in a heater with a furnace cavity. The silicon carbide seed crystal is bonded to the graphite support with an adhesive. The graphite support is connected to the graphite rod and fixed to the lifting rod.

[0021] The lowering lifting rod places the silicon carbide seed crystal above the mixed material. The furnace chamber is connected to the vacuum pump. After the furnace chamber is sealed, the vacuum pump is turned on to purify the atmosphere inside the furnace. When the pressure inside the furnace chamber reaches 0.01pa-10pa, a nitrogen-argon mixed gas is introduced.

[0022] Step 2: After inflation is complete, the graphite crucible is heated by a coil. After heating to the specified temperature, the material is melted at a constant temperature. Before the temperature is constant, the lifting rod is lowered while the lifting rod and the graphite crucible are rotated in opposite directions.

[0023] Step 3: After the constant temperature is completed, lower the silicon carbide seed crystal, and then continue to heat the graphite crucible. At the same time, observe the change of gravity reading in the gravity sensing system connected to the lifting rod. Determine the position of the liquid surface by the gravity reading until the silicon carbide seed crystal is lowered below the liquid surface and melts back at a constant position.

[0024] After the remelting is completed, the graphite crucible is heated again. During heating, the silicon carbide seed crystal is pulled upward. When the temperature is constant and the position of the silicon carbide seed crystal remains unchanged, the growth of silicon carbide crystal begins, and the growth time is 0.5-100h.

[0025] Step four: After growth is complete, control the lifting rod to lift the crystal until it leaves the liquid surface, turn off the rotation system, and cool to room temperature to complete crystal growth.

[0026] Optionally, in step one, Si x Cr y M z In this process, the molar percentage of Si (x) is 40-76%, and the molar percentage of Cr (y) is 20-60%.

[0027] Preferably, the molar ratio of M to Si in the n-type silicon carbide crystal growth raw material is 1:(30-59).

[0028] In the liquid phase growth method of this application, the doped M element can play a positive role in the aggregation of steps, and at the above ratio, it can further suppress the evaporation of solution components, improve the long-term stability of the liquid phase growth system, not only obtain silicon carbide crystals with more uniform surface steps, but also suppress the generation of polytypes and dislocations, reduce the growth stress of silicon carbide crystals, reduce resistivity and improve resistivity distribution uniformity, and improve carrier concentration and carrier distribution uniformity.

[0029] If the ratio is exceeded or the molar percentage of M is more than 5%, the solution components are prone to evaporation, making it difficult to maintain the stability of the growth system. This will increase the resistivity of the silicon carbide crystal, reduce the carrier concentration, and cause uneven distribution of resistivity and carriers in the silicon carbide crystal, thus reducing the stability of the device.

[0030] Optionally, in step one, the doping element M is one or more of Sc, Ti, V, Mn, Fe, Co, Cu, Zn, Y, Zr, Nb, Mo, Ce, La, Tb, Nd, Ta, and Pr.

[0031] Preferably, the doping element M is one or more of Zn, Zr, La, Tb, Nd, Ta, and Pr. When the above elements are selected and the molar percentage of the elements is limited to 1-4%, the generation of polytypes in n-type silicon carbide crystals can be significantly suppressed, and the resistivity and carrier distribution uniformity in n-type silicon carbide substrates can be significantly improved while reducing resistivity and increasing carrier concentration.

[0032] In addition, when the doping element M is Zn, Zr, La, Tb, Nd, Ta, or Pr, it can suppress step aggregation, so that the height difference between adjacent steps of the silicon carbide crystal is no greater than 50 nm.

[0033] Optionally, in step one, the silicon carbide seed crystal is positioned 5-40 mm above the mixture; a nitrogen-argon mixture gas of 0.8-1.3 atm is introduced, wherein the mass percentage of nitrogen in the nitrogen-argon mixture gas is 0.5%-5%.

[0034] Optionally, in step two, the graphite crucible is heated at a heating rate of 5-30℃ / min to 1500-1800℃, and held at that temperature for 20-40 minutes to melt the material. The lifting rod is lowered at a speed of 150-300mm / h until the silicon carbide seed crystal is 5-10mm above the estimated liquid surface. The rotation speed of the lifting rod is 3-35rpm, and the rotation speed of the graphite crucible is 1-10rpm.

[0035] Optionally, in step three, the graphite crucible is heated at a heating rate of 1.5-5℃ / min to 1600-1900℃, and the silicon carbide seed crystal is lowered to 5-20mm below the liquid surface, with a remelting time of 1-90min.

[0036] Optionally, in step three, the graphite crucible is heated at a heating rate of 2.5-20℃ / min to 1650-1900℃, and the silicon carbide seed crystal is pulled upward at a speed of 30-300mm / h to a position 0-1mm above the liquid surface or 0-3mm below the liquid surface.

[0037] Preferably, in step four, the lifting rod is lifted at a speed of 20-300 mm / h and cooled to room temperature at a cooling rate of 0.5-30℃ / min.

[0038] The beneficial effects of this application include, but are not limited to: 1. The present invention provides a liquid phase growth method for n-type silicon carbide crystals, which, by doping other elements on the basis of the Si-Cr system, finds elements that suppress step aggregation and thus replaces Al to improve the crystal surface morphology. At the same time, the effective role of doping elements in suppressing the evaporation of solution components and maintaining the stability of the growth system for a longer time is considered, thereby enabling the growth of n-type silicon carbide crystals with more uniform surface steps.

[0039] 2. The present invention provides a liquid phase growth method for n-type silicon carbide crystals, wherein the molar ratio of M to Si in the growth raw materials is 1:(30-59). This method can further improve the resistivity and carrier distribution uniformity on the basis of reducing the resistivity of silicon carbide crystals and increasing the carrier concentration of silicon carbide crystals, so as to obtain silicon carbide substrates with more uniform quality.

[0040] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0041] Figure 1 This is an image of the crystal obtained in Comparative Example 1 of this invention under an optical microscope;

[0042] Figure 2 This is an image of the crystal obtained in Embodiment 1 of the present invention under an optical microscope. Detailed Implementation

[0043] This invention provides a liquid-phase growth method for n-type silicon carbide crystals, specifically including the following steps:

[0044] Step 1: Clean Si, Cr, and dopant element M separately using an ultrasonic cleaner. After cleaning, dry the water and mix Si, Cr, and dopant element M to obtain a mixture Si. x Cr y M z The mixture is placed at the bottom of a graphite crucible as a growth material. The graphite crucible containing the mixture is wrapped with insulation material and placed in a heater with a furnace cavity. The silicon carbide seed crystal is bonded to the graphite support with an adhesive. The graphite support is connected to a graphite rod and fixed to a lifting rod.

[0045] In the mixture Si of the present invention x Cr y M z In this process, the molar percentage of Si (x) is 40-76%, the molar percentage of Cr (y) is 20-60%, and the molar percentage of M (z) is 1-4%.

[0046] Preferably, the molar percentage of Si (x) is 60%, the molar percentage of Cr (y) is 38%, and the molar percentage of M (z) is 2%.

[0047] Preferably, the molar percentage of Si (x) is 59%, the molar percentage of Cr (y) is 40%, and the molar percentage of M (z) is 1%.

[0048] Preferably, the molar percentage of Si (x) is 58%, the molar percentage of Cr (y) is 38%, and the molar percentage of M (z) is 4%.

[0049] The doping element M is one or more of the following: Sc, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Y, Zr, Nb, Mo, Ce, La, Tb, Nd, Ta, and Pr.

[0050] The lowering lifting rod places the silicon carbide seed crystal 5-40mm above the mixture. The furnace chamber is connected to the vacuum pump. After the furnace chamber is sealed, the vacuum pump is turned on to purify the atmosphere inside the furnace. When the pressure inside the furnace chamber reaches 0.01pa-10pa, a nitrogen-argon mixture of 0.8-1.3atm is introduced.

[0051] In this invention, the mass percentage of nitrogen in the nitrogen-argon mixture is 0.5%-5%.

[0052] Step 2: After the gas filling is completed, heat the graphite crucible with a coil at a heating rate of 5-30℃ / min from room temperature to 1500-1800℃. After reaching the specified temperature, hold the temperature for 20-40 minutes to process the material. Before holding the temperature, slowly lower the silicon carbide seed crystal to a position 5-10mm above the estimated liquid surface at a speed of 150-300mm / h. At the same time, rotate the lifting rod at a speed of 3-35rpm and rotate the graphite crucible at a speed of 1-10rpm. The lifting rod and the graphite crucible rotate in opposite directions.

[0053] Step 3: After the isothermal period ends, start the program to lower the silicon carbide seed crystal. At the same time, control the program to raise the temperature of the graphite crucible to 1600-1900℃ at a heating rate of 1.5-5℃ / min. Observe the change of gravity reading in the gravity sensor system connected to the lifting rod. Determine the position of the liquid surface by the gravity reading. Stop when the silicon carbide seed crystal is lowered to 5-20mm below the liquid surface. Remelt at a constant position for 1-90min.

[0054] After the remelting is completed, the control program raises the temperature of the graphite crucible to 1650-1900℃ at a heating rate of 2.5-20℃ / min. During the heating period, the silicon carbide seed crystal is pulled upward at a speed of 30-300mm / h until the silicon carbide seed crystal reaches 0-1mm above the liquid surface or 0-3mm below the liquid surface and the pulling stops. When the temperature is constant and the position of the silicon carbide seed crystal remains unchanged, crystal growth begins, and the growth time is 0.5-100h.

[0055] Step four: After growth is complete, control the lifting rod to lift at a speed of 20-300 mm / h until the crystal leaves the liquid surface, turn off the rotation system, set the cooling program, and cool down to room temperature at a cooling rate of 0.5-30℃ / min to complete crystal growth.

[0056] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention. Furthermore, it should be understood that after reading the contents of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims and are all within the protection scope of the present invention.

[0057] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0058] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0059] Unless otherwise specified, the reagents, instruments, and equipment used in this invention are all commonly used by those skilled in the art.

[0060] Example 1

[0061] This embodiment provides a liquid-phase growth method for n-type silicon carbide crystals, including the following steps:

[0062] (1) Si, Cr, and Cu were cleaned separately using an ultrasonic cleaner. After cleaning, the moisture was dried, and the Si, Cr, and Cu were mixed to obtain a mixture of Si. 0.6 Cr 0.38 Cu 0.02 The mixture is placed at the bottom of a graphite crucible as a growth material. The graphite crucible containing the mixture is wrapped with insulation material and placed in a heater with a furnace cavity. The silicon carbide seed crystal is bonded to the graphite support with an adhesive. The graphite support is connected to a graphite rod and fixed to a lifting rod.

[0063] (2) Lower the lifting rod to place the silicon carbide seed crystal 20mm above the material. Connect the furnace body to the vacuum pump. After the furnace cavity is sealed, turn on the vacuum pump to purify the atmosphere inside the furnace. When the pressure inside the furnace cavity reaches 1pa, inject 1.1atm of nitrogen-argon mixed gas, in which the proportion of nitrogen is 1%.

[0064] (3) After the gas filling is completed, the graphite crucible is heated by the coil at a heating rate of 20℃ / min from room temperature to 1720℃. After reaching the specified temperature, the temperature is kept constant for 30 minutes for material processing. Before the temperature is kept constant, the silicon carbide seed crystal is slowly lowered to the position 6mm above the estimated liquid surface at a speed of 250mm / h. At the same time, the lifting rod is rotated at a speed of 25rpm, and the graphite crucible is rotated at a speed of 5rpm. The lifting rod and the graphite crucible rotate in opposite directions.

[0065] (4) After the constant temperature is completed, start the program to lower the silicon carbide seed crystal. At the same time, control the program to raise the temperature of the graphite crucible to 1790℃ at a heating rate of 2℃ / min. Observe the change of gravity reading in the gravity sensor system connected to the lifting rod. Determine the position of the liquid surface by the gravity reading. Stop when the silicon carbide seed crystal is lowered to 10mm below the liquid surface. Remelt at a constant position for 25min.

[0066] (5) After the remelting is completed, the control program raises the graphite crucible to 1800℃ at a heating rate of 5℃ / min. During the heating period, the silicon carbide seed crystal is pulled upward at a speed of 200mm / h until the silicon carbide seed crystal reaches 0.5mm below the liquid surface and the pulling stops. When the temperature is constant and the position of the silicon carbide seed crystal remains unchanged, crystal growth begins and the growth time is 3h.

[0067] (6) After growth is complete, control the lifting rod to lift at a speed of 200 mm / h until the crystal leaves the liquid surface, turn off the rotation system, set the cooling program, and cool down to room temperature at a cooling rate of 8℃ / min to complete crystal growth.

[0068] Example 2

[0069] This embodiment provides a liquid-phase growth method for n-type silicon carbide crystals. The only difference from Embodiment 1 is that the growth raw material for the silicon carbide crystals is configured as Si. 0.6 Cr 0.38 Nd 0.02 The rest are the same as in Example 1, and will not be repeated here.

[0070] Example 3

[0071] This embodiment provides a liquid-phase growth method for n-type silicon carbide crystals. The only difference from Embodiment 1 is that the growth raw material for the silicon carbide crystals is configured as Si. 0.58 Cr 0.38 Zn 0.04 The nitrogen content in the background atmosphere nitrogen-argon mixture was 1.5%, and the rest was the same as in Example 1, so it will not be repeated here.

[0072] Example 4

[0073] This embodiment provides a liquid-phase growth method for n-type silicon carbide crystals. The only difference from Embodiment 1 is that the growth raw material for the silicon carbide crystals is configured as Si. 0.59 Cr 0.4 V 0.01 The nitrogen content in the background atmosphere nitrogen-argon mixture is 0.5%, and the rest is the same as in Example 1, so it will not be repeated here.

[0074] Example 5

[0075] This embodiment uses the silicon carbide crystal growth material formulation from Embodiment 1. 0.6 Cr 0.38 Cu 0.02 The difference lies in the reaction conditions for liquid-phase silicon carbide crystal growth. Specifically, it includes the following steps:

[0076] (1) Clean Si, Cr and Cu separately with an ultrasonic cleaner. After cleaning, dry the water. Place the mixture obtained by mixing Si, Cr and Cu as growth material in a graphite crucible. Wrap the graphite crucible containing the growth material with heat insulation material and place it in a heater with a furnace cavity. Adhere the silicon carbide seed crystal to the graphite support with an adhesive. Connect the graphite support to the graphite rod and fix it to the lifting rod.

[0077] (2) Lower the lifting rod to place the silicon carbide seed crystal 5mm above the material. Connect the furnace body to the vacuum pump. After the furnace cavity is sealed, turn on the vacuum pump to purify the atmosphere inside the furnace. When the pressure inside the furnace cavity reaches 0.01pa, inject 0.8atm nitrogen-argon mixture gas, in which the proportion of nitrogen is 0.5%.

[0078] (3) After the gas filling is completed, the graphite crucible is heated by the coil at a heating rate of 5℃ / min from room temperature to 1500℃. After reaching the specified temperature, the temperature is kept constant for 40 minutes for material processing. Before the temperature is kept constant, the silicon carbide seed crystal is slowly lowered to a position 5mm above the estimated liquid surface at a speed of 150mm / h. At the same time, the lifting rod is rotated at a speed of 3rpm, and the graphite crucible is rotated at a speed of 10rpm. The lifting rod and the graphite crucible rotate in opposite directions.

[0079] (4) After the constant temperature is completed, start the program to lower the silicon carbide seed crystal. At the same time, control the program to raise the temperature of the graphite crucible to 1600℃ at a heating rate of 5℃ / min. Observe the change of gravity reading in the gravity sensing system connected to the lifting rod. Determine the position of the liquid surface by the gravity reading. Stop when the silicon carbide seed crystal is lowered to 2mm below the liquid surface. Remelt at a constant position for 90min.

[0080] (5) After the remelting is completed, the control program raises the graphite crucible to 1650℃ at a heating rate of 2.5℃ / min. During the heating period, the silicon carbide seed crystal is pulled upward at a speed of 30mm / h until the silicon carbide seed crystal reaches 1mm above the liquid surface and the pulling stops. When the temperature is constant and the position of the silicon carbide seed crystal remains unchanged, crystal growth begins and the growth time is 0.5h.

[0081] (6) After growth is complete, control the lifting rod to lift at a speed of 20 mm / h until the crystal leaves the liquid surface, turn off the rotation system, set the cooling program, and cool down to room temperature at a cooling rate of 30℃ / min to complete the crystal growth.

[0082] Example 6

[0083] This embodiment uses the silicon carbide crystal growth material formulation from Embodiment 2. 0.6 Cr 0.38 V 0.02 The difference lies in the reaction conditions for liquid-phase silicon carbide crystal growth. Specifically, it includes the following steps:

[0084] (1) Clean Si, Cr and Y separately with an ultrasonic cleaner. After cleaning, dry the water. Place the mixture obtained by mixing Si, Cr and Y as growth material in a graphite crucible. Wrap the graphite crucible containing the mixture with heat insulation material and place it in a heater with a furnace cavity. Adhere the silicon carbide seed crystal to the graphite support with an adhesive. Connect the graphite support to the graphite rod and fix it to the lifting rod.

[0085] (2) Lower the lifting rod to place the silicon carbide seed crystal 40mm above the material. Connect the furnace body to the vacuum pump. After the furnace cavity is sealed, turn on the vacuum pump to purify the atmosphere inside the furnace. When the pressure inside the furnace cavity reaches 10pa, inject 1.3atm of nitrogen-argon mixture, in which the proportion of nitrogen is 5%.

[0086] (3) After the gas filling is completed, the graphite crucible is heated by the coil at a heating rate of 30℃ / min from room temperature to 1800℃. After reaching the specified temperature, the temperature is kept constant for 20 minutes for material processing. Before the temperature is kept constant, the silicon carbide seed crystal is slowly lowered to a position 10mm above the estimated liquid surface at a speed of 300mm / h. At the same time, the lifting rod is rotated at a speed of 35rpm, and the graphite crucible is rotated at a speed of 1rpm. The lifting rod and the graphite crucible rotate in opposite directions.

[0087] (4) After the constant temperature is completed, start the program to lower the silicon carbide seed crystal. At the same time, control the program to raise the temperature of the graphite crucible to 1900℃ at a heating rate of 1.5℃ / min. Observe the change of gravity reading in the gravity sensing system connected to the lifting rod. Determine the position of the liquid surface by the gravity reading. Stop when the silicon carbide seed crystal is lowered to 20mm below the liquid surface. Remelt at a constant position for 1 minute.

[0088] (5) After the remelting is completed, the control program raises the graphite crucible to 1900℃ at a heating rate of 10℃ / min. During the heating period, the silicon carbide seed crystal is pulled upward at a speed of 300mm / h until the silicon carbide seed crystal reaches 3mm below the liquid surface and the pulling stops. When the temperature is constant and the position of the silicon carbide seed crystal remains unchanged, crystal growth begins and the growth time is 100h.

[0089] (6) After growth is complete, control the lifting rod to lift at a speed of 300 mm / h until the crystal leaves the liquid surface, turn off the rotation system, set the cooling program, and cool down to room temperature at a cooling rate of 0.5℃ / min to complete crystal growth.

[0090] Comparative Example 1

[0091] This comparative example provides a liquid-phase growth method for silicon carbide crystals, differing from Example 1 only in that the growth raw material for the silicon carbide crystals is configured as Si. 0.6 Cr 0.4 The rest are the same as in Example 1, and will not be repeated here.

[0092] Comparative Example 2

[0093] This comparative example provides a liquid-phase growth method for silicon carbide crystals, differing from Example 1 only in that the growth raw material for the silicon carbide crystals is configured as Si. 0.57 Cr 0.38 Cu 0.05 The rest are the same as in Example 1, and will not be repeated here.

[0094] After the silicon carbide crystals in Example 1 and Comparative Example 1 were grown, the furnace was opened, the crystals were removed, and the crystal surface was cleaned with hydrochloric acid and hydrofluoric acid. The surface morphology of the crystals was observed using an optical microscope, and the results are as follows: Figure 1 and Figure 2 As shown, it can be seen that the silicon carbide crystals prepared using the growth materials and growth method of this application have more uniform steps and better crystal quality.

[0095] Polymorphism, step, and Hall effect tests were performed on the crystal obtained from the Si-Cr-Cu system in Example 1. The results are shown in Table 1. All the test results were performed at room temperature.

[0096] Table 1

[0097]

[0098]

[0099] The degree of evaporation of solution components was compared by measuring the weight changes of the above embodiments and comparative examples before and after growth using the lifting rod, as shown in Table 2 below.

[0100] Table 2

[0101] Growth raw materials Weight gain of seed crystal rod (g) Example 1 0.8 Example 2 0.5 Example 3 0.7 Example 4 0.5 Example 5 0.9 Example 6 0.6 Comparative Example 1 2.0 Comparative Example 2 1.2

[0102] As can be seen from the data in Table 1, the Hall coefficient of the silicon carbide crystal is negative, which proves that the obtained crystal is an n-type silicon carbide crystal. The resistivity of the obtained crystal is below 21.8 mΩ·cm, which proves that the silicon carbide crystal meets the requirements of electrical performance.

[0103] As can be seen from the data in Table 2, the liquid phase growth method of this application suppresses the evaporation of solution components, which is beneficial to maintaining the stability of the crystal growth system, thereby obtaining silicon carbide crystals with lower resistivity and higher charge carriers, and the uniformity of resistivity and charge carriers in the silicon carbide crystal is also higher.

[0104] Currently, the systems used for growing large-size silicon carbide crystals using the liquid-phase method are almost all Cr-Si-Al systems. For n-type silicon carbide crystals doped with N atoms, Al doping increases the resistivity and decreases the carrier concentration, resulting in higher power losses in the fabricated silicon carbide-based power devices, thus affecting the device's efficiency and stability. Figures 1-2 As can be seen from the data in Tables 1 and 2, in the comparative example of this invention, removing Al and using the Si-Cr system resulted in larger crystal surface steps and greater evaporation of solution components, which is not conducive to the growth of n-type silicon carbide crystals. The embodiments of this invention, by doping other elements on the Si-Cr system, identified elements related to inhibiting step aggregation and thus replacing Al to improve the crystal surface morphology. At the same time, the effective role of doping elements in inhibiting solution component evaporation and maintaining the stability of the growth system for a longer period of time was considered, thereby enabling the growth of n-type silicon carbide crystals with more uniform surface steps. Example 1, using the Si-Cr-Cu system, reduced step aggregation, which is beneficial to improving the surface morphology of the crystal.

[0105] Therefore, the present invention provides a liquid phase growth method for n-type silicon carbide crystals. By changing the doping elements in the Si-Cr system and combining it with the method described in this invention, the step aggregation on the crystal surface is suppressed, resulting in the growth of crystals with better surface morphology. At the same time, it reduces the evaporation of solution components and improves the long-term stability of the crystal growth system.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. An n-type silicon carbide crystal, characterized in that, The resistivity of the n-type silicon carbide crystal is not higher than 21.8 mΩ·cm, the difference in resistivity between any two points is less than 2 mΩ·cm, and the carrier concentration is not lower than 5.0 E18 / cm. -3 .

2. The n-type silicon carbide crystal according to claim 1, characterized in that, The Hall coefficient of the n-type silicon carbide crystal is -0.57 to -1.25 cm⁻¹. -3 / C.

3. The n-type silicon carbide crystal according to claim 1, characterized in that, The step height of the n-type silicon carbide crystal is less than 3 μm; Preferably, the height difference between adjacent steps of the n-type silicon carbide crystal is no greater than 500 nm.

4. The n-type silicon carbide crystal according to claim 1, characterized in that, The n-type silicon carbide crystal is obtained by liquid phase growth. In the growth raw material, the molar percentage of Si (x) is 40-76%, the molar percentage of Cr (y) is 20-60%, and the molar percentage of M (z) is 1-4%. M is one or more of Sc, Ti, V, Mn, Fe, Co, Cu, Zn, Y, Zr, Nb, Mo, Ce, La, Tb, Nd, Ta, and Pr. Preferably, the molar ratio of M to Si in the n-type silicon carbide crystal growth raw material is 1:(30-59); and / or The diameter of the n-type silicon carbide crystal is not less than 4 inches, and the silicon carbide crystal has no polytype.

5. A liquid-phase growth method for n-type silicon carbide crystals, characterized in that, Specifically, the following steps are included: Step 1: Mix Si, Cr, and dopant element M to obtain a mixture Si. x Cr y M z The molar percentage of M is 1-4%. The mixture is placed in a graphite crucible, and then the silicon carbide seed crystal is placed on top of the mixture. Step 2: After removing impurities, heat the material to process it, while rotating the silicon carbide seed crystal and the graphite crucible in opposite directions. Step 3: After melting, lower the silicon carbide seed crystal below the liquid surface and remelt it. After remelting, pull the silicon carbide seed crystal upward to grow silicon carbide crystals. The growth time is 0.5-100 hours. Step four: After growth is complete, remove the grown silicon carbide crystal from the liquid surface, stop rotating, and cool it to room temperature to obtain the final product.

6. The liquid-phase growth method for n-type silicon carbide crystals according to claim 5, characterized in that: In step one, Si x Cr y M z In the n-type silicon carbide crystal growth raw material, the molar percentage of Si (x) is 40-76%, and the molar percentage of Cr (y) is 20-60%. Preferably, the molar ratio of M to Si in the raw material is 1:(30-59); and / or In step one, the dopant element M is one or more of the following: Sc, Ti, V, Mn, Fe, Co, Cu, Zn, Y, Zr, Nb, Mo, Ce, La, Tb, Nd, Ta, and Pr.

7. The liquid-phase growth method for n-type silicon carbide crystals according to claim 5, characterized in that: In step one, the silicon carbide seed crystal is placed 5-40 mm above the mixture; and / or In step two, during the impurity removal process, a vacuum is first drawn to 0.01 Pa - 10 Pa, and then a nitrogen-argon mixed gas of 0.8 - 1.3 atm is introduced, wherein the mass percentage of nitrogen in the nitrogen-argon mixed gas is 0.5% - 5%.

8. The liquid-phase growth method for n-type silicon carbide crystals according to claim 5, characterized in that: In step two, the graphite crucible is heated at a heating rate of 5-30℃ / min to 1500-1800℃ and held at that temperature for 20-40 minutes to prepare the silicon carbide seed crystal. At this time, the silicon carbide seed crystal is 5-10mm above the estimated liquid surface. The rotation speed of the silicon carbide seed crystal is 3-35rpm, and the rotation speed of the graphite crucible is 1-10rpm.

9. The liquid-phase growth method for n-type silicon carbide crystals according to claim 5, characterized in that: In step three, the graphite crucible is heated at a heating rate of 1.5-5℃ / min to 1600-1900℃, and the silicon carbide seed crystal is lowered to 5-20mm below the liquid surface. The remelting time is 1-90min.

10. The liquid-phase growth method for n-type silicon carbide crystals according to claim 5, characterized in that: In step three, the graphite crucible is heated at a heating rate of 2.5-20℃ / min to 1650-1900℃. The silicon carbide seed crystal is then pulled upwards at a speed of 30-300mm / h, to a position 0-1mm above the liquid surface or 0-3mm below the liquid surface; and / or In step four, the lifting rod is lifted at a speed of 20-300 mm / h and cooled to room temperature at a cooling rate of 0.5-30℃ / min.

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