Method and system for growing low-resistivity silicon carbide single crystal and single crystal

Abstract

The invention belongs to the technical field of crystal growth, and provides a low-resistivity silicon carbide single crystal growth method and system and a single crystal, silicon carbide powder is uniformly paved at the bottom of a graphite crucible, metal carbide material particles are uniformly paved on the surface of the silicon carbide powder, and silicon carbide seed crystals are adhered to the top of the graphite crucible; the graphite crucible is sealed, and the interior of the graphite crucible is vacuumized; heating the graphite crucible subjected to vacuumizing treatment, filling carrier gas into the graphite crucible, then slowly replacing the carrier gas with doped source gas, slowly increasing the growth pressure to a set pressure, and growing a buffer layer; after the growth of the buffer layer is completed, changing the growth condition to grow the heavily doped silicon carbide single crystal; and after the growth of the crystal is completed, cooling the graphite crucible subjected to vacuumizing treatment, so that the crystal is naturally cooled, and the low-resistivity silicon carbide single crystal is obtained. The doping concentration of the silicon carbide single crystal can be improved, and the resistivity of the silicon carbide material can be reduced.

Description

Technical Field

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

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] As a third-generation semiconductor material, silicon carbide (SiC) has been widely used in recent years as the development of 5G, new energy and other industries has led to a rapid growth in demand for high-frequency, high-power RF and power electronic devices. It has become an important semiconductor material due to its advantages such as high temperature resistance, radiation resistance, high thermal conductivity, large bandgap, high electron saturation drift rate and high breakdown voltage.

[0004] At present, the mainstream conductive single-crystal silicon carbide substrate is N-type silicon carbide substrate. The doping concentration of commercial N-type single-crystal silicon carbide substrate is 5×10 18 cm -3 The resistivity is about 17-25 mΩ·cm. High-power electronic devices require N-type silicon carbide substrates to have lower resistivity. Low resistivity means less conduction loss of electronic devices, which means that N-type silicon carbide single crystals are required to have higher nitrogen doping concentrations. Theoretically, the theoretical maximum solubility of N atoms in SiC crystals can reach 5×10 20 cm -3 However, in the actual growth process, the N doping concentration in SiC crystals is difficult to reach 1×10 20 cm -3 Because N atoms replace C atoms in SiC single crystals, the entry of N atoms into the SiC single crystal lattice will cause lattice distortion, thereby limiting the solubility of N atoms in SiC crystals. At the same time, during the growth of single crystals, heavy doping will lead to changes in the C / Si ratio at the growth interface in the early stage of growth and unstable component partial pressure at the growth front, which will make it difficult to stably control the crystal form. At the same time, when the doping concentration is higher than 5×10 18 cm -3 Under such circumstances, stacking faults in SiC single crystals proliferate severely, seriously affecting the quality of the epitaxial layer and device performance. Therefore, driven by the demand for electronic power devices with low conduction losses, N-type SiC single crystal substrates must have lower resistivity and higher crystal quality.

[0005] Smart Cut technology can provide effective technical support for cost reduction and efficiency improvement of electronic power devices with low on-resistance. This technology can obtain high-quality low-resistivity silicon carbide single crystal layers, and greatly improve the utilization rate of silicon carbide single crystal substrates, effectively reducing costs. This technology requires the use of low-resistivity N-type SiC substrates. Currently, due to the limitations of low-resistivity N-type Si C substrate technology, low-resistivity silicon single crystal substrates and polycrystalline silicon carbide substrates are generally used as two mainstream donors. However, the lattice matching between silicon single crystals and silicon carbide single crystals is low, and the temperature in the post-processing stage is higher than the melting point of silicon crystals, which cannot meet the preparation requirements of composite SiC material substrates; although the polycrystalline silicon carbide substrate has a low resistivity, the lattice matching is still low, which affects the performance of composite SiC materials to a certain extent. Heavily doped N-type silicon carbide single crystal substrates are urgently needed materials in Smart Cut technology due to their low resistivity and high lattice matching.

[0006] Prior art CN 101724906 A controls the temperature of the raw materials and the temperature of the growth interface, and controls the nitrogen pressure of the growth system to rapidly grow high-quality, low-resistivity silicon carbide crystals under the condition of 0.01 to 200 Pa. Although the prior art discloses fast, high-quality, low-resistivity silicon carbide crystals, it is unable to achieve a single stable crystal form of single crystal growth, and is unable to solve the problem of serious stacking fault proliferation in low-resistivity crystals due to a faster growth rate, and the practical application field is relatively small.

[0007] Although the prior art CN 118727155 A discloses a low-resistivity substrate or wafer for multi-crystalline wafers, a low-resistivity single-crystalline silicon carbide layer is obtained by coupling a low-resistivity, low-warpage silicon carbide polycrystalline substrate with a silicon carbide single crystal substrate. However, the lattice matching degree between polycrystalline silicon carbide and single-crystalline silicon carbide is low, and high-quality, low-resistivity silicon carbide single crystal growth cannot be achieved, and the problems of excessive stress and severe dislocation proliferation caused by lattice distortion cannot be solved.

[0008] Prior art CN 110857476 B discloses a method for growing low resistivity, low dislocation density, and high crystal quality N-type SiC single crystals using co-doping technology. In the invention, auxiliary dopants are added during the growth of SiC single crystals, and the doping characteristics of different elements are utilized to increase the doping concentration of N atoms in SiC single crystals, so that N-type SiC single crystals with low resistivity below 10mΩ·cm can be prepared. However, the method in the invention introduces auxiliary dopants such as Al2O3, Al4C3, Ge, TiO2, etc. These doping atoms will enter the single crystal, seriously affecting the purity of the single crystal, and the invention cannot solve the serious problem of stacking fault proliferation caused by high doping concentration. Therefore, the low resistivity SiC single crystal material in the invention cannot be used in power electronic devices and other fields. Summary of the invention

[0009] In order to solve the above problems, the present invention proposes a growth method, system and single crystal of low-resistivity silicon carbide single crystal. The present invention realizes the stability of the crystal form in the initial nucleation stage of the crystal under a heavily doped environment by setting a buffer layer with special growth conditions; by regulating the N partial pressure in the internal environment of crystal growth, the C / Si at the crystal growth front, and using a low-temperature large axis ladder to achieve heavy doping, the doping concentration of the silicon carbide single crystal is increased and the resistivity of the silicon carbide material is reduced.

[0010] According to some embodiments, the present invention adopts the following technical solutions:

[0011] In a first aspect, a method for growing a low-resistivity silicon carbide single crystal is provided, comprising the following steps:

[0012] Evenly spread silicon carbide powder on the bottom of the graphite crucible, evenly spread metal carbide particles on the surface of the silicon carbide powder, and bond silicon carbide seed crystals to the top of the graphite crucible;

[0013] The graphite crucible is sealed and the interior thereof is evacuated;

[0014] The vacuum-treated graphite crucible is heated and filled with a carrier gas, and then the carrier gas is slowly replaced with a doping source gas, and the growth pressure is slowly increased to a set pressure to grow a buffer layer;

[0015] After the growth of the buffer layer is completed, the growth conditions are changed to grow a heavily doped silicon carbide single crystal;

[0016] After the crystal growth is completed, the temperature of the vacuum-treated graphite crucible is lowered to allow the crystal to cool naturally, thereby obtaining a low-resistivity silicon carbide single crystal.

[0017] As an optional implementation, the following steps are also included:

[0018] The processing steps of cutting, grinding and polishing the silicon carbide crystal to process the crystal into a silicon carbide single crystal substrate, and then testing and characterizing the substrate:

[0019] Observe the color of the crystal and perform Raman spectroscopy tests on substrate areas with different colors to evaluate the effect of the buffer layer on the crystal stability of the silicon carbide single crystal growth;

[0020] Measure the nitrogen doping content in the crystal and determine the doping concentration in the crystal to evaluate the effects of regulating N partial pressure, gas flow, metal carbides and low-temperature large axis ladder on the crystal doping concentration;

[0021] Perform a resistivity test on the crystal to evaluate the magnitude of the crystal's resistivity.

[0022] As an optional implementation, the thickness of the buffer layer is 5% to 10% of the total thickness of the crystal, and the buffer layer is a silicon carbide single crystal growth layer with slowly changing pressure and gas flow established at the initial stage of crystal growth.

[0023] As an optional implementation manner, the growth pressure change rate of the buffer layer is 30-200 Pa / h.

[0024] As an optional implementation, the gas flow rate change rate in the growth atmosphere of the buffer layer is 3 to 10 sccm / h.

[0025] As an optional embodiment, the metal carbide material includes at least one of tantalum carbide and niobium carbide. The metal carbide material particles have the effect of changing the C / Si at the front of the crystal growth interface, and the metal elements in metal carbides such as tantalum carbide and niobium carbide will not be incorporated into the crystal, which can ensure that the purity of the crystal is not affected.

[0026] As an optional embodiment, the particle size of the silicon carbide powder does not exceed 1 mm, and the nitrogen content in the powder is not less than 100 PPM;

[0027] As an optional embodiment, the carrier gas is one or more of argon and helium, and the doping source gas is one or more of nitrogen and ammonia;

[0028] When growing the buffer layer, the carrier gas is filled to a growth pressure of 100 Pa to 3000 Pa, and the measuring temperature of the upper cover of the graphite crucible is controlled to be 2100 to 2500°C.

[0029] As an optional implementation, during the growth of heavily doped silicon carbide single crystal by regulating the N partial pressure at the growth front by changing the growth pressure, the nitrogen doping content in the crystal is regulated, and the growth pressure is 3000Pa to 20000Pa.

[0030] As an optional implementation, in the process of changing the growth conditions to grow heavily doped silicon carbide single crystals, the doping efficiency of the crystal is improved by changing the growth temperature in the growth chamber, the measuring temperature of the upper cover of the graphite crucible is controlled to be 1900-2100°C, and the stable growth time is 100-150h.

[0031] As an optional implementation, in the process of growing a heavily doped silicon carbide single crystal by changing the growth conditions, the nitrogen component inside the growth system is regulated by changing the flow rates of the doping source gas and the carrier gas in the growth atmosphere, thereby regulating the nitrogen doping content in the crystal, and the flow rates of the two gases are both within a range of 0 to 100 sccm;

[0032] As an optional implementation, in the process of changing the growth conditions to grow the heavily doped silicon carbide single crystal, the gas flow ratio of the doping gas to the carrier gas is 50% to 100%;

[0033] As an optional implementation, in the process of changing the growth conditions to grow heavily doped silicon carbide single crystals, the doping efficiency of the silicon carbide single crystal is increased by setting an axis ladder, and the axis ladder is set at 50-150°C / cm. If the axis ladder is too small, the growth rate of the single crystal will be too low and the crystal growth efficiency will be low; if the axis ladder is too large, the crystal will deviate from the growth equilibrium state to a greater extent, and the quality of the single crystal will deteriorate.

[0034] In a second aspect, a low-resistivity silicon carbide single crystal is provided, which is grown using the above method.

[0035] In a third aspect, a growth system of a low-resistivity silicon carbide single crystal is provided, which is applied to the above-mentioned generation method, and includes a graphite crucible, wherein the graphite crucible includes a matching crucible body and a crucible cover, wherein silicon carbide powder is arranged in the crucible body, metal carbide particles are spread on the silicon carbide powder, and silicon carbide seed crystals are arranged on the crucible cover;

[0036] A heating system is arranged on the periphery of the graphite crucible;

[0037] The graphite crucible is arranged in a closed system.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. The method of the present invention, by setting a buffer layer with special growth conditions at the initial stage of crystal growth to grow a low-resistivity silicon carbide single crystal, slows down the growth pressure and gas flow rate change rate at the initial stage of growth, ingeniously reduces the lattice distortion of the silicon carbide single crystal caused by the incorporation of nitrogen atoms during the growth process, and solves the problem of polymorphic inclusions caused by the drastic changes in pressure and gas flow at the initial stage of growth;

[0040] 2. The present invention adjusts the nitrogen partial pressure at the front of the silicon carbide single crystal growth interface by setting different internal pressures of the growth system and the ratio of the doping source gas; ingeniously realizes the increase of nitrogen adsorbed atoms at the front of the growth interface, and effectively increases the nitrogen doping concentration in the crystal;

[0041] 3. The present invention makes full use of the characteristic that low temperature is conducive to N doping during the growth of SiC single crystals by using a large temperature axis gradient in the growth chamber, reduces the temperature of the growth front under the premise of a suitable growth rate, further improves the adsorption capacity of nitrogen atoms at the growth front, and effectively improves the nitrogen doping efficiency of the crystal;

[0042] 4. The present invention reduces the consumption of silicon components in the growth chamber by evenly spreading metal carbide particles on the surface of silicon carbide powder, effectively reduces the C / Si at the front of the growth interface, improves the nitrogen atom doping efficiency, and effectively reduces the crystal resistivity.

[0043] 5. The method of the present invention will not introduce metal impurities into the SiC single crystal, is compatible with the current growth process of silicon carbide single crystals, and can be adjusted and adapted accordingly based on existing silicon carbide growth equipment, making it easy to promote and use.

[0044] 6. The silicon carbide single crystal substrate grown and prepared by the present invention has a single crystal form, a resistivity below 5 mΩ·cm, and a doping concentration higher than 5×10 19 cm -3 , low dislocation density, and the proportion of stacking faults is less than 0.2%. It can be used in power electronic devices to reduce the conduction loss of the devices; it can also be used in the SiC Smartcut field to provide low resistivity material support for this field.

[0045] 7. The present invention is applicable to the growth of low resistivity SiC single crystals by physical vapor transport, liquid phase and high temperature chemical vapor deposition. 4H-SiC, 6H-SiC and the like can be prepared by changing the growth surface of the seed crystal and fine-tuning the single crystal growth process.

[0046] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0048] Figure 1 A schematic diagram of a growth system for growing a low-resistivity silicon carbide single crystal according to an embodiment;

[0049] Figure 2 A resistivity distribution diagram of a silicon carbide single crystal slice grown in an embodiment obtained after resistivity testing;

[0050] Figure 3 A nitrogen doping concentration diagram obtained by testing secondary ion mass spectrometry of a silicon carbide single crystal slice grown in one embodiment;

[0051] Figure 4 This is a scanning image of a wafer after slicing of a silicon carbide single crystal grown in an embodiment. Due to the high nitrogen doping concentration, the color of the wafer is darker;

[0052] Figure 5This is a wafer scan of the silicon carbide single crystal grown in Comparative Example 5 after slicing. Due to the low nitrogen doping concentration, the color of the wafer is lighter;

[0053] Figure 6 This is a stacking fault detection diagram of a wafer after slicing of a silicon carbide single crystal grown in an embodiment. In this embodiment, the stacking fault ratio of the wafer is less than 0.2%;

[0054] Among them, 1 is a silicon carbide seed crystal, 2 is a buffer layer, 3 is a grown silicon carbide single crystal, 4 is a graphite crucible, 5 is a metal carbide particle, 6 is a silicon carbide powder, and 7 is a heating system. DETAILED DESCRIPTION

[0055] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0056] It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0057] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0058] In the absence of conflict, the embodiments in this application and the features in the embodiments may be combined with each other.

[0059] First, some necessary explanations of terms:

[0060] Terminology explanation:

[0061] Low resistivity: in the present invention, it refers to the situation where the maximum resistivity of the silicon carbide single crystal does not exceed 5 mΩ·cm.

[0062] Heavily doped: In the present invention, it refers to the nitrogen doping concentration in the silicon carbide crystal not less than 5×10 19 cm -3 situation.

[0063] The initial nucleation stage of crystal: in the present invention, it refers to the initial nucleation of silicon carbide crystal growth. The conditions at the front of the growth interface are in an unstable fluctuation stage. In this stage, the lattice at the front of the growth interface is easily affected by fluctuations in external conditions and easily induces polymorphism. Therefore, from the perspective of growing crystals, the more stable the conditions in the initial nucleation stage of the crystal, the better.

[0064] C / Si: in the present invention, it refers to the molar ratio of carbon component to silicon component at the front edge of the crystal growth interface. The larger the C / Si, the more favorable the crystal is for forming 4H-Si C, and the lower the nitrogen doping concentration in the crystal.

[0065] Large axial gradient: In the present invention, it refers to the large axial temperature gradient in the growth chamber constructed from the seed crystal to the powder surface. Generally, a large axial gradient can be achieved by increasing the upper insulation temperature measurement hole and thinning the upper insulation. The larger the axial gradient, the greater the growth driving force and the faster the component transmission speed.

[0066] Small axial gradient: In the present invention, it refers to a small axial temperature gradient in the growth chamber constructed from the seed crystal to the powder surface. Generally, a small axial gradient can be achieved by reducing the upper insulation temperature measurement hole and increasing the total thickness of the upper insulation. The smaller the axial gradient, the smaller the growth driving force and the slower the component transmission speed.

[0067] Net adsorbed atoms: in the present invention, it refers to the difference between nitrogen adsorbed atoms and desorbed atoms at the front edge of the crystal growth interface. The more net adsorbed atoms there are, the more nitrogen atoms enter the silicon carbide single crystal, and the higher the doping concentration in the crystal.

[0068] In order to meet the demand for low conduction loss of high-quality silicon carbide single crystal substrates required by electronic power devices and to provide a donor with better lattice matching for Smart Cut technology, the present invention stabilizes the initial crystal form of heavily doped silicon carbide single crystals by setting a buffer layer with special growth conditions, and increases the nitrogen doping concentration in the silicon carbide single crystal and reduces the resistivity of the silicon carbide single crystal by regulating the N partial pressure at the front of the growth interface, changing the C / Si at the front of the growth interface, and adopting a low-temperature large-axis ladder method.

[0069] The present invention provides a method for growing a low-resistivity silicon carbide single crystal, comprising the following steps:

[0070] S1. Evenly spread silicon carbide powder on the bottom of a graphite crucible, evenly spread metal carbide particles on the surface of the silicon carbide powder, and bond silicon carbide seed crystals to the top of the graphite crucible;

[0071] S2, placing the graphite crucible into a closed system, sealing it, and evacuating the interior thereof;

[0072] S3, heating the growth environment and filling it with carrier gas, then slowly replacing the carrier gas with a doping source gas, slowly increasing the growth pressure to a set pressure, and growing a buffer layer;

[0073] S4. After the growth of the buffer layer is completed, the growth conditions are changed to grow a heavily doped silicon carbide single crystal;

[0074] S5. After the crystal growth is completed, the temperature is lowered to allow the crystal to cool naturally to obtain a low resistivity silicon carbide single crystal.

[0075] S6. Cut, grind, and polish the silicon carbide crystal to process it into a silicon carbide single crystal substrate, and then test and characterize the substrate: observe the color of the crystal through a white light lamp, and perform Raman spectroscopy tests on substrate areas with different colors to evaluate the effect of the buffer layer on the crystalline stability of silicon carbide single crystal growth. Use a secondary ion mass spectrometer to measure the nitrogen doping content in the crystal and determine the size of the doping concentration in the crystal to evaluate the effect of regulating the N partial pressure, gas flow, metal carbide, and low-temperature large axis ladder on the crystal doping concentration. Use a resistivity tester to test the resistivity of the wafer to evaluate the size of the crystal resistivity.

[0076] In the present invention, in step S1, the metal carbide material spread on the surface of the silicon carbide powder includes at least one of tantalum carbide and niobium carbide. The metal carbide has the function of changing the C / Si at the front of the crystal growth interface. At the same time, the metal elements in the metal carbide will not be incorporated into the crystal, which can ensure that the purity of the crystal is not affected.

[0077] In the present invention, in step S3, the carrier gas is one or more of argon and helium, and the doping source gas is one or more of nitrogen and ammonia. The carrier gas is filled to a growth pressure of 100 Pa to 3000 Pa, and the measurement temperature of the graphite crucible cover is controlled to be 2100 to 2500°C.

[0078] In the present invention, the buffer layer is suitable for a graphite crucible with a silicon carbide seed crystal on the top and containing silicon carbide powder inside. The thickness of the buffer layer is 5% to 10% of the total thickness of the crystal. The buffer layer is a silicon carbide single crystal growth layer with slowly changing pressure and gas flow established at the initial stage of crystal growth.

[0079] In the present invention, the growth pressure change rate of the buffer layer is 30-200 Pa / h.

[0080] In the present invention, the gas flow rate change rate in the growth atmosphere of the buffer layer is 3 to 10 sccm / h.

[0081] In the present invention, during the growth of the buffer layer, the temperature measured on the upper cover of the graphite crucible is 2100-2500°C.

[0082] The buffer layer of the present invention uses a special growth pressure change rate. If the buffer layer growth pressure change rate is too fast, it will cause the growth gas phase component transmission change rate to be too fast, so that the native step width of the growth surface is increased, resulting in the growth step being easy to spontaneously nucleate and induce polymorphic inclusions, affecting the polymorphic stability; if the buffer layer growth pressure change rate is too slow, although it effectively increases the stability of the crystal form, due to its too slow pressure change rate, the crystal growth rate decreases, the buffer layer accounts for a large part of the total crystal thickness, and reduces the utilization rate of the silicon carbide single crystal. In addition, the buffer layer used in the present invention uses a special gas flow rate change rate, that is, the rate of transition from the initial carrier gas input state to the doping source gas input state required for growing low-resistivity silicon carbide single crystals. If the gas flow rate change rate is too fast, it will cause the C / Si at the growth interface front in the early stage of growth to be unstable, affecting the supersaturation and saturated vapor pressure of the growth interface front component, causing polymorphic inclusions, and leading to instability of the crystal form; if the gas flow rate change rate is too slow, although it effectively improves the stability of the crystal form, the too slow change rate will cause the long interface front to be in a non-equilibrium state for a long time, thereby affecting the dislocation distribution in the growing crystal. By setting a reasonable growth pressure change rate to predict the gas flow rate change rate of the buffer layer, the crystal form is stabilized. At the same time, the thickness of the buffer layer only accounts for 5% to 10% of the total thickness of the crystal, so the utilization rate of the crystal is high.

[0083] In the present invention, in step S4, the nitrogen doping content in the crystal is regulated by adjusting the N partial pressure at the growth front by changing the growth pressure, and the growth pressure is 3000Pa to 20000Pa; the increase of the growth pressure is conducive to increasing the N doping concentration in the single crystal;

[0084] In the present invention, in step S4, the doping efficiency of the crystal is improved by changing the growth temperature in the growth chamber, the measurement temperature of the graphite crucible cover is controlled to be 1900-2100° C., and the stable growth time is 100-150 hours.

[0085] In the present invention, in step S4, the nitrogen component inside the growth system is regulated by changing the flow rates of the doping source gas and the carrier gas in the growth atmosphere, thereby regulating the nitrogen doping content in the crystal, and the flow rates of the two gases are both within a range of 0 to 100 sccm;

[0086] In the present invention, in S4, the gas flow ratio of the doping gas to the carrier gas is 50% to 100%;

[0087] In the present invention, in step S4, the doping efficiency of the silicon carbide single crystal is increased by setting a large axis ladder, and the axis ladder is set at 50-150°C / cm. If the axis ladder is too small, the growth rate of the single crystal will be too low, and the crystal growth efficiency will be low; if the axis ladder is too large, the crystal will deviate from the growth equilibrium state to a greater extent, and the quality of the single crystal will deteriorate.

[0088] like Figure 2-4 and Figure 6 As shown, the silicon carbide single crystal substrate grown and prepared by the present invention has a single crystal form, a resistivity below 5 mΩ·cm, and a doping concentration higher than 5×10 19 cm -3 , low dislocation density, and the proportion of stacking faults is less than 0.2%. It can be used in power electronic devices to reduce the conduction loss of the devices; it can also be used in the SiC Smartcut field to provide low resistivity material support for this field.

[0089] The present invention also provides a low-resistivity silicon carbide single crystal, which is grown using the above method.

[0090] The present invention also provides a low-resistivity silicon carbide single crystal growth system, which is applied to the above-mentioned generation method, comprising a graphite crucible, wherein the graphite crucible comprises a matching crucible body and a crucible upper cover, wherein silicon carbide powder is arranged in the crucible body, metal carbide particles are spread on the silicon carbide powder, and silicon carbide seed crystals are arranged on the crucible upper cover;

[0091] A heating system is arranged on the periphery of the graphite crucible;

[0092] The graphite crucible is arranged in a closed system.

[0093] The technical solutions and effects of the present invention are described below in conjunction with a number of specific embodiments and comparative examples.

[0094] Example 1

[0095] Growth system for growing low resistivity silicon carbide single crystals, such as Figure 1 As shown, it includes a graphite crucible 4, a heating system 7 outside the graphite crucible, and a closed system for constructing a growth environment. A gas valve and a gas flowmeter for controlling the internal pressure are arranged inside the closed system. A silicon carbide seed crystal 1 is bonded to the top of the graphite crucible 4, and a silicon carbide powder 6 is spread on the bottom. A layer of metal carbide particles 5 is spread on the surface of the silicon carbide powder 6. Nitrogen is introduced through the gas flowmeter to grow a low-resistivity silicon carbide single crystal 3. The buffer layer 2 is a transition layer used to stabilize the crystal form in the early stage of crystal growth, and its thickness accounts for 5% to 10% of the total thickness of the crystal.

[0096] The growth system is used to grow a low resistivity silicon carbide single crystal, and the steps are as follows:

[0097] (1) Bonding a silicon carbide seed crystal to the top of a graphite crucible for crystal growth.

[0098] (2) Spread the silicon carbide powder evenly on the bottom of the graphite crucible, and then spread the metal carbide particles on the surface of the powder.

[0099] (3) Place the graphite crucible in a closed system, construct an axial ladder of 50°C / cm in the growth chamber, open the gas valve to make the internal pressure of the system reach a near-vacuum state, heat the graphite crucible to a temperature of 2200°C on the upper cover to grow a silicon carbide single crystal, and at the same time slowly increase the internal environmental pressure of the closed system, turn on the gas flowmeter, slowly increase the gas flow, and introduce carrier gas and nitrogen into the system, wherein the pressure increase rate is 100 Pa / h, the flow rate change rate is 5 sccm / h, and the duration is 20 hours to grow a crystal buffer layer.

[0100] (4) After the growth of the crystal buffer layer is completed, the pressure and gas flow rate inside the system have stabilized. The internal growth pressure is maintained at 3000Pa, the upper cover temperature is controlled to be 2100℃, and the nitrogen and carrier gas flows are both stabilized at 100sccm. At this time, the silicon carbide single crystal is grown stably and maintained for 150h. After the growth is completed, the growth system is cooled to cool the crystal and the silicon carbide single crystal is taken out from the graphite crucible.

[0101] The minimum thickness of silicon carbide single crystal tested with a vernier caliper is 20 mm. The surface morphology of silicon carbide crystal is observed. The surface of the crystal is bright and smooth, and no polymorphic stripes and clustered microtubules are found. After the crystal is processed into a wafer, the wafer is observed through a white light lamp. The wafer is a single color dark yellow-brown, almost opaque. Raman test shows that the crystal has a single crystal form. This shows that this embodiment can effectively stabilize the crystal form of silicon carbide single crystal. The nitrogen content in the crystal characterized by secondary ion mass spectrometry is 5×10 19 cm -3 The maximum resistivity of the wafer was 4.8 mΩ·cm using a resistivity tester.

[0102] Example 2

[0103] Different from Example 1, the axial ladder constructed in the growth chamber is 100°C / cm. After the growth of the crystal buffer layer is completed, the pressure inside the system is controlled at 10000Pa, and the temperature of the upper cover is controlled at 2000°C.

[0104] After the growth was completed, the minimum thickness of the silicon carbide single crystal was tested with a vernier caliper and was 23 mm. The surface morphology of the silicon carbide crystal was observed to be bright and smooth, with no polymorphic stripes or clustered microtubule proliferation. After the crystal was processed into a wafer, the wafer was observed through a white light lamp and was opaque. Raman testing showed that the crystal had a single crystal form. Secondary ion mass spectrometry was used to characterize the nitrogen content in the crystal to be 7×10 19 cm -3 The highest resistivity of the wafer characterized by a resistivity tester was 3.6 mΩ·cm.

[0105] Example 3

[0106] Different from Example 1, the axial ladder constructed in the growth chamber is 150℃ / cm. After the growth of the crystal buffer layer is completed, the internal pressure of the system is controlled at 20000Pa, the upper cover temperature is controlled at 1900℃, and only ammonia is introduced into the growth system, and the ammonia flow rate is controlled to be 100sccm.

[0107] After the growth was completed, the minimum thickness of the silicon carbide single crystal was tested with a vernier caliper and was found to be 25 mm. The surface morphology of the silicon carbide crystal was observed to be bright and smooth, with no polymorphic stripes or clustered microtubule proliferation. After the crystal was processed into a wafer, the wafer was observed through a white light lamp and was opaque. Raman testing showed that the crystal had a single crystal form. Secondary ion mass spectrometry was used to characterize the nitrogen content in the crystal to be 1×10 20 cm -3 The highest resistivity of the wafer characterized by a resistivity tester was 2 mΩ·cm.

[0108] Comparative Example 1

[0109] In this embodiment, there is no buffer layer preparation process, and the existing process is used to achieve the growth of low resistivity silicon carbide single crystals. The other growth conditions are exactly the same as in Example 1. After the growth is completed, the graphite crucible in the growth system is taken out to obtain a silicon carbide single crystal. The native surface of the crystal is observed, and it is found that the surface has polymorphic stripes, and there are outcropping points of clustered microtubes caused by polymorphic inclusions on the crystal surface, which indicates that polymorphic inclusions appear during the crystal growth process. After the crystal is processed into wafers, all the wafers are observed through white light, and it is found that starting from the third wafer, there are three different color areas in the wafer. A Raman spectrometer is used at 100-300cm -1 Three different peaks were found in the internal detection, indicating that the crystal had polymorphic inclusions in the early growth stage. This indicates that since the comparative example does not use a buffer layer, the relatively fast pressure change rate and flow rate change rate in the early stage lead to the appearance of polymorphic inclusions in the early stage, and the crystal is scrapped.

[0110] Comparative Example 2

[0111] Different from Example 1, during the process of generating the buffer layer in the initial stage of crystal growth, the rate of change of the internal growth pressure is 250Pa / h. After the growth is completed, the native surface of the crystal is observed. Polymorphic stripes appear on the surface of the crystal, and there are a large number of micropipe outcropping points. Polymorphic inclusions appeared in the crystal during the growth process. After the crystal is processed into wafers, all the wafers are observed through a white light lamp. It is found that starting from the second wafer, there are different color areas on the wafer, and polymorphic inclusions are generated in the early stage of crystal growth. This shows that in the process of growing the buffer layer in this comparative example, the pressure changes too quickly, thus failing to stabilize the partial pressure of the components at the front of the growth interface in the initial stage of growth, resulting in the appearance of initial polymorphic inclusions in the silicon carbide single crystal, and the crystal is scrapped.

[0112] Comparative Example 3

[0113] Different from Example 1, during the process of generating the buffer layer at the initial stage of crystal growth, the rate of change of the internal nitrogen flow rate was 15 sccm / h. After the growth was completed, the native surface of the crystal was observed, and a large number of micropipe outcrops appeared on the surface of the crystal. After the crystal was processed into a wafer, it was found that different color areas appeared on the third wafer, and polymorphic inclusions appeared in the initial stage of crystal growth. This shows that the buffer layer in this comparative example did not play a role in stabilizing the growth interface front C / Si at the initial stage of growth due to the excessively fast rate of change of the nitrogen flow rate, resulting in the appearance of polymorphic inclusions in the silicon carbide single crystal at the initial stage, and the crystal was scrapped.

[0114] Comparative Example 4

[0115] Different from Example 1, after the growth of the buffer layer is completed, the internal growth pressure of the system is controlled to be 25000Pa. After the growth is completed, the native surface of the crystal is observed, and the crystal surface is smooth without polymorphic inclusions. The minimum thickness of the silicon carbide single crystal tested with a vernier caliper is 5mm. The available thickness of the crystal is too low, and the utilization rate of the single crystal decreases. This shows that in this comparative example, due to the increase in the internal growth pressure of the system, the transmission of components is inhibited during the growth of the single crystal, resulting in a too slow crystal rate, low single crystal utilization, and the crystal is scrapped.

[0116] Comparative Example 5

[0117] The difference from Example 1 is that after the growth of the buffer layer is completed, the internal pressure of the system is controlled to be 500 Pa. Figure 5 As shown in the figure, after the growth is completed, the native surface of the crystal is observed. The crystal surface is smooth and there is no polymorphic inclusion phenomenon. The nitrogen doping content in the crystal is characterized by secondary ion mass spectrometry and is 7×10 18 cm -3 The lowest resistivity of the crystal characterized by the resistivity tester is 14 mΩ·cm, which is relatively high. This indicates that the reduction in growth pressure in this comparative example leads to a reduction in the N partial pressure at the front of the growth interface during single crystal growth, resulting in a low nitrogen doping content in the crystal and a high crystal resistivity.

[0118] Comparative Example 6

[0119] Different from Example 1, the axial ladder constructed in the growth chamber is 20°C / cm. After the growth is completed, the native surface of the crystal is observed, and the crystal surface is smooth without polymorphic inclusions. The minimum thickness of the silicon carbide single crystal tested with a vernier caliper is 3mm. The available thickness of the crystal is too low, and the utilization rate of the single crystal decreases. This shows that in this comparative example, due to the small axial ladder in the growth chamber, the component transmission rate is slow, which affects the transmission rate of the growing component in the growth chamber, resulting in too low crystal utilization and the crystal being scrapped.

[0120] Comparative Example 7

[0121] The difference from Example 1 is that the axial ladder constructed in the growth chamber is 200℃ / cm. After the growth is completed, the minimum thickness of the silicon carbide single crystal is 28mm when tested with a vernier caliper. The native surface of the crystal is observed, and polymorphic stripes appear on the surface of the crystal, and there are a large number of micropipe outcropping points. The crystal has polymorphic inclusions during the growth process. After the crystal is processed into wafers, all the wafers are observed through a white light lamp, and it is found that the second wafer has different color areas, and polymorphic inclusions are generated in the early stage of crystal growth. This shows that in this comparative example, due to the excessive size of the axial ladder, the rate of transmission of the growth component to the front of the growth interface is too fast, and the supersaturation of the component at the front of the growth interface is too large, which triggers spontaneous nucleation in the early stage of growth, resulting in the appearance of initial polymorphic inclusions in the silicon carbide single crystal, and the crystal is scrapped.

[0122] Comparative Example 8

[0123] Different from Example 1, after the growth of the buffer layer is completed, the temperature of the upper cover is controlled to be 1700°C for crystal growth. After the growth is completed, the minimum thickness of the silicon carbide single crystal tested by a vernier caliper is 4mm, and decomposition occurs on the back of the crystal. This shows that in this comparative example, due to the low growth temperature, the transmission efficiency of the growth components is too low, the crystal growth rate is too slow, resulting in low single crystal utilization, decomposition on the back of the crystal, and the crystal is scrapped.

[0124] Comparative Example 9

[0125] Different from Example 1, after the growth of the buffer layer, the temperature of the upper cover was controlled to be 2200°C for crystal growth. After the growth, the native surface of the crystal was observed, and the crystal surface was smooth without polymorphic inclusions. The nitrogen doping content in the crystal was characterized by secondary ion mass spectrometry and was 8×10 18 cm -3 The lowest resistivity of the crystal characterized by the resistivity tester is 14 mΩ·cm, which is relatively high. This indicates that in this comparative example, due to the high temperature at the growth interface front, the desorption rate of nitrogen atoms at the growth interface front is high, resulting in low nitrogen doping content in the crystal and high crystal resistivity.

[0126] Comparative Example 10

[0127] Different from Example 1, after the silicon carbide powder is spread on the lower part of the graphite crucible, no metal carbide particles are spread on the surface of the silicon carbide powder. After the growth is completed, the native surface of the crystal is observed, and the crystal surface is smooth without polymorphic inclusions. The N content in the crystal is characterized by secondary ion mass spectrometry and is 9×10 18 cm -3 The lowest resistivity of the crystal characterized by the resistivity tester is 13mΩ·cm, which is relatively high. This indicates that in this comparative example, since the metal carbide particles are not spread on the surface of the silicon carbide powder, the C / Si at the front of the growth interface is not changed, which affects the doping efficiency of N atoms, resulting in a low nitrogen doping content in the crystal and a high crystal resistivity.

[0128] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made by those skilled in the art within the spirit and principle of the present invention without creative labor shall be included in the protection scope of the present invention.

Claims

1. A method for growing a low-resistivity silicon carbide single crystal, characterized in that: The following steps are involved: Evenly spread silicon carbide powder on the bottom of the graphite crucible, evenly spread metal carbide particles on the surface of the silicon carbide powder, and bond silicon carbide seed crystals to the top of the graphite crucible; The graphite crucible is sealed and the interior thereof is evacuated; The vacuum-treated graphite crucible is heated and filled with a carrier gas, and then the carrier gas is slowly replaced with a doping source gas, and the growth pressure is slowly increased to a set pressure to grow a buffer layer; After the growth of the buffer layer is completed, the growth conditions are changed to grow a heavily doped silicon carbide single crystal; After the crystal growth is completed, the temperature of the vacuum-treated graphite crucible is lowered to allow the crystal to cool naturally, thereby obtaining a low-resistivity silicon carbide single crystal.

2. A method for growing a low resistivity silicon carbide single crystal as claimed in claim 1, characterized in that: The following steps are also included: The processing steps of cutting, grinding and polishing the silicon carbide crystal to process the crystal into a silicon carbide single crystal substrate, and then testing and characterizing the substrate: Observe the color of the crystal and perform Raman spectroscopy tests on substrate areas with different colors to evaluate the effect of the buffer layer on the crystal stability of the silicon carbide single crystal growth; Measure the nitrogen doping content in the crystal and determine the doping concentration in the crystal to evaluate the effects of regulating N partial pressure, gas flow, metal carbides and low-temperature large axis ladder on the crystal doping concentration; Perform a resistivity test on the crystal to evaluate the magnitude of the crystal's resistivity.

3. A method for growing a low resistivity silicon carbide single crystal as claimed in claim 1, characterized in that: The thickness of the buffer layer is 5% to 10% of the total thickness of the crystal. The buffer layer is a silicon carbide single crystal growth layer with slowly changing pressure and gas flow established at the initial stage of crystal growth.

4. A method for growing a low resistivity silicon carbide single crystal as claimed in claim 1, characterized in that: The growth pressure change rate of the buffer layer is 30 to 200 Pa / h; The gas flow rate change rate in the growth atmosphere of the buffer layer is 3-10 sccm / h.

5. A method for growing a low resistivity silicon carbide single crystal as claimed in claim 1, characterized in that: The metal carbide material includes at least one of tantalum carbide and niobium carbide.

6. A method for growing a low resistivity silicon carbide single crystal as claimed in claim 1, characterized in that: The carrier gas is one or more of argon and helium, and the doping source gas is one or more of nitrogen and ammonia; When the buffer layer is grown, the carrier gas is filled to a growth pressure of 100 Pa to 3000 Pa, and the measuring temperature of the upper cover of the graphite crucible is controlled to be 2100 to 2500° C.

7. A method for growing a low resistivity silicon carbide single crystal as claimed in claim 1, characterized in that: By changing the growth pressure, the N partial pressure at the growth front is regulated, and the nitrogen doping content in the crystal is regulated. The growth pressure is 3000Pa to 20000Pa. In the process of changing the growth conditions to grow heavily doped silicon carbide single crystals, the doping efficiency of the crystal is improved by changing the growth temperature in the growth chamber, the measuring temperature of the upper cover of the graphite crucible is controlled to be 1900-2100°C, and the stable growth time is 100-150h.

8. A method for growing a low resistivity silicon carbide single crystal as claimed in claim 1, characterized in that: In the process of growing heavily doped silicon carbide single crystals by changing the growth conditions, the nitrogen component inside the growth system is regulated by changing the flow rates of the doping source gas and the carrier gas in the growth atmosphere, thereby regulating the nitrogen doping content in the crystal. The flow rates of the two gases are both within the range of 0 to 100 sccm. In the process of changing the growth conditions to grow the heavily doped silicon carbide single crystal, the gas flow ratio of the doping gas to the carrier gas is 50% to 100%.

9. A method for growing a low resistivity silicon carbide single crystal as claimed in claim 1, characterized in that: In the process of changing the growth conditions to grow heavily doped silicon carbide single crystals, the doping efficiency of the silicon carbide single crystal is increased by setting the axis ladder, and the axis ladder is set at 50-150℃ / cm. If the axis ladder is too small, the growth rate of the single crystal will be too low and the crystal growth efficiency will be low; if the axis ladder is too large, the crystal will deviate from the growth equilibrium state to a greater extent, and the quality of the single crystal will deteriorate.

10. A method for growing a low resistivity silicon carbide single crystal as claimed in claim 1, characterized in that: The particle size of the silicon carbide powder does not exceed 1 mm, and the nitrogen content in the powder is not less than 100 PPM.

11. A low resistivity silicon carbide single crystal, characterized in that: The method according to any one of claims 1 to 10 is used for growing the polypropylene.

12. A low resistivity silicon carbide single crystal growth system, used to perform the method according to any one of claims 1 to 10, characterized in that: It comprises a graphite crucible, which comprises a matching crucible body and a crucible cover, wherein silicon carbide powder is arranged in the crucible body, metal carbide particles are spread on the silicon carbide powder, and silicon carbide seed crystals are arranged on the crucible cover; A heating system is arranged on the periphery of the graphite crucible; The graphite crucible is arranged in a closed system.

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