A method for growing SiC crystals using a low-temperature solution method

Abstract

The present invention relates to a method for growing SiC crystals by a low-temperature solution method, and belongs to the technical field of crystal growth. After high-purity silicon, metal Fe or Cr, and rare earth metals are mixed and alloyed and smelted, the smelting time is 5-30min to obtain a Si-Me-RE alloy with uniform composition; the Si-Me-RE alloy is loaded into a high-purity dense graphite crucible or a SiC crucible in a crystal growth furnace, and the melting temperature is kept above 1823K for at least 1 hour, so that C or SiC is dissolved in the high-temperature melt to obtain a SiC-saturated Si-Me-RE-C melt; the SiC-saturated Si-Me-RE-C melt is subjected to solution method growth of SiC single crystals or polycrystalline SiC. The method for growing SiC crystals by a low-temperature solution method provided by the present invention solves the problem of low solubility of C or SiC when growing SiC crystals by a solution method, and can greatly increase the solubility of C or SiC in the Si melt at low temperature (at least 400K lower than the existing PVT method), and is a method for growing SiC crystals with low energy consumption, low cost, high efficiency, and no pollution.

Description

Technical Field

[0001] The invention relates to a method for growing SiC crystals using a low-temperature solution method, belonging to the technical field of crystal growth. Background Art

[0002] SiC single crystal is a new generation of electronic core material, mainly used as the core substrate material of the third generation wide bandgap and high-power semiconductor devices. Compared with the first and second generation semiconductor materials, SiC single crystal has the characteristics of high temperature resistance, high pressure, high power and radiation resistance, and can be used to manufacture high-power devices that can operate at high speed and high frequency in harsh environments such as high temperature, high pressure and strong radiation.

[0003] At present, the physical vapor transport method is the mainstream technology for the industrial production of SiC single crystals at home and abroad, but the method has a low yield rate, high growth temperature, and high energy consumption for preparing SiC single crystals, resulting in high production costs, and the grown SiC single crystals are accompanied by defects such as microtubes, which affect their material properties. In addition, the physical vapor transport method is to decompose SiC raw materials into a complex mixed gas phase at ultra-high temperature, but the mixed gas phase reaction obtained by this sublimation is relatively complex, and the crystal growth process is difficult to control. Therefore, the price of SiC single crystals grown by the physical vapor transport method is relatively expensive, which limits the popularization and use of SiC single crystals in semiconductor devices.

[0004] The solution method is another method for growing SiC single crystals. This method can currently obtain low defect density and high-quality SiC single crystals under laboratory conditions. The solution method can achieve the growth of high-quality SiC single crystals in a state close to thermodynamic equilibrium. This method has the advantages of fewer grown crystal microtubes, more controllable growth process, and easy p-type doping. When growing SiC single crystals by the solution method, the solubility of C in the silicon melt is the key factor determining the growth rate of SiC single crystals. The solubility of C in the silicon melt below 2273K is very low, which limits the mass transfer process of C in the silicon melt. Therefore, it is difficult to achieve rapid growth of SiC single crystals using pure silicon melt. How to increase the solubility of C in the silicon melt is a technical problem that needs to be solved for the rapid growth of SiC single crystals at low temperatures.

[0005] In response to the problem of low C solubility when growing SiC single crystals by solution method, researchers proposed a method of adding solvents to silicon melt to increase the solubility of C in the melt. This solution method of adding solvents is called solvent method. In addition, the added solvent can form a low melting point melt with silicon, so the solvent method is also a technology for growing SiC single crystals at low temperature. The solvents that have been reported so far mainly include chromium, titanium, iron, cobalt, etc. Compared with pure silicon melt, when these are used as solvents, the solubility of C can be significantly improved, which is conducive to the growth of SiC single crystals under low temperature conditions, but the solubility of C in the melt is still limited. Therefore, it is necessary to continue to develop new solvents to increase the solubility of C in silicon melt to solve the problem of limited growth rate of SiC single crystals. On the other hand, high-purity polycrystalline SiC is an important raw material for growing SiC single crystals. When polycrystalline SiC is purified by recrystallization, the problem of too low solubility of SiC in the melt is also faced, and the recrystallization method cannot be used to purify polycrystalline SiC. In summary, whether growing SiC single crystals by solution method or preparing high-purity polycrystalline SiC crystals by recrystallization method, it is necessary to solve the problem of low solubility of SiC in silicon melt, and it is necessary to develop new solvents to improve the solubility of C or SiC in silicon melt. Summary of the invention

[0006] In view of the problems existing in the above-mentioned prior art, the present invention provides a method for growing SiC crystals by a low-temperature solution method. The present invention can significantly increase the solubility of C in silicon melt under low temperature conditions, and provides the possibility for the low-temperature rapid growth of high-quality SiC single crystals and polycrystalline SiC by a solution method. The present method solves the technical problem of low solubility of C in silicon melt. The present invention is implemented by the following technical solutions.

[0007] A method for growing SiC crystals using a low-temperature solution method, comprising the following steps:

[0008] Step 1: high-purity silicon, metal Fe or Cr (Me), and rare earth metal (RE) are mixed and alloyed and smelted for 5-30 minutes to obtain a Si-Me-RE alloy with uniform composition. The smelting atmosphere is a high-purity inert gas (purity> 99.999%) under normal pressure or negative pressure. The smelting temperature is higher than the melting point of the Si-Me-RE alloy. The alloying smelting method adopts a water-cooled copper crucible technology or an electromagnetic suspension melting technology, and the water-cooled copper crucible technology is preferred.

[0009] Step 2, the Si-Me-RE alloy obtained in step 1 is loaded into a high-purity dense graphite crucible or SiC crucible in a crystal growth furnace, and kept warm at a melting temperature above 1823K for at least 1 hour to dissolve C or SiC into the high-temperature melt to obtain a SiC-saturated Si-Me-RE-C melt; the melting atmosphere is a high-purity inert gas or a mixed gas of hydrogen and a high-purity inert gas, and the volume content of hydrogen in the mixed gas is ≤10%;

[0010] Step 3: The SiC-saturated Si-Me-RE-C melt obtained in step 2 is subjected to a solution method to grow a SiC single crystal or polycrystalline SiC; the crystal growth method is a conventional crystal growth method, including but not limited to a top seed solution growth method or a crucible descent method, the crystal growth temperature is higher than 1823K, and the SiC crystal growth atmosphere is a high-purity inert gas (purity>99.999%) or a mixed gas of hydrogen and high-purity inert gas, and the volume content of hydrogen in the mixed gas is ≤10%.

[0011] In the step 1, the content of Me in the Si-Me-RE alloy is ≤45 at.%, Me represents one or two of Fe or Cr; the total content of RE is ≤35 at.%, and RE represents one or more of rare earth metals; under the above conditions, the ratio of Me, RE and Si is adjusted so that the total content of Me, RE and Si is 100 at.%.

[0012] In the step 1, the mixture of metal Fe or Cr and rare earth metal is a flux; the rare earth metal is one or more of the rare earth elements, including scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu) One or more mixtures in any proportion.

[0013] In the above step 3, the crystal growth conditions other than the temperature are not limited, that is, the temperature gradient, the type of SiC seed crystal, the rotation speed of the seed crystal rod or the crucible, and the heating method of the crystal furnace (electromagnetic induction or resistance heating) are not limited.

[0014] The beneficial effects of the present invention are:

[0015] (1) The present invention provides a method for improving the solubility of C or SiC in silicon melt by using a new solvent, that is, a mixed metal of Me+RE is used as a solvent, which solves the problem of low solubility of C or SiC when growing SiC crystals by a low-temperature solution method;

[0016] (2) The solvent for growing SiC crystals by the low-temperature solution method proposed in the present invention can not only be used to grow SiC single crystals, but also can be used as a material for preparing high-purity polycrystalline SiC;

[0017] (3) When rare earth is used as a flux, the rare earth melts before silicon, and the molten rare earth reacts with the crucible to generate rare earth carbides, which affects the quality of the grown SiC crystal. The present invention solves this problem by using a pre-melted alloy method.

[0018] (4) When rare earth is used as a solvent, the rare earth easily reacts with a trace amount of oxygen in the furnace, reducing the solubility of SiC in the melt. The present invention solves this problem by using a method of mixing hydrogen and inert gas (hydrogen content ≤ 10%).

[0019] (5) The present invention is a technology for growing SiC crystals with low energy consumption, no pollution and low cost;

[0020] (6) The method for growing SiC crystals by a low-temperature solution method provided by the present invention solves the problem of low solubility of C or SiC when growing SiC crystals by a solution method, and can significantly increase the solubility of C or SiC in Si melt at a low temperature (at least 400K lower than the existing PVT method). It is a method for growing SiC crystals with low energy consumption, low cost, high efficiency and no pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0022] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods.

[0023] Example 1

[0024] like Figure 1 As shown, the method for growing SiC crystal by low temperature solution method comprises the following steps:

[0025] Step 1, high-purity silicon (purity 99.9999wt%), metal Cr (purity 99.99wt%), and rare earth metal Nd (purity 99.9wt%) are mixed and alloyed and smelted for 5 minutes to obtain a 50at.%Si-35at.%Cr-15at.%Nd alloy with uniform composition. The smelting atmosphere is a high-purity inert gas (argon, purity>99.999wt%) under negative pressure. The smelting temperature is higher than the melting point of the 50at.%Si-35at.%Cr-15at.%Nd alloy. The alloying smelting method is an electric arc furnace smelting technology with a water-cooled copper crucible;

[0026] Step 2: The 50at.%Si-35at.%Cr-15at.%Nd alloy obtained in step 1 is placed in a high-purity dense graphite crucible in a crystal growth furnace, and kept at a melting temperature of 1823K for 1 hour to dissolve C into the high-temperature melt to obtain a SiC-saturated Si-Cr-Nd-C melt (C content is 4.44 wt.%); the melting atmosphere is high-purity argon (99.999wt%) + 10%H 2 Mixed gases;

[0027] Step 3: growing SiC single crystal by solution method in the SiC saturated Si-Cr-Nd-C melt obtained in step 2; the crystal growth method is top seed solution growth method, the crystal growth temperature is 1823K, and the SiC crystal growth atmosphere is high purity argon (99.999wt%) + 10%H 2 Mixed gases.

[0028] Example 2

[0029] like Figure 1 As shown, the method for growing SiC crystal by low temperature solution method comprises the following steps:

[0030] Step 1, high-purity silicon (purity 99.9999wt%), metal Fe (purity 99.99wt%), and rare earth metal Pr (purity 99.9wt%) are mixed and alloyed and smelted for 6 minutes to obtain a 50at.%Si-15at.%Fe-35at.%Pr alloy with uniform composition. The smelting atmosphere is a high-purity inert gas (argon, purity>99.999wt%) under negative pressure. The smelting temperature is higher than the melting point of the 50at.%Si-15at.%Fe-35at.%Pr alloy. The alloying smelting method is an electric arc furnace smelting technology with a water-cooled copper crucible;

[0031] Step 2: The 50at.%Si-15at.%Fe-35at.%Pr alloy obtained in step 1 is loaded into a SiC crucible in a crystal growth furnace, and kept at a melting temperature of 1923K for 1 hour to dissolve SiC into the high-temperature melt to obtain a SiC-saturated Si-Fe-Pr-C melt (C content is 6.78 wt.%); the melting atmosphere is high-purity argon (99.999wt%);

[0032] Step 3, growing a SiC single crystal by solution method in the SiC-saturated Si-Fe-Pr-C melt obtained in step 2; the crystal growth method is the top seed solution growth method, the crystal growth temperature is 1923K, and the SiC crystal growth atmosphere is a high-purity inert gas (argon, purity> 99.999%).

[0033] Example 3

[0034] like Figure 1 As shown, the method for growing SiC crystal by low temperature solution method comprises the following steps:

[0035] Step 1, high-purity silicon (purity 99.9999wt%), metal Fe (purity 99.99wt%), and rare earth metal La (purity 99.9wt%) are mixed and alloyed and smelted for 10 minutes to obtain a 50at.%Si-45at.%Fe-5at.%La alloy with uniform composition. The smelting atmosphere is a high-purity inert gas (argon, purity>99.999wt%) under negative pressure. The smelting temperature is higher than the melting point of the 50at.%Si-45at.%Fe-5at.%La alloy. The alloying smelting method is an electric arc furnace smelting technology with a water-cooled copper crucible;

[0036] Step 2: The 50at.%Si-45at.%Fe-5at.%La alloy obtained in step 1 is placed in a SiC crucible in a crystal growth furnace, and the melting temperature is kept at 1923K for 1.5 hours to dissolve SiC into the high-temperature melt to obtain a SiC-saturated Si-Fe-La-C melt (C content is 0.4wt.%); the melting atmosphere is high-purity helium (99.999wt%) + 10%H 2 Mixed gas;

[0037] Step 3: growing SiC single crystal by solution method in the SiC-saturated Si-Fe-La-C melt obtained in step 2; the crystal growth method is top seed solution growth method, the crystal growth temperature is 1923K, and the SiC crystal growth atmosphere is high purity helium (99.999wt%) + 10%H 2 Mixed gases.

[0038] Example 4

[0039] like Figure 1 As shown, the method for growing SiC crystal by low temperature solution method comprises the following steps:

[0040] Step 1, high-purity silicon (purity 99.9999wt%), metal Fe (purity 99.99wt%), and a mixture of rare earth metals Y and Pr (purity of Y and Pr are both 99.9wt%, and the mass ratio of Y to Pr is 1:20) are mixed and alloyed and smelted for 10 minutes to obtain a 60at.%Si-10at.%Fe-30at.%(Y+Pr) alloy with uniform composition, the smelting atmosphere is a high-purity inert gas (argon, purity>99.999wt%) under negative pressure, the smelting temperature is higher than the melting point of 60at.%Si-10at.%Fe-30at.%(Y+Pr), and the alloying smelting method is an arc furnace smelting technology with a water-cooled copper crucible;

[0041] Step 2: The 60at.%Si-10at.%Fe-30at.%(Y+Pr) alloy obtained in step 1 is placed in a high-purity dense graphite crucible in a crystal growth furnace, and kept at a melting temperature of 1923K for 1.5 hours to dissolve C into the high-temperature melt to obtain a SiC-saturated Si-Fe-(Y+Pr)-C melt (C content is 3.23 wt.%); the melting atmosphere is high-purity helium (99.999wt%) + 10%H 2 Mixed gases;

[0042] Step 3: In the SiC-saturated Si-Fe-(Y+Pr)-C melt obtained in step 2, a SiC single crystal is grown by solution method; the crystal growth method is the top seed solution growth method, the crystal growth temperature is 1923K, and the SiC crystal growth atmosphere is the melting atmosphere of high-purity helium (99.999wt%) + 10%H 2 Mixed gases.

[0043] Example 5

[0044] Step 1, high-purity silicon (purity 99.9999wt%), metal Fe and Cr (purity of 99.99wt%, Fe to Cr mass ratio of 4:3), rare earth metal La (99.9wt%) are mixed and alloyed and smelted for 10 minutes to obtain a 50at.%Si-35at.%(Fe+Cr)-15at.%La alloy with uniform composition, the smelting atmosphere is a high-purity inert gas (argon, purity>99.999wt%) under negative pressure, the smelting temperature is higher than the melting point of the 50at.%Si-35at.%(Fe+Cr) -15at.%La alloy, and the alloying smelting method is an arc furnace smelting technology with a water-cooled copper crucible;

[0045] Step 2: The 50at.%Si-35at.%(Fe+Cr)-15at.%La alloy obtained in step 1 is placed in a high-purity dense graphite crucible in a crystal growth furnace, and kept at a melting temperature of 1823K for 1.5 hours to dissolve C into the high-temperature melt to obtain a SiC-saturated Si-(Fe+Cr)-La-C melt (C content is 2.4 wt.%); the melting atmosphere is high-purity helium (99.999wt%) + 10%H 2 Mixed gases;

[0046] Step 3: In the SiC-saturated Si-(Fe+Cr)-La-C melt obtained in step 2, a solution method is used to grow SiC polycrystals; the crystal growth method is a crucible descent method, the crystal growth temperature is 1823K, and the SiC crystal growth atmosphere is a melting atmosphere of high-purity helium (99.999wt%) + 10%H 2 Mixed gases.

[0047] The specific implementation modes of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A method for growing SiC crystals by a low temperature solution method, Features The following steps are involved: Step 1, high-purity silicon, metal Fe or Cr, and rare earth metal are mixed and alloyed and smelted for 5-30 minutes to obtain a Si-Me-RE alloy with uniform composition. The smelting atmosphere is a high-purity inert gas under normal pressure or negative pressure. The smelting temperature is higher than the melting point of the Si-Me-RE alloy. The alloying smelting method adopts a water-cooled copper crucible technology or an electromagnetic suspension smelting technology; Step 2, the Si-Me-RE alloy obtained in step 1 is loaded into a high-purity dense graphite crucible or SiC crucible in a crystal growth furnace, and kept warm at a melting temperature of 1823K or 1923K for at least 1 hour to dissolve C or SiC into the high-temperature melt to obtain a SiC-saturated Si-Me-RE-C melt; the melting atmosphere is a high-purity inert gas or a mixed gas of hydrogen and a high-purity inert gas, and the volume content of hydrogen in the mixed gas is ≤10%; Step 3, growing SiC single crystal or polycrystalline SiC by solution method in the SiC-saturated Si-Me-RE-C melt obtained in step 2; the crystal growth method is a conventional crystal growth method, including but not limited to a top seed solution growth method or a crucible descent method, the crystal growth temperature is 1823K or 1923K, the SiC crystal growth atmosphere is a high-purity inert gas or a mixed gas of hydrogen and high-purity inert gas, and the volume content of hydrogen in the mixed gas is ≤10%; In the step 1, the content of Me in the Si-Me-RE alloy is ≤35at.%, Me represents one of Fe or Cr; the total content of RE is 15at.%, 30at.% or 35at.%, and RE represents one or more of rare earth metals; under the above conditions, the ratio of Me, RE and Si is adjusted so that the total content of Me, RE and Si is 100at.%.

2. The method for growing SiC crystal by low temperature solution method according to claim 1, Features: In step 1, the mixture of metal Fe or Cr and rare earth metal is a solvent; the rare earth metal is one or more rare earth elements, including one or more mixtures of scandium, yttrium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium in any proportion.

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