CN116837456A - Seed crystal treatment method and silicon carbide crystal growth method - Google Patents
Seed crystal treatment method and silicon carbide crystal growth method Download PDFInfo
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- CN116837456A CN116837456A CN202310874871.5A CN202310874871A CN116837456A CN 116837456 A CN116837456 A CN 116837456A CN 202310874871 A CN202310874871 A CN 202310874871A CN 116837456 A CN116837456 A CN 116837456A
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- 238000000034 method Methods 0.000 title claims abstract description 61
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 title claims abstract description 57
- 229910010271 silicon carbide Inorganic materials 0.000 title claims abstract description 56
- 238000002109 crystal growth method Methods 0.000 title description 4
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- 238000010000 carbonizing Methods 0.000 claims abstract description 8
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- 238000000576 coating method Methods 0.000 claims abstract description 8
- -1 carbonizing Substances 0.000 claims abstract description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 38
- 239000010439 graphite Substances 0.000 claims description 37
- 229910002804 graphite Inorganic materials 0.000 claims description 37
- 239000011230 binding agent Substances 0.000 claims description 36
- 239000007789 gas Substances 0.000 claims description 28
- 238000003763 carbonization Methods 0.000 claims description 25
- 238000010438 heat treatment Methods 0.000 claims description 21
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 18
- BLRPTPMANUNPDV-UHFFFAOYSA-N Silane Chemical compound [SiH4] BLRPTPMANUNPDV-UHFFFAOYSA-N 0.000 claims description 14
- 229910000077 silane Inorganic materials 0.000 claims description 14
- 230000001681 protective effect Effects 0.000 claims description 12
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 10
- 229910052757 nitrogen Inorganic materials 0.000 claims description 9
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- 239000011261 inert gas Substances 0.000 claims description 7
- 239000002994 raw material Substances 0.000 claims description 7
- 238000005498 polishing Methods 0.000 claims description 6
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 5
- 238000001816 cooling Methods 0.000 claims description 5
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B23/00—Single-crystal growth by condensing evaporated or sublimed materials
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/36—Carbides
Abstract
The invention provides a seed crystal treatment method and a growth method of silicon carbide crystal, wherein the seed crystal treatment method comprises the following steps: (1) Introducing etching gas into a container where the seed crystal is positioned, and performing annealing etching; (2) Bonding the bonding surface of the seed crystal and a first bonding plate by adopting a first bonding agent, carbonizing, coating a second bonding agent on the back surface of the bonding plate, bonding with the second bonding plate, and curing to obtain the treated seed crystal; wherein the porosity of the first adhesive sheet is greater than the porosity of the second adhesive sheet. According to the invention, firstly, the silicon carbide seed crystal is pretreated, so that not only is the seed crystal stress released and a foundation is laid for reducing dislocation defects of the crystal, but also a compact protective layer is formed on the surface of the seed crystal, and dislocation proliferation is effectively inhibited; and then growing on the seed crystal by adopting a secondary growth mode to obtain the silicon carbide crystal with low dislocation density. The method is simple to operate, and promotes the mass production process of large-size silicon carbide crystals.
Description
Technical Field
The invention belongs to the technical field of silicon carbide growth, and particularly relates to a seed crystal treatment method and a silicon carbide crystal growth method.
Background
Silicon carbide (SiC) single crystal is one of the most widely used third generation semiconductor materials in the fields of power electronics, radio frequency devices, optoelectronic devices and the like at present, and a 6-inch substrate slice has been commercialized for mass production. The physical vapor transport method (PVT method) is a mainstream process method for growing a silicon carbide single crystal at present, and is a method in which a seed crystal is fixed to the bottom of a crucible cover, a raw material in the crucible is sublimated by heating, and the sublimated gas is crystallized on the seed crystal under specific conditions to obtain the silicon carbide single crystal. Many factors influence the growth of silicon carbide single crystals, wherein seed crystals are key factors, and the threading dislocation, the surface type parameters and the fixing process of the seed crystals can directly influence the crystal quality: such as threading dislocations in the seed crystal can be inherited into the crystal, dislocation of the grown crystal is caused by stress of the seed crystal, thermal stress is easily generated due to uneven gap between the seed crystal and the crucible cover caused by uneven brushing of the binder, mechanical stress is caused by difference of thermal expansion coefficients between the crystal and the crucible cover, and the like, so that the process of seed crystal treatment is very important.
At present, the SiC material has higher dislocation density, and is restricted to be widely applied to electronic devices. Along with the rapid development of the market, the growth of large-diameter and high-quality SiC single crystals is a key for reducing the cost of an industrial chain and promoting the realization of device application. 8 inch crystals are a trigger, and although there have been reports of production from various large substrate manufacturers, dislocation is still at a high level, and the 8 inch mass production process is still not mature.
Therefore, how to effectively reduce dislocation density of silicon carbide crystals and promote mass production process of large-size silicon carbide crystals is the focus of current research.
Disclosure of Invention
In view of the shortcomings of the prior art, the invention aims to provide a seed crystal treatment method and a silicon carbide crystal growth method. According to the invention, firstly, the silicon carbide seed crystal is pretreated, so that not only is the seed crystal stress released and a foundation is laid for reducing dislocation defects of the crystal, but also a compact protective layer is formed on the surface of the seed crystal, and dislocation proliferation is effectively inhibited; and then growing on the seed crystal by adopting a secondary growth mode to obtain the silicon carbide crystal with low dislocation density. The method is simple to operate, and promotes the mass production process of large-size silicon carbide crystals.
To achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a seed treatment method for silicon carbide crystal growth, the method comprising the steps of:
(1) Introducing etching gas into a container where the seed crystal is positioned, and performing annealing etching;
(2) Bonding the bonding surface of the seed crystal and a first bonding plate by adopting a first bonding agent, carbonizing, coating a second bonding agent on the back surface of the bonding plate, bonding with the second bonding plate, and curing to obtain the treated seed crystal;
wherein the porosity of the first adhesive sheet is greater than the porosity of the second adhesive sheet.
According to the invention, firstly, the silicon carbide seed crystal is pretreated, so that not only is the seed crystal stress released, a foundation is laid for reducing dislocation defects of the crystal, but also a compact protective layer is formed on the surface of the seed crystal, dislocation proliferation is effectively inhibited, and a vital pushing effect is played for subsequently reducing dislocation density of the silicon carbide crystal.
According to the invention, stress is released after annealing etching, so that seed crystal stress is reduced, and meanwhile, an etching pit is formed, and as the etching pit has a certain depth, uneven temperature distribution is formed on the surface of the seed crystal during growth, nucleation is induced on the side wall of the etching pit, so that transverse growth is induced, the purpose of eliminating axial defects is achieved, uniform growth of silicon carbide crystals can be carried out when the etching pit is filled up, and crystal dislocation defects are reduced.
In the carbonization process, a large amount of gas and solvent are released due to carbonization of the adhesive, and the adhesive plate with larger porosity is selected to be capable of exhausting better, so that a gap is prevented from being formed between the seed crystal and the adhesive plate, and the protection effect on the seed crystal is improved; and then, the back of the bonding plate is coated with the adhesive again and is bonded with the bonding plate with low porosity, so that the purpose of the bonding plate is to seal the pores of the bonding plate, thereby forming a compact protective layer, avoiding the generation of an uneven pore layer on the back of the seed crystal, further improving the temperature uniformity of the growth surface, avoiding multi-island nucleation in the initial growth stage and inhibiting dislocation proliferation.
As a preferable technical scheme of the invention, the etching gas in the step (1) is hydrogen.
Preferably, the annealing etching pressure in the step (1) is 5-100KPa, for example, 5KPa, 10KPa, 20KPa, 30KPa, 40KPa, 50KPa, 60KPa, 70KPa, 80KPa, 90KPa or 100KPa, etc.
Preferably, the annealing etching temperature in the step (1) is 1500-2100 ℃, and may be 1500 ℃, 1600 ℃, 1700 ℃, 1800 ℃, 1900 ℃, 2000 ℃, 2100 ℃, or the like.
Preferably, the heat preservation time of the annealing etching in the step (1) is 1-50h, for example, 1h, 5h, 10h, 15h, 20h, 25h, 30h, 40h, 45h or 50h, etc.
As a preferable technical scheme of the invention, before the etching gas is introduced in the step (1), introducing silicon-containing inert gas into a container where the seed crystal is positioned, and heating to reach the preheating temperature.
In the invention, the purpose of introducing the silicon-containing inert gas is to prevent Si atoms on the surface of the seed crystal from escaping to form a layer of graphite structure at high temperature, thereby changing the surface structure of the growth surface and bringing new defects.
Preferably, the inert gas containing silicon comprises silane and nitrogen.
Preferably, in the inert gas containing silicon, the volume fraction of silane is 0.1-5%, for example, 0.1%, 0.3%, 0.5%, 1%, 2% or 5%, etc.
In the present invention, if the volume fraction of silane is too large, more Si is generated by decomposition at high temperature, and is liable to accumulate on the seed crystal surface to change its surface structure, and if the volume fraction is too small, the effect of suppressing the escape of Si atoms on the seed crystal surface is not exerted.
Preferably, the preheating temperature is 1000-1500 ℃, for example 1000 ℃, 1100 ℃, 1200 ℃, 1300 ℃, 1400 ℃ or 1500 ℃.
As a preferable technical scheme of the invention, after the annealing etching in the step (1), polishing and cleaning are carried out on the seed crystal.
As a preferred embodiment of the present invention, the first binder in the step (2) includes any one or a combination of at least two of an organic gel, a graphite gel and a photoresist.
Preferably, the second binder of step (2) comprises an organic gum and/or a graphite gum.
The organic glue or the graphite glue is not particularly limited, and examples thereof include AB glue, epoxy resin glue, phenolic resin glue, furfural resin glue or graphite glue, and the like.
Preferably, the mass ratio of the first binder to the second binder in the step (2) is (1.1-3): 1, for example, 1.1:1, 1.5:1, 2:1, 2.5:1 or 3:1, etc.
In the invention, if the mass ratio of the first adhesive to the second adhesive is too small, namely the dosage of the second adhesive is too large, most of the adhesive cannot be absorbed and discharged to the periphery of the bonding plate, and cleaning is difficult, and because the pores in the first bonding plate are filled with the first adhesive, the porosity of the second bonding plate is very low, and the amount of the absorbed adhesive is small; if the mass ratio of the first binder to the second binder is too large, that is, the amount of the second binder is too small, the curing effect becomes poor, and the seed crystal is easily detached.
Preferably, the first and second adhesive sheets of step (2) independently comprise graphite paper or graphite, preferably graphite.
Preferably, the thickness of the first adhesive sheet in step (2) is 0.1-10mm, and may be, for example, 0.1mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm or 10mm.
Preferably, the first adhesive sheet in step (2) has a porosity of 10-20%, for example, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%, etc.
In the invention, if the porosity of the first bonding plate is too small, the gas generated by the first bonding agent is not easy to be discharged in the carbonization process, and a local gap is formed between the seed crystal and the bonding plate, so that the protection effect on the seed crystal is reduced.
Preferably, the second adhesive sheet in the step (2) is in a shape of a round plate or a round ring.
Preferably, the porosity of the second adhesive sheet of step (2) is < 1%, for example, may be 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2% or 0.1%.
In the invention, if the porosity of the second adhesive plate is too large, the second adhesive can still infiltrate into the adhesive plate in a large amount, holes appear in the holes due to gas generation in the curing process, so that a compact protective layer cannot be formed, the protection effect on seed crystals is reduced, an uneven air hole layer can be generated on the back of the seed crystals in the growth process, and the nucleation and even ablation of multiple islands in the initial growth stage are initiated.
As a preferable embodiment of the present invention, the carbonization temperature in the step (2) is 200-1200 ℃, for example, 200 ℃, 400 ℃, 600 ℃, 800 ℃, 1000 ℃, 1200 ℃ or the like.
In the present invention, if the carbonization temperature is too low, the carbonization of the binder is insufficient, and the adhesion force is lowered; if the carbonization temperature is too high, silicon atoms on the surface of the seed crystal are easily escaped to damage the surface structure of the seed crystal.
Preferably, the carbonization time in the step (2) is 1-20h, for example, 1h, 5h, 10h, 15h or 20h, etc.
Preferably, the temperature of the curing in step (2) is 200-1200 ℃, for example, 200 ℃, 400 ℃, 600 ℃, 800 ℃, 1000 ℃, 1200 ℃ or the like.
In the present invention, if the curing temperature is too low, the curing of the adhesive is insufficient and the adhesive force is lowered; if the curing temperature is too high, the silicon atoms on the surface of the seed crystal are easily escaped to damage the surface structure of the seed crystal.
Preferably, the curing time of step (2) is 0.5-10h, for example, 0.5h, 1h, 3h, 5h, 7h, 9h or 10h, etc.
As a preferred technical solution of the present invention, the method comprises the steps of:
heating a container in which a seed crystal is positioned to 1000-1500 ℃ in a nitrogen atmosphere with the volume fraction of silane of 0.1-5%, then introducing etching gas for replacement, heating to 1500-2100 ℃ for annealing etching, and maintaining the temperature for 1-50h and the pressure at 5-100KPa;
(II) polishing the seed crystal after annealing etching, and cleaning;
(III) bonding the bonding surface of the seed crystal and the first bonding plate by adopting a first bonding agent, carbonizing for 1-20h at the temperature of 200-1200 ℃, coating a second bonding agent on the back surface of the first bonding plate after carbonization, bonding with the second bonding plate, and curing for 0.5-10h at the temperature of 200-1200 ℃ to obtain the treated seed crystal;
wherein the first bonding plate and the second bonding plate independently comprise graphite paper or graphite, the thickness of the first bonding plate is 0.1-10mm, the porosity is 10-20%, the second bonding plate is in a round plate shape or a circular ring shape, the porosity is less than 1%, and the dosage ratio of the first bonding agent to the second bonding agent is (1.1-3): 1.
In a second aspect, the present invention provides a method for growing a silicon carbide crystal, the method comprising the steps of:
treating a seed crystal for silicon carbide crystal growth using the seed crystal treatment method of the first aspect, and then growing a silicon carbide crystal on the treated seed crystal.
As a preferred technical scheme of the invention, the growth method comprises the following specific steps:
(a) Fixing the treated seed crystal on the crucible cover in a manner that the bonding plate faces the crucible cover;
(b) Combining a crucible cover for fixing seed crystals and a crucible filled with silicon carbide raw materials, placing the combined materials into a growth furnace, vacuumizing, and then filling protective gas;
(c) Performing a first growth under conditions of a first temperature and a first pressure;
(d) Performing a second growth under conditions of a second temperature and a second pressure;
(e) And (5) charging protective gas, and cooling to obtain the silicon carbide crystal.
According to the invention, in the first growth stage, the transverse growth of the corrosion pit can be realized, the extension of axial dislocation to the inside of the crystal is eliminated, the transition process from the first growth stage to the second growth stage can lead the nucleation in the initial growth stage to be more uniform, the dislocation proliferation is inhibited, and the thickness of the high-quality crystal is increased in the second growth stage.
As a preferred embodiment of the present invention, the fixing means in the step (a) includes a mechanical method or an adhesive method.
Preferably, the vacuum is applied in step (b) to a pressure of < 10 -2 Pa may be, for example, 8×10 -3 Pa、6×10 -3 Pa、5×10 -3 Pa、4×10 -3 Pa、3×10 -3 Pa、2×10 -3 Pa or 1X 10 -3 Pa, and the like.
Preferably, the protective gas is introduced in step (b) to a pressure of 10-800mbar, for example 10mbar, 50mbar, 100mbar, 200mbar, 300mbar, 400mbar, 500mbar, 600mbar, 700mbar or 800mbar, etc., preferably 200-700mbar.
The present invention is not limited to the specific type of the protective gas, and may be exemplified by nitrogen.
Preferably, the first temperature in step (c) is 1800-2200 ℃, for example 1800 ℃, 1900 ℃, 2000 ℃, 2100 ℃, 2200 ℃, etc.
Preferably, the temperature increase rate of the first temperature in step (c) is 1-5 ℃/min, for example, 1 ℃/min, 1.2 ℃/min, 2 ℃/min, 3 ℃/min, 4 ℃/min or 5 ℃/min.
Preferably, the first pressure in step (c) is in the range of 1 to 100mbar, for example 1mbar, 5mbar, 10mbar, 20mbar, 30mbar, 40mbar, 50mbar, 60mbar, 70mbar or 80mbar, etc., preferably 10 to 50mbar.
Preferably, the time of the first growth in step (c) is 1-50h, for example, 1h, 5h, 10h, 20h, 30h, 40h or 50h, etc., preferably 10-30h.
Preferably, the second temperature in step (d) is 2000-2300 ℃, for example 2000 ℃, 2100 ℃, 2200 ℃, 2300 ℃, or the like.
Preferably, the second temperature in step (d) has a heating rate of 0.5-3 ℃/min, for example, 0.5 ℃/min, 0.8 ℃/min, 1 ℃/min, 1.5 ℃/min, 2 ℃/min or 3 ℃/min.
Preferably, said second pressure of step (d) is in the range of 0.2 to 80mbar, e.g. 0.2mbar, 1mbar, 5mbar, 10mbar, 20mbar, 30mbar, 40mbar, 50mbar, 60mbar, 70mbar or 80mbar etc., preferably 1 to 20mbar.
Preferably, the second growth time in step (d) is 10-200h, for example, 10h, 30h, 50h, 70h, 90h, 110h, 130h or 200h, etc., preferably 70-150h.
Preferably, the protective gas is introduced in step (e) to a pressure of 200-800mbar, for example 200mbar, 300mbar, 400mbar, 500mbar, 600mbar, 700mbar or 800mbar etc.
Preferably, the temperature after cooling in step (e) is room temperature.
The room temperature is not limited to the present invention, and may be, for example, 25±5 ℃, including 20 ℃, 22 ℃, 24 ℃, 26 ℃, 28 ℃, 30 ℃, or the like.
The numerical ranges recited herein include not only the above-listed point values, but also any point values between the above-listed numerical ranges that are not listed, and are limited in space and for the sake of brevity, the present invention is not intended to be exhaustive of the specific point values that the stated ranges include.
Compared with the prior art, the invention has the following beneficial effects:
(1) According to the invention, firstly, the silicon carbide seed crystal is pretreated, so that not only is the seed crystal stress released and a foundation is laid for reducing dislocation defects of the crystal, but also a compact protective layer is formed on the surface of the seed crystal, and dislocation proliferation is effectively inhibited; and then growing on the seed crystal by adopting a secondary growth mode to obtain the silicon carbide crystal with low dislocation density.
(2) The method is simple to operate, and greatly promotes the mass production process of large-size silicon carbide crystals.
Detailed Description
The technical scheme of the invention is further described by the following specific embodiments. It will be apparent to those skilled in the art that the examples are merely to aid in understanding the invention and are not to be construed as a specific limitation thereof.
In the examples which follow, room temperature is referred to as 25 ℃.
Example 1
The embodiment provides a seed crystal treatment method for silicon carbide crystal growth, which comprises the following steps:
(1) Heating a furnace in which seed crystals are positioned to 1300 ℃ in a nitrogen atmosphere with the volume fraction of silane of 2.5%, then introducing hydrogen for replacement, heating to 1800 ℃ for annealing etching, and maintaining the pressure at 50KPa for 15 hours;
(2) Polishing the annealed and etched seed crystal, and cleaning to eliminate transverse penetrating lines;
(3) Bonding the bonding surface of the seed crystal and graphite with the thickness of 5mm and the porosity of 15% by adopting a first binder, carbonizing at the temperature of 700 ℃ for 10 hours, coating a second binder on the back surface of the graphite after carbonization, bonding with disc-shaped graphite paper with the porosity of 0.5%, and curing at the temperature of 700 ℃ for 5 hours to obtain the treated seed crystal;
the first adhesive is organic adhesive, the second adhesive is organic adhesive, and the mass ratio of the first adhesive to the second adhesive is 1.5:1.
The embodiment also provides a seed crystal treatment method for silicon carbide crystal growth, and then the silicon carbide crystal is grown on the treated seed crystal, which comprises the following specific steps:
(a) Bonding the treated seed crystal on the crucible cover in a manner that the bonding plate faces the crucible cover;
(b) Combining the crucible cover for fixing seed crystal and crucible containing silicon carbide raw material, placing into growth furnace, vacuum-pumping to pressure of 5×10 -3 Pa, then charging nitrogen as protective gas to a pressure of 400mbar;
(c) Heating to a first temperature at a speed of 2 ℃/min, controlling the pressure to be the first pressure, and performing first growth for 25 hours;
wherein the first temperature is 2100℃and the first pressure is 50mbar;
(d) Heating to a second temperature at a speed of 0.5 ℃/min, controlling the pressure to be the second pressure, and performing second growth for 110 hours;
wherein the second temperature is 2200 ℃, and the second pressure is 8mbar
(e) Nitrogen is filled to a pressure of 500mbar and cooled to room temperature to obtain silicon carbide crystals.
Example 2
The embodiment provides a seed crystal treatment method for silicon carbide crystal growth, which comprises the following steps:
(1) Heating a furnace in which seed crystals are positioned to 1000 ℃ in a nitrogen atmosphere with the volume fraction of 1% of silane, then introducing hydrogen for replacement, heating to 1500 ℃ for annealing etching, and maintaining the pressure at 10KPa for 50 hours;
(2) Polishing the annealed and etched seed crystal, and cleaning to eliminate transverse penetrating lines;
(3) Bonding the bonding surface of the seed crystal and graphite with the thickness of 1mm and the porosity of 10% by adopting a first binder, carbonizing for 15 hours at the temperature of 400 ℃, coating a second binder on the back surface of the graphite after carbonization, bonding with annular graphite paper with the porosity of 0.8%, and curing for 3 hours at the temperature of 400 ℃ to obtain the treated seed crystal;
the first binder is graphite glue, the second binder is graphite glue, and the mass ratio of the first binder to the second binder is 2:1.
The embodiment also provides a seed crystal treatment method for silicon carbide crystal growth, and then the silicon carbide crystal is grown on the treated seed crystal, which comprises the following specific steps:
(a) Bonding the treated seed crystal on the crucible cover in a manner that the bonding plate faces the crucible cover;
(b) Combining the crucible cover for fixing seed crystal and crucible containing silicon carbide raw material, placing into growth furnace, vacuum-pumping to pressure of 5×10 -3 Pa, then charging nitrogen as protective gas to a pressure of 100mbar;
(c) Heating to a first temperature at a speed of 3.5 ℃/min, controlling the pressure to be the first pressure, and carrying out first growth for 30 hours;
wherein the first temperature is 2000 ℃ and the first pressure is 10mbar;
(d) Heating to a second temperature at a speed of 2 ℃/min, controlling the pressure to be the second pressure, and performing second growth for 70h;
wherein the second temperature is 2250deg.C and the second pressure is 10mbar
(e) Nitrogen was introduced to a pressure of 200mbar and cooled to room temperature to give silicon carbide crystals.
Example 3
The embodiment provides a seed crystal treatment method for silicon carbide crystal growth, which comprises the following steps:
(1) Heating a furnace in which seed crystals are positioned to 1500 ℃ in a nitrogen atmosphere with the volume fraction of silane of 5%, then introducing hydrogen for replacement, heating to 2100 ℃ for annealing etching, and maintaining the pressure at 100KPa for 10 hours;
(2) Polishing the annealed and etched seed crystal, and cleaning to eliminate transverse penetrating lines;
(3) Bonding the bonding surface of the seed crystal and graphite with the thickness of 10mm and the porosity of 20% by adopting a first binder, carbonizing for 2 hours at the temperature of 1000 ℃, coating a second binder on the back surface of the graphite after carbonization, bonding with disc-shaped graphite paper with the porosity of 0.2%, and curing for 1.5 hours at the temperature of 1000 ℃ to obtain the treated seed crystal;
the first binder is photoresist, the second binder is organic glue, and the mass ratio of the first binder to the second binder is 1.1:1.
The embodiment also provides a seed crystal treatment method for silicon carbide crystal growth, and then the silicon carbide crystal is grown on the treated seed crystal, which comprises the following specific steps:
(a) Bonding the treated seed crystal on the crucible cover in a manner that the bonding plate faces the crucible cover;
(b) Combining the crucible cover for fixing seed crystal and crucible containing silicon carbide raw material, placing into growth furnace, vacuum-pumping to pressure of 5×10 -3 Pa, then charging nitrogen as protective gas to a pressure of 800mbar;
(c) Heating to a first temperature at a speed of 1 ℃/min, controlling the pressure to be the first pressure, and carrying out first growth for 50 hours;
wherein the first temperature is 2200 ℃, and the first pressure is 100mbar;
(d) Heating to a second temperature at a speed of 0.5 ℃/min, controlling the pressure to be the second pressure, and performing second growth for 200 hours;
wherein the second temperature is 2300 ℃, and the second pressure is 80mbar
(e) And (3) charging nitrogen to a pressure of 800mbar, and cooling to room temperature to obtain silicon carbide crystals.
Example 4
This example differs from example 1 in that the nitrogen atmosphere of step (1) does not contain silane.
The remaining preparation methods and parameters remain the same as in example 1.
Example 5
This example differs from example 1 in that the volume fraction of silane in the nitrogen atmosphere of step (1) is 10%.
The remaining preparation methods and parameters remain the same as in example 1.
Example 6
The present embodiment differs from embodiment 1 in that the mass ratio of the first binder to the second binder in step (3) is 0.4:1.
The remaining preparation methods and parameters remain the same as in example 1.
Example 7
The difference between this embodiment and embodiment 1 is that the mass ratio of the first binder to the second binder in step (3) is 6:1.
The remaining preparation methods and parameters remain the same as in example 1.
Example 8
This example differs from example 1 in that the porosity of the graphite in step (3) is 5%. The remaining preparation methods and parameters remain the same as in example 1.
Example 9
This example differs from example 1 in that the porosity of the graphite paper in step (3) is 5%. The remaining preparation methods and parameters remain the same as in example 1.
Example 10
This example differs from example 1 in that the carbonization temperature in step (3) is 100 ℃. The remaining preparation methods and parameters remain the same as in example 1.
Example 11
This example differs from example 1 in that the carbonization temperature in step (3) is 1300 ℃. The remaining preparation methods and parameters remain the same as in example 1.
Example 12
This example differs from example 1 in that the temperature of curing in step (3) is 100 ℃. The remaining preparation methods and parameters remain the same as in example 1.
Example 13
This example differs from example 1 in that the temperature of curing in step (3) is 1300 ℃.
The remaining preparation methods and parameters remain the same as in example 1.
Example 14
This example differs from example 1 in that step (d) is not performed.
The remaining preparation methods and parameters remain the same as in example 1.
Example 15
This example differs from example 1 in that step (c) is not performed.
The remaining preparation methods and parameters remain the same as in example 1.
Comparative example 1
The present comparative example is different from example 1 in that the curing treatment in step (3) was not performed, that is, graphite paper was not bonded to the back surface of graphite after carbonization.
The remaining preparation methods and parameters remain the same as in example 1.
Comparative example 2
This comparative example differs from example 1 in that the porosity of both graphite and graphite paper in step (3) was 15%.
The remaining preparation methods and parameters remain the same as in example 1.
Performance testing
The silicon carbide crystals prepared in the above examples and comparative examples were subjected to dislocation density testing.
Test conditions: each scheme is repeated for 5 times, cutting is carried out at a position which is 2mm away from the seed crystal surface, corrosion detection is carried out on the silicon surface, and the dislocation average value is obtained.
The test results are shown in Table 1.
TABLE 1
Analysis:
as can be seen from the table, the silicon carbide seed crystal is pretreated, so that the stress of the seed crystal is released, a foundation is laid for reducing dislocation defects of the crystal, and a compact protective layer is formed on the surface of the seed crystal, thereby effectively inhibiting dislocation proliferation; and then a secondary growth mode is adopted to grow on the seed crystal to obtain the silicon carbide crystal with low dislocation density, thereby greatly promoting the mass production process of the large-size silicon carbide crystal.
From the data of examples 1 and 4-5, it is clear that if the nitrogen atmosphere in step (1) does not contain silane, si atoms on the surface of the seed crystal largely escape during the etching and heating process, and a carbonized layer is formed on the surface to bring about new defects, thereby leading to proliferation of dislocation in the early growth stage; if the silane content in the nitrogen atmosphere of the step (1) is too high, the Si decomposed at high temperature is too high, so that the excessive Si is gathered on the surface of the seed crystal, the surface structure of the seed crystal is changed, and dislocation cannot be effectively inhibited in the early growth stage. As can be seen from the data results of examples 1 and 6-7, the use amount ratio of the first binder to the second binder is too small, so that a large amount of glue overflow is generated in the seed crystal curing process, the cleaning difficulty is increased, and the dislocation is not obviously influenced; and if the dosage ratio of the first adhesive to the second adhesive is too large, the second adhesive plate is easy to fall off in the growth process, so that the local temperature difference is too large, the stability of a growth interface is affected, and the local stress and dislocation are increased.
As can be seen from the data of examples 1 and 8-9, the porosity of the first bonding plate graphite is too small, so that the gas generated by the first binder in the carbonization process is not easy to be discharged, and a local gap is formed between the seed crystal and the bonding plate, so that the local temperature of the seed crystal is too high, and the protection effect on the seed crystal is reduced; the second adhesive agent can still infiltrate into the adhesive plate in a large amount if the porosity of the second adhesive plate graphite paper is too large, holes appear in the holes due to gas generation in the curing process, so that a compact protection layer cannot be formed on the seed crystal, an uneven air hole layer can still be generated on the back of the seed crystal in the growth process, multi-island nucleation even ablation in the initial growth stage is initiated, and dislocation is increased.
As is clear from the data of examples 1 and 10 to 11, the carbonization temperature is too low, so that the bonding force is reduced, the growth process is fallen off, an uneven air layer is formed between the seed crystal and the bonding plate, and the crystal stress and dislocation are increased; when the carbonization temperature is too high, si atoms on the surface of the seed crystal escape in the carbonization process, the surface structure of the seed crystal is destroyed, so that new defects are generated, and dislocation is proliferated in the early growth stage.
As is clear from the data of examples 1 and 12 to 13, the curing temperature is too low, the curing of the binder is insufficient, so that the bonding force is reduced, the falling off occurs in the growth process, and an uneven air layer is formed between the seed crystal and the bonding plate, and the crystal stress and dislocation are increased; when the curing temperature is too high, si atoms on the surface of the seed crystal escape in the curing process, the surface structure of the seed crystal is destroyed, new defects are generated, and dislocation is proliferated in the early growth stage.
From the data of examples 1 and 14-15, it is clear that the second growth rate is slightly higher and the growth direction in the etch pit is not uniform, which is not effective in inhibiting the extension of the axial defects into the crystal; without the second growth, however, the axial defects are merely eliminated from extending toward the crystal, and the vertical growth defects are not effectively reduced due to the non-uniformity of the growth direction.
As is apparent from the data of example 1 and comparative example 1, if graphite paper is not bonded to the back surface of graphite after carbonization, the gas generated during carbonization of the binder leaves pores of different depths due to the larger porosity of the first bonding plate, so that the local temperature difference of the seed crystal is larger, multi-island nucleation is easily formed in the early growth stage, and even ablation occurs, and dislocation proliferation occurs.
As can be seen from the data of example 1 and comparative example 2, if the porosities of the first adhesive plate and the second adhesive plate are equal, the adhesive can still penetrate into the second adhesive plate in a large amount due to the larger porosity, and holes appear in the pores caused by gas generation during carbonization, so that a dense protective layer cannot be formed, the protection effect on the seed crystal is reduced, an uneven air hole layer may be generated on the back of the seed crystal during growth, and multi-island nucleation even ablation in the early growth stage is initiated.
The applicant states that the process of the invention is illustrated by the above examples, but the invention is not limited to, i.e. it does not mean that the invention has to be carried out in dependence on the above examples. It should be apparent to those skilled in the art that any modification of the present invention, equivalent substitution of raw materials for the product of the present invention, addition of auxiliary components, selection of specific modes, etc., falls within the scope of the present invention and the scope of disclosure.
Claims (10)
1. A seed treatment method for silicon carbide crystal growth, the method comprising the steps of:
(1) Introducing etching gas into a container where the seed crystal is positioned, and performing annealing etching;
(2) Bonding the bonding surface of the seed crystal and a first bonding plate by adopting a first bonding agent, carbonizing, coating a second bonding agent on the back surface of the bonding plate, bonding with the second bonding plate, and curing to obtain the treated seed crystal;
wherein the porosity of the first adhesive sheet is greater than the porosity of the second adhesive sheet.
2. The method of claim 1, wherein the etching gas of step (1) is hydrogen;
preferably, the annealing etching pressure in the step (1) is 5-100KPa;
preferably, the annealing etching temperature in the step (1) is 1500-2100 ℃;
preferably, the heat preservation time of the annealing etching in the step (1) is 1-50h.
3. The method according to claim 1 or 2, wherein before the etching gas is introduced in the step (1), introducing inert gas containing silicon into a container where the seed crystal is located, and raising the temperature to reach a preheating temperature;
preferably, the silicon-containing inert gas comprises silane and nitrogen;
preferably, in the inert gas containing silicon, the volume fraction of silane is 0.1-5%;
preferably, the preheating temperature is 1000-1500 ℃.
4. A method according to any one of claims 1 to 3, wherein the seed crystal is polished and cleaned after the anneal etching of step (1).
5. The method of any one of claims 1-4, wherein the first binder of step (2) comprises any one or a combination of at least two of an organic gel, a graphite gel, or a photoresist;
preferably, the second binder of step (2) comprises an organic gum and/or a graphite gum;
preferably, the mass ratio of the first binder to the second binder in the step (2) is (1.1-3): 1;
preferably, the first and second adhesive sheets of step (2) independently comprise graphite paper or graphite, preferably graphite;
preferably, the thickness of the first adhesive plate in the step (2) is 0.1-10mm;
preferably, the first adhesive sheet of step (2) has a porosity of 10 to 20%;
preferably, the second adhesive plate in the step (2) is in a circular plate shape or a circular ring shape;
preferably, the porosity of the second adhesive sheet of step (2) is < 1%.
6. The method of any one of claims 1-5, wherein the carbonization of step (2) is at a temperature of 200-1200 ℃;
preferably, the carbonization time in the step (2) is 1-20h;
preferably, the temperature of the curing in step (2) is 200-1200 ℃;
preferably, the curing time of step (2) is from 0.5 to 10 hours.
7. The method according to any one of claims 1-6, characterized in that the method comprises the steps of:
heating a container in which a seed crystal is positioned to 1000-1500 ℃ in a nitrogen atmosphere with the volume fraction of silane of 0.1-5%, then introducing etching gas for replacement, heating to 1500-2100 ℃ for annealing etching, and maintaining the temperature for 1-50h and the pressure at 5-100KPa;
(II) polishing the seed crystal after annealing etching, and cleaning;
(III) bonding the bonding surface of the seed crystal and the first bonding plate by adopting a first bonding agent, carbonizing for 1-20h at the temperature of 200-1200 ℃, coating a second bonding agent on the back surface of the first bonding plate after carbonization, bonding with the second bonding plate, and curing for 0.5-10h at the temperature of 200-1200 ℃ to obtain the treated seed crystal;
wherein the first bonding plate and the second bonding plate independently comprise graphite paper or graphite, the thickness of the first bonding plate is 0.1-10mm, the porosity is 10-20%, the second bonding plate is in a round plate shape or a circular ring shape, the porosity is less than 1%, and the mass ratio of the first bonding agent to the second bonding agent is (1.1-3): 1.
8. A method for growing a silicon carbide crystal, comprising the steps of:
seed crystal for silicon carbide crystal growth is treated by the seed crystal treatment method according to any one of claims 1 to 7, and then a silicon carbide crystal is grown on the treated seed crystal.
9. The growth method according to claim 8, characterized in that the specific steps of the growth method comprise:
(a) Fixing the treated seed crystal on the crucible cover in a manner that the bonding plate faces the crucible cover;
(b) Combining a crucible cover for fixing seed crystals and a crucible filled with silicon carbide raw materials, placing the combined materials into a growth furnace, vacuumizing, and then filling protective gas;
(c) Performing a first growth under conditions of a first temperature and a first pressure;
(d) Performing a second growth under conditions of a second temperature and a second pressure;
(e) And (5) charging protective gas, and cooling to obtain the silicon carbide crystal.
10. The growth method according to claim 9, wherein the fixing means of step (a) comprises a mechanical method or a bonding method;
preferably, the vacuum is applied in step (b) to a pressure of < 10 -2 Pa；
Preferably, said protective gas is introduced in step (b) to a pressure of 10-800mbar, preferably 200-700mbar;
preferably, the first temperature of step (c) is 1800-2200 ℃;
preferably, the temperature rising rate of the first temperature in the step (c) is 1-5 ℃/min;
preferably, said first pressure of step (c) is in the range 1 to 100mbar, preferably 10 to 50mbar;
preferably, the time of the first growth of step (c) is from 1 to 50 hours, preferably from 10 to 30 hours;
preferably, the second temperature of step (d) is in the range of 2000-2300 ℃;
preferably, the second temperature in step (d) has a heating rate of 0.5-3 ℃/min;
preferably, said second pressure of step (d) is in the range of 0.2 to 80mbar, preferably 1 to 20mbar;
preferably, the second growth of step (d) takes from 10 to 200 hours, preferably from 70 to 150 hours;
preferably, said protective gas is introduced in step (e) to a pressure of 200-800mbar;
preferably, the temperature after cooling in step (e) is room temperature.
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