CN112144110B - Growth method for growing silicon carbide crystal by PVT (physical vapor transport) method - Google Patents
Growth method for growing silicon carbide crystal by PVT (physical vapor transport) method Download PDFInfo
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- CN112144110B CN112144110B CN202011011423.5A CN202011011423A CN112144110B CN 112144110 B CN112144110 B CN 112144110B CN 202011011423 A CN202011011423 A CN 202011011423A CN 112144110 B CN112144110 B CN 112144110B
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- 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
- C30B23/002—Controlling or regulating
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- 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 growth method for growing silicon carbide crystals by a PVT method, which comprises the following steps: providing a crucible; placing a silicon carbide raw material and seed crystals in a crucible; putting the crucible into a growth chamber, vacuumizing, introducing protective gas, and setting the temperature of the chamber; raising the temperature to a first preset temperature, introducing chlorine-containing gas through a gas dredging device in the crucible, raising the temperature to a second preset temperature, and stopping introducing or continuing introducing the chlorine-containing gas for a first preset time; and raising the temperature to a third preset temperature, and annealing the silicon carbide crystal after the silicon carbide crystal starts to grow for a second preset time to obtain the silicon carbide crystal. The growth method can effectively control the release rate and uniformity of the chlorine-containing gas, and avoid the formation of crystal defects caused by the condensation of gas-phase silicon on the surface of the crystal; the crystallization defect can be further avoided by controlling the introduction time and the flow of the chlorine-containing gas; the porous graphite block is arranged to allow the escape of the introduced excessive chlorine-containing gas and carbon particles suspended in the growing atmosphere, and reduce the defects of carbon inclusions in the crystal.
Description
Technical Field
The invention relates to the technical field of silicon carbide crystal preparation, in particular to a growth method for growing silicon carbide crystals by a PVT (physical vapor transport) method.
Background
Compared with a silicon-based semiconductor, a third-generation semiconductor represented by silicon carbide has the characteristics of high forbidden bandwidth, high saturated electron mobility, high breakdown electric field strength, high thermal conductivity and the like, has superior performances of high frequency, high temperature resistance, chemical corrosion resistance, high efficiency, strong radiation resistance, high pressure resistance and the like, and becomes a support material for core electronic devices in the fields of intelligent communication, new energy automobiles, aerospace, internet of things, intelligent transportation, intelligent power grids, nuclear energy technology, petroleum exploration and mining and the like along with the increasing maturity of the silicon carbide semiconductor preparation technology.
The silicon carbide crystal can be prepared by High Temperature Chemical Vapor Deposition (HTCVD), Liquid phase epitaxy (Liquid phase epitaxy), and Physical Vapor Transport (PVT) methods. The currently common method for preparing crystals is the PVT method. The PVT method, i.e., the modified Lely method, is, as shown in fig. 1, to sublimate a silicon carbide raw material 102 in a high temperature region, to transport the gas phase to a silicon carbide seed crystal 100 with a lower temperature under the drive of an axial temperature gradient to become saturated vapor, to form a silicon carbide crystal through condensation nucleation, growth and recrystallization. The PVT method has the advantages of low cost and flexible temperature field adjustment, and can obviously improve the growth quality of the crystal by changing the heat preservation design. When the PVT method is adopted to prepare the silicon carbide crystal, the silicon carbide raw material is decomposed and sublimated along with the temperature rise to 1800 ℃, and the decomposition reaction equation is as follows:
in the above-mentioned formula, the compound of formula,
is the equilibrium constant of reaction equation n; piIs the equilibrium partial pressure of the i component, viAre the equation coefficients for the i component. From the thermodynamic equation for equilibrium constants:
in the formula, hi0And si0Is the ideal gas molar enthalpy constant and molar entropy constant of the i component; c. CpiIs the ideal gas constant-pressure molar heat capacity of the i component. Calculation of the equilibrium constant to obtain SiC2、Si、Si2Equilibrium partial pressure of C. As known from the literature (weapon materials science and engineering, 2013, 36(6):72-74), the equilibrium partial pressure of Si is far greater than that of Si2C and SiC2Therefore, in the initial stage of crystal growth, the growth atmosphere is rich in gas-phase silicon. Under the action of axial temperature gradient, steam is conveyed to a low-temperature seed crystal area, the saturated vapor pressure of the silicon-rich gas phase is reduced, and the silicon-rich gas phase is condensed into liquid-phase silicon, so that crystal crystallization defects are caused.
The silicon vapor has high chemical activity at high temperature, and can react with halogen and hydrogen halide to generate halide, and also react with nonmetal such as carbon, nitrogen, oxygen and the like to generate silicide. The excess silicon vapor at the initial stage of crystal growth can be consumed by introducing chlorine gas and hydrogen chloride gas into the growth atmosphere. At high temperature, the reaction equation of the silicon vapor, chlorine and hydrogen chloride is as follows:
Si(g)+Cl2(g)→SiCl4(g)
Si(g)+HCl(g)→SiHCl3(g)+H2(g)
however, the silicon carbide crystal formed by introducing the gas capable of reacting with silicon vapor at a high temperature into the silicon carbide raw material still has crystal defects, and the quality of the silicon carbide crystal is low.
Disclosure of Invention
In view of the above drawbacks of the prior art, an object of the present invention is to provide a growth method for growing a silicon carbide crystal by a PVT method, which is used to solve the problem that when the silicon carbide crystal is formed by the PVT method in the prior art, silicon-rich vapor deposition condenses on the crystal surface into silicon droplets to form crystal defects, which results in lower growth quality of the silicon carbide crystal.
In order to achieve the above and other related objects, the present invention provides a growth method for growing silicon carbide crystals by the PVT method, the growth method comprising:
providing a crucible for growing silicon carbide crystals by a PVT method, wherein the crucible comprises: the graphite crucible comprises a graphite crucible body, a graphite crucible cover, a porous graphite plate and an air-dredging device; the graphite crucible body comprises a bottom wall and a side wall extending from the bottom wall, and an accommodating cavity is defined by the bottom wall and the side wall; the graphite crucible cover covers the graphite crucible body to realize the sealing of the accommodating cavity; the porous graphite plate is arranged in the accommodating cavity, and the porous graphite plate is completely contacted with the side wall of the graphite crucible body in the circumferential direction; the gas-distributing device is arranged between the bottom wall of the graphite crucible body and the porous graphite plate, and is formed by laminating hollow porous graphite pipes and graphite soft felts which are sequentially and alternately arranged with the transverse shaft from inside to outside;
placing a silicon carbide raw material on a porous graphite plate in the crucible and placing a silicon carbide seed crystal above an accommodating cavity of the crucible;
placing the crucible into a silicon carbide single crystal growth chamber;
vacuumizing the silicon carbide single crystal growth chamber, introducing protective gas, setting the temperature of the chamber, and starting to heat;
when the temperature rises to a first preset temperature, introducing chlorine-containing gas into the accommodating cavity of the crucible through the gas dredging device in the crucible, when the temperature rises to a second preset temperature, stopping introducing the chlorine-containing gas, or after the temperature rises to the second preset temperature, continuing introducing the chlorine-containing gas for a first preset time, and then stopping introducing the chlorine-containing gas;
and when the temperature rises to a third preset temperature, the silicon carbide crystal starts to grow and stably grows for a second preset time, and then the required silicon carbide crystal is obtained through annealing treatment.
Optionally, the shielding gas comprises argon or helium.
Optionally, the chlorine-containing gas comprises chlorine gas or hydrogen chloride gas or a mixed gas of argon and chlorine gas or a mixed gas of argon and hydrogen chloride gas.
Optionally, the chlorine-containing gas is a mixture of 1: 5, the volume ratio of the mixed gas of hydrogen chloride gas and argon gas is 1: 3 of chlorine and argon.
Optionally, the flow rate of the chlorine-containing gas is between 2ml/min and 20 ml/min.
Optionally, the first preset temperature is 1750-1850 ℃, the second preset temperature is 2150-2250 ℃, the third preset temperature is 2300-2400 ℃, the first preset time is 10-15 min, and the second preset time is 25-33 h.
Optionally, the graphite crucible cover is further provided with two porous graphite blocks penetrating through the graphite crucible cover, and the two porous graphite blocks are arranged on two sides of the silicon carbide seed crystal projected on the graphite crucible cover region.
Optionally, the porosity of the hollow porous graphite tube increases gradually from the inside to the outside.
Optionally, the graphite crucible body has an outer diameter of 140mm to 180mm and a thickness of 6mm to 18 mm; the air-dredging device is formed by stacking 5 layers of the hollow porous graphite tube and the graphite soft felt.
Optionally, the outer diameter of the innermost layer of the hollow porous graphite tube is between 10mm and 20 mm; the wall thickness of the hollow porous graphite tube is between 2mm and 10 mm; the porosity of the hollow porous graphite tube is between 35% Vol% and 60% Vol%; the thickness of the graphite soft felt is between 2mm and 8 mm; the thickness of the porous graphite plate is between 5mm and 10mm, and the porosity is between 30 percent Vol percent and 55 percent Vol percent; the diameter of the porous graphite block is between 4mm and 10mm, and the porosity is between 35 percent Vol percent and 50 percent Vol percent; the gas dredging device is arranged at a position 2 mm-10 mm above the bottom wall of the graphite crucible body; the porous graphite plate is arranged at the position 5 mm-20 mm above the air-dredging device.
As mentioned above, the growth method for growing the silicon carbide crystal by the PVT method of the invention adopts the multilayer coaxial gas dredging device formed by alternately laminating and coating the hollow porous graphite tube and the graphite soft felt, so that the introduced chlorine-containing gas is uniformly released into a growth system through the evacuation of materials with different porosities, thereby effectively controlling the release rate and uniformity of the chlorine-containing gas and avoiding the formation of crystal defects caused by the condensation of gas-phase silicon on the crystal surface; in addition, the chlorine-containing gas can completely react with the redundant silicon vapor in the initial growth stage of the crystal by controlling the introduction time and the flow rate of the chlorine-containing gas, so that the crystallization defect formed by the condensation of gas-phase silicon on the surface of the crystal is further avoided; and moreover, the arrangement of the porous graphite block can enable the introduced redundant chlorine-containing gas and carbon particles suspended in the growing atmosphere to escape, so that the defects of carbon inclusions in the crystal are reduced to a certain extent, and the quality of the silicon carbide crystal is improved.
Drawings
FIG. 1 shows a schematic diagram of a crucible for growing silicon carbide crystals by the conventional PVT method.
FIG. 2 shows a top view of a crucible for growing silicon carbide crystals by the PVT method of the present invention.
FIG. 3 is a schematic cross-sectional view of a crucible for growing silicon carbide crystals by the PVT method of the present invention.
FIG. 4 is a schematic cross-sectional view along AA in FIG. 3 of an apparatus for evacuating gas from a crucible for growing silicon carbide crystals by the PVT method of the present invention.
Description of the element reference numerals
100 silicon carbide seed crystal
101 graphite crucible
102 silicon carbide feedstock
1 graphite crucible body
10 bottom wall
11 side wall
12 containing cavity
2 graphite crucible cover
3 porous graphite plate
4 air-dredging device
40 hollow porous graphite tube
41 graphite soft felt
42 hollow shaft
5 porous graphite block
6 silicon carbide seed crystal
7 silicon carbide feedstock
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Please refer to fig. 2 to 4. It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the present invention, and the drawings only show the components related to the present invention rather than being drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of each component in actual implementation may be changed according to actual needs, and the layout of the components may be more complicated.
Example one
As described in the background art, in the initial growth stage of a silicon carbide crystal, a growth atmosphere is rich in gas-phase silicon, steam is conveyed to a low-temperature silicon carbide seed crystal region under the action of an axial temperature gradient, the saturated vapor pressure of the silicon-rich gas phase is reduced, and the silicon-rich gas phase is condensed into liquid-phase silicon to cause the crystal crystallization defect. However, the silicon carbide crystals produced by this method still have crystalline defects.
Based on the problems and the detailed analysis of various factors, the inventor determines that the main reason for causing the crystal defects of the silicon carbide crystal is poor uniformity and unstable release rate of chlorine-containing gas entering a growth system, and based on the fact, provides a crucible suitable for growing the silicon carbide crystal by a PVT method, wherein an air dredging device is additionally arranged in the crucible, and the chlorine-containing gas can be uniformly introduced into the growth system of the silicon carbide by the air dredging device at a controllable release rate in the process of growing the silicon carbide crystal by the PVT method, so that the condensation of gas phase silicon on the surface of the silicon carbide crystal to form crystal defects is avoided, and the growth quality of the silicon carbide crystal is improved.
As shown in fig. 2 to 3, the crucible includes: a graphite crucible body 1, a graphite crucible cover 2, a porous graphite plate 3 and an air-dredging device 4;
the graphite crucible body 1 comprises a bottom wall 10 and a side wall 11 extending from the bottom wall 10, and an accommodating cavity 12 is enclosed by the bottom wall 10 and the side wall 11 (shown in FIG. 3);
the graphite crucible cover 2 is covered on the graphite crucible body 1 to realize the sealing of the accommodating cavity 12 (as shown in fig. 2);
the porous graphite plate 3 is arranged in the accommodating cavity 12, and the porous graphite plate 3 is completely contacted with the side wall 11 of the graphite crucible body 1 in the circumferential direction (as shown in FIG. 3);
the gas distributing device 4 is arranged between the bottom wall 10 of the graphite crucible body 1 and the porous graphite plate 3 (as shown in fig. 3), and the gas distributing device 4 is formed by stacking a hollow porous graphite tube 40 and a graphite soft felt 41 which are sequentially arranged with a cross shaft from inside to outside in turn.
The gas dredging device 4 is formed by laminating hollow porous graphite pipes 40 and graphite soft felts 41 which are alternately arranged in sequence, chlorine-containing gas uniformly enters a crystal growth system at a controllable release rate after passing through the laminated structure, so that the chlorine-containing gas and saturated silicon steam are fully and uniformly reacted, the crystallization defect caused by condensation of gas-phase silicon on the surface of the silicon carbide crystal is effectively avoided, and the growth quality of the silicon carbide crystal is improved.
For example, the number of the laminated layers of the hollow porous graphite tube 40 and the graphite soft felt 41 in the gas evacuation device 4 is determined according to the inner diameter of the graphite crucible body 1, and preferably 4 to 26 layers, and more preferably 4 to 8 layers may be provided. The hollow porous graphite tube 40 and the graphite soft felt 41 are only required to be coaxially arranged, so that the shape is not limited, and the hollow porous graphite tube 40 and the graphite soft felt 41 can be arranged in a cylindrical shape in consideration of the preparation difficulty and cost.
As shown in fig. 2 and 3, the graphite crucible cover 2 is further provided with two porous graphite blocks 5 penetrating the graphite crucible cover 2, and the two porous graphite blocks 5 are provided on both sides of a region where the silicon carbide seed crystal 6 is projected on the graphite crucible cover 2. Because silicon steam not only can cause the crystallization defect, also can react with graphite simultaneously, set up porous graphite piece can carry the tiny carbon particle of suspension in the atmosphere of growing through this porous graphite piece to grow the system loss, avoids the formation of carbon inclusion in the crystal, further improves the growth quality of silicon carbide crystal.
As an example, the porosity of the hollow porous graphite tube 40 in the gas dispersing device 4 increases gradually from the inside to the outside. Considering the gradient diffusion of the gas, the gradual increase of the porosity can ensure that the gas is dispersed more uniformly, and the local aggregation phenomenon is reduced.
As shown in fig. 2 to 4, the graphite crucible body 1 has an outer diameter of 140mm to 180mm and a thickness of 6mm to 18mm, as an example; the air-dredging device 4 is formed by stacking 5 layers of the hollow porous graphite tube 40 and the graphite soft felt 41. Preferably, the outer diameter of the innermost layer of the hollow porous graphite tube 40 is between 10mm and 20 mm; the wall thickness of the hollow porous graphite tube 40 is between 2mm and 10 mm; the porosity of the hollow porous graphite tube 40 is between 35% Vol% and 60% Vol%; the thickness of the graphite soft felt 41 is between 2mm and 8 mm; the thickness of the porous graphite plate 3 is between 5mm and 10mm, and the porosity is between 30 percent Vol percent and 55 percent Vol percent; the diameter of the porous graphite block 5 is between 4mm and 10mm, and the porosity is between 35 percent Vol percent and 50 percent Vol percent; the gas dredging device 4 is arranged at the position 2 mm-10 mm above the bottom wall 10 of the graphite crucible body 1; the porous graphite plate 3 is arranged at the position 5 mm-20 mm above the air-dredging device 4. The thickness of the hollow porous graphite tube 40 and the graphite soft felt 41 are matched to effectively control the release rate of the gas, and then the gas can be uniformly released into a growth system by matching with the porosity of the hollow porous graphite tube 40. The gas distributing device is arranged on the bottom wall of the graphite crucible body and keeps a certain distance, the gas distributing device is arranged on the porous graphite plate and keeps a certain distance, and the gas distributing device is mainly used for avoiding gas from coming out of the gas distributing device and enabling gas to be blocked to enable gas to be turbulent, so that gas can not uniformly enter a growth system.
By way of example, the porous graphite plate 3 may be connected to the graphite crucible body 1 in any suitable manner, for example by a threaded or embedded connection. The porous graphite plate 3 is completely contacted with the side wall 11 of the graphite crucible body 1 in the circumferential direction, so that firstly, the silicon carbide raw material is prevented from falling into the gas dredging device, and secondly, the chlorine-containing gas is prevented from entering a growth system from a gap between the silicon carbide raw material and the gas dredging device, so that the chlorine-containing gas is not uniformly released.
By way of example, the graphite soft felt 41 may be a pitch-based, polyacrylonitrile-based (PAN) graphite felt, or a viscose-based graphite felt.
Example two
The present embodiment provides a method for growing a silicon carbide crystal, which is implemented based on the crucible for growing a silicon carbide crystal by the PVT method described in the first embodiment, and for the beneficial effects that the crucible can achieve, reference may be made to the first embodiment, which is not described in detail below.
As shown in fig. 2 to 4, the growth method includes the steps of:
1) providing a crucible for growing silicon carbide crystals by the PVT method according to the embodiment, placing a silicon carbide raw material 7 on a porous graphite plate 3 in the crucible, and placing a silicon carbide seed crystal 6 above a containing cavity 12 of the crucible;
2) placing the crucible into a silicon carbide single crystal growth chamber, wherein the silicon carbide single crystal growth chamber is mainly used for heating, the growth temperature of the silicon carbide single crystal is above 2000 ℃, eddy current heating is adopted, namely, an induction coil is placed around the silicon carbide single crystal growth chamber, and the silicon carbide raw material is heated by electrifying induction heating;
3) vacuumizing the silicon carbide single crystal growth chamber, introducing protective gas, setting the temperature of the chamber, and starting to heat;
4) when the temperature rises to a first preset temperature, introducing chlorine-containing gas into the accommodating cavity 12 of the crucible through the gas dredging device 4 in the crucible, when the temperature rises to a second preset temperature, stopping introducing the chlorine-containing gas, or after the temperature rises to the second preset temperature, continuing introducing the chlorine-containing gas for a first preset time, and then stopping introducing the chlorine-containing gas;
5) and when the temperature rises to a third preset temperature, the silicon carbide crystal starts to grow and stably grows for a second preset time, and then the required silicon carbide crystal is obtained through annealing treatment.
Chlorine-containing gas uniformly enters a crystal growth system at a controllable release rate after passing through the gas dredging device, and the chlorine-containing gas and saturated silicon steam are fully and uniformly reacted, so that the crystallization defect caused by condensation of gas-phase silicon on the surface of the silicon carbide crystal is effectively avoided; in addition, since the silicon-rich vapor not only causes crystal defects, but also reacts with graphite, and has a corrosive effect on the crucible, the reaction equation is as follows:
the chlorine-containing gas is introduced to consume the silicon-rich steam, so that the crucible is prevented from being corroded by the silicon steam; furthermore, the timing of introducing the chlorine-containing gas is maintained before the silicon carbide crystal starts and grows stably, and the excessive consumption of the silicon vapor by the chlorine-containing gas is ensured while the silicon-rich vapor is consumed, because the proper carbon-silicon ratio can obtain the silicon carbide single crystal with better quality.
By way of example, the shielding gas comprises argon or helium. The protective gas is used as gas protection for the growth of the silicon carbide crystals so as to avoid side reactions.
As an example, the chlorine-containing gas includes chlorine gas or hydrogen chloride gas or a mixed gas of argon and chlorine gas or a mixed gas of argon and hydrogen chloride gas. Preferably, the chlorine-containing gas is a mixture of 1: 5, the volume ratio of the mixed gas of hydrogen chloride gas and argon gas is 1: 3 of chlorine and argon. The density of effective reaction gas can be adjusted by adding argon inert gas into the chlorine-containing gas, the unit time input amount of the effective reaction gas is controlled, the reaction rate is further controlled, and the controllable reaction degree is realized.
As an example, the flow rate of the chlorine-containing gas is between 2ml/min and 20 ml/min.
By way of example, the first preset temperature is 1750-1850 ℃, the second preset temperature is 2150-2250 ℃, the third preset temperature is 2300-2400 ℃, the first preset time is 10-15 min, and the second preset time is 25-33 h.
As an example, when the silicon carbide single crystal growth chamber is vacuumized, the vacuum degree is pumped to be below 10 Pa.
The method for growing a silicon carbide crystal according to the present example is further described below with reference to 3 test examples.
Test example 1
The growing method comprises the following steps:
1) a gas-dredging device 4 is horizontally arranged at a position 4mm away from the inner surface of the bottom wall 10 of the graphite crucible body 1;
2) placing a porous graphite plate 3 at a position 8mm above an air-dredging device 4 arranged in a graphite crucible body 1, and ensuring that the side surface of the porous graphite plate 3 is completely contacted with the inner wall of a side wall 12 of the graphite crucible body 1;
3) placing a silicon carbide raw material 7 on a porous graphite plate 3 arranged in a graphite crucible body 1;
4) arranging a silicon carbide seed crystal 6 at the top of a graphite crucible body 1, and putting the crucible into a silicon carbide single crystal growth chamber;
5) two porous graphite blocks 5 are arranged on the graphite crucible cover 2, and the two porous graphite blocks 5 are distributed on two sides of the silicon carbide seed crystal 6;
6) pumping the vacuum degree of a silicon carbide single crystal growth chamber to 3Pa, introducing argon, setting the temperature of the chamber, and starting to heat;
7) raising the temperature to 1800 ℃, introducing chlorine into the crucible through a hollow shaft 42 of the gas dredging device 4, wherein the gas flow rate is 2ml/min, raising the temperature to 2200 ℃, and stopping introducing the chlorine;
8) and raising the temperature to 2300 ℃, and annealing and cooling the silicon carbide crystal after the silicon carbide crystal starts to grow and stably grows for 26 hours to obtain the high-quality silicon carbide crystal.
In this test example, the parameters of the crucible were set as follows: the graphite crucible body 1 has an outer diameter of 180mm and a thickness of 10 mm; the diameter of the porous graphite block 5 is 10mm, the porosity is 40% Vol%, and the existence of the porous graphite block 5 can lead the introduced redundant chlorine and SiCl which is a reaction product of silicon vapor and chlorine4To avoid its impact on the quality of the growing crystal; meanwhile, free carbon can be carried by the escape of the gas, so that the free carbon is prevented from being attached to the surface of the crystal to form a carbon wrap; the diameter of the porous graphite plate 3 is 160mm, the thickness is 6mm, and the porosity is 45%Vol%; the air-dredging device 4 is formed by laminating 5 layers of hollow porous graphite tubes 40 and graphite soft felt 41, the outer diameter of the innermost layer of the hollow porous graphite tube 40 is 20mm, the wall thickness is 3mm, and the porosity is 35% Vol%; the thickness of the second layer of graphite soft felt 41 is 5 mm; the wall thickness of the third layer of hollow porous graphite tube 40 is 6mm, and the porosity is 40% Vol; the thickness of the fourth layer of graphite soft felt 41 is 5 mm; the wall thickness of the fifth layer hollow porous graphite tube 40 is 6mm, and the porosity is 50% Vol. Chlorine gas is effectively dispersed and uniformly released into a growth system under the action of hollow porous graphite tubes with different porosities and the graphite soft felt, and reacts with redundant silicon vapor in the initial growth stage, so that silicon drop defects caused by silicon vapor deposition are remarkably reduced; meanwhile, under the action of gas, fine graphite particles suspended in the growth system are dissipated through porous graphite blocks at the top of the graphite crucible, so that the formation of carbon inclusions in crystals is reduced.
Test example 2
The growing method comprises the following steps:
1) a gas-dredging device 4 is horizontally arranged at a position 6mm away from the inner surface of the bottom wall 10 of the graphite crucible body 1;
2) placing a porous graphite plate 3 at a position 6mm above an air-dredging device 4 arranged in a graphite crucible body 1, and ensuring that the side surface of the porous graphite plate 3 is completely contacted with the inner wall of a side wall 12 of the graphite crucible body 1;
3) placing a silicon carbide raw material 7 on a porous graphite plate 3 arranged in a graphite crucible body 1;
4) arranging a silicon carbide seed crystal 6 at the top of a graphite crucible body 1, and putting the crucible into a silicon carbide single crystal growth chamber;
5) two porous graphite blocks 5 are arranged on the graphite crucible cover 2, and the two porous graphite blocks 5 are distributed on two sides of the silicon carbide seed crystal 6;
6) pumping the vacuum degree of a silicon carbide single crystal growth chamber to 2Pa, introducing argon, setting the temperature of the chamber, and starting to heat;
7) the temperature is raised to 1800 ℃, and the crucible is aerated by a hollow shaft 42 of an air-dredging device 4 according to the volume ratio of 1: 3, the flow rate of the mixed gas of chlorine and argon is 4ml/min, the temperature is raised to 2200 ℃, and the mixed gas of chlorine and argon is stopped to be introduced after the mixed gas is continuously introduced for 10 min;
8) and raising the temperature to 2400 ℃, starting to grow and stably growing the silicon carbide crystal for 30 hours, and annealing and cooling to obtain the high-quality silicon carbide crystal.
The crucible used in this test example was the same as the crucible used in test example 1, and compared to test example 1, the chlorine-containing gas introduced in this test example was a mixed gas of chlorine and argon, and the volume ratio was adjusted to 1: 3, through control gas letting in time, can effectively control the reaction degree of unnecessary silicon steam and chlorine in the growth atmosphere under the high temperature, free carbon in the growth atmosphere simultaneously passes through porous graphite piece loss under the air current effect, has avoided the formation of carbon parcel thing.
Test example 3
The growing method comprises the following steps:
1) a gas-dredging device 4 is horizontally arranged at a position 5mm away from the inner surface of the bottom wall 10 of the graphite crucible body 1;
2) placing a porous graphite plate 3 at a position 6mm above an air-dredging device 4 arranged in a graphite crucible body 1, and ensuring that the side surface of the porous graphite plate 3 is completely contacted with the inner wall of a side wall 12 of the graphite crucible body 1;
3) placing a silicon carbide raw material 7 on a porous graphite plate 3 arranged in a graphite crucible body 1;
4) arranging a silicon carbide seed crystal 6 at the top of a graphite crucible body 1, and putting the crucible into a silicon carbide single crystal growth chamber;
5) two porous graphite blocks 5 are arranged on the graphite crucible cover 2, and the two porous graphite blocks 5 are distributed on two sides of the silicon carbide seed crystal 6;
6) pumping the vacuum degree of a silicon carbide single crystal growth chamber to 2Pa, introducing helium, setting the temperature of the chamber, and starting to heat;
7) the temperature is raised to 1800 ℃, and the crucible is aerated by a hollow shaft 42 of an air-dredging device 4 according to the volume ratio of 1: 5, the flow rate of the mixed gas of hydrogen chloride gas and argon is 6ml/min, the temperature is raised to 2200 ℃, and the mixed gas of hydrogen chloride gas and argon is stopped being introduced after the mixed gas is continuously introduced for 15 min;
8) and raising the temperature to 2400 ℃, starting to grow and stably growing the silicon carbide crystal for 32 hours, and annealing and cooling to obtain the high-quality silicon carbide crystal.
In this test example, the parameters of the crucible were set as follows: the graphite crucible body 1 has the outer diameter of 180mm and the thickness of 8 mm; the diameter of the porous graphite block 5 is 8mm, the porosity is 40% Vol%, and the existence of the porous graphite block 5 can lead the introduced redundant chlorine and SiCl which is a reaction product of silicon vapor and chlorine4To avoid its impact on the quality of the growing crystal; meanwhile, free carbon can be carried by the escape of the gas, so that the free carbon is prevented from being attached to the surface of the crystal to form a carbon wrap; the diameter of the porous graphite plate 3 is 164mm, the thickness is 5mm, and the porosity is 40% Vol%; the air-dredging device 4 is formed by laminating 5 layers of hollow porous graphite tubes 40 and graphite soft felt 41, the outer diameter of the innermost layer of the hollow porous graphite tube 40 is 18mm, the wall thickness is 3mm, and the porosity is 35% Vol%; the thickness of the second layer of graphite soft felt 41 is 5 mm; the wall thickness of the third layer of hollow porous graphite tube 40 is 6mm, and the porosity is 45% Vol; the thickness of the fourth layer of graphite soft felt 41 is 5 mm; the wall thickness of the fifth layer hollow porous graphite tube 40 is 6mm, and the porosity is 60% Vol. The volume ratio of the introduced chlorine-containing gas is 1: 5, the chlorine-containing gas is uniformly released into a growth system through the hollow porous graphite tube with different porosities and the graphite soft felt, and reacts with the redundant silicon vapor in the initial growth stage, so that the crystal defects are reduced.
In summary, the present embodiment provides a crucible for growing silicon carbide crystals by PVT method and a method for growing silicon carbide crystals, wherein a multi-layer coaxial gas evacuation device formed by alternately laminating and coating hollow porous graphite tubes and graphite soft felt is adopted, so that introduced chlorine-containing gas is uniformly released into a growth system through evacuation of materials with different porosities, thereby effectively controlling the release rate and uniformity of chlorine-containing gas, and avoiding the formation of crystal defects due to condensation of gas phase silicon on the crystal surface; in addition, the chlorine-containing gas can completely react with the redundant silicon vapor in the initial growth stage of the crystal by controlling the introduction time and the flow rate of the chlorine-containing gas, so that the crystallization defect formed by the condensation of gas-phase silicon on the surface of the crystal is further avoided; and moreover, the arrangement of the porous graphite block can enable the introduced redundant chlorine-containing gas and carbon particles suspended in the growing atmosphere to escape, so that the defects of carbon inclusions in the crystal are reduced to a certain extent, and the quality of the silicon carbide crystal is improved. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (7)
1. A growth method for growing a silicon carbide crystal by a PVT method, the growth method comprising:
providing a crucible for growing silicon carbide crystals by a PVT method, wherein the crucible comprises: the graphite crucible comprises a graphite crucible body, a graphite crucible cover, a porous graphite plate and an air-dredging device; the graphite crucible body comprises a bottom wall and a side wall extending from the bottom wall, and an accommodating cavity is defined by the bottom wall and the side wall; the graphite crucible cover covers the graphite crucible body to realize the sealing of the accommodating cavity; the porous graphite plate is arranged in the accommodating cavity, and the porous graphite plate is completely contacted with the side wall of the graphite crucible body in the circumferential direction; the gas-distributing device is arranged between the bottom wall of the graphite crucible body and the porous graphite plate, and is formed by laminating hollow porous graphite pipes and graphite soft felts which are sequentially and alternately arranged with the transverse shaft from inside to outside; the graphite crucible cover is also provided with two porous graphite blocks which penetrate through the graphite crucible cover, and the two porous graphite blocks are arranged on two sides of the silicon carbide seed crystal projected on the graphite crucible cover region;
placing a silicon carbide raw material on the porous graphite plate in the crucible and placing a silicon carbide seed crystal above the containing cavity of the crucible;
placing the crucible into a silicon carbide single crystal growth chamber;
vacuumizing the silicon carbide single crystal growth chamber, introducing protective gas, setting the temperature of the chamber, and starting to heat;
when the temperature rises to a first preset temperature, introducing chlorine-containing gas into the accommodating cavity of the crucible through the gas dredging device in the crucible, when the temperature rises to a second preset temperature, stopping introducing the chlorine-containing gas, or after the temperature rises to the second preset temperature, continuing introducing the chlorine-containing gas for a first preset time, and then stopping introducing the chlorine-containing gas; wherein the flow rate of the chlorine-containing gas is between 2ml/min and 20 ml/min; the first preset temperature is 1750-1850 ℃, the second preset temperature is 2150-2250 ℃, the third preset temperature is 2300-2400 ℃, the first preset time is 10-15 min, and the second preset time is 25-33 h;
and when the temperature rises to a third preset temperature, the silicon carbide crystal starts to grow and stably grows for a second preset time, and then the required silicon carbide crystal is obtained through annealing treatment.
2. The growth method of a silicon carbide crystal by PVT method according to claim 1, wherein: the shielding gas comprises argon or helium.
3. The growth method of a silicon carbide crystal by PVT method according to claim 1, wherein: the chlorine-containing gas comprises chlorine gas or hydrogen chloride gas or a mixed gas of argon gas and chlorine gas or a mixed gas of argon gas and hydrogen chloride gas.
4. The growth method of a silicon carbide crystal by PVT method according to claim 3, wherein: the chlorine-containing gas is mixed with the chlorine-containing gas in a volume ratio of 1: 5, the volume ratio of the mixed gas of hydrogen chloride gas and argon gas is 1: 3 of chlorine and argon.
5. The growth method of a silicon carbide crystal by PVT method according to claim 1, wherein: the porosity of the hollow porous graphite tube is gradually increased from inside to outside.
6. The growth method of a silicon carbide crystal by PVT method according to claim 1 or 5, wherein: the outer diameter of the graphite crucible body is between 140mm and 180mm, and the thickness of the graphite crucible body is between 6mm and 18 mm; the air-dredging device is formed by stacking 5 layers of the hollow porous graphite tube and the graphite soft felt.
7. The method according to claim 6, wherein the silicon carbide crystal is grown by the PVT method, and the method comprises the following steps: the outer diameter of the innermost layer of the hollow porous graphite tube is between 10mm and 20 mm; the wall thickness of the hollow porous graphite tube is between 2mm and 10 mm; the porosity of the hollow porous graphite tube is between 35% Vol% and 60% Vol%; the thickness of the graphite soft felt is between 2mm and 8 mm; the thickness of the porous graphite plate is between 5mm and 10mm, and the porosity is between 30 percent Vol percent and 55 percent Vol percent; the diameter of the porous graphite block is between 4mm and 10mm, and the porosity is between 35 percent Vol percent and 50 percent Vol percent; the gas dredging device is arranged at a position 2 mm-10 mm above the bottom wall of the graphite crucible body; the porous graphite plate is arranged at the position 5 mm-20 mm above the air-dredging device.
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| CN109402731A (en) * | 2018-10-17 | 2019-03-01 | 福建北电新材料科技有限公司 | A kind of high-purity semi-insulating silicon carbide crystalloid grower and its method |
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| CN109402731A (en) * | 2018-10-17 | 2019-03-01 | 福建北电新材料科技有限公司 | A kind of high-purity semi-insulating silicon carbide crystalloid grower and its method |
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