CN113832545A - Method for producing silicon carbide seed crystal by adopting liquid phase epitaxy - Google Patents
Method for producing silicon carbide seed crystal by adopting liquid phase epitaxy Download PDFInfo
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- 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
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- 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
- C30B19/00—Liquid-phase epitaxial-layer growth
- C30B19/12—Liquid-phase epitaxial-layer growth characterised by the substrate
Abstract
The invention provides a method for producing silicon carbide seed crystals by adopting liquid phase epitaxy, which comprises the following steps: s1, cutting the single crystal silicon carbide crystal with a certain thickness into a plurality of sub-crystal plates, beveling the sub-crystal plates along a fixed angle with a C surface, and polishing the carbon surfaces and the silicon surfaces of the sub-crystal plates to ensure a consistent surface type; s2, splicing the sub-crystal plates according to the target shape to obtain a splicing plate with a splicing gap, and preparing a first metal film on the silicon surface of the splicing plate; s3, bonding the splice plate and the seed crystal tray in an isostatic pressing manner to obtain a bonded crystal plate; s4, performing liquid phase epitaxy repair on the bonded crystal plate; and S5, slicing to obtain the silicon carbide seed crystal. According to the method, the single crystal silicon carbide crystal is cut to obtain the sub-crystal plate, and the sub-crystal plate is spliced, repaired by liquid phase epitaxy and then cut into a plurality of wafers, so that the probability of obtaining high-quality wafers is high, a plurality of large-size silicon carbide seed crystals with low defect density are obtained, and the cost is lower.
Description
Technical Field
The invention belongs to the technical field of silicon carbide crystal growth, and particularly relates to a method for producing silicon carbide seed crystals by adopting liquid phase epitaxy.
Background
The third generation semiconductor material gradually becomes the core support of the new generation information technology, the mainstream products in the domestic silicon carbide single crystal substrate market are gradually changed from 4-inch substrates to 6-inch substrates, and more enterprises in the world promote the mass production of 8-inch silicon carbide. At present, most domestic enterprises cannot obtain high-quality single crystal wafers with the diameter of more than 200mm, and the single crystal wafers are used as seed crystals, so that the overall development progress of large-size crystals is seriously influenced.
In order to solve the situation, the current mainstream solution obtains large-size crystals, and one is to utilize 4 inches or 6 inches of seed crystals to expand the diameter; the second is to splice 4 inch or 6 inch wafers followed by PVT (physical vapor transport) or CVD (chemical vapor deposition) lateral growth.
The diameter expanding scheme, such as the schemes proposed in patents CN111705363A and CN202110484326.6, has a feeding amount of about 3kg at one time and a crystal size of about 15mm due to the size matching problem of the crucible and the thermal field, so that only when the diameter expanding angle is extremely large, a large-size crystal can be obtained at one time, and the internal stress of the crystal is huge. If multiple expanding is selected, the seed crystal tray needs to be replaced in each expanding process, the growth process is changed, although the quality of a newly expanded part can be guaranteed, partial defects of repeated growth in the center of the crystal are increased geometrically, and finally the available area of the obtained crystal is greatly reduced and cannot be used as the basis of subsequent growth.
The post-stitching repair method, such as the methods proposed in patents CN105671638A, CN106435732B, CN110541199A and CN111945220A, uses 4 inch or 6 inch wafers to be cut into a proper shape and then stitched with an adhesive, and backfills the joints by using the anisotropy of crystal growth by PVT/CVD, etc., to obtain a large-sized wafer. The main difficulties with such schemes are: 1. the joint is too deep, when PVT/CVD is repaired, gas-phase components cannot uniformly permeate, so that the concentration of the part close to the tray is low, the surface concentration of the wafer is high, pores are generated with high probability when the joint is closed, and then various defects are generated at the joint due to poor heat dissipation of the pores in the growth process; 2. the seam is too shallow, the transverse growth advantage is insufficient during repair, polycrystal is exposed from the seam due to the nucleation of the polycrystal on the graphite support, and the polycrystal defect is caused in the subsequent growth; 3. the PVT repairing temperature reaches 2200 ℃, the difference of the wafer surface types is easy to fall off during multi-layer bonding, and the back thermal conductivity of the outermost side crystal surface is not uniform and the growth interface is unstable due to the difference of the thermal conductivities of the fillers and the silicon carbide at the joint of each layer; 4. during CVD repair, as the step growth is utilized, the transverse growth advantage of the gap is not obvious by controlling the component concentration; 5. the obtained wafer has low thickness and high single-chip cost.
Due to the factors and great process difficulty, the method tries to repair the spliced crystal by utilizing liquid phase epitaxy. There are many optimized solutions for liquid phase epitaxial growth, such as the solutions provided in patents CN106012021B and CN108977885A, but the fundamental problem of liquid phase growth is that the solubility of carbon in the melt is very low and the transportation effect is not ideal, and patent CN110747504B provides a method for growing silicon carbide single crystal, which utilizes rare earth and stirring to improve the solubility of graphite, but silicon further reduces the solubility of carbon after forming silicon carbide on the surface of a graphite crucible, and crystal seam filling is not solved.
Therefore, there is a need to provide an improved solution to the above-mentioned deficiencies of the prior art.
Disclosure of Invention
In view of the above disadvantages of the prior art, an object of the present invention is to provide a method for producing silicon carbide seed crystals by liquid phase epitaxy, which is used to solve the problems of large process difficulty and high monolithic cost of the obtained wafers due to large process difficulty and more influencing factors when large-sized crystals are obtained by splicing after cutting and then backfilling the joints by PVT or CVD repair, and the problems of low carbon solubility in the melt and unsatisfactory transportation effect when liquid phase growth is adopted, and further lowering the carbon solubility after silicon forms silicon carbide on the surface of a graphite crucible, and failing to solve the problem of crystal joint filling.
To achieve the above and other related objects, the present invention provides a method for producing a silicon carbide seed crystal by liquid phase epitaxy, the method comprising the steps of:
s1, cutting the single crystal silicon carbide crystal with a certain thickness into a plurality of sub-crystal plates, beveling the sub-crystal plates along a fixed angle with a C surface, and polishing the carbon surfaces and the silicon surfaces of the sub-crystal plates to ensure a consistent surface type;
s2, splicing the plurality of the sub-crystal plates according to a target shape to obtain a splicing plate with a splicing gap, keeping the silicon surface of the splicing plate upward, and preparing a first metal film on the silicon surface of the splicing plate;
s3, carrying out isostatic pressing bonding on the splice plate and the seed crystal tray to obtain a bonded crystal plate;
s4, performing liquid phase epitaxy repair on the bonded crystal plate;
and S5, slicing to obtain the silicon carbide seed crystal.
Preferably, the single crystal form of the single crystal silicon carbide crystal in step S1 is 4H, 6H, 3C, or 15R, the single crystal region is greater than 95%; the thickness of the monocrystalline silicon carbide crystal is 5 mm-55 mm; the thickness of the sub-crystal plate is 3 mm-15 mm, the sub-crystal plate is a convex polygon or a concave polygon, and a defect area is cut off; the fixed angle is 26.6-61 degrees; BOW <50 μm, Warp <100 μm, TTV <50 μm in the face form.
Preferably, the ratio of the area of the defect-free region of the splice plate in step S2 to the total area of the entire target shape is greater than 90%; the proportion of the total area of the splicing gap to the total area of the whole target shape is less than 10%, and the width of the splicing gap is 0.1 mm-5 mm.
Preferably, the first metal film in step S2 is prepared by an ion sputtering coating method; the thickness of the first metal film is 2-100 mu m; the first metal film is made of one or a combination of Ni, Ti, Rh and Ir; in the step S3, a second metal film is provided on the surface of the seed crystal tray, and the second metal film is the same as the first metal film in material.
Preferably, the method of isostatically bonding the splice and the seed tray in step S3 includes contacting the first metal film and the second metal film at a vacuum of 10 degrees-5Pa-10 Pa, the temperature is 200-1200 ℃, and the pressure is 0.1 Mpa-10 GPa.
Preferably, the method for liquid phase epitaxy repair in step S4 includes the following steps:
providing a graphite crucible, wherein a graphite salient point is arranged at the bottom of the graphite crucible, and the graphite salient point is arranged corresponding to the splicing gap of the bonded crystal plate;
loading the graphite crucible with a melt;
immersing the bonded crystal plate in the melt such that the bonded crystal plate is in full contact with the melt;
the height of the melt in the graphite crucible is 4 mm-20 mm, and the distance between the lower surface of the bonding crystal plate and the bottom of the graphite crucible is 0.1 mm-5 mm.
Preferably, the bottom of the graphite crucible is further provided with an ultrasonic instrument, the frequency of the ultrasonic instrument is 150-250 kHz, and the power density of the ultrasonic instrument is 0.3-0.8W/cm2。
Preferably, the melt in the liquid phase epitaxy repair in step S4 includes a molten Si alloy, where the molten Si alloy is a molten liquid containing Si and X, and X accounts for 30% to 70% by mass of the molten Si alloy, where X is Fe or Ti.
Preferably, NaCl or KCl is also added into the melt, and the addition amount of the NaCl or KCl is 0.1% -5% of the total mass of the molten Si alloy.
Preferably, rare earth metal and rare earth metal compound are also added into the melt; the rare earth metal comprises Ce, the rare earth metal compound comprises CeO, and the addition amount of the rare earth metal and the rare earth metal compound is 0.1-5% of the total mass of the molten Si alloy.
As described above, the method for producing silicon carbide seed crystal by liquid phase epitaxy according to the present invention has the following beneficial effects:
the invention provides a method for producing silicon carbide seed crystals by adopting liquid phase epitaxy, which comprises the steps of cutting a single-crystal silicon carbide crystal to obtain a plurality of sub-crystal plates with the thickness of 3-15 mm, splicing, repairing by liquid phase epitaxy, cutting to obtain 5-25 wafers, selecting the wafers to obtain high-quality wafers, obtaining a plurality of silicon carbide seed crystals with low defect density, wherein the outer diameter of the produced silicon carbide seed crystals is larger than 200mm, and the production cost is lower.
According to the invention, the R surface and the N surface are cut from the daughter crystal plate along the angle of 26.6-61 degrees with the C surface, the crystal has the advantage of anisotropic growth, the repair speed of the splicing gap is high, and the splicing gap is allowed to be larger; after the silicon surface of the splice plate is plated with the first metal film, the first metal film and the second metal film can ensure that the splice plate is fully and firmly attached to the seed crystal tray, and a vacuum bonding mode is adopted to ensure that no vacuole exists between the seed crystal tray and the splice plate and the thermal resistance is uniform; the temperature of liquid phase epitaxy repair is low, the wafer surface shape is not easy to fall off during multilayer bonding, the repair efficiency is higher than that of PVT and CVD repair, the first metal film effectively isolates the silicon solution from contacting graphite, and polycrystalline nucleation is avoided; the addition of Fe or Ti in the melt during liquid phase epitaxy repair is beneficial to dissolving more carbon in the melt; the dynamic performance of the carbon element is effectively improved by adding NaCl or KCl, so that liquid phase transportation is facilitated; the addition of Ce or CeO is beneficial to improving the crystal quality and maintaining the crystal form; the ultrasonic apparatus of specific frequency is applyed to graphite crucible's bottom, can avoid graphite surface to generate carborundum, hinders graphite and continues to dissolve, and the ultrasonic wave improves graphite surface, effectively reduces graphite surface growth carborundum and then improves the solubility of graphite in the fuse-element, avoids the crystal to decompose.
Drawings
FIG. 1 is a schematic view of a structure of a daughter crystal plate cut at an angle of 26.6 degrees to the C-plane according to an embodiment of the present invention.
Fig. 2 is a schematic view of the structure of the edge area of two fan-shaped plates cut at an angle of 26.6 ° to the C plane according to the embodiment of the present invention.
FIG. 3 is a schematic structural diagram of a carbon-side-spliced daughter crystal plate to form a splice plate according to an embodiment of the present invention.
FIG. 4 is a schematic diagram showing the structure of a seed crystal of silicon carbide produced by liquid phase epitaxy in an embodiment of the present invention.
Description of the element reference numerals
1. An edge region; 2. splicing carbon surfaces; 3. a seed crystal tray; 4. bonding the crystal plate; 5. a graphite crucible; 6. melting the materials; 7. graphite salient points; 8. provided is an ultrasonic instrument.
Detailed Description
The following description of the embodiments of the present invention is provided for illustrative purposes, and other advantages and effects of the present invention will become apparent to those skilled in the art from the present disclosure.
Before the present embodiments are further described, it is to be understood that the scope of the invention is not limited to the particular embodiments described below; it is also to be understood that the terminology used in the examples is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention. Test methods in which specific conditions are not specified in the following examples are generally carried out under conventional conditions or under conditions recommended by the respective manufacturers.
When numerical ranges are given in the examples, it is understood that both endpoints of each of the numerical ranges and any value therebetween can be selected unless the invention otherwise indicated. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In addition to the specific methods, devices, and materials used in the examples, any methods, devices, and materials similar or equivalent to those described in the examples may be used in the practice of the invention in addition to the specific methods, devices, and materials used in the examples, in keeping with the knowledge of one skilled in the art and with the description of the invention.
The invention provides a method for producing silicon carbide seed crystals by adopting liquid phase epitaxy, which comprises the steps of cutting a single-crystal silicon carbide crystal to obtain a plurality of sub-crystal plates with the thickness of 3-15 mm, splicing, repairing by liquid phase epitaxy, cutting to obtain 5-25 wafers, selecting the wafers to obtain high-quality wafers with higher probability, obtaining a plurality of silicon carbide seed crystals with low defect density, wherein the outer diameter of the produced silicon carbide seed crystals is larger than 200mm, and the production cost is lower; according to the invention, the R surface and the N surface are cut from the daughter crystal plate along the angle of 26.6-61 degrees with the C surface, the crystal has the advantage of anisotropic growth, the repair speed of the splicing gap is high, and the splicing gap is allowed to be larger; after the silicon surface of the splice plate is plated with the first metal film, the first metal film and the second metal film can ensure that the splice plate is fully and firmly attached to the seed crystal tray, and a vacuum bonding mode is adopted to ensure that no vacuole exists between the seed crystal tray and the splice plate and the thermal resistance is uniform; the temperature of liquid phase epitaxy repair is low, the wafer surface shape is not easy to fall off during multilayer bonding, the repair efficiency is higher than that of PVT and CVD repair, the first metal film effectively isolates the silicon solution from contacting graphite, and polycrystalline nucleation is avoided; the addition of Fe or Ti in the melt during liquid phase epitaxy repair is beneficial to dissolving more carbon in the melt; the dynamic performance of the carbon element is effectively improved by adding NaCl or KCl, so that liquid phase transportation is facilitated; the addition of Ce or CeO is beneficial to improving the crystal quality and maintaining the crystal form; the ultrasonic apparatus of specific frequency is applyed to graphite crucible's bottom, can avoid graphite surface to generate carborundum, hinders graphite and continues to dissolve, and the ultrasonic wave improves graphite surface, effectively reduces graphite surface growth carborundum and then improves the solubility of graphite in the fuse-element, avoids the crystal to decompose.
Considering that the liquid phase epitaxial growth speed mainly hinders the solubility of carbon in a melt, and the silicon carbide hinders the continuous dissolution of graphite after being attached to the graphite surface, the scouring effect of shock waves on the periphery is considered after ultrasonic waves induce cavitation under a specific morphology and cause bursting, and the excessive deposition of the silicon carbide on the graphite surface can be effectively prevented.
According to the kinetic equation [1] of the cavitation and the shock wave [2] generated by cavitation collapse:
wherein R is the size of the induced vacuole,
in order to obtain the density of the melt,
the pressure of the melt is controlled by the pressure of the melt,
the surface tension of the melt is controlled by the melt,
is the pressure within the hollow bubble and,
the sound pressure of the ultrasonic excitation is controlled,
and (4) excitation period.
Wherein P is the pressure generated by the collapse of the cavitation bubbles, c is the sound velocity in the melt,
which is representative of the velocity of the shock wave,
representing the density of the attached silicon carbide on the graphite surface,
the speed of sound in the silicon carbide,
and excitation
It is related.
According to the structure of the scheme, the vacuoles are just induced on the graphite surface and then burst to avoid being close to the crystal, so that the vacuoles need to be closed quickly, and therefore, the vacuoles need to be closed quickly
The sound pressure of the ultrasonic excitation is controlled,
the excitation period is particularly important, and it is calculated that the power density should be at 0.2W/cm2To 10W/cm2The period is 100KHz to 10 MHz.
Also, excitation may be considered to be multicycle such as:
+
+
the three periods are overlapped simultaneously, so that vacuole closing is accelerated; meanwhile, the graphite surface is increased after scouring, so that the graphite surface is more easily combined with the melt, and the dissolving speed is improved.
According to the above theory to solve the technical problems existing in the prior art, the invention provides a method for producing silicon carbide seed crystals by liquid phase epitaxy, which comprises the following steps:
s1, cutting the single crystal silicon carbide crystal with a certain thickness into a plurality of sub-crystal plates, beveling the sub-crystal plates along a fixed angle with the C surface, and polishing the carbon surface and the silicon surface of the sub-crystal plates to ensure a consistent surface type.
Specifically, the hexagonal system adopts 4 indexes to represent crystal directions and crystal planes, and adopts four crystal axes of C, a1, a2 and a3, wherein the C axis is vertical to a1, a2 and a3, and included angles among a1, a2 and a3 are all 120 degrees, the index of the crystal plane of the C plane is (0001), (10-10) is an M plane, (11-20) is an A plane, R plane and N plane have specific angles with the C plane, and the A/M plane is vertical to the C plane.
As an example, the single crystal form of the single crystal silicon carbide crystal in step S1 is 4H, 6H, 3C, or 15R, the single crystal region is greater than 95%; the thickness of the monocrystalline silicon carbide crystal is 5 mm-55 mm, such as 5mm, 10mm, 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm, 50mm, 55mm and the like; the fixed angle is 26.6-61 degrees, such as 26.6 degrees, 30 degrees, 35 degrees, 40 degrees, 45 degrees, 50 degrees, 55 degrees, 60 degrees, 61 degrees and the like.
Specifically, the monocrystalline silicon carbide crystal is a monocrystalline region except for gaps, and the monocrystalline region is more than 95%; in addition, in the invention, the single-crystal silicon carbide crystal is obliquely cut at 26.6-61 degrees with the C surface to cut the R surface and the N surface, the crystal has the advantage of anisotropic growth, the repair speed of the splicing gap is high, the closing speed of the splicing gap is high when the R surface and the N surface are spliced, the closing speed of the splicing gap is nearly 3 times that of C surface splicing and nearly 1.5 times that of A/M surface splicing, and the closing speed of the splicing gap is higher when the obliquely cut sub-crystal plates are spliced, so that the splicing gap is allowed to be larger.
As an example, in step S1, the thickness of the sub-crystal plate is 3mm to 15mm, such as 3mm, 5mm, 7mm, 9mm, 11mm, 13mm, 15mm, etc., the sub-crystal plate is a convex polygon or a concave polygon, and the defect region is cut; and (3) grinding and polishing the carbon surfaces and the silicon surfaces of the plurality of the sub-crystal plates to ensure consistent surface types, namely ensuring that the BOW of the sub-crystal plates is less than 50 mu m, the Warp of the sub-crystal plates is less than 100 mu m, and the TTV of the sub-crystal plates is less than 50 mu m.
Specifically, the specific shape of the plurality of sub-crystals needs to be cut according to the actual requirement, and the specific shape of the sub-crystal plate is not limited herein; moreover, BOW is BOW, a measure of the concave-convex deformation of the central plane of the wafer, and is a bulk property of the wafer rather than a surface property, regardless of any thickness variation that may exist in the wafer; warp, the difference between the maximum and minimum distances between the central plane of the wafer and the reference plane, is the bulk property of the wafer rather than the surface properties; TTV is the total thickness variation, which is the absolute difference between the maximum thickness and the minimum thickness of the measured wafer in a thickness scan or series of thickness measurements.
S2, splicing the sub-crystal plates according to the target shape to obtain a splicing plate with a splicing gap, keeping the silicon surface of the splicing plate upward, and preparing a first metal film on the silicon surface of the splicing plate.
As an example, the outer diameter of the target shape in step S2 is greater than 200 mm; the proportion of the area of the non-defective area of the splice plate to the total area of the whole target shape is more than 90%, such as 91%, 93%, 95%, 97%, 99% and the like; the proportion of the total area of the splicing gaps in the total area of the whole target shape is less than 10%, such as 0.1%, 1%, 3%, 5%, 7%, 9%, 9.9% and the like, and the width of the splicing gaps is 0.1 mm-5 mm, such as 0.1mm, 0.5mm, 1mm, 2mm, 3mm, 4mm, 4.5mm, 5mm and the like.
As an example, the first metal film in step S2 is prepared by ion sputter coating; the thickness of the first metal film is 2 μm to 100 μm, such as 2 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, etc.; the material of the first metal film is one or a combination of Ni, Ti, Rh and Ir.
Specifically, ion sputtering coating is glow discharge in a partial vacuum sputtering chamber to generate positive gas ions; under the acceleration action of voltage between a cathode (target) and an anode (sample), positively charged ions bombard the surface of the cathode to atomize the surface material of the cathode; the formed neutral atoms are sputtered from all directions and are shot to the surface of the sample, so that a uniform film is formed on the surface of the sample; the detailed steps of the ion sputtering coating method are not described herein.
And S3, carrying out isostatic pressing bonding on the splice plate and the seed crystal tray 3 to obtain a bonded crystal plate 4.
As an example, in step S3, the surface of the seed tray 3 is provided with a second metal film, and the second metal film is made of the same material as the first metal film.
Specifically, the material of the second metal film is one or a combination of Ni, Ti, Rh, and Ir, and how the second metal film is plated is not within the protection scope of the present invention, and it is only required to ensure that the material of the second metal film on the surface of the seed crystal tray 3 is the same as that of the first metal film without being limited excessively.
As an example, the method for isostatic bonding of a splice and a seed tray in step S3 is to contact a first metal film on the silicon surface of the splice with a second metal film on the seed tray at a vacuum of 10 degrees-5Pa-10 Pa, e.g. 10Pa-5Pa、10-3Pa、10- 1Pa, 1Pa, 3Pa, 5Pa, 7Pa, 9Pa, 10Pa, etc., at a temperature of 200-1200 deg.C, such as 200 deg.C, 400 deg.C, 600 deg.C, 800 deg.C, 1000 deg.C, 1200 deg.C, etc., and at a pressure of 0.1 MPa-10 Gpa, such as 0.1MPa, 1MPa, 50MPa, 100MPa, 500MPa, 1Gpa, 5Gpa, 10Gpa, etc., so that the splice plate and the seed crystal tray 3 are bonded together under low-temperature high-vacuum pressure, thereby avoiding vacuole and falling off.
Specifically, after the silicon surface of the splice plate is plated with the first metal film, the splice plate and the seed crystal tray 3 can be fully attached firmly by the first metal film and the second metal film on the surface of the seed crystal tray 3, and a vacuum bonding mode is adopted, so that no vacuole is formed between the seed crystal tray 3 and the splice plate, and the thermal resistance is uniform.
S4, liquid phase epitaxy repairing is carried out on the bonded crystal plate 4 obtained in the step S3.
As an example, the method of liquid phase epitaxy repair in step S4 includes the following steps:
providing a graphite crucible 5, wherein a graphite salient point 7 is arranged at the bottom of the graphite crucible 5, and the graphite salient point 7 is arranged corresponding to a splicing gap of the bonding crystal plate 4;
loading a melt 6 into a graphite crucible 5;
the bonded crystal plate 4 is immersed in the melt 6 such that the bonded crystal plate 4 is in full contact with the melt 6.
Specifically, the graphite bump 7 is consistent with the shape of the splicing gap of the bonded crystal plate 4, so that the flow of a melt at the splicing gap can be reduced, impurity diffusion is avoided, and meanwhile, when the bottom of the graphite crucible is vibrated by adopting an ultrasonic instrument, the cleaning of the deposit at the tip end of the graphite bump 7 is facilitated, so that the carbon solubility is further improved.
Preferably, the height of the melt 6 in the graphite crucible 5 is 4mm to 20mm, such as 4mm, 6mm, 8mm, 10mm, 12mm, 14mm, 16mm, 18mm, 20mm, etc., and the distance between the lower surface of the bonded crystal plate 4 and the bottom of the graphite crucible 5 is 0.1mm to 5mm, such as 0.1mm, 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, etc.;
as an example, the bottom of the graphite crucible 5 is further provided with an ultrasonic instrument 8, the frequency of the ultrasonic instrument 8 is 150 to 250kHz, and the power density of the ultrasonic instrument 8 is 0.3 to 0.8W/cm2E.g. 0.3W/cm2、0.4W/cm2、0.5W/cm2、0.6W/cm2、0.7W/cm2、0.8W/cm2And the power density output mode of the ultrasonic meter 8 is a sine wave with a period of 0.5 s.
As an example, the melt 6 in the liquid phase epitaxy repair in step S4 includes a molten Si alloy, where the molten Si alloy is a molten liquid containing Si and X, and the mass fraction of X in the molten Si alloy is 30% to 70%, such as 30%, 40%, 50%, 60%, 70%, and the like, where X is Fe or Ti.
By way of example, NaCl or KCl is also added to the melt 6 in an amount of 0.1% to 5% of the total mass of the molten Si alloy, such as 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, etc.
As an example, a rare earth metal and a rare earth metal compound are also added to the melt 6; the rare earth metal comprises Ce, the rare earth metal compound comprises CeO, and the addition amount of the rare earth metal and the rare earth metal compound is 0.1-5% of the total mass of the molten Si alloy, such as 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5% and the like.
And S5, slicing to obtain the silicon carbide seed crystal.
To further illustrate the method of producing silicon carbide seed crystals by liquid phase epitaxy in accordance with the present invention, the following specific examples and comparative examples are used for further illustration.
Example 1
The embodiment provides a method for producing silicon carbide seed crystals by liquid phase epitaxy, which comprises the following steps:
s1, taking a 4H single crystal silicon carbide crystal with a single crystal form of more than 15mm in thickness, cutting the single crystal silicon carbide crystal into three sub-crystal plates with the thickness of 5mm, and grinding and polishing the carbon surface and the silicon surface of each sub-crystal plate to ensure consistent surface type, so that the surface type of the sub-crystal plates is BOW =15 μm, Warp =50 μm and TTV =25 μm; as shown in fig. 1, the extension edge of one of the sub-crystal plates is cut at an angle of 26.6 ° away from the C-plane, and the other two sub-crystal plates are fan-ring-shaped plates, as shown in fig. 2, the edge regions 1 of the two fan-ring-shaped plates are cut at an angle of 26.6 ° away from the C-plane, so as to cut off the defect region;
s2, splicing the sub-crystal plates according to the target shape to obtain a splice plate with the outer diameter of 200mm, keeping the silicon surface of the splice plate upward, preparing a first metal film made of Ti material with the thickness of 50 microns on the silicon surface by using an ion sputtering method, and polishing the first metal film surface to prevent oxidation; referring to fig. 3, 5 sub-crystal plates are used, that is, a central sub-crystal plate is located in the middle, and 4 edge sub-crystal plates are located at the periphery of the central sub-crystal plate, but the number and the shape of the sub-crystal plates are not limited thereto. Splicing a plurality of sub-crystal plates according to the carbon surface shown in figure 3, wherein the width of a carbon surface seam 2 is 4.37mm, the proportion of the area of the carbon surface seam 2 to the total area of the whole target shape is 8.93%, tightly splicing silicon surfaces, the width of the silicon surface seam is 0.1mm, and the proportion of the area of the silicon surface seam to the total area of the whole target shape is less than 0.5%;
s3, forming a second metal film of Ti material on the surface of the seed crystal tray 3, and polishing the surface to prevent oxidation, wherein the vacuum degree is 10-4pa, at a temperature of 500 ℃, and referring to fig. 4, contacting one surface of the seed crystal tray 3 plated with the second metal film with one surface of the splice plate plated with the first metal film, applying a pressure of 5MPa between the two surfaces, and keeping for 4 hours to bond the splice plate and the seed crystal tray 3 together to obtain a bonded crystal plate 4;
s4, loading the melt 6 into the graphite crucible 5, heating the melt 6 to 1750 ℃, enabling the height of the melt 6 to be 5mm, immersing the bonded crystal plate 4 into the melt in the graphite crucible 5, ensuring that the bonded crystal plate 4 is completely contacted with the melt 6, and performing liquid phase epitaxy repair for 5 hours; wherein the melt 6 comprises a molten Si alloy, KCl and Ce, and the molten Si alloy is prepared from the following components in a mass ratio of 6.8: 3.2, melting the silicon and the iron, wherein the addition amount of KCl is 1 percent of the total mass of the molten Si alloy, and the addition amount of Ce is 1.5 percent of the total mass of the molten Si alloy; the distance between the lower surface of the bonded crystal plate 4 and the bottom of the graphite crucible 5 is 0.7mm, the bottom of the graphite crucible 5 is provided with graphite salient points 7 with the same shape as the splicing gap of the bonded crystal plate 4, the bottom of the graphite crucible 5 is also provided with an ultrasonic instrument 8, the frequency of the ultrasonic instrument 8 is 200kHz, and the power density is 0.5W/cm2And the power density output mode is a sine wave with a period of 0.5 s;
and S5, rounding and slicing the repaired crystal, and selecting the crystal with qualified quality for subsequent use to obtain the silicon carbide seed crystal.
In the embodiment, after splicing and liquid phase epitaxy repair, 5-25 wafers are obtained by cutting, the probability that high-quality wafers can be obtained from the wafers through wafer selection is high, a plurality of low-defect-density silicon carbide seed crystals are obtained, and the silicon carbide seed crystals are large-size silicon carbide seed crystals with the outer diameter larger than 200 mm.
Comparative example 1
The embodiment provides a method for producing silicon carbide seed crystals by liquid phase epitaxy, which comprises the following steps:
s1, taking a single crystal silicon carbide crystal with a single crystal form of 4H and a thickness of more than 15mm, cutting the single crystal silicon carbide crystal into three sub-crystal plates with a thickness of 5mm, wherein the surface type of the sub-crystal plates is BOW =5 μm, Warp =15 μm and TTV =25 μm, the diameter of a single crystal area of each sub-crystal plate is not less than 150mm, and the edge of each sub-crystal plate is not treated;
s2, splicing the sub-crystal plates according to the target shape to obtain a spliced plate with the diameter of 200mm, coating a layer of organic resin on the silicon surface of the spliced plate, and heating to 60 ℃ to solidify the organic resin and enable the organic resin to have elasticity; wherein, the silicon surface of the sub-crystal plate is tightly spliced, the splicing seam is 0.1mm, and the proportion of the area of the splicing seam to the total area of the whole target shape is less than 0.5%;
s3, selecting the seed crystal tray 3 made of graphite material, and keeping the vacuum degree at 10-3pa, under the temperature of 500 ℃, mutually contacting the seed crystal tray 3 with the silicon surface of the splice plate, applying the pressure of 2Mpa between the seed crystal tray and the splice plate, keeping for 4h, cooling and cooling to obtain a bonded crystal plate 4;
s4, loading the melt 6 into the graphite crucible 5, heating the melt 6 to 1750 ℃, enabling the height of the melt 6 to be 5mm, immersing the bonded crystal plate 4 into the melt 6 in the graphite crucible 5, ensuring that the bonded crystal plate 4 is completely contacted with the melt 6, and performing liquid phase epitaxy repair for 5 hours; the melt 6 comprises a molten Si alloy, KCl and Ce, and the molten Si alloy is prepared from the following components in a mass ratio of 7: 3, melting silicon and iron, wherein the addition amount of KCl is 1 percent of the total mass of the molten Si alloy, and the addition amount of Ce is 1.5 percent of the total mass of the molten Si alloy; the distance between the lower surface of the bonded crystal plate 4 and the bottom of the graphite crucible 5 is 0.7mm, and an ultrasonic instrument 8 is arranged at the bottom of the graphite crucible 5, the frequency of the ultrasonic instrument 8 is 200kHz, and the power density is 0.5W/cm2And the power density output mode is a sine wave with a period of 0.5 s;
and S5, slicing the repaired crystal and selecting.
In the embodiment, the silicon surface of the splice plate is coated with a layer of organic resin, the first metal film is not plated, the splicing seam is supplemented with the carbonized organic resin, the preferential nucleation on graphite causes the growth of gap polycrystals, the edge of the sub-crystal plate before splicing is not treated, the R surface and the N surface are not cut out, the anisotropic growth advantage of the crystal is not obvious, the repairing speed of the splicing gap is low, the quality of the prepared wafer is poor, and the silicon carbide seed crystal with large size and low defect density can not be selected.
Comparative example 2
The embodiment provides a method for producing silicon carbide seed crystals by liquid phase epitaxy, which comprises the following steps:
s1, taking a 4H silicon carbide crystal with a single crystal form of more than 10mm in thickness, cutting the silicon carbide crystal into three sub-crystal plates with the thickness of 3mm, and grinding and polishing the carbon surface and the silicon surface of each sub-crystal plate to ensure that the surface types of the sub-crystal plates are BOW =5 μm, Warp =15 μm and TTV =5 μm; referring to fig. 1, the extension of one of the sub-crystal plates is cut by deviating 26.6 degrees along the C plane, and the other two sub-crystal plates are fan-ring-shaped plates as shown in fig. 2, and the edge regions 1 of the two fan-ring-shaped plates are cut by deviating 26.6 degrees along the C plane, so as to cut off the defect region;
s2, splicing the sub-crystal plates according to the target shape to obtain a splice plate with the outer diameter of 200mm, keeping the silicon surface of the splice plate upward, preparing a first metal film made of Ti material with the thickness of 50 microns on the silicon surface by using an ion sputtering method, and polishing the first metal film surface to prevent oxidation; referring to fig. 3, the carbon face of the daughter crystal plate is spliced and placed according to the graph shown in fig. 3, the width of a carbon face seam 2 is 4.37mm, the ratio of the seam area to the total area of the whole target shape is 8.93%, the silicon face is tightly spliced, the seam width is 0.1mm, and the ratio of the seam area to the total area of the whole target shape is less than 0.5%;
s3, forming a second metal film of Ti material on the surface of the seed crystal tray 3, and polishing the surface to prevent oxidation, wherein the vacuum degree is 10-4pa, at the temperature of 500 ℃, referring to fig. 4, contacting the surface of the seed crystal tray 3 plated with the second metal film with the surface of the splice plate plated with the first metal film, applying a pressure of 5MPa between the surfaces, and keeping for 4h to bond the splice plate and the seed crystal tray 3 together, thereby obtaining a bonded crystal plate 4;
s4, loading the melt 6 into the graphite crucible 5, heating the melt 6 to 1900 ℃, wherein the height of the melt 6 is 10mm, immersing the bonded crystal plate 4 into the melt 6 in the graphite crucible 5, ensuring that the bonded crystal plate 4 is completely contacted with the melt 6, and performing liquid phase epitaxy repair for 15 h; the melt 6 comprises a molten Si alloy, KCl and Ce, and the molten Si alloy is prepared from the following components in percentage by mass of 6.5: 3.5, melting the silicon and the iron, wherein the addition amount of KCl is 1 percent of the total mass of the molten Si alloy, and the addition amount of Ce is 1.5 percent of the total mass of the molten Si alloy; and the distance between the lower surface of the bonding crystal plate 4 and the bottom of the graphite crucible 5 exceeds 10 mm;
s5, slicing the obtained crystal and selecting.
In the repairing process of the bonded crystal plate 4 in the embodiment, the lower surface of the bonded crystal plate 4 is far away from the bottom of the graphite crucible 5, and the concentration of graphite in the melt 6 is low, so that the crystal is decomposed; and because the surface of the graphite crucible is continuously generated with silicon carbide, the graphite is prevented from being continuously dissolved, and the activity of the graphite is not improved by utilizing ultrasonic waves, so that the repairing process is slow, and the quality of the prepared crystal is poor.
In conclusion, the invention provides a method for producing silicon carbide seed crystals by adopting liquid phase epitaxy, a plurality of sub-crystal plates with the thickness of 3-15 mm can be obtained by cutting a single crystal silicon carbide crystal, 5-25 wafers can be obtained by splicing and liquid phase epitaxy repair and then cutting, the probability of obtaining high-quality wafers from the wafers is high by selecting the wafers, a plurality of silicon carbide seed crystals with low defect density are obtained, the outer diameter of the produced silicon carbide seed crystals is larger than 200mm, and the production cost is lower; according to the invention, the R surface and the N surface are cut from the daughter crystal plate along the angle of 26.6-61 degrees with the C surface, the crystal has the advantage of anisotropic growth, the repair speed of the splicing gap is high, and the splicing gap is allowed to be larger; after the silicon surface of the splice plate is plated with the first metal film, the first metal film and the second metal film can ensure that the splice plate is fully and firmly attached to the seed crystal tray, and a vacuum bonding mode is adopted to ensure that no vacuole exists between the seed crystal tray and the splice plate and the thermal resistance is uniform; the temperature of liquid phase epitaxy repair is low, the wafer surface shape is not easy to fall off during multilayer bonding, the repair efficiency is higher than that of PVT and CVD repair, the first metal film effectively isolates the silicon solution from contacting graphite, and polycrystalline nucleation is avoided; the addition of Fe or Ti in the melt during liquid phase epitaxy repair is beneficial to dissolving more carbon in the melt; the dynamic performance of the carbon element is effectively improved by adding NaCl or KCl, so that liquid phase transportation is facilitated; the addition of Ce or CeO is beneficial to improving the crystal quality and maintaining the crystal form; the ultrasonic apparatus of specific frequency is applyed to graphite crucible's bottom, can avoid graphite surface to generate carborundum, hinders graphite and continues to dissolve, and the ultrasonic wave improves graphite surface, effectively reduces graphite surface growth carborundum and then improves the solubility of graphite in the fuse-element, avoids the crystal to decompose. 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 (10)
1. A method of producing a silicon carbide seed crystal by liquid phase epitaxy, the method comprising the steps of:
s1, cutting the single crystal silicon carbide crystal with a certain thickness into a plurality of sub-crystal plates, beveling the sub-crystal plates along a fixed angle with a C surface, and polishing the carbon surfaces and the silicon surfaces of the sub-crystal plates to ensure a consistent surface type;
s2, splicing the plurality of the sub-crystal plates according to a target shape to obtain a splicing plate with a splicing gap, keeping the silicon surface of the splicing plate upward, and preparing a first metal film on the silicon surface of the splicing plate;
s3, carrying out isostatic pressing bonding on the splice plate and the seed crystal tray to obtain a bonded crystal plate;
s4, performing liquid phase epitaxy repair on the bonded crystal plate;
and S5, slicing to obtain the silicon carbide seed crystal.
2. A method for producing a silicon carbide seed crystal by liquid phase epitaxy as claimed in claim 1, wherein: the single crystal form of the single crystal silicon carbide crystal in the step S1 is 4H, 6H, 3C or 15R, and the single crystal area is more than 95%; the thickness of the monocrystalline silicon carbide crystal is 5 mm-55 mm; the thickness of the sub-crystal plate is 3 mm-15 mm, the sub-crystal plate is a convex polygon or a concave polygon, and a defect area is cut off; the fixed angle is 26.6-61 degrees; BOW <50 μm, Warp <100 μm, TTV <50 μm in the face form.
3. A method for producing a silicon carbide seed crystal by liquid phase epitaxy as claimed in claim 1, wherein: in the step S2, the proportion of the area of the non-defective area of the splice plate in the total area of the whole target shape is more than 90%; the proportion of the total area of the splicing gap to the total area of the whole target shape is less than 10%, and the width of the splicing gap is 0.1 mm-5 mm.
4. A method for producing a silicon carbide seed crystal by liquid phase epitaxy as claimed in claim 1, wherein: in the step S2, the first metal film is prepared by adopting an ion sputtering coating method; the thickness of the first metal film is 2-100 mu m; the first metal film is made of one or a combination of Ni, Ti, Rh and Ir; in the step S3, a second metal film is further disposed on the surface of the seed crystal tray, and the second metal film is the same as the first metal film in material.
5. A method for producing a silicon carbide seed crystal by liquid phase epitaxy as claimed in claim 1, wherein: the method for isostatic bonding the splice plate and the seed tray in step S3 includes contacting the first metal film and the second metal film at a vacuum degree of 10-5Pa-10 Pa, the temperature is 200-1200 ℃, and the pressure is 0.1 Mpa-10 GPa.
6. A method for producing a silicon carbide seed crystal by liquid phase epitaxy as claimed in claim 1, wherein: the liquid phase epitaxy repair method in the step S4 comprises the following steps:
providing a graphite crucible, wherein a graphite salient point is arranged at the bottom of the graphite crucible, and the graphite salient point is arranged corresponding to the splicing gap of the bonded crystal plate;
loading the graphite crucible with a melt;
immersing the bonded crystal plate in the melt such that the bonded crystal plate is in full contact with the melt;
the height of the melt in the graphite crucible is 4 mm-20 mm, and the distance between the lower surface of the bonding crystal plate and the bottom of the graphite crucible is 0.1 mm-5 mm.
7. A method for producing a silicon carbide seed crystal by liquid phase epitaxy as claimed in claim 6, wherein: the bottom of the graphite crucible is also provided with an ultrasonic instrument, the frequency of the ultrasonic instrument is 150-250 kHz, and the power density of the ultrasonic instrument is 0.3-0.8W/cm2。
8. A method for producing a silicon carbide seed crystal by liquid phase epitaxy as claimed in claim 1, wherein: the melt in the liquid phase epitaxy repair in the step S4 comprises a molten Si alloy, wherein the molten Si alloy is a molten liquid containing Si and X, and the mass percentage of X in the molten Si alloy is 30-70%, wherein X is Fe or Ti.
9. A method for producing a silicon carbide seed crystal by liquid phase epitaxy as claimed in claim 8, wherein: NaCl or KCl is also added into the melt, and the addition amount of the NaCl or KCl is 0.1-5% of the total mass of the molten Si alloy.
10. A method for producing a silicon carbide seed crystal by liquid phase epitaxy as claimed in claim 8, wherein: rare earth metal and rare earth metal compound are also added into the melt; the rare earth metal comprises Ce, the rare earth metal compound comprises CeO, and the addition amount of the rare earth metal and the rare earth metal compound is 0.1-5% of the total mass of the molten Si alloy.
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