Flow field control method for growing SiC through PVT method

Abstract

According to the flow field control method for growing SiC by the PVT method, a cylindrical graphite crucible and a porous graphite cylinder are coaxially placed, and the porous graphite cylinder divides the space in the graphite crucible into a central area and an annular area; silicon carbide powder with high stacking density is filled in the annular area, and silicon carbide powder with low stacking density is filled in the central area; covering an isostatic pressing graphite ring above the silicon carbide powder in the annular area, and covering a porous graphite sheet above the silicon carbide powder in the central area; the high-stacking-density powder has low porosity, and the low-stacking-density powder has high porosity, so that SiC steam is conveyed upwards in the center of the powder preferentially, meanwhile, the graphite flow guide component in the powder plays an important role in guiding airflow conveying, the SiC steam generated on the side edge is gathered towards the center through the porous graphite cylinder, and the SiC steam is conveyed to the center through the porous graphite cylinder. Upward mass transfer of the center is promoted, carbon wrappage is effectively reduced, and growth of crystals in a step flow mode is facilitated, so that the quality of the crystals is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of growing silicon carbide crystals using a PVT method. Background Art

[0002] Silicon carbide is a new generation of power electronic materials that is internationally recognized to have excellent performance. It has made its mark in high power and high energy efficiency, and is widely used in various fields of the national economy. Physical vapor transport (PVT) is the main growth method for preparing high-quality silicon carbide crystals. This method places powdered raw materials in a closed container, sublimates the material at high temperature to form vapor, and then condenses the vapor into crystals by controlling the temperature gradient and pressure. In this process, the heat transfer and powder properties of the powder have an important influence on the growth of the crystal. However, the existing technology has some problems in this field.

[0003] First, the area of ​​SiC powder is affected by heat transfer and powder characteristics. The edge of the powder is easily carbonized and forms a thermal resistance layer, making it difficult to heat the internal powder evenly. Secondly, the porosity of the powder carbonized at the edge is high, and SiC vapor mainly transfers mass at the edge. The carbon particles at the edge are easily transported to the growth area with the airflow, affecting the quality of the crystal.

[0004] For example, patent CN 110565167 A discloses a charging device and a charging method for growing SiC single crystals by the PVT method. The charging method uses large edge particles, intending to reduce carbon particles by inhibiting the carbonization of the side powder. However, the large particle powder itself has a large porosity, which will cause the SiC vapor to transfer mainly at the edge. The carbon particles generated by local overheating at the edge are easily transported to the growth domain with the airflow, affecting the quality of the crystal.

[0005] In addition, in the existing technology, the powder is usually stacked uniformly. This uniform stacking method cannot effectively reduce the carbonization degree of the edge of the powder, nor can it promote the steam to be preferentially transmitted upward in the center of the powder, thereby affecting the quality of the crystal.

[0006] The prior art urgently needs to be improved in the charging method of growing silicon carbide crystals by the PVT method and the SiC vapor mass transfer path. Summary of the invention

[0007] The present invention aims to provide a flow field control method for growing SiC by a PVT method, which reduces the carbonization degree of the edge of the powder, promotes the steam to be preferentially transmitted upward in the center of the powder, improves the uniformity of the SiC steam flow field, and improves the heat transfer efficiency from the edge of the crucible to the central area.

[0008] In order to achieve the above purpose, the technical solutions adopted are as follows:

[0009] A flow field control method for growing SiC by a PVT method comprises the following steps:

[0010] (1) placing a cylindrical graphite crucible and a porous graphite tube coaxially, wherein the porous graphite tube isolates the space inside the graphite crucible into a central area and an annular area;

[0011] (2) filling the silicon carbide powder with high bulk density in the annular area, and filling the silicon carbide powder with low bulk density in the central area;

[0012] (3) An isostatic graphite ring is placed on top of the silicon carbide powder in the annular area, and a porous graphite sheet is placed on top of the silicon carbide powder in the central area.

[0013] According to the above scheme, the inner diameter D1 of the graphite crucible is 160-240 mm, the wall thickness T1 is 5-25 mm, and the depth H1 is 120-200 mm; the inner diameter D2 of the porous graphite cylinder is 70-200 mm, the wall thickness T2 is 0.5-5 mm, and the depth H2 is 110-190 mm; the numerical relationship D1>D2, T1>T2, H1>H2 is satisfied.

[0014] According to the above scheme, the density of the porous graphite cylinder and the porous graphite sheet is 1.0-1.3 g / cm 3 , corresponding to a porosity of 35-60%; the isostatically pressed graphite ring is made of the same material as the crucible, and its density is 1.6-2.0 g / cm 3 , corresponding to a porosity of 5 to 15%.

[0015] According to the above scheme, the silicon carbide powder is obtained by a self-propagating method or a chemical vapor deposition method, and has a crystal form of 6H phase, 4H phase or 3C phase, and a spherical particle shape.

[0016] According to the above scheme, the high bulk density silicon carbide powder in step 2 is optimized by grading or vibrating to make the bulk density ≥1.45g / cm 3 .

[0017] According to the above scheme, the low bulk density silicon carbide powder in step 2 adopts a single particle size powder with a bulk density of 1.10-1.45 g / cm 3 .

[0018] According to the above scheme, in step 2, the annular area is first filled and compacted, and the density after compaction is ≥1.55g / cm 3 ; Then fill the center area without compaction operation; The charging height of the two is consistent.

[0019] According to the above scheme, in step 2, a crystal stabilizer is also added to the central area; the crystal stabilizer is CeSi2, CeO2 or Ce-Si metal compound.

[0020] According to the above scheme, the outer diameter and inner diameter of the isostatic graphite ring in step 3 respectively match the inner diameter of the graphite crucible and the outer diameter of the porous graphite tube, and form a closed space in combination with the bottom of the graphite crucible.

[0021] According to the above scheme, the inner diameters of the porous graphite sheet and the porous graphite cylinder in step 3 match each other, and a closed space is formed in combination with the bottom of the graphite crucible.

[0022] According to the above scheme, the thickness and height of the isostatically pressed graphite ring in step 3 are consistent with those of the porous graphite sheet, and the thickness is 0.5 to 5 mm; the height of the isostatically pressed graphite ring is close to or maintains a distance S from the powder, S < 20 mm, and the maximum height is not higher than the height of the porous graphite cylinder.

[0023] Compared with the existing technology, the beneficial effects of this technical solution are as follows:

[0024] 1. Reduce the carbonization degree of the powder edge: The present invention fills the high bulk density powder in the area close to the crucible with high bulk density powder, and fills the low bulk density powder in the center of the powder. This special powder stacking method can effectively reduce the carbonization degree of the powder edge. This is because the high bulk density powder has a lighter carbonization degree after being heated, which helps the temperature of the crucible to be transferred to the inside of the powder, thereby reducing the carbonization phenomenon of the powder edge.

[0025] 2. Promote steam to preferentially transfer upward in the center of the powder: The present invention uses high stacking density powder with low porosity and low stacking density powder with high porosity, so that SiC vapor is preferentially transferred upward in the center of the powder, which is in sharp contrast to the uniform powder stacking method of the prior art. The graphite guide component in the powder plays an important role in guiding the air flow transmission. The SiC vapor generated on the side converges to the center through the porous graphite tube, promoting mass transfer from the center upward. The packing method and flow field control component of the present invention can effectively reduce carbon inclusions, which is conducive to the growth of crystals in a step flow manner, thereby improving the quality of the crystals, which will greatly improve the performance and reliability of semiconductor devices.

[0026] 3. Improve production efficiency: The high bulk density powder used in the present invention has good heat transfer performance, which helps to transfer heat to the center, increase the center temperature of the powder, thereby improving the utilization rate of the powder in the center area and greatly improving production efficiency.

[0027] 4. Strong adaptability: The flow field control method of the present invention is applicable to the growth of SiC crystals of various sizes. This is because the PVT method is mainly used for the growth of 6-inch, 8-inch, and even 12-inch SiC, and the control effect of the flow field is interoperable. The flow field control method of the present invention has a positive effect on the quality improvement of SiC crystals of various sizes by optimizing the stacking method of the powder, and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 : Schematic diagram of the charging process of growing SiC single crystal by the PVT method of the present invention.

[0029] Figure 2 : Crystal growth defect analysis chart of embodiment and comparative example.

[0030] Among them, 1-cylindrical graphite crucible; 2-porous graphite cylinder; 3-annular area; 4-central area; 5-isostatic graphite ring; 6-porous graphite sheet; 7-SiC crystal; 8-graphite guide ring. DETAILED DESCRIPTION

[0031] The following examples further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.

[0032] The specific embodiment provides a charging method for growing SiC single crystal by PVT method, referring to the attached Figure 1 As shown:

[0033] (1) placing a cylindrical graphite crucible 1 and a porous graphite tube 2 coaxially, and the porous graphite tube isolates the space inside the graphite crucible into a central area 4 and an annular area 3;

[0034] (2) Silicon carbide powder with high bulk density is filled in the annular area 3, and silicon carbide powder with low bulk density is filled in the central area 4;

[0035] (3) An isostatically pressed graphite ring 5 is placed on top of the silicon carbide powder in the annular region, and a porous graphite sheet 6 is placed on top of the silicon carbide powder in the central region.

[0036] The high bulk density powder provided by the specific implementation method can be obtained by vibration or grading, wherein the vibration operation is completed on the vibration equipment, and the grading method is to mix and pack the fine powder with an average particle size of 0.1-0.4 mm and the coarse powder with an average particle size of 0.5-1.2 mm in a weight ratio of (30-40%): (60-70%), and the bulk density of the graded powder is ≥1.45 g / cm 3 , density after compaction ≥1.55g / cm 3 .

[0037] Example 1

[0038] This embodiment provides a flow field control method for SiC crystal growth, and the specific steps are as follows:

[0039] 1) Prepare a graphite crucible made of isostatic graphite with a density of 1.83 g / cm 3 , inner diameter 200mm, wall thickness 15mm, depth 170mm, prepare porous graphite cylinder, density 1.16g / cm3 , inner diameter 150mm, wall thickness 2mm, depth 150mm;

[0040] 2) placing the porous graphite cylinder inside the graphite crucible, the porous graphite cylinder and the graphite crucible are coaxial, and the bottom surface of the graphite crucible is in contact with the bottom surface of the graphite cylinder;

[0041] 3) The annular area is filled with powder with high bulk density, the average particle size of the powder is 0.1-0.4 mm, and the loose density of the powder is ≥1.50 g / cm 3 , place the crucible on the vibration equipment and vibrate it. The density of the powder after vibration is ≥1.60g / cm 3 , loading height 148mm;

[0042] 4) The center area is filled with low bulk density powder, the average particle size of the powder is 0.6-1.0 mm, and the loose density of the powder is 1.10-1.30 g / cm 3 , and place a small crucible doped with CeSi2 at the same time, without vibrating the center area, and the loading height is 148mm;

[0043] 5) Place an isostatic graphite ring on top of the high bulk density powder with a density of 1.83 g / cm 3 , outer diameter 200mm, inner diameter 154mm, thickness 2mm; porous graphite sheet with density of 1.16g / cm is placed on the top of low bulk density powder 3 , outer diameter 150mm, thickness 2mm, the upper surfaces of the porous graphite cylinder, isostatic graphite ring and porous graphite sheet are kept horizontal;

[0044] 6) Assemble the remaining components of the growth crucible, place the crucible in a hot field, set the growth temperature to 2100-2250° C., the growth pressure to 0.5-20 mbar, the crystal growth time to 180 h, and start the SiC crystal growth experiment.

[0045] 7) After the crystal growth is completed, the crystal is cut, ground and polished, and defect analysis is performed. The results are shown in Figure 2 shown.

[0046] Example 2

[0047] This embodiment provides a flow field control method for SiC crystal growth, and the specific steps are as follows:

[0048] 1) Prepare a graphite crucible made of isostatic graphite with a density of 1.83 g / cm 3 , inner diameter 200mm, wall thickness 15mm, depth 170mm, prepare porous graphite cylinder, density 1.16g / cm 3 , inner diameter 160mm, wall thickness 4mm, depth 150mm;

[0049] 2) placing the porous graphite cylinder inside the graphite crucible, the porous graphite cylinder and the graphite crucible are coaxial, and the bottom surface of the graphite crucible is in contact with the bottom surface of the graphite cylinder;

[0050] 3) The annular area is filled with powder with high bulk density, the average particle size of the powder is 0.1-0.4 mm, and the loose density of the powder is ≥1.50 g / cm 3 , place the crucible on the vibration equipment and vibrate it. The density of the powder after vibration is ≥1.60g / cm 3 , loading height 146mm;

[0051] 4) The center area is filled with low bulk density powder, the average particle size of the powder is 0.6-1.0 mm, and the loose density of the powder is 1.10-1.30 g / cm 3 , and place a small crucible doped with CeO2 at the same time, without vibrating the center area, and the loading height is 146mm;

[0052] 5) Place an isostatic graphite ring on top of the high bulk density powder with a density of 1.83 g / cm 3 , outer diameter 200mm, inner diameter 168mm, thickness 4mm; porous graphite sheet with density of 1.16g / cm is placed on the top of low bulk density powder 3 , outer diameter 160mm, thickness 4mm, the upper surfaces of the porous graphite cylinder, isostatic graphite ring and porous graphite sheet are kept horizontal;

[0053] 6) Assemble the remaining components of the growth crucible, place the crucible in a hot field, set the growth temperature to 2100-2250° C., the growth pressure to 0.5-20 mbar, the crystal growth time to 180 h, and start the SiC crystal growth experiment.

[0054] 7) After the crystal growth is completed, the crystal is cut, ground and polished, and defect analysis is performed. The results are shown in Figure 2 shown.

[0055] Example 3

[0056] This embodiment provides a flow field control method for SiC crystal growth, and the specific steps are as follows:

[0057] 1) Prepare a graphite crucible made of isostatic graphite with a density of 1.83 g / cm 3 , inner diameter 200mm, wall thickness 15mm, depth 170mm, prepare porous graphite cylinder, density 1.16g / cm 3 , inner diameter 150mm, wall thickness 5mm, depth 150mm;

[0058] 2) placing the porous graphite cylinder inside the graphite crucible, the porous graphite cylinder and the graphite crucible are coaxial, and the bottom surface of the graphite crucible is in contact with the bottom surface of the graphite cylinder;

[0059] 3) The annular area is filled with powder with high bulk density, the average particle size of the powder is 0.1-0.4 mm, and the loose density of the powder is ≥1.50 g / cm 3 , place the crucible on the vibration equipment and vibrate it. The density of the powder after vibration is ≥1.65g / cm 3 , loading height 145mm;

[0060] 4) The center area is filled with low bulk density powder, the average particle size of the powder is 0.6-1.0 mm, and the loose density of the powder is 1.10-1.30 g / cm 3 , and place a small crucible doped with CeSi2 at the same time, without vibrating the center area, and the loading height is 145mm;

[0061] 5) Place an isostatic graphite ring on top of the high bulk density powder with a density of 1.83 g / cm 3 , outer diameter 200mm, inner diameter 160mm, thickness 5mm; porous graphite sheet with density of 1.16g / cm is placed on the top of low bulk density powder 3 , outer diameter 150mm, thickness 5mm, the upper surfaces of the porous graphite cylinder, isostatic graphite ring and porous graphite sheet are kept horizontal;

[0062] 6) Assemble the remaining components of the growth crucible, place the crucible in a hot field, set the growth temperature to 2100-2250° C., the growth pressure to 0.5-20 mbar, the crystal growth time to 180 h, and start the SiC crystal growth experiment.

[0063] 7) After the crystal growth is completed, the crystal is cut, ground and polished, and defect analysis is performed. The results are shown in Figure 2 shown.

[0064] Comparative Example

[0065] The specific steps of powder filling of the comparative example are as follows:

[0066] 1) Prepare a graphite crucible made of isostatic graphite with a density of 1.83 g / cm 3 , inner diameter 200mm, wall thickness 15mm, depth 170mm;

[0067] 2) Prepare powder with a bulk density of 1.10-1.30 g / cm 3 , the powder is evenly filled in the entire crucible, the powder height is 150mm, a CeSi2-doped small crucible is placed in the powder, and the powder is not vibrated;

[0068] 3) Assemble the remaining components of the growth crucible, place the crucible in a hot field, set the growth temperature to 2100-2250° C., the growth pressure to 0.5-20 mbar, the crystal growth time to 180 h, and start the SiC crystal growth experiment.

[0069] 4) After the crystal growth is completed, the crystal is cut, ground and polished, and defect analysis is performed. The results are shown in Figure 2 shown.

Claims

1. A flow field control method for growing SiC by PVT method, characterized in that The following steps are involved: (1) placing a cylindrical graphite crucible and a porous graphite tube coaxially, wherein the porous graphite tube isolates the space inside the graphite crucible into a central area and an annular area; (2) filling the silicon carbide powder with high bulk density in the annular area, and filling the silicon carbide powder with low bulk density in the central area; (3) An isostatic graphite ring is placed on top of the silicon carbide powder in the annular area, and a porous graphite sheet is placed on top of the silicon carbide powder in the central area.

2. The flow field control method for growing SiC by PVT method according to claim 1, characterized in that The inner diameter D1 of the graphite crucible is 160-240 mm, the wall thickness T1 is 5-25 mm, and the depth H1 is 120-200 mm; the inner diameter D2 of the porous graphite cylinder is 70-200 mm, the wall thickness T2 is 0.5-5 mm, and the depth H2 is 110-190 mm; the numerical relationships D1>D2, T1>T2, and H1>H2 are satisfied.

3. The flow field control method for growing SiC by PVT method according to claim 1, characterized in that The density of the porous graphite cylinder and the porous graphite sheet is 1.0-1.3 g / cm 3 , corresponding to a porosity of 35-60%; the isostatically pressed graphite ring is made of the same material as the crucible, and its density is 1.6-2.0 g / cm 3 , corresponding to a porosity of 5 to 15%.

4. The flow field control method for growing SiC by PVT method according to claim 1, characterized in that The silicon carbide powder is obtained by a self-propagating method or a chemical vapor deposition method, has a crystal form of 6H phase, 4H phase or 3C phase, and is in the form of spherical particles.

5. The flow field control method for growing SiC by PVT method according to claim 1, characterized in that The high bulk density silicon carbide powder in step 2 is optimized by grading or vibrating to make the bulk density ≥1.45g / cm 3 The low bulk density silicon carbide powder adopts a single particle size powder with a bulk density of 1.10 to 1.45 g / cm 3 .

6. The flow field control method for growing SiC by PVT method according to claim 1, characterized in that In step 2, the annular area is first filled and compacted. The density after compaction is ≥1.55g / cm 3 ; Then fill the center area without compaction operation; The charging height of the two is consistent.

7. The flow field control method for growing SiC by PVT method according to claim 1, characterized in that In step 2, a crystal stabilizer is also added to the central area; the crystal stabilizer is CeSi2, CeO2 or Ce-Si metal compound.

8. The flow field control method for growing SiC by PVT method according to claim 1, characterized in that The outer diameter and inner diameter of the isostatic graphite ring in step 3 respectively match the inner diameter of the graphite crucible and the outer diameter of the porous graphite cylinder, and form a closed space in combination with the bottom of the graphite crucible.

9. The flow field control method for growing SiC by PVT method according to claim 1, characterized in that The inner diameters of the porous graphite sheet and the porous graphite cylinder in step 3 are matched, and a closed space is formed in combination with the bottom of the graphite crucible.

10. The flow field control method for growing SiC by PVT method according to claim 1, characterized in that The thickness and height of the isostatically pressed graphite ring in step 3 are consistent with those of the porous graphite sheet, and the thickness is 0.5 to 5 mm; the height of the isostatically pressed graphite ring is close to or maintains a distance S from the powder, S < 20 mm, and the maximum height is not higher than the height of the porous graphite cylinder.

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