阅读说明：本技术 用于碳化硅单晶生长的碳化硅粉体的制备方法 (Preparation method of silicon carbide powder for silicon carbide single crystal growth ) 是由 徐洙莹 金宰年 叶宏伦 钟其龙 刘崇志 于 2021-01-29 设计创作，主要内容包括：本发明涉及一种用于碳化硅单晶生长的碳化硅粉体的制备方法,其针对市面可采购的高纯度β碳化硅粉体通过进一步的热处理,经过热处理工序的高纯度β碳化硅粉末有效的转化为α碳化硅粉末,而α-碳化硅具有合适的计量成分,适合作为晶体生长原料,以最大限度地减少多孔粉末的影响,并最大限度地提高晶体粉末在生长晶体的效果。本发明的优化热处理最佳温度曲线,时间不足或温度太低不能完金消除原粉体中的自由金属硅和粉末中的多孔粉末；反之时间太长或太高会造成粉末石墨化。(The invention relates to a preparation method of silicon carbide powder for growing silicon carbide single crystals, which is characterized in that high-purity beta silicon carbide powder which is purchased from the market is subjected to further heat treatment, the high-purity beta silicon carbide powder subjected to the heat treatment process is effectively converted into alpha silicon carbide powder, and the alpha-silicon carbide has proper metering components and is suitable for being used as a crystal growth raw material, so that the influence of porous powder is reduced to the maximum extent, and the crystal growth effect of the crystal powder is improved to the maximum extent. According to the invention, the optimal temperature curve of the optimized heat treatment is short in time or too low in temperature, so that the free metal silicon in the original powder and the porous powder in the powder cannot be completely removed; conversely, too long or too high a time may cause graphitization of the powder.)

1. A preparation method of silicon carbide powder for silicon carbide single crystal growth is characterized by comprising the following steps: comprises that

Step 1, placing beta-silicon carbide powder in a graphite crucible, and placing the graphite crucible in a vacuum high-temperature furnace; then, vacuumizing the vacuum high-temperature furnace to below 1 torr;

2, introducing argon into the cavity of the vacuum high-temperature furnace, and increasing the pressure to 500 +/-50 torr;

step 3, heating the cavity of the vacuum high-temperature furnace, and heating in three stages, wherein the heating rates in the three stages are different: in the first stage, heating to 800 ℃ at a first heating rate; in the second stage, heating to 1800 ℃ at a second heating rate; in the third stage, the temperature of the cavity is increased to 2100 +/-63 ℃ within 30 minutes and is maintained at the temperature for 6 +/-0.3 hours;

and 4, starting cooling, and cooling the cavity of the vacuum high-temperature furnace to room temperature within 10 +/-1 hours to obtain the powder source material suitable for the growth of the silicon carbide single crystal.

2. The method for producing a silicon carbide powder for silicon carbide single crystal growth according to claim 1, characterized in that: in the step 1, the purity of the beta-silicon carbide powder is more than 5N, and the beta-silicon carbide powder is aggregated into a porous spheroid by 2-3 mu m particles, and the size of the spheroid is 300-500 mu m.

3. The method for producing a silicon carbide powder for silicon carbide single crystal growth according to claim 1, characterized in that: in the step 3, the first heating rate is (100 ℃ +/-20 ℃) per hour, and the second heating rate is (200 ℃ +/-20 ℃) per hour.

Technical Field

The invention relates to the field of semiconductor materials, in particular to a preparation method of silicon carbide powder for silicon carbide single crystal growth.

Background

Silicon carbide crystals have excellent chemical, physical and mechanical properties, are widely recognized as broad-band semiconductor materials suitable for high-temperature, high-frequency, high-power devices, and as substrate materials for optoelectronic and electronic communication devices, such as blue/white light emitting diodes, and gallium nitride microwave devices SiC grown on silicon carbide. For these device applications, techniques for growing large-size silicon carbide crystals with low defect densities have been well developed. However, although many studies and developments have been completed and disclosed, the occurrence of defects caused by crystal growth, such as micropipes, planar defects, dislocations and polytype inclusions, is still under discussion, and the mechanism of the entire occurrence is not completely understood at present. In particular, published studies have demonstrated that the polytype formed during crystal growth is significantly affected by the chemical species within the silicon carbide growth source.

Recent publications report different silicon/carbon ratios, and that the powder phase (α and β) of the starting material is the main cause of the occurrence of polymorphic forms. In the case of beta silicon carbide, various polymorphic forms occur because the silicon atoms have random orientations on the seed surface, resulting from higher Si partial pressure at the initial growth because beta silicon carbide powder has a higher silicon to carbon ratio and more metallic silicon. The polymorphic crystalline state occurs in connection with a relatively high excess of free metal Si. On the other hand, it is well known that α -silicon carbide has a suitable metered composition, but there is currently no commercial supplier of high purity α -silicon carbide. In addition, simulation results report that the porosity and the grain size of the growth source are related to the thermal field distribution in the graphite furnace, but no research report is provided on the influence of the porosity of individual powder on the growth characteristics.

In view of the above, the present inventors have made extensive studies on the problems of the silicon carbide powder, and as a result, have made the present invention.

Disclosure of Invention

The invention aims to provide a preparation method of silicon carbide powder for growing silicon carbide single crystals so as to improve the quality of crystals prepared from the silicon carbide powder.

In order to achieve the purpose, the invention adopts the technical scheme that:

a method for preparing silicon carbide powder for silicon carbide single crystal growth comprises

Step 1, placing beta-silicon carbide powder in a graphite crucible, and placing the graphite crucible in a vacuum high-temperature furnace; then, vacuumizing the vacuum high-temperature furnace to below 1 torr;

2, introducing argon into the cavity of the vacuum high-temperature furnace, and increasing the pressure to 500 +/-50 torr;

step 3, heating the cavity of the vacuum high-temperature furnace, and heating in three stages, wherein the heating rates in the three stages are different: in the first stage, heating to 800 ℃ at a first heating rate; in the second stage, heating to 1800 ℃ at a second heating rate; in the third stage, the chamber temperature was raised to 2100 ℃. + -. 63 ℃ over 30 minutes and maintained at that temperature for 6. + -. 0.3 hours.

And 4, starting cooling, and cooling the cavity of the vacuum high-temperature furnace to room temperature within 10 +/-1 hours to obtain the powder source material suitable for the growth of the silicon carbide single crystal.

In the step 1, the purity of the beta-silicon carbide powder is more than 5N, and the beta-silicon carbide powder is aggregated into a porous spheroid by 2-3 mu m particles, and the size of the spheroid is 300-500 mu m.

In the step 3, the first heating rate is (100 ℃ +/-20 ℃) per hour, and the second heating rate is (200 ℃ +/-20 ℃) per hour.

After the scheme is adopted, the high-purity beta silicon carbide powder which is purchased in the market is subjected to further heat treatment, the high-purity beta silicon carbide powder subjected to the heat treatment process is effectively converted into the alpha silicon carbide powder, and the alpha-silicon carbide has proper metering components and is suitable to be used as a crystal growth raw material, so that the influence of porous powder is reduced to the maximum extent, and the crystal growth effect of the crystal powder is improved to the maximum extent. According to the invention, the optimal temperature curve of the optimized heat treatment is short in time or too low in temperature, so that the free metal silicon in the original powder and the porous powder in the powder cannot be completely removed; conversely, too long or too high a time may cause graphitization of the powder.

The silicon carbide powder prepared by the invention is applied to crystal growth, and the crystal has relatively low micro-pipeline density, plane holes and other defects; meanwhile, the nitrogen-doped n-type silicon carbide single crystal is prepared, and the doping concentration of the crystal is improved. The silicon carbide powder after heat treatment is suitable for the growth of silicon carbide single crystals and epitaxial wafers of various crystalline states.

Drawings

FIG. 1 is a graph of the temperature profile of the heat treatment of the present invention;

FIG. 2 is a graph showing the area ratio of beta-SiC to alpha-SiC in each example;

FIG. 3 is a cross-sectional photograph of a silicon carbide crystal produced from the silicon carbide powder obtained in each example;

FIG. 4 shows the half width height @ plane optical mode and micro-pipe density of silicon carbide crystals prepared from the silicon carbide powder obtained in each example;

FIG. 5 is a graph showing the half-width height and peak wave intensity of a silicon carbide crystal produced from the silicon carbide powder obtained in each example.

Detailed Description

The invention discloses a preparation method of silicon carbide powder for silicon carbide single crystal growth, which comprises the following steps:

step 1, placing beta-silicon carbide powder in a graphite crucible, and placing the graphite crucible in a vacuum high-temperature furnace; then, the vacuum high temperature furnace was evacuated to 1torr or less.

In this example, the purity of the β -silicon carbide powder was 5N or more, and the particles of 2 μm to 3 μm were aggregated into a porous spheroid, and the size of the spheroid was 300 μm to 500 μm.

The vacuum high-temperature furnace in the invention can also be silicon carbide PVT long crystal furnace or other containers which can be vacuumized and heated at high temperature. The PVT crystal growth furnace is used for completion, so that the requirements on equipment can be simplified, and the investment cost can be reduced.

And 2, introducing argon into the cavity of the vacuum high-temperature furnace, and increasing the pressure to 500 +/-50 torr.

Step 3, heating the cavity of the vacuum high-temperature furnace, and heating in three stages: in the first stage, the temperature is raised to 800 ℃ at the rate of (100 +/-20 ℃) per hour; in the second stage, the temperature rise rate is (200 +/-20 ℃) per hour, and the temperature rises to 1800 ℃; in the third stage, the chamber temperature was raised to 2100 ℃. + -. 63 ℃ over 30 minutes and maintained at that temperature for 6. + -. 0.3 hours.

The temperature rise rates of the above three stages are different, and (100 ℃. + -. 20 ℃) per hour is a first temperature rise rate, and (200 ℃. + -. 20 ℃) per hour is a second temperature rise rate.

And 4, starting cooling, and cooling the cavity of the vacuum high-temperature furnace to room temperature within 10 +/-1 hours to obtain the powder source material suitable for the growth of the silicon carbide single crystal.

The heat treatment of the present invention is composed of step 3 and step 4, and the temperature profile thereof is shown in FIG. 1.

In order to elaborate on the technical scheme of the invention and the technical effect achieved by the technical scheme, the following embodiment is listed for detailed description. The purity and relative size of the beta-silicon carbide powder used in the following examples, as well as the vacuum high temperature furnace used, were the same, except for the heat treatment time and temperature, as shown in table 1.

TABLE 1 Heat treatment conditions for beta-SiC powder

The area ratio of the conversion of beta-silicon carbide to alpha-silicon carbide in each example is shown in fig. 2. As can be seen from fig. 2, the conversion rate from β -silicon carbide to α -silicon carbide increases with the heat treatment time, but stabilizes after the heat treatment time exceeds 6 hours, and the results of example 3 are not much different from those of example 4.

A cross-sectional photograph of a silicon carbide crystal produced using the silicon carbide powder produced in the above example is shown in fig. 3, in which (a) is example 1, (b) is example 3, (c) is example 4, and (d) is example 6. As can be seen in fig. 3: the crystal quality of examples 3 and 4 was the best.

The silicon carbide crystal prepared by the silicon carbide powder prepared in the above embodiment has a half-width height @ plane optical mode and microchannel density as shown in fig. 4, and it can be seen from fig. 4 that: the half width height @ plane optical mode and the average microtube density of the crystal decrease sand with increasing heat treatment time, but become stable after the heat treatment time exceeds 6 hours.

The silicon carbide crystal prepared by using the silicon carbide powder prepared in the above example has a half-width height and a peak wave intensity as shown in fig. 5. As can be seen from fig. 5: the behavior in the case of nitrogen-doped n-type silicon carbide crystals shows that the doping concentration increases with increasing heat treatment time, but becomes stable after heat treatment times of more than 6 hours.

In summary, the present invention is directed to a method for efficiently converting commercially available high-purity β -silicon carbide powder into α -silicon carbide powder by further heat treatment, wherein the α -silicon carbide has a suitable amount of components and is suitable as a crystal growth raw material, thereby minimizing the influence of porous powder and maximizing the crystal growth effect of the crystal powder. According to the invention, the optimal temperature curve of the optimized heat treatment is short in time or too low in temperature, so that the free metal silicon in the original powder and the porous powder in the powder cannot be completely removed; conversely, too long or too high a time may cause graphitization of the powder.

The silicon carbide powder prepared by the invention is applied to crystal growth, and the crystal has relatively low micro-pipeline density, plane holes and other defects; meanwhile, the nitrogen-doped n-type silicon carbide single crystal is prepared, and the doping concentration of the crystal is improved. The silicon carbide powder after heat treatment is suitable for the growth of silicon carbide single crystals and epitaxial wafers of various crystalline states.

The above description is only exemplary of the present invention and is not intended to limit the technical scope of the present invention, so that any minor modifications, equivalent changes and modifications made to the above exemplary embodiments according to the technical spirit of the present invention are within the technical scope of the present invention.