Synthesis process of high purity silicon powder
The thin films were deposited at 1250 ~ 1350℃ by chemical vapor deposition with flake graphite as substrate and methyl chloroalkane/hydrogen as reaction gas and carrier gas. Then, the high purity silicon powders with particle size of 200 ~ 1200 microns were obtained by oxidation, pickling and pulverization.
Although the high purity and high purity silicon powder was prepared by this method, the subsequent process was complicated, the raw material was expensive and the yield was low.
W. Zhu et al. produced ultra-fine and high-purity powders at 1200 ~ 1400℃ by chemical vapor deposition, using silane and acetylene as reaction gases and hydrogen as carrier gas.
Using hexamethylsilane as reaction source and hydrogen and argon as carrier gas, Anaguta et al. also prepared ultrafine high-purity and high-purity silicon powder by chemical vapor deposition at 1050 ~ 1250℃.
Both groups used chemical vapor deposition (CVD) to produce high-purity silicon powders from organic gas sources. However, it is nanoscale ultrafine powder that is made. Although the purity is high, it is not easy to collect, and is not suitable for mass production of high-purity high-purity silicon powder, which is not conducive to the development of later industrialization.
A manufacturing method for automatic transmission
In this method, silica powder and carbon black were used as raw materials, and other activators were added to produce powder directly at 1000 ~ 1150℃. The introduction of catalyst will inevitably affect the purity and quality of high purity silicon powder.
Therefore, many researchers have proposed an improved self-propagation synthesis method on this basis. The main improvement is to avoid the introduction of activators and to ensure continuous and efficient manufacturing reactions by increasing the manufacturing temperature and continuous heating.
As early as 1999, Japan with ethyl osilicate as silicon source, phenolic resin as carbon source, in the range of 1700 ~ 2000℃ using combustion method to produce particle size of 10 ~ 500μm powder, the mass fraction of impurity content is less than 0.5×10-6.
However, the reactants of this method use organic matter, so the raw material cost is high, which is not conducive to the large-scale production of high-purity silicon powder. Researchers at the Shanghai Institute of Silicon Research, Chinese Academy of Sciences, produced 99.9 percent and 99.999 percent mass fractions in an atmosphere of argon at high temperatures.
Et al. used activated carbon (particle size 20-100 micron) and flake graphite (particle size 5-25 micron) as carbon sources (mass fraction 99.9%) and high-purity silicon as silicon sources (particle size 10-270 micron, mass fraction 99.999%) respectively.
High purity silicon powder was prepared in a vacuum sintering furnace under the atmosphere of argon at 1900℃. The results show that the purity of high vacuum silicon powder is better than that of carrier gas. In addition, the high purity silicon powder produced under high vacuum is used to grow single crystal. The results show that the grown single crystals have high purity and excellent semi-insulating properties, which meet the requirements of the semi-insulating substrates for related devices. Prospect of high purity powder manufacturing technology
Improved self-propagating manufacturing is a common method for growing single crystals in the laboratory because of its low raw material cost and simple process. It is found that different manufacturing process parameters have certain influence on the manufacturing products.
Today, it is necessary to strengthen research in the following aspects:
1. The manufacturing mechanism of high-purity silicon powder was studied in depth, especially the basic theory of effectively controlling parameters such as particle size, shape, particle size distribution and purity.
2. How to further strengthen the research to improve high purity silicon powder manufacturing method of automatic transmission, in order to prepare high purity powder with good quality and high purity, suitable for single crystal growth on the basis of low cost and simple process, thus effectively improve the quality of the growth of SiC single crystal substrate, promote the development of application equipment industry in China.
