Electronic Grade Silicon Tetrafluoride Production By Pyrolysis Sodium Fluorosilicate

Silicon tetrafluoride（Si F₄）is a kind of important raw materials in the electronics and semiconductor industry.It is mainly used as etching agent of tantalum silicide and silicon nitride,P dopant and epitaxial deposition diffusion silicon source,and it can be also used to produce electronic-grade silane or polycrystalline silicon.Silicon tetrafluoride can be used to produce optical fibre pure quartz glass because it can produce heat sink Si O₂with high specific surface area in high temperature hydrolysis.Moreover,in optical fiber production,silicon tetrafluoride is an important component of the ion implantation method used in the production of silicon-based semiconductor devices.Furthermore,Silicon tetrafluoride is widely used in production of cement,electronic materials,solar cell,photosensitive drum of copier,and very large scale integrated circuit.With the development of application of laser in organic reactions,it will be used as photosensitizer.In Guizhou Province,a large number of phosphorus rock resources are available.A lot of sodium fluorosilicate by-products are produced in phosphorus chemical industry every year.Currently,the sodium fluorosilicate by-products produced by Kalin Group and Wengfu Group have been reached 100,000 tons every year in Guizhou Province.If it is all used in the production of silicon tetrafluoride gas,economic benefit will be very significant.A method of producing silicon tetrafluoride with sodium fluorosilicate at high temperature is introduced in this paper.In production procedure,an additive sodium fluride is added,and the production is by means of some self-designed reaction equipments.The purity of sodium fluorosilicate can be 99.981%after being purified by washing method,,and it can be 99.997%after being purified by recrystallization,.,The purity of sodium fluride can be 99.984%after calcining and removing the sulfate and carbonate which can be easily decomposed.It is shown that the best ratio between sodium fluride and sodium fluorosilicate in producing silicon tetrafluoride is 3:1,and the optimum condition is that the decomposition temperature is 700℃and the decompositon time is 45 minutes.In this case,the decomposition ratio of sodium fluorosilicate can be 98.8%,and the decomposition products are loose without agglomeration.It is shown that silicon tetrafluoride can be purified by molecular sieve,modified molecular sieve,activated carbon.The purity of silicon tetrafluoride can be up to 99.906%after being purified by 4A molecular sieve,while the purity can be99.904%after being purified by 5A modified molecular sieve and the purity can be99.849%after being purified by activated carbon by the ionized helium gas chromatograph.In addition,new ideas about the subsequent purification of silicon tetrafluoride have been put forward in this paper.