With the vigorous development of the photovoltaic industry, the domestic polysilicon industry has reached the world’s largest output in just over a dozen years, and the production cost has also reached the world’s advanced level. High-purity polysilicon material is the basic raw material of the information industry and solar photovoltaic power generation industry, and many developed countries in the world have listed it as a strategic material.
Electronic Grade Polysilicon Classification and Applications
The purity requirements of electronic grade polysilicon are extremely high, and it is the purest substance that can be obtained by human industrialization.
Electronic grade polysilicon can be divided into electronic grade polysilicon for zone melting and electronic grade Czochralski polysilicon. The quality requirements of polysilicon for electronic grade zone melting are more stringent. The monocrystalline silicon produced by the zone melting method has low oxygen and carbon content, low carrier concentration and high resistivity. It is mainly used in the manufacture of IGBTs, high-voltage rectifiers, thyristors, and high-voltage transistors. and other high-voltage and high-power semiconductor devices. The monocrystalline silicon wafers produced by the Czochralski method are widely used in integrated circuit memories, microprocessors, mobile phone chips, low-voltage transistors, electronic devices and other electronic products, and are more widely used. more than nine percent.
Electronic grade polysilicon production technology analysis
Judging from the current international development of electronic-grade polysilicon production technology, the production processes mainly include silane method, gas-liquid deposition method, fluidized bed, and improved Siemens.
The production cost of the silane method is high, and the silane used is explosive, flammable, and has poor safety. Even at room temperature, there will be a fire hazard. The gas-liquid deposition method was developed and controlled by Japan. In production, a tubular reactor is mainly used, and the operating temperature condition is controlled at 1500 °C to generate liquid silicon directly in the gas. Currently, it is still in the research and test stage. Not used for mass production. The fluidized bed process method mainly controls the product impurities comprehensively, so it cannot produce high-quality electronic-grade polysilicon.
An introduction to the modified Siemens method
At present, the mainstream production process of electronic-grade polysilicon is the modified Siemens method.
The improved Siemens process flow is as follows: silicon powder and hydrogen chloride produce trichlorosilane in the synthesis process, and the produced trichlorosilane enters the rectification process for purification to produce high-purity trichlorosilane. The trichlorosilane and the high-purity hydrogen produced in the exhaust gas recovery workshop enter the reduction process to produce polysilicon. The reduction workshop uses chemical deposition to produce polysilicon. The polysilicon is finally crushed, weighed and packaged and stored.
This method originated around 1960, and after more than half a century of development, it has achieved the ultimate in technology in all aspects. The domestic improved Siemens method was originally used for photovoltaic polysilicon. In the process of technological upgrading, insurmountable technical bottlenecks appeared in many fields, which limited the development of electronic-grade polysilicon. There are still many deficiencies in the quality control of polysilicon products in the production process. At present, my country has not fully mastered the core technology of Siemens method in the core technology testing of electronic grade polysilicon.
The main advantage of using this method to produce electronic-grade polysilicon is that it has a reliable and mature process. However, when using this method to produce electronic-grade polysilicon, the most obvious disadvantage is that it is difficult to effectively purify the raw material SiHCl3, compared with tail gas recovery and rectification. , its requirements are more stringent; in actual production, the process is also difficult to control, and the performance and structure requirements of electronic-grade polysilicon in the reduction furnace are also very high; in addition, because of the presence of Cl in the process gas, if it cannot be effectively controlled The production conditions of the process will seriously corrode the corresponding facilities and pipelines.
Electronic grade polysilicon is the most basic strategic material in the electronic information industry, which is related to my country’s national economy, society and national defense security. How to continuously and stably produce high-purity electronic-grade polysilicon to meet the needs of downstream enterprises for electronic-grade silicon materials is an important research topic faced by polysilicon enterprises. It is necessary to strictly control all processes in the whole process of polysilicon production, reduce various factors that may cause pollution to a minimum, and further implement lean and refined operations in the operation process, change bad habits, and improve management. Electronic grade polysilicon has a place in the market.