Processes for Production of Solar-Grade Silicon Using Hydrogen Reduction and/or Thermal Decomposition

High-purity Si used for photovoltaic applications, namely, solar-grade Si (SOG-Si), is commercially manufactured using the Siemens process. Although the present levels of supply satisfy the demand, there can potentially be a shortage of SOG-Si in the long term. To overcome the low productivity of the Siemens process, various types of SOG-Si production/purification processes have been developed as post-Siemens processes. Some processes are under development as new commercial processes. These processes can be classified into the following three categories: (1) hydrogen reduction and/or thermal decomposition of silane-based gases in improved Siemens-based processes, (2) metallothermic reduction of silicon halides by Zn or Al, and (3) upgrading metallurgical-grade Si by employing metallurgical purification methods. This paper presents a review of various types of SOG-Si production processes, particularly those based on the hydrogen reduction and/or thermal decomposition of halides and silane-based gases. These processes are classified on the basis of Si compounds used and the reaction types; further, the features of these processes are also analyzed. Future prospects for the development of new high-purity Si production process are also presented.