TCS Purification

Trichlorosilane Purification Process Technology Package

Poly Plant Project’s (PPP’s) TCS Purification Process Technology Package includes the chemical processes, equipment, operating parameters, mass and energy balance, control systems, co-products, and co-product recovery systems for the production of purified trichlorosilane (TCS) used in the deposition of polysilicon. The Package includes start-up and operating technology, passivation, commissioning, storage methods, quality control techniques, risk analysis, and safety recommendations.

First, TCS is separated from the metal chlorides and heavy impurities. The TCS is then piped to a series of distillation columns for purification to the part-per-billion impurity level. In the distillation columns, the chlorine compounds of the impurities are collected and separated. The liquid chlorine compounds are sent to waste disposal because they are contaminated with boron, phosphorus, carbon, and various other metals. The STC from the process is collected and sent to the reactors for conversion to TCS. The purified TCS is collected in a storage tank to be used as a feed gas for the CVD reactors.

The distillation columns are designed to:

• Remove heavy impurities, metal chlorides, and higher order chlorosilanes
• Separate and collect STC for conversion to TCS
• Remove hydrocarbons and light-boiling compounds
• Remove carbon chlorosilanes compounds

TCS is purified by distillation and adsorption columns. An advanced design uses computer simulation, based on operational plant experience, to design the number of trays, reflux ratios, column sizes, and number of columns required to efficiently purify TCS.

In the distillation process, some of the trichlorosilane is consumed as the impurity species are separated and removed. A cost-efficient process requires recovery and purification of unreacted TCS and co-product STC from the CVD reactors. Therefore, the purification system must be designed to process a large amount of recycled chlorosilanes. The recycled chlorosilanes affect the number and size of the columns. An efficient purification system uses a minimum number of columns which are sized to process all initial and recycled volumes. Demand for a higher purity than solar grade polysilicon requires using more columns and/or higher reflux ratios, thereby increasing energy use.

Benefits of PPP’s Advanced TCS Purification Technology:

• Technology based on designs by experienced engineers to reduce capital expense and operating cost, with minimal loss of chlorosilanes
• Library of impurities data enabling the optimum process design to achieve purity specifications
• Design capacity to include recycling of chlorosilanes from vent gas recovery system
• Plant operational experience to meet production goals while meeting process and product specifications
• Start-up and operating technology
• Passivation of piping, columns, tanks
• Commissioning of all processes and equipment
• Storage methods
• Quality control techniques
• Risk analysis and safety recommendations