The SST Polysilicon Process

The production of polysilicon is a cleaning process that can be likened to a washing machine: in various purification steps, metallurgical silicon with a low purity level of 98% is converted into high-purity polysilicon with a specification of "10N+" (=9.999999999+). "Solar grade" poysilicon corresponds to 9N, "electronic grade" poysilicon corresponds to 11N. The SST process facilitates production of solar, as well as electronic grade polysilicon.

Common processes are dealing with limitations like high energy consumption and not being able to produce highest quality material.

SST developed a process that excells because of its guaranteed quality standard at significant lower energy consumption compared to conventional production methods. 



1. Hydrochlorination

TCS (Trichlorosilane) is produced in a fluidized bed reactor using STC (Silicon Tetra Chloride), mgSi (metallurical Silicon) and H2 (Hydrogen) as feedstock. The SST Hydrochlorination incorporates two chemical process steps in one reactor: first, the conversion of STC to TCS, second, the synthesis of mgSi with HCl from an intermediate reaction to TCS.

The SST Hydrochlorination can be easily integrated into existing Siemens plants. The process saves about 70% of energy in comparison to direct chlorination in combination with STC/TCS converters.

Start-up and operation are easy and safe.

2. Disproportionation

The process is based on catalytical disproportionation of TCS to Monosilane (25%) and STC (75%) in one process step. The disproportionation is followed by a Monosilane purification. An (optionally available) purification step removes residuals of nitrogen, hydrogen and oxygen containing compounds to meet electronic grade Polysilicon specification or high-end Monosilane Gas specification.

3. Chemical Vapor Deposition


The MS-CVD Deposition System of SST is the only monosilane based high-efficiency CVD system on the market.

It has many advantages:

1. does not require any kind of vent gas recovery unit

2. no chlorides or by-products such as STC or HCl produced in the deposition process

3. low deposition temperature for reduced energy consumption compared to TCS deposition

4. low material intensity CVD system with highly reliable and automated processing system

5. minimized emissions of amorphous silicon, less than 2%

6. easy to integrate into existing plants

The SST MS-CV System is available with 2 different reactor capacities (18 and 27) for a maximum of flexibility in production. It is equipped with a medium voltage ignition system for safe start up of the process.