Quality of silicon as a driver for competitiveness
The international polysilicon market is facing a longer-lasting oversupply situation leading to a high pressure and price decline. To overcome this price-based competition product quality and sustainability may play a more important role in the future. Several equipment improvements and process optimizations enabled the SPB and SPT team during the past years to achieve better and better material quality in its own production plant.
Using the Bitterfeld site, originally designed for solar-grade quality, the impurity content could be reduced to accomplish the SEMI Cat. I. This evolution is illustrated in the graph below.
A representative amount of a silicon was also used for Cz-crystallisation. Low levels of impurities in SPB polysilicon leads to high yields in Cz-crystallization and excellent crystal quality measured by QSSPC with lifetimes beyond 1,000 μs.
Material from our plant was converted into ingots/blocks and cut into wafers. Up to now all silicon and produced wafers were converted into solar cells by different customers and solar cell efficiency was as good as cells produced from material purchased from major silicon producers in Europe, US and Japan.
Furthermore, not only impurities but also mechanical and crystallographic material properties could be harmonized and enhanced to achieve product suitable for float zone (FZ) processing, which is an ultimate requirement in polysilicon manufacturing.
The continuous efforts for the optimization and development which we implement in our plant lead to the production of high quality polysilicon for the FZ processes. We are able to identify the influencing variables and to control quality parameters to achieve target specification for the FZ rod.
See also our Company flyer feed rod for FZ
Key of our success
This successful story of producing different silicon qualities is founded in our capabilities in chlorosilane processing, i.e. distillation parameters, impurity removal steps, namely boron, or contamination-low STC conversion. Also other key factors, i.e. the own slim rod manufacturing, are well under control, delivering the basis for a well-defined high-class product. This underlines the importance of powerful impurity removal, and additionally the relevance of no-contamination schemes throughout the entire supply chain.