A Study of the Technology for Recovery of the Polysilicon Attached to Graphite Chucks in Siemens Process of Polysilicon Production
|Keywords||Siemens Process polysilicon silicon on graphite chuck coating|
In PV industry, crystalline silicon solar cells predominate in solar cell, which lead to a huge demand for high purity polysilicon. The mainstream process to produce polysilicon is Siemens Process., in this process the graphite chuck is used to connect the initial filament silicon with the metal electrode to work as the basement for the silicon deposition, so there is some silicon attached to the graphite chuck. To make full use of this part of silicon can help to reduce the comprehensive unit price cost of crystalline silicon solar cells. In this paper we report the analysis of interface of graphite and silicon, a method and process to strip the silicon from graphite. We also report the study and method to prepare the coating layer on graphite electrode before the deposition of silicon, which can help to strip the silicon from graphite and prevent carbon contamination and have a good conductivity on high temperature and does not cause new contamination to silicon.In this paper, our results include:The SiC found in the interface between graphite and silicon and the silicon deposited into the hole of graphite make it difficult to remove the graphite from silicon; The mixture of concentrated sulfuric acid and nitric can crack the graphite from bulk into small particles so that the graphite particles will drop from silicon gradually, it is most powerful when with a volμme ratio about3:1, but there is always a few graphite and SiC remained on the surface of silicon; with a more concentrated hydrofluoric acid and nitric treatment, the remaining graphite and SiC are removed and the silicon is obtained with a silicon loss less than10%; The coating layer of glass carbon on graphite chuck we prepared has a smooth and good densification surface and a good conductivity, the glass carbon is a good coating layer material for graphite chuck. The SiC coating layer on graphite chuck we prepared is promising. From our investigation, we suggest the silicon material can also be a option of coating layer for graphite electrode by a low temperature CVD reaction.