Solar Grade-Silicon, Ingot, Wafer Technology and Market Trend

Solar Grade-Silicon, Ingot, Wafer Technology and Market Trend (2008~2012)
Figure 2.19. Tube Reactor in Joint Solar Silicon (JSSi) Process
Source: Joint Solar Silicon
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The traditional Siemens process decomposes silane in silicon seed (U-rod),
whereas the Joint Solar Silicon reactor decomposes silane in reactor’s interior
space that it is called “free space reactor method”. The method supplies
hydrogen and silane to the reactor’s interior and enters heat to walls to
decompose silane away from the walls. Like in the Siemens process, the free
space reactor method does not require equipments for silicon seed preheating
and is able to prevent pollutions from graphite which composes the preheating
equipments. The method uses monosilane rather than chlorosilane for raw
materials because the monosilane enables low temperature processes and
decomposes well that it converts gasses to silicon in reactors with single
process. However, the monosilane may possibly explode when it is in contact
with oxygen that reactors must be designed carefully to prevent such outcome.
It is also more expensive than trichlorosilane. The thermal decomposition
reaction of silane is like the following.
SAMPLE
SiH4 -> SiH2+H2
SiH2 + SiH4–> Si2H6
SiH2 +Si2H6 -> Si3H8
The silicon powder manufactured through reactors undergoes high density
process for easy handling, delivery, and loading. Here, the density increases
from 50g/L to 500g/L. The figure below shows silicon powder that finished the
high density process. The powder is melted and produced into ingot to be
manufactured into final products.
Jan’09