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Figure 7:
Parameter 4 - metal contamination level after process
The surface metal impurities for the different size classes after the process had been
measured. Impurities were tested for Fe, Ni, Cr, Zn, Na, Al, by ICP-MS, total over
170 single samples.
Due to no direct contact of the Si with the electrodes lowest surface contamination
could be measured on average below 9ppb/w over all measured size classes. Coarser
products show due to the better surface/weight ratio lower impurities. A chemical
treatment step (etching) is not required for solar grade materials.
3 Industry implementation and key factors
For the Si-producers key factors can be defined which justify an implementation of
the described process into manufacturing lines.
1.
Product yield
2.
Product shape
3.
Low metal impurities
4.
Total cost of ownership
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