Inductively Coupled-Plasma Mass Spectrometry (ICP-MS) for PV Silicon Solar
By Kevin Nguyen, SEMI Standards
Manufacturers of single crystalline and polycrystalline silicon used in solar cells purchase or produce their own silicon feedstock materials. This silicon is referred to as silicon feedstock for silicon solar cells and can take many physical forms including granules, powders, polycrystalline silicon chunks, wafers, reclaimed silicon, or top and tail cuts from silicon boules.
The purity level of silicon feedstock for silicon solar cells can affect solar cell efficiency, as well as the productivity of some processes used to transform silicon into solar cells.
SEMI provides several standardized test methods in detecting trace element in silicon feedstock for production of silicon solar cell. For instance, SEMI PV1 (GDMS), PV10 (INAA), PV25 (SIMS), and PV43 (Infrared Detection) describe various test methods using different instrumentations. However, the existing SEMI test methods do not provide for the direct measurement of a broad range of elemental impurities concentration in parts per billion (ppb) level in all grades of silicon feedstock by bulk digestion Inductively Coupled-Plasma Mass Spectrometry (ICP-MS).
The ICP-MS test method was initially started in 2008 by Dr. Hugh Gotts (Balazs NanoAnalysis). Until now, this test method has been balloted 4 times under the stringent review of the SEMI International Standards community. Under Dr. Gott’s thoughtful determination to achieve industry consensus, this test method was finally approved by the SEMI North America PV Materials Committee which recently met on April 3, 2013 in San Jose, California.
Further procedural review is being conducted by the International Standards Committee Audit and Review Subcommittee. When completed, the document is expected to be published in June 2013 and will add to the Photovoltaics volume of 43 already published SEMI PV Standards.
As with most SEMI PV test methods standards, a round robin test is performed to validate the ICP-MS test method. The Analytical Test Method Task Force is now pursuing an interlaboratory study to obtain the precision statement for this test method.
When the ICP-MS Test Method is published, solar cell manufacturer and others may use it to monitor the bulk trace elemental impurities in silicon feedstock that affect the performance of the silicon solar cell.
In addition, this test method can be used to qualify PV silicon feedstock for production of single crystal or polycrystalline silicon. Included among the many other benefits are unifying protocol and test results among worldwide laboratories for research and development, purchase or sale of silicon.
If you have any questions about participation or would like to join our task force to address additional test method needs, please contact Kevin Nguyen at email@example.com. For more information on Standards activities at SEMI or upcoming meetings, please visit: www.semi.org/standards or www.pvgroup.org/standards
SEMI, Standards Watch – May 2013