LIBS Technique for Fast Impurities Identification in Metallurgic Grade Silicon

Abstract

Thanks to the rapid growth of the photovoltaic market the silicon demand is continuously increasing. The shortage of purified silicon between 2004 and 2008 induced a strong price increase and trigged a capacity expansion as well as the introduction in ingot production of the so called “upgraded metallurgic grade silicon” (UMG-Si) as a feedstock. However, new solar grade silicon might contain significant higher fractions of impurities. It is well known their impact on the final cell quality but the debate is open about what are the acceptable contamination levels within the purified silicon feedstock also because it is well known that during the growth process and cell manufactory the material quality improves. In the recent period in the market there is an increasing availability of silicon feedstock at lower cost but its quality is not always guaranteed. In this paper we report a new fast in line characterization tools for feedstock analysis based on the Laserinduced breakdown spectroscopy. We applied this technique to the characterization of metallurgic grade silicon feedstock with the aim of valuate the applicability of this technique in the photovoltaic industry as in-line portable characterization tool. Different silicon grade feedstock were analyzed and selectivity and detection limit for the main impurities present in the silicon feedstock were determined.