Silicon on Dust Substrate: The Effect of Powder Size on Ribbon Production

Abstract

The silicon on dust substrate process is a two-step technique to produce multicrystalline silicon (mc-Si) ribbons directly from gaseous feedstock. Silicon pre-ribbons of very small grain size (ranging from nano to microcrystalline), with a porous structure and dimensions up to 25 Â 100 mm 2 , are obtained using an inline optical chemical vapor deposition (CVD) system operating at atmospheric pressure and at low temperatures (<600 C). Using silane as the gaseous precursor, nano or microcrystalline silicon layers can be grown, on top of silicon powder substrates, moving at constant speed, and crossing three hot deposition regions several times. The growth rates (GR) vary from 13.4 to 73.2 μm min À1 , depending on the grain size of silicon powder. The last step is a floating zone (FZ) recrystallization technique, where the silicon pre-ribbons obtained in the CVD step, become solid mc-Si ribbons. The success of recrystallization depends on the grain size of silicon powder used as substrate on the CVD step, with lower grain sizes powders delivering better results. For the lower size powder substrates, multi-crystalline areas of 5-20 mm 2 were obtained, with an average crystal size in the (0.1; 1) mm range.