Transition metal co-precipitation mechanisms in silicon

Formation mechanisms of precipitates containing multiple-metal species in silicon are elucidated by nano-scale morphology and phase investigations performed by synchrotron-based X-ray microprobe techniques. Precipitates formed at low (655 degrees C and high (1200 degrees C+) temperatures exhibit distinguishing features indicative of unique formation mechanisms. After lower-ternperature annealing, co-localized single-metal silicide phases are observed, consistent with classical models predicting that dissolved, supersaturated metal atoms will precipitate into solid second-phase particles. Precise precipitate morphologies are found to depend on the local crystallographic environment. In precipitates formed during slow cooling from higher-temperature anneals, nano-scale phase separation and intermetallic phases are evident, suggestive of a high-temperature transition through a liquid phase. Based on experimental results and phase diagram information, it is proposed that under certain conditions, liquid metal-silicon droplets may form within the silicon matrix, possibly with the potential to getter additional metal atoms via liquid-solid segregation. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.