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 °C) and high (1200 °C+) temperatures exhibit distinguishing features indicative of unique formation mechanisms. After lower-temperature 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.