Cold-container crystal growth of “last-to-freeze” silicon samples, and enhanced detection of metallic impurities by ICP-MS

摘要

Inductively-coupled cold containers are used to melt silicon samples of various shapes, and the electromagnetic forces on the melt form an isolated, well-controlled last-to-freeze region where impurities in the sample are concentrated by their small segregation coefficients. Inductively-coupled plasma mass spectrographic (ICP-MS) values for impurity concentrations in the ∼0.1 g enriched region are related back to the ∼30 g original sample, providing lower limits for impurity concentrations that are below the typical ICP-MS 0.1 ppb detection limit. There is no rod or granular sample geometry restriction as with float-zone impurity concentration techniques, and no obfuscating impurity introduction from quartz crucibles or graphite hot zones.