Impurity composition of high-purity isotopically enriched monosilane and monogermane

Abstract

The impurity composition of ²⁸SiH₄, ²⁹SiH₄, and ³⁰SiH₄ silanes and ⁷²GeH₄, ⁷³GeH₄, ⁷⁴GeH₄, and ⁷⁶GeH₄ germanes isotopically enriched to above 99.9 at % has been studied by gas chromatography/mass spectrometry using capillary adsorption columns. Impurities have been identified by comparing their mass spectra with NIST data and information available in the literature, and by inferring their structure from fragment ions and retention times. We have identified 53 impurity substances in silanes and 42 in germanes: permanent gases; saturated, unsaturated, halogen-containing, and aromatic C₁–C₉ hydrocarbons; their homologues; alkyl derivatives of silane and germane; chlorogermane; siloxanes; fluorosiloxanes; sulfur compounds; and dioxane. The silicon- and germanium-containing impurities have been shown to be isotopically enriched, as the major component. The detection limits of the impurities are 5 × 10^–8 to 3 × 10^–5 vol %, comparing well with the best results in the literature.