The 147 nm photolysis of phosphine—silane mixtures

Abstract

The 147 nm photochemistry of PH 3SiH 4 mixtures was investigated at various ratios of the substrates such that more than 90% of the radiation was absorbed by PH 3. The photodecomposition of PH 3SiH 4 mixtures results in the formation of H 2, Si 2H 6, PH 2SiH 3 and P 2H 4 in the gas phase and a solid deposit which is probably a mixture of phosphorus and polymeric phosphorus silicon hydrides PSiH x . On photolyses of mixtures of the deuterated derivatives the analogous deuterated products are formed. The quantum yields for the gaseous products and for depletion of the substrates were measured. For the PH 3SiH 4 system it was found that quantum yields depend on the composition of the reactant mixture and on the light intensity of the incident radiation. When deuterated compounds were used significant changes in all quantum yields were observed. Parent-ion mass spectrometric analysis of phosphorus- and silicon-containing volatile products indicates that PH 2SiH 3 is formed by two pathways: (i) combination of PH 2 and SiH 3 radicals; (ii) insertion of SiH 2 into PH 3. A mechanism involving primary photodissociation of PH 3 is proposed which is in accord with the experimental observations as well as with our knowledge of the photochemistry of pure PH 3 and SiH 4.