Optical diagnostic studies of trimethyl phosphine-containing radio-frequency discharges

We have investigated the decomposition of P(CH₃)₃ in 13-MHz, radio-frequency discharges in He and H₂. Relative concentrations of atomic phosphorus were estimated actinometrically by measuring P emission intensities, relative to Ar, while quantitative, relative P₂ number densities were measured by ArF excimer laser-induced fluorescence. A radiative lifetime of 10.5±1.0 ns was measured for the v=11 level of the C¹ _u ⁺ state, resonantly excited by the 193 nm laser. Additions of P(CH₃)₃ to He discharges reduce the electron energy distribution as sensed by the quenching of optical emission from He and trace amounts of added Ar, and thereby causes the overall process P(CH₃)₃P+3CH₃ to occur with maximum efficiency at very low (0.5%) P(CH₃)₃ additions. H₂ discharges are 10 times less efficient at producing P and P₂, due to the lower electron energies, and possibly to hydrogenation reactions. P₂ production in both He and H₂ discharges increases linearly with pressure up to at least 10 torr. Under optimum conditions, plasma decomposition of P(CH₃)₃ (and by analogy PH₃) promises to be an attractive source of phosphorus for growth of phosporus-containing thin films.