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

Abstract

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)3→P+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.