Study of the phosphine plasma decomposition and its formation by ablation of red phosphorus in hydrogen plasma

Mass spectrometry and optical emission spectroscopy have been used to study the chemistry of PH3 plasma decomposition as well as its formation by ablation of red phosphorus in hydrogen plasma. It has been shown that PH3 decomposition easily equilibrates at low levels of PH3 depletion (15%–30 %), this depending mainly on the rf power. The ablation of red phosphorus in H2 plasma produces phosphine in significant amount, depending mainly on the total pressure but also on the rf power. It has also been found that H* and PH* emitting species originate not only by the dissociative excitation of H2 and PH3, respectively, but also by the direct excitation of the same species in the ground state. Considerations are developed on how to derive the H-atom and PH radical densities by actinometry, under specific experimental conditions. Besides, the linear dependence of PH3 formation rate, rPH3, on H-atom density, [H], leads to the definition of the kinetic equation rPH3=k[H], and to the hypothesis that the formation of PH radical on the surface or its desorption is the dominant mechanism for PH3 production.