Plasma chemistry of He/02/SiH4 and He/N20/SiH4 mixtures for remote plasma-activated chemical-vapor deposition of silicon dioxide

Remote plasma-activated chemical-vapor deposition (RPACVD) provides a means to deposit thin dielectric films with low ion bombardment and while having high selectivity in generating precursors. In RPACVD of SiO,, gas mixtures of He/O2 or He/N20 are passed through a plasma, producing radicals and excited states that are mixed with silane downstream. Excited states produced in the plasma and precursor species produced by these reactions then flow to the substrate. Although high-quality SiOs films can be produced by RPACVD, the gas-phase deposition precursors have not been identified. A two-dimensional plasma chemistry model is described, and results from that model are used in a discussion of possible gas-phase precursors for SiOs deposition. In particular, the formation and transport of silanols (SiHsO and SiHsO) are examined as a function of gas mixture, power deposition, and geometry. It is found that the fluxes of SiHZO, SiHsO, and SiHs are sufficient to account for the observed deposition rates; whiie systematic dependencies of the fluxes of HSiO and SiO discount them as being deposition precursors. He/N,O/SiH+ mixtures differ from He/O,/SiHh mixtures by providing larger fluxes of SiHs to the substrate, while the fluxes of SiH*O, SiHsO, and O,(‘A) are significantly less.