Published online by Cambridge University Press: 25 February 2011
A model for the role of H atoms as an etchant specie during deposition of microcrystalline (μc) films of Si:H and SiC:H is explored. Growth rates and etch rates of films made by Hg-sensitized photo-CVD have been measured as a function of reactor pressure (between 5 and 0.5 torr) and H2 dilution (up to 30:1). Gas phase reactions and diffusion to the substrate of depositing and etching species, have been modelled. It is found that high H radical flux (not necessarily high H2 dilution) promotes μc film growth. There are two surface etching reactions by H radicals: (i) selective etching of uncoordinated Si surface atoms (amorphous phase) from the film, leaving behind the more etch-resistant μc phase; (ii) in SiC:H alloy systems, a selective etching of C species, causing a decrease in C incorporation into the growing microcrystalline film. Films with increasing carbon content do not contain a μc-SiC phase because hydrogen is not eliminated from the carbon containing film precursors, thus inhibiting the development of crystalline Si-C network.