CHEMICAL-VAPOR-DEPOSITION OF SILICON-NITRIDE IN A MICROWAVE PLASMA-ASSISTED REACTOR

Microwave plasma assisted chemical vapour deposition was used to produ ce silicon nitride films on silicon substrates from mixtures of methan e and nitrogen. Deposition temperatures varied from 800 to 1000 degree s C and pressure varied from 53.2 to 79.8 x 10(2) Pa. Gas mixtures wit h low methane content resulted in no reaction. Gas mixtures with high methane content produced an amorphous carbon film on the silicon wafer surface. At intermediate methane contents, the process produces a mix ture of alpha and beta silicon nitride. A mechanism is proposed accord ing to which the silicon surface is chemically etched by the activated methyl radicals forming Si(CH3)(4), which then reacts with nitrogen a toms (or ions) to form the silicon nitride. The morphology of the indi vidual crystals evolves from platelets to needle-like depending on the deposition conditions, and on the surface coverage of the silicon sur face.