Synthesis of silicon oxynitride from a polymeric precursor

Previous studies suggest that silicon oxynitride can be synthesized by pyrolysing polymers which are produced by the copolymerization of cyclic polysiloxanes and cyclic polysilazanes. The cyclic polysiloxanes required are [CH₃Si(H)O]_m with m=4, 5 and 6, and these can be produced by the hydrolysis of dichloromethylsilane. In the present work, a significantly improved combined yield of these cyclic polysiloxanes is reported. Three main reasons are attributed to this achievement: an improved hydrolysis procedure; optimization of the initial acidity of the reaction medium; and changes in the total reaction time. Thus a mixture containing > 95 mol% cyclic tetramer, pentamer and hexamer has been prepared and this represents a 20 mol% improvement over previously reported results. Investigations of the preparation and characterization of the cyclic polysilazanes, copolymers and silicon oxynitride will be described in Parts II–IV, respectively.