Effect of Glow Discharge Conditions on Structure and Thermal Properties of Polysilazane Thin Films

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Abstract
Polysilazane thin films were prepared by glow discharge polymerization of hexamethylcyclotrisilazane in mixture with various gases: argon, nitrogen, hydrogen and ammonia. The effect of gas type on thermal stability and chemical structure of glow discharge polysilazane was studied. Thermo-gravimetric measurements performed within a temperature range of 20–1000° C, showed that the best thermal stability was exhibited by polysilazane prepared at the presence of ammonia in the reaction mixture. IR analyses data revealed that polymers prepared from mixture with ammonia or hydrogen contained more Si-H groups than those obtained with argon or nitrogen. It proves that in the presence of ammonia or hydrogen, greater monomer fragmentation through Si-C bonds cleavage takes place. More detailed investigations were carried out for polysilazanes prepared in mixture with ammonia. It was found that thermal stability as well as chemical structure of polymer depend strongly on polymerization conditions, i. e., ammonia contents in the reaction mixture, deposition time, discharge current density. Thermal stability of polysilazane improved with the increase in deposition time and current density. Increasing these parameters caused also the Si-NH-Si bonds content in the polymer to grow. The results prove that ammonia is a reactive comonomer and that the polymerization of hexamethylcyclotrisilazane at the presence of this gas may proceed through the formation of Si-NH-Si bonds.