The deposition of thin films by the decomposition of tetra-ethoxy silane in a radio frequency glow discharge

Abstract

Thin films of organo-silicon polymer and silicon oxide have been prepared by the decomposition of tetra-ethoxy silane in a radio frequency (1 MHz) glow discharge. The rate of deposition has been studied as a function of time, total pressure, nature of background gas, partial pressure of tetra-ethoxy silane, substrate temperature, subtrate position. With argon as background gas or with no background gas electron impact with the tetra-ethoxy silane molecule in the vapour phase is the dominant factor leading to its decomposition. With oxygen background gas the interaction of the tetra-ethoxy silane vapour and oxygen atoms is the main factor in the reaction mechanism. In an oxygen plasma non-crystalline silicon oxide films are formed, but in an argon plasma or in the absence of any background gas organo-silicon polymer films are formed. Both oxide and polymeric films were transparent, smooth, free from pin holes and strongly adherent to metals and non-metals. The infra-red spectra of the non-crystalline silica films deposited at high oxygen to tetra-ethoxy silane vapour ratios are similar, but not identical, to the spectra of thermally grown silica films. The composition of the silica films becomes oxygen deficient when deposition is carried out under low oxygen to vapour ratios at a temperature of 500°C and above. The nature of the hydroxyl groups present in the films deposited at low substrate temperatures was investigated by infra-red spectroscopy.