The pyrolytic decomposition of metal alkoxides (di-acetoxy-di-t-butoxy-silane, DADBS) during chemical vapour deposition of thin oxide films

In this study the effects of the nature of metal alkoxides on their vapour pressures and thermal decomposition chemistry are reported. The vapour pressure and the volatility of a metal alkoxide strongly depends on the steric effect of its alkoxy group. The thermal decomposition chemistry of one metal alkoxide (di-acetoxy-di-t-butoxysilane, DADBS) has been studied by mass spectrometry at temperatures between 423 and 923 K. The pyrolytic products were acetic acid anhydride and 2-methyl propene. The acetic acid anhydride is formed at temperatures above 473 K and 2-methyl propene is formed above 673 K by a P-hydride elimination mechanism. In these steps, a 6-ring intermediate is supposed to be formed. The silicon acid finally remaining is proposed to react by poly-condensation to SiOz coatings or powder.