Thermal decomposition of tetraethoxysilane(TEOS) has been investigated in a vertical type LP-CVD reactor. The mass spectrum of reacting gas was found to have a feature corresponding to hexaethoxysiloxane ((H5C2O)3SiOSi(OC2H5)3). Trapped byproducts were found to include ethanol and ethoxy-based silica. Kinetic analysis of deposition rate profile indicated the existence of two intermediates. Feed gas residence time, as well as substrate temperature. directly affected the film quality.
A vapor phase reaction model was proposed to explain these results. According to this model. TEOS decomposes into ethylene and triethoxysilanol. The latter reacts with TEOS to form hexaethoxysiloxane as observed by mass spectrometry. The triethoxysilanol, hexaethoxysiloxane and TEOS should be actual deposition precursors. Similar reaction continues to form ethoxybased siloxane polymers which are trapped from the exhaust gas.