CO2-LASER CHEMICAL-VAPOR-DEPOSITION OF SILICA FILMS IN A PARALLEL CONFIGURATION - A STUDY OF GAS-PHASE PHENOMENA

Low-temperature silicon oxide films were successfully grown using SiH4-N2O mixtures by a continuous wave-CO2 laser tuned at 10.6 mum in a parallel configuration. The reaction was initiated by high gas temperatures obtained as a result of multiple successive absorption of photons by silane molecules, followed by energy redistribution through intermolecular collisions. The study of film growth rate and properties as influenced by both total gas pressure and substrate temperature for a gas mole ratio psi=P(N2O)/P(SiH4)=30 demonstrated that peak gas temperature controls the deposition rate, revealing that the process is driven by gas phase reactions. For the process, apparent activation energy was determined to be 45 kcal/mol, and apparent overall order of the reaction m=-1.5. The gas temperature distribution was calculated by means of a steady-state energy balance in the gas volume, explaining very well the experimental growth rates and the properties of the obtained films.