Low temperature deposition of Al_2O_3 insulating thin films by photo-CVD

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Al_2O_3 thin films were deposited by photo-CVD using Aluminum- triisopropoxide(ATI) as a source material, and their properties were characterized. 1. The deposition rate increased under N_2+O_2 or N_2+H_2 atmosphere compared with that under N_2 atmosphere (without UV). The activation energy of deposition was 1.5 kcal/mol and 3.5 kcal/mol for N_2+O_2 and N_2+H_2 atmosphere, respectively. These values are small compared with the value of 18-20 kcal/mol for the decomposition deposition under the N_2 atmosphere, which shows that reactions of ATI with O_2 or H_2 help Al_2O_3 deposition. It turned out from the O_2 flow rate dependence of the deposition rate that the deposition due to the Langmuir-Hinshelwood mechanism of ATI and O_2 molecules occurred as well as the deposition due to the thermal decomposition of ATI.With UV irradiation of low-pressure Hg lamps under N_2+O_2 atmosphere, the deposition rate increased largely at low substrate temperatures less than 300 C, and the activation energy of the deposition reaction was as small as 1.5 kcal/mol. The deposition rates were almost constant in the O_2 flow rate range of 60 - 300 sccm. The 185 nm light from the Hg lamps was found to be strongly responsible for the increase in the deposition rate. 2. The Al_2O_3 films deposited were characterized mainly by the dielectric loss factor tan at, 100 Hz. The samples prepared by photo-CVD under N_2+O_2 atmosphere at 260 C showed smaller tan values compared with those of the samples prepared by thermal CVD under N_2 or N_2+O_2 atmosphere, that is, the film quality was improved largely by photo-CVD. The values of tan were almost constant under the conditions of the O_2 flow rate of 20 - 300 sccm and the substrate temperature of 280 - 340 C. The typical value of tan was 2.5 % at the substrate temperature of 280 C.In conclusion, Al_2O_3 films with high quality were obtained at high deposition rates at low substrate temperatures less than 300 C by photo-CVD under N_2+O_2 atmosphere.