Chemical vapor deposition of silicon dioxide barrier layers for conductivity enhancement of tin oxide films

Abstract

Silicon dioxide for use as a diffusion barrier between soda lime glass and fluorine-doped tin oxide is deposited uniformly by atmospheric chemical vapor deposition from silane. oxygen, and nitrogen using a simple single-slot injector head. With a sufficiently thick silicon dioxide layer, the conductivity of the tin oxide is greatly improved by reducing the diffusion of sodium into the tin oxide as it is deposited between about 500 to 600 °C. Based upon the conductivity of thin lightly doped tin oxide films, it appears that at least 250 nm of silicon dioxide deposited on soda lime glass are required to essentially eliminate the diffusion of sodium into the tin oxide. However, only about 10 nm of silicon dioxide are required to obtain almost the full benefit of 250 nm thick films for moderately doped tin oxide films approximately 500 nm thick, The silicon dioxide deposition process is examined between 350 and 580 °C. The activation energy for the deposition is about 27 kJ/mole. Peak and average film deposition rates greater than 50 nm/sec and 10 nm/sec, respectively, may be obtained. The dependence of the film growth rate on the silane, oxygen, and propylene (an inhibitor) concentration is examined. The deposition rate is found to be limited by the rate of gas-phase reactions. Deposition conditions which yield high silane utilization and good film uniformity are discussed. The origin of undesirable by-product powder is studied. At low silane concentration, powder is mainly formed as the gases cool due to condensation from intermediate species.