The influence of total pressure in the reactor and carrier gas on the chemical vapor deposition of Al from tri-isobutyl aluminum

Abstract

The influence of total pressure in the chamber and carrier gases on the chemical vapor deposition of aluminum using tri-isobutyl aluminum was studied. The superior penetrability of chemical vapor deposition is expected to make it effective for aluminum deposition onto complex-shaped materials such as turbo-charger rotors, fibrous preform, and multifilament. It may also be a suitable method for the development of fiber-reinforced composite materials. The apparatus was composed of a raw material gas supply system, a three-zone electric furnace, a reaction chamber, an auto pressure controller, and an exhaust system. Aluminum was deposited onto a graphite fiber in the quartz reactor. The results show that, in the diffusion rate-determining stage of aluminum thermal decomposition, the rate of deposition for aluminum shows a marked increase as the pressure increases; in contrast, in the reaction rate-determining stage, this tendency is limited. This can be explained by the fact that, as the total pressure decreases, the gas diffusion coefficient becomes larger, and there is an increase in the uniformity of film formation. On the other hand, as the carrier gas flow rate increases, the amount of raw material supplied increases; consequently, a higher rate of deposition is obtained. Moreover, in the diffusion rate-determining stage, there is a tendency for an increase in flow rate to elevate the probability of arrival of the raw material, and, in combination with high temperatures, for nucleus generation to be accelerated and the average diameter of aluminum granules to become smaller. In the reaction rate-determining stage, there appears to be hardly any dependency of granule diameter on the flow rate. When Ar or He is used as the carrier gas, under the same conditions argon, rather than helium, is seen to increase the rate of deposition.