The influence of total pressure in the reactor and carrier gas on the chemical vapor deposition of Al from tri-isobutyl
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The influence of total pressure in the reactor and carrier gas on the chemical vapor deposition of Al from tri-isobutyl aluminum Takakazu Suzuki National Institute for Materials and Chemical Research, Tsukuba 305, Japan (Received 6 November 1995; accepted 14 December 1996)
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.
I. INTRODUCTION
Almost all papers on aluminum metallizing using organic aluminum have focused either on chemical vapor deposition (CVD) in a system at normal pressure (1 atm), as represented by the studies of Pierson1 and Malazgirt and Evans2 , or on low-pressure CVD in the range of less than 102 Pa (1 Torr), as found in the reports of Cooke et al.,3 Levy et al.,4 and Schmaderer et al.5 There have been virtually no papers focusing on the intermediate region between these two, that is, CVD under reduced pressures, from the 102 Pa to the 102 KPa level. However, it can be thought that the conditions under reduced pressures are also worthy of research, from the perspectives of film formation unity6 and the rates of film formation. Research into this area would make possible the systematization of aluminum deposition by means of CVD, especially the rates and film formation, it
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