Chemical vapor deposition (CVD) is a dominant process in the semiconductor industry for growing thin solid films on substrates. Crucial to the success of a CVD process is the design of the reactor. A typical reactor design consists of a quartz jar and a susceptor. The substrates are placed on the susceptor which is maintained at a constant temperature by either RF induction or radiant heating. Reactant gases are introduced into a flow chamber formed by a quartz jar and the susceptor. The shape of the flow chamber is designed to deliver reactants to the wafers efficiently to yield uniform deposition. The performance of the reactor is measured in terms of growth uniformity, throughput and chemical consumption.
The demand for improved performance of CVD reactor systems and processes has increased rapidly with the advent of very large scale integrated circuits which necessitates the growth of films with highly uniform thickness and composition to meet the decrease in feature size. Further, new devices for fiber optic and high speed digital applications demand new capabilities in growing epitaxial layers by CVD of different materials. The need for improved CVD reactors and processes is more critical for the growth of electronic materials such as the III-V or II-VI semiconductor compounds which have been found to be very difficult to deposit uniformly using existing reactors developed for CVD of silicon. This difficulty is due to the different rate-controlling mechanism of the chemical reactions: the growth rate for III-V or II-VI epitaxial layers is generally controlled by a mass transfer process (commonly called diffusion-controlled process) while the growth rate of silicon epitaxial layers is controlled by the reaction kinetics at the surface of the silicon wafer substrates. A suitable reactor for a diffusion-controlled system is generally more difficult to design since it is strongly dependent on the flow geometry which influences the mass transfer process. Recent reports indicate that even for the relatively simple epitaxial deposition of gallium arsenide, good uniformity is difficult to achieve. Consequently, good deposition of such material has been accomplished potentially in single wafer reactors in which the chemical flow over the one wafer can be fully controlled and thoroughly mixed. However, for commercial production one must be able to simultaneously and uniformly deposit layers on a multiplicity of substrates. Also, epitaxial deposition of ternary or quaternary layers is even more difficult due to the increase in the number of chemical reactants and the added parasitic deposition on the reactor walls. Hence, improved apparatus design is required to obtain better thickness uniformity, with high throughput and processing yields, especially in the case of diffusion-controlled CVD systems.
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