Synchronously Excited Discrete Chemical Vapor Deposition of Ta2 O 5

Abstract

A versatile chemical vapor deposition (CVD) technique is proposed which has two noteworthy technical features: (i) alternate or intermittent introduction of source vapors followed by evacuation and (if) one or more excitations synchronized with the sequence of vapor introduction. Since it can select and identify the place and time for the occurrence of reactions and excitation among source molecules, this technique also promises to be valuable in investigating the use of conventional CVD processes with unfamiliar materials. In this work, the technique is used to investigate the conventional photo and thermal CVD processes of tantalum pentoxide film using tantalum pentachloride and oxygen. The results indicate that significant deposition occurs even without the vapor phase reactions among source vapors and that photoexcitation of the substrate surface greatly enhances film deposition. In the course of the investigation, it was observed that temporary photoexcitation and ozone supply produced a high rate of film deposition even at temperatures lower than 300°C.Chemical vapor deposition (CVD) consists of mixing several kinds of source molecules in the vapor phase followed by reacting and, in some cases, exciting them and finally growing a solid film on the substrate. A CVD process generally involves a large number of complex elementary processses I'2 such as reduction, oxidation, abstraction, addition, and decomposition, as well as adsorption, desorption, and excitation by photons and plasma. In addition, the participants in the process include not only source molecules but also intermediates and even waste molecules. 3'4 Since these elementary processes involving various participants occur simultaneously and irregularly both in the vapor phase and on the substrate, I CVD often yields less reproducibility and undesirable mixtures containing several kinds of components with different properties and compositions. Obviously, these aspects arise from a lack of both a clear understanding of and better control over the elementary processes, especially the rate-determining steps.This paper proposes a versatile CVD technique, which is called "synchronously excited discrete chemical vapor deposition" (SEDCVD). Versatility stems from two noteworthy features of this technique: (i) two types of discrete (alsternate and intermittent) introduction of source vapors followed by complete evacuation and (if) one or more excitations synchronized with the sequence of vapor introduction. These features make it possible to select and identify whether certain reactions and excitation among source vapors occur in the vapor phase or on the substrate.The following section will describe the concept of SEDCVD and explain why the technique can provide such an improved performance. An example of the usefulness of SEDCVD will be described in subsequent sections. Specifically, this technique will be used in an investigation into rate-determining steps (elementary processes) in photo and thermal CVD of tantalum pentoxide (Ta2Os) using tantalum pent...

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