Mass transport characteristics in a pulsed plasma enhanced chemical vapor deposition reactor for thin polymer film deposition

Abstract

A pulsed plasma enhanced chemical vapor deposition (PECVD) reactor is used for the preparation of thin polyacetylene films. A theoretical model based on the mass transport characteristics of the reactor is developed in order to correlate with experimentally obtained spatial deposition profiles for the acetylene plasma polymer film deposited within the cylindrical reactor. Utilizing a free radical mechanism with gas phase initiation of the polymerization reaction as the rate controlling step, a system parametric study is performed to predict the Peclet number range of operation for the pulsed PECVD reactor. This parametric study indicates radical decay by diffusion to the reactor walls to be the significant physical phenomenon in the system. It is concluded that a quasi-steady-state model is a good tool for predicting the important mass transfer phenomena occurring in the pulsed plasma reactor. Index Terms-Damkohler and Peclet numbers, plasma polymer, radical decay, thin film. I. INTRODUCTION P LASMA processing techniques for thin film deposition have gained increasing importance in the semiconductor industry due to the advantages of lower processing temperatures as well as the wider parameter choices they provide for the manipulation of desirable film properties. The mechanism of plasma-induced chemical reactions is quite complex, with the physical and chemical properties of the deposited film being influenced by a large number of system parameters. These include, for example, the type of electrical discharge, reactor geometry, substrate characteristics, substrate potential, substrate location with respect to the plasma, plasma energy density, and operating pressure [1]. Because of such variety and complexity, plasma processing is often practiced as an art, with the theoretical developments, if any, usually following way behind. This paper describes, for our studies on the polymerization of acetylene in a pulsed PECVD reactor, a mass transport model developed in order to predict spatial deposition profiles for the polymer within the reactor.

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