Deposition and Etching Mechanisms in Plasma Thin Film Processes

Abstract

Plasma etching/reactive ion etching and plasma enhanced chemical vapour deposition are two critical thin film technologies used in preparing advanced microelectronics such as very large scale integrated circuits, VLSICs, and thin film transistors, TFTs. Both technologies include similar mechanisms: plasma phase chemical reactions, particle transport, and surface reactions. For etching applications, the film surface atoms are constantly reacted with chemicals supplied from the plasma phase reactions. Reaction products are instantaneously removed. For deposition applications, chemicals supplied from the plasma phase react on the film surface. Reaction products remain and accumulate on the surface. In an actual plasma process, the etch and deposition mechanisms may not be exclusive. In this lecture, the author presents a general model of the thin film plasma process, where both deposition and etching mechanisms are assumed to coexist. With the variation of process parameters such as reactive gases, power/frequency, ion bombardment energy, and the surface temperature, one of the mechanisms may become the dominate factor. Examples of the transition between film etching and deposition phenomena in several plasma etching and deposition processes will be given. For microelectronics applications, the plasma process affects the film quality as well as device characteristics. Examples on these issues also will be given. In summary, a general model on plasma thin film processes used in the TFT fabrication, which includes both deposition and etching mechanisms, is presented.