CONTROL OF PLASMA CHEMISTRY IN AN Ar/c-C_4F_8 INDUCTIVELY COUPLED DISCHARGE

摘要

A 2-dimensional model has been used to understand the dynamics of an Ar/c-C_4F_8 inductively coupled plasma discharge. It has been found that c-C_4F_8 readily dissociates in the discharge, and CF_2 and F are the dominant neutral products. With c-C_4F_8 < 20%, Ar~+ is the primary positive ion, F~- is the dominant negative ion, and the plasma is mildly electronegative. Increase in inductively coupled power decreases CF and CF_2 fluxes to the wafer due to enhanced dissociation of these fragments. F flux is however not much affected as increase in production rate is compensated by enhanced diffusional loss to walls. Increase in c-C_4F_8 concentration increases fluxes of F, CF and CF_2 to the wafer. It is also demonstrated that one can control plasma chemistry by changing the composition of the buffer gas. Partial replacement of Ar by He results in an increase of CF and CF_2 fluxes to the wafer due to enhancement of c-C_4F_8 dissociation rate.