Investigation of Etch Rate Uniformity of 60 MHz Plasma Etching Equipment

When the driving frequency of etching equipment using capacitively coupled parallel-plate plasma (CCP) becomes high, the etch rate tends to indicate a center peak. In this paper we discuss the improvement of the etch rate by leveling the center peak. From the results of numerical simulation using FEM, it can be considered that the center peak shape of the RF electric field distribution, which is enhanced by the resistivity of plasma, causes the center peak shape of the etch rate. Experimental results using an improved CCP, which possesses the ability to control the electric field distribution, demonstrate a refined etch rate. That is to say, the improvement of making a cavity behind the electrode provides the ability to control the electric field distribution. This distribution is governed by the dimensions of the cavity and the resistivity of the electrode. Less than 3% uniformity is obtained at 60 MHz for a wafer of 200 mm diameter using the improved electrode.