Improvement in Etch Rate Uniformity Using Resistive Electrodes with Multistep Cavity

When the driving frequency of etching equipment using capacitively coupled parallel-plate plasma (CCP) increases, etch rate tends to rapidly increase at the center of a wafer (i.e., center peaked). The use of a resistive electrode with a cavity behind it at the center is an effective method of reducing the intensity of this peak. Even though the center peak is removed, the etch rate at the wafer edge is typically low. Because of this, controlling etch rate uniformity within 3% is problematic. The use of multistep cavity behind the resistive electrode has been found to be an effective method of improving the uniformity over the entire wafer and is described in this paper. Finite element method (FEM) simulations are performed to show that the use of a multistep cavity improves the ability of controlling sheath field when compared with the use of a single-step cavity configuration. Experiments confirm uniformity control within ±1.8% (3σ) with the multistep cavity configuration for 300 mm diameter wafers etched in 60 MHz plasma sources.