Shinji Himori

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.

Dual-Frequency Superimposed RF Capacitive-Coupled Plasma Etch Process

A dual-frequency superimposed (DFS) 100 MHz and 3.2 MHz rf capacitive-coupled plasma etch process for sub-90 nm devices has been developed. The electron density of DFS reactive ion etching (RIE) plasma at 40 mTorr was controlled from 4.0×1010 to 3.6×1011 cm-3 by adjusting the 100 MHz rf power, and the self-bias voltage (-Vdc) was controlled from 20 to 760 V by adjusting the superimposed 3.2 MHz rf power. DFS RIE demonstrated independent control of electron density and self-bias voltage in a wide range. In the damascene etch process of SiOC film using Si3N4 as an etch mask, it was found that mask edge erosion is dependent on ion energy regardless of the selectivity of SiOC to Si3N4. DFS RIE offers the most suitable process for damascene etching of SiOC, which requires precise ion energy control.

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.