Evolution of etch profile of copper thin films in high density plasmas of alcohol-based gases

Abstract

Dry etching of copper thin films patterned with SiO2 masks was performed using inductively coupled plasmas of CH3OH/Ar, C2H5OH/Ar, and O2/C2H5OH gases. The etch rates of copper films in CH3OH/Ar plasma were slightly faster than those in C2H5OH/Ar plasma while the etch profiles in C2H5OH/Ar plasma were better than those in CH3OH/Ar plasma. Upon varying the etch parameters, high coil RF power, high dc-bias voltage to substrate, and low process pressure were found to cause increased redeposition of the etched materials on the copper sidewalls and increased etch slopes. Optical emission spectroscopy, energy dispersive X-ray spectroscopy, and the evolution of the etch profiles revealed the etch mechanism of copper films in C2H5OH/Ar gas. X-ray photoelectron spectroscopy confirmed that the etching of copper films by C2H5OH/Ar takes place via a chemical mechanism involving the formation of copper compounds and a sputtering mechanism by the ions, depending on the C2H5OH concentration. Good etch profiles of copper films without the redeposition were achieved using the optimized O2/C2H5OH gas.