High Rate Copper Isotropic Wet Chemical Etching

Abstract

A high-rate copper isotropic wet-etching process has been developed. The process is found to be surface-kinetic controlled, so the etching rate within the isolated feature does not increase upon removal of all metal from the field, as well as remains flat and uniform across individual feature and across an array of features, independent of feature size. Also discussed are some of the issues and means of implementing this low cost but inherently-unstable peroxide/alkaline etching solution, as well as some general chemical-variant behavior trends of the amine based etching chemistry. Combining a straightforward, robust 300 mm spin-spray reactor design with optimized chemical formulations and process conditions enabled a tunable removal-profile that can be tailored to match the copper plating profile. Copper removal rates of >1.5 um/min, WIW removal-rate variability <1.5% (full range, 2 mm edge exclusion), post-etch mirror like-surfaces, reflectivity rates of change of < 2% per 5 um of removal, and a wafer to wafer rate and uniformity variability of less than 2% have been implemented.