Aqueous Cleaning of Sidewall Redepositions Formed by Reactive Ion Etching of Platinum

Abstract

Removal of platinum sidewall redepositions formed due to patterning of electrodes during reactive ion etching for an embedded dynamic random access memory project has been investigated. During etching of these devices, nonvolatile etch products commonly deposit onto the pattern sidewall. Removal of these residues without damaging other exposed materials is a challenging process. A mixture of argon and chlorine plasma was used to etch the platinum electrodes used in this study. Following the etching step the wafers were processed in an oxygen plasma (ashed) to remove the photoresist on the wafer. The effectiveness of various postash‐cleaning methods was investigated. Results are presented for wafers that were heated at different temperatures for varying times in different ambients, wafers that were cleaned in aqueous hydrochloric acid of varying concentrations, and wafers that were cleaned in a 40 kHz ultrasonic bath in water, in aqueous hydrochloric acid, and in aqueous ammonium hydroxide. At the conditions studied, it was determined that dissolution of the residues was not the controlling removal mechanism. Rather, a combination of dissolution and physical displacement appeared to control the cleaning process. Specifically, the application of ultrasonic energy to baths of 6 M hydrochloric acid provided the best cleaning results. © 1999 The Electrochemical Society. All rights reserved.