Removal of platinum sidewall redepositions formed due to patterning of elec
trodes during reactive ion etching for an embedded dynamic random access me
mory project has been investigated. During etching of these devices, nonvol
atile etch products commonly deposit onto the pattern sidewall. Removal of
these residues without damaging other exposed materials is a challenging pr
ocess. 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 wafe
r. 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 aqueo
us hydrochloric acid of varying concentrations, and wafers that were cleane
d in a 40 kHz ultrasonic bath in water, in aqueous hydrochloric acid, and i
n 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
. (C) 1999 The Electrochemical Society. S0013-4651(98)11-029-7. All rights
reserved.