Etchant for Titanium in Presence of Gold
Original Publication Date: 1985-Oct-01
Included in the Prior Art Database: 2005-Feb-19
To etch a resist-masked pattern of metallic contacts consisting of layers of titanium, gold and chromium, existing etchants will remove the chromium and gold layers satisfactorily. It has been found that an aqueous solution of a fluoride salt with an oxidizing agent, specifically ammonium fluoride with chromium trioxide, will prevent overetching of the titanium layer with consequent undercutting of the gold. A plain wafer coated with 1200 ˜ of Ti, 200 ˜ titanium-gold, 1000 ˜ of gold and 1000 A of chromium was coated with HC resist, 1.6 m thick and the required pattern (having typically 3 micron spaces) defined. The following etching process was then carried out. 1. Chromium was etched in alkaline ferricyanide pH 12.8 at 40ŒC for 4 minutes. 2. Gold was etched in potassium iodide-iodine at room temperature for 6 seconds.