Uniform Etching of Chromium
Original Publication Date: 1985-Oct-01
Included in the Prior Art Database: 2005-Feb-19
In processing wafers having gold contacts protected by a chromium layer, only one of which is connected to the substrate, it is required in one step to remove the protective chromium layer. From all the pads the best known etchant for this is an alkaline solution of ferricyanide. This etchant uniformly removes the chromium from all the pads except that pad which is connected to the substrate. This failure to etch properly may be overcome by making the substrate electrically positive with respect to a counter electrode for a few seconds. The substrate pad is electrochemically protected by a complex galvanic coupling via the wafer which keeps it at a potential too negative to etch.