Abstract
The etching of gold films deposited on chromium adhesion layers in iodine solution creates cavities at the base of the films. These cavities or abnormal undercutting are revealed and studied by means of the scanning electron microscope. The abnormal undercutting causes the lifting of gold in the etching of high resolution patterns. The alkali cyanide etching solution creates normal undercutting and its use is recommended. It is suggested that the abnormal undercutting results from the formation of an electrochemical cell in the final stage of the etching process when the chromium layer and the gold layer are simultaneously exposed to the electrolyte. The partial oxidation reaction of gold dissolution at the gold surface is balanced by triiodide reduction at the chromium surface as well as at the gold surface. The electrochemical cell formation accelerates the etching of gold near the chromium‐gold boundary and causes the formation of cavities. The mechanisms for the normal and abnormal undercutting processes are discussed.
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