Improved Wet Etching of Polyimide With Cooled Etchant
Original Publication Date: 1985-Aug-01
Included in the Prior Art Database: 2005-Feb-19
By reducing the temperature of the TMAH (Tetra-methyl Ammonium Hydroxide) in water (5% TMAH:H2O, 1:5) etchant from the usual 25 degrees Celsius to 5-20 degrees Celsius, 1) the process time window for controlled hole size is greatly expanded, and 2) swelling of the polyimide, with resultant photoresist cracking and polyimide hole edge "scalloping", is eliminated. The reduced temperature process not only enhances yield of current products with, e.g., 40-micron diameter holes, but also permits use of wet etching for much smaller hole sizes. To maintain acceptable process control of the room temperature wet etching process of 40- to 50-micron diameter holes, it has been necessary to control the nominal 20-second etch time to within a few seconds.