High Resolution Tungsten Patterning Using Buffered, Mildly Basic Etching Solutions

Prior to this work, commonly available chemical etches for tungsten were difficult to use for high resolution patterns because of their incompatibility with available positive and negative photoresists. Rapid attack by basic hydrolysis made the use of positive resists impossible and the use of negative resists difficult. It was found that solutions of which were buffered in the mildly basic pH range of 7.5–9.5 etch tungsten as fast as the previously used highly alkaline etches (pH 13–14) but are far better in the practical fabrication of tungsten‐based integrated circuits. These etches can be used to delineate patterns of high resolution (1–2 μm range) limited only by the photolithography, with no evidence of failure of either positive or negative photoresists.