Etching of Partially Cured Polyimide

The fabrication of patterns in partially cured polyimide films may be accomplished by wet etching with potassium hydroxide. In practice, problems encountered in obtaining uniform etching result from thickness variations in coatings and temperature variations in typical process ovens. The relationship between coating thickness, thermal exposure, degree of cyclization, and etchability was studied. The degree of cyclization was determined by Fourier Transform Infrared Spectroscopy and etch rates were measured by monitoring coating thickness. It was found that the level of imidization was directly influenced by coating thickness as well as thermal exposure. For films exposed to the same thermal conditions, the etch rate decreased as the thickness increased beyond 15 pm. However, when films of various thicknesses were brought to the same level of imidization, a constant etch rate was obtained. A significant improvement in the etch rate can be achieved by reducing the level of imidization, increasing the etchant temperature, or enhancing the solubility of the carboxylate salt of the polyamic acid produced during etching.