Abstract: A thin film of organic resin material (17), such as novolac, is used as an etch mask and openings (32) are formed in the mask in a predetermined pattern to allow processing in selected areas defined by the openings. The openings (32) are formed by applying a pattern of droplets (76) of caustic etchant, such as sodium hydroxide (NaOH) or potassium hydroxide (KOH) in the areas where the openings are to be formed. The droplets (76) are applied using a inkjet printer (90) which is scanned over the surface of the organic resin as the droplets are applied. The droplets (76) are of a size which defines the dimension of the openings (32) and allows the organic resin (17) under the droplet (76) to be completely removed. After the etchant has etched through the organic resin to expose an underlying surface (12), the etchant is washed from the organic resin and the openings (32).