A NEW METHOD FOR PROMOTING PHOTORESIST ADHESION ON TUNGSTEN FILMS FORSELF-ALIGNED REFRACTORY GATES ON GAAS

A new method has been developed for promoting the adhesion of a cresol -formaldehyde novolak resin-based photoresist (AZ5214-E) on tungsten f ilms sputter-deposited on GaAs. Tungsten treated with heated propylene glycol monomethyl ethyl acetate followed by a solvent rinse results i n a nonpolar surface which is suitable for reliable photoresist adhesi on promotion. This Si-free process has allowed a subtractive dry etch tungsten patterning process to be applied for the first time to the fa brication of self-aligned refractory gates for a novel field-effect tr ansistor. Systematic testing of the new method suggests that dissociat ive chemisorption of the photoresist solvent is responsible for creati ng a nonpolar surface for adhesion of the photoresist. In addition to these results, an explanation for the failure of a number of alkylsily l-based compounds to promote photoresist adhesion on tungsten is prese nted.