MICROPATTERNED FILMS OF TUNGSTEN NUCLEI FOR SUBSEQUENT METALLIZATION FORMED OF A PHOSPHOTUNGSTIC ACID-BASED NEGATIVE RESIST

Tungsten nuclei, for the subsequent electroless deposition of nickel, were formed of a water-based tungsten-rich microlithographic resist consisting of phosphotungstic acid and polyvinyl alcohol (PVA). Spinning the aqueous resist solution at 4000 RPM yields a pinhole-free 10(3) angstrom thick negative resist film, containing approximately 60 weight percent (w/o) tungsten. Exposure (less-than-or-equal-to 100 mJ cm-2) of the resists to 254 nm light, postbaking and developing in an aqueous developer produces 0.3 mum features. Removal of the PVA at 400-degrees-C in air leaves a tungsten oxide film, with grains that are small enough to allow moderate temperature (450-degrees-C) furnace, or ambient temperature plasma hydrogen reduction to tungsten metal. The resulting patterned film, of 3 x 10(2) angstrom thickness, consists of fine less-than-or-equal-to 0.05 mum tungsten grains. After palladium-activation, the grains are selective nucleation sites for electroless deposition of nickel. 2000 angstrom thick nickel deposits on patterned nucleating films with 1 mum features did not show opens or shorts and had sharply defined boundaries. Because of the PVA's wetting ability, the spun aqueous resist also coats walls of vertical, 1 mum deep, 1 mum diam via holes. Upon processing, the wall-coatings are converted into metallic tungsten nuclei. Palladium activation, followed by electroless deposition of nickel, produces nickel plugs in the vias. When nickel is deposited on small-grained nuclei, the nickel grains are also small and the metal, growing from the wall inbound, fills the vias completely.