DEEP ULTRAVIOLET PHOTORESIST BASED ON TUNGSTEN POLYOXOMETALATES AND POLY(VINYL ALCOHOL) FOR BILAYER PHOTOLITHOGRAPHY

A negative tone deep ultraviolet resist, a mixture of phosphotungstic acid and poly(vinyl alcohol) is described. This resist has < 100 mJ cm-2 sensitivity and resolves less-than-or-equal-to 0.3-mu-m features. Even though the photochemistry involves chemical amplification, the exposed patterns are stable and the process tolerates hours between the exposure and the post-bake steps. The resist is spun from an aqueous solution, and its wet processing is also aqueous. This resist is used in a bilayer scheme, where advantage is taken of both the resistance of the tungsten oxide to oxygen plasmas and its easy stripping in fluorine-containing plasmas. Because poly(vinyl alcohol) is intrinsically a wetting agent, pinhole-free resist films of approximately 1000 angstrom thickness can be spun. These thin coatings provide sufficient oxygen plasma etch resistance to allow patterning of a thick 1.5-mu-m novolac planarizing layer underneath the resist.