METHYLATED POLY(4-HYDROXYSTYRENE) - A NEW RESIN FOR DEEP-ULTRAVIOLET RESIST APPLICATION

Positive photoresists which function on the basis of dissolution inhibition are the mainstay of optical lithographic technology at long wavelength. Described in this paper is a new type of material which permits the dissolution inhibition mechanism to be extended to deep-UV wavelengths. Methylated poly(4-hydroxystyrene) resins are prepared by a copolymerization reaction which results in a final product whose dissolution properties can be defined by the ratio of the two monomers used in the reaction. The deep-UV optical absorbance of the methylated resin is about one-half the absorbance of novolac at 248 nm which makes these materials attractive for application in deep-UV resist formulations. Binary photoresists using diazo compounds as dissolution inhibitors have been prepared with the methylated poly(4-hydroxystyrene) as the host resin. These materials function very similarly to the familiar diazonaphthoquinone/novolac photoresists at long wavelength. For deep-UV application, both binary and three component resists have been evaluated. The three component system has high sensitivity ( < 5 mJ/cm2) and contrast (lambda- > 3). The high contrast is due in part to the induction effect observed from dissolution data. Projection printed images have steep wall profiles indicative of high contrast photoresists.