Poly(t‐BOC‐styrene sulfone)‐based chemically amplified resists for deep‐UV lithography

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Abstract
The unique ability of the tert‐butoxycarbonyl protecting group (t‐BOC) to be removed by a catalytic amount of strong acid has intensified the search towards new chemically amplified resist systems based on this chemistry. A series of new copolymers of t‐BOC‐styrene and sulfur dioxide have been prepared by free radical polymerization. These polysulfones function as chemical amplification positive resists for deep‐UV lithography when mixed with either 2,6‐dinitrobenzyl tosylate or triarylsulfonium salt acid precursors. The lithographic characteristics of 2:1 and 3:1 polysulfones have been evaluated. The new positive deep‐UV photoresists are aqueous base developed and are capable of 0.5 μm resolution. Even though the photoresists containing 2,6‐dinitrobenzyl tosylate are less sensitive than the onium salt formulations, they displayed greater contrast values. For example the poly(t‐BOC‐styrene sulfone) (2:1) 15 wt % tosylate resist formulation exhibits a sensitivity of 26 mJ/cm2and a contrast of ∼20.