Poly(methacrylic anhydride) positive electron beam resist

Poly(methacrylic anhydride) (PMAH) is a positive resist for use in electron beam (e‐beam) lithography. It is derived by heating coatings of the precursor polymer, poly(tert‐butyl methacrylate) or PtBMA, on the wafer. Crosslinks are introduced during the thermal conversion. The sensitivity and line profiles of PMAH e‐beam images are significantly affected by the synthesis route, the pre‐exposure processing, and the development method. Development with organic solvents can swell and soften the resist, especially in areas that received some exposure to radiation. This causes the walls of the image to expand or flow into the image cavity, thereby limiting the sensitivity at which high resolution can be achieved. However, the use of a new, nonswelling, basic developer gives PMAH a sensitivity of 2.5 μC/cm² with better than 0.5 μm resolution.