Lithographic Evaluation of an o‐Nitrobenzyl Ester Based Deep U.V. Resist System

We have previously reported preliminary experiments with a new deep u.v. (230–300 nm) positive resist based on the resin‐solution inhibition mechanism. The resin is an optically transparent copolymer of methyl methacrylate and methacrylic acid which is soluble in alkaline developers but is protected from dissolution by a photosensitive solution inhibitor. The latter is one of a family of o‐nitrobenzyl esters of large‐molecule organic acids such as cholic acid. It is initially insoluble in aqueous alkaline developers but is cleaved to soluble components upon irradiation. This resist system has good sensitivity for λ < 300 nm and it can be made sensitive to longer wavelengths by the use of external photosensitizers. It is capable of 0.5 μm resolution and has unusually high contrast ( γ > 5 ) . We report here a detailed lithographic evaluation of this two‐component system. Parameters such as copolymer molecular weight, o‐nitrobenzyl ester concentration, and developer composition are examined and related to sensitivity and contrast. Reactive ion etching rates are comparable to those of HPR‐204 resist.