Lithographic evaluation and processing of chlorinated polymethylstyrene

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Abstract
Chlorinated polymethylstyrene has been shown to behave as a negative resist upon electron beam exposure. Polymethylstyrene was prepared by both anionic and free radical techniques and chlorinated to produce a series of polymers with a range from 0 to 2.5 chlorine atoms per polymer repeat unit (0 to 42.5 wt. % chlorine). Sensitivity and contrast were found to be a function of chlorine content, molecular weight, and polydispersity. Sensitivity was maximum for materials with 0.6 to 0.9 chlorine atoms per repeat unit, depending on the chlorination technique chosen. Nearly monodisperse polymers exhibited much higher contrast than broader molecular weight materials and showed improved resolution. Thermogravimetric analysis was employed to study solvent removal from spun films and to determine prebaking and postbaking conditions. A chlorinated polymethylstyrene (0.92 chlorines/monomer unit) with a molecular weight of 70 000 and polydispersity of 1.06 had a sensitivity of 2.0 μC/cm2 and contrast of 2.0. This material demonstrated half-micron resolution for line and space patterns in both single level and trilevel processing.

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