Chloromethylated Polystyrene as Deep UV and X-Ray Resist

The deep uv and X-ray lithographic characteristics of high-performance negative electron resist chloromethylated polystyrene (CMS) were investigated. The sensitivity and resolution of a series of CMS's synthesized from nearly monodispersed polystyrene were evaluated as functions of molecular parameters. In CMS with a molecular weight of 1.8×105 showing a resolution better than 1.5 µm, a high sensitivity of 29 mJ/cm2 to X-rays and a sensitivity to deep uv about 40 times higher than that of PMMA was achieved. This high sensitivity is attributed to the high reactivity of the chloromethyl group, as verified by the high G value of CMS (5.4), 50 times larger than that of polystyrene. In contrast to most negative resists, where oxygen in air depresses the sensitivity, the sensitivity of CMS is hardly affected by the atmosphere. The sensitivity and resolution in the deep uv system are particularly affected by light absorption, because CMS exhibits strong absorption between 200 to 300 nm.