Poly(4‐chlorostyrene), a new high contrast negative E‐beam resist

PCS(poly‐4‐chlorostyrene) has previously been evaluated as a negative e‐beam resist, but although the sensitivity was good [2 to 5μC/square centimeter (cm2)], the contrast (γ) was poor (1.1 to 1.5). Recent experiments have shown that contrast is not only a function of molecular weight distribution (MWD), but can also be affected by polymerization conditios. Among these are: branching, head to head linkages, and oxygen in backbone. PCS was prepared via thermal free radical solution polymerization, and then fractionated by differential solvation techniques. Reactions occurring during polymerization and crosslink formation on irradiation will be discussed. For molecular weights of 700 and 300K respectively (same MWD), the sensitivity was 2 and 5μC/cm2, while the contrast (γ) was 3.5 for both. This is the highest reported contrast for a polymeric negative resist. The resist can then be UV hardened after development, and will not flow at 200°C. The RIE etch rate is ∼1/2 that of PMMA in various plasmas. Copyright © 1983 Society of Plastics Engineers, Inc.