Poly(4-methylstyrene-co-chloromethylstyrene): A negative electron beam resist-synthesis and lithography evaluation

Synthesis and lithographic characterization of a series of negative acting electron sensitive resists based on poly(4‐methylstyrene‐co‐chloromethylstyrene) are reported. The sensitivity and contrast of these resists were found to depend on the chloromethylstyrene (CMS) content and an optimum value of 5 wt% was determined from consideration of parameters associated with the reproducibility of the synthetic method and also the lithographic performance. Both the sensitivity and resolution were found to depend on the molecular weight and CMS content of the copolymer. Several methods of scale up for the synthesis were explored, the route having a very significant influence on the film formation characteristics of the resists. The reactivity ratios of the monomers were measured in order that the compositional drift, which occurs during the synthesis, could be quantified. The effect of solvent composition and molecular weight of the copolymer were explored in relation to the quality of the resulting lithography. These studies have indicated that the copolymer has the potential of being used as a VLSI sub‐micron resist with good plasma etch resistance.