Negative PMMA as a high-resolution resist - the limits and possibilities

Poly(methylmethacrylate) (PMMA) which is commonly used as a positive resist can also be used in a negative manner with exposure at higher dose levels. In this paper we investigate the full potential of this resist for high-resolution pattern definition. We show that although the point spread exposure distribution is similar to that for positive PMMA, features of the order of 10 nm are easily achieved. These resist structures can be transferred into the underlying materials using plasma etch techniques to a similar degree of resolution. The density of resist features is also greater than for positive PMMA with features of nm in width being possible on a 30 nm pitch. The instability of the resist structures at extreme linewidths has been identified as a potential problem in utilizing the process.