In-situ investigation of as-cast homopolymer-based resists

Recently, the use of homopolymers as photoresists has gained interest due to their uniformity in chain length and chemical homogeneity. Typically, these types of systems undergo a solubility switch via chain scission mechanisms. Chain breaks are expected to occur randomly in the resist, this may result in a wide distribution of different molecular weights and thus contribute to non-ideal performance. We examined a series of as-cast polymethylmethacrylate, PMMA, resists with varying molecular weights (35 to 950kDa) with nano-projectile secondary ion mass spectrometry, NP-SIMS. We found trends in the measured abundance of main-chain ions and end-groups of PMMA which depend on the molecular weight of the homopolymer. Further, the ratio among several characteristic PMMA fragments revealed significant differences as a function of molecular weight. These results are promising and suggest that NP-SIMS could be used to identify the molecular weight of homopolymers in-situ. We expect that due to the high lateral resolution of NP-SIMS, studies can be carried out on treated resists or systems of mixed homopolymers and allow for identification of regions where the molecular weight differs.