Investigation of as-cast polymethylmethacrylate based homopolymer resists in negative ion mode with nano projectile secondary ion mass spectrometry

Polymethylmethacrylate (PMMA) undergoes chain scission under exposure of high-energy photons or electrons, leading to a solubility switch in exposed areas. It is often used as a model photoresist for mechanistic studies due to its chemical and mechanistic simplicity. Nano projectile secondary ion mass spectrometry (NP-SIMS) can be used to gain chemical information about the surface composition of a sample with high lateral resolution. NP-SIMS involves the bombardment of the surface with primary ions, Au4004+ in this case, and the collection of the ejected secondary ions. The separation of the primary ions in time and space enables the analysis of the secondary ions from each individual impact. Thin films (≈25 nm thickness) of spin-cast PMMA of different molecular weights (between 1.3 and 950 kDa) on the silicon substrate were investigated regarding postincident fragmentation patterns. Three circular areas of 125 μm diameter were analyzed and a total of 2–3 × 106 spectra were taken for each sample.