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

Polymethylmethacrylate (PMMA) is a positive tone photoresist, which undergoes chain scission under extreme ultraviolet exposure and is often used as a model photoresist for mechanistic studies due to its simplicity. Nano projectile secondary ion mass spectrometry (NP-SIMS) can be used to gain chemical information about the surface composition of a sample. NP-SIMS involves the bombardment of the sample surface with primary ions and the collection of the ejected secondary ions. The primary ions, Au4004+, are separated in time and space, and this enables the analysis of the secondary ions from each individual impact. Thin films (≈25 nm thick) of spin-cast PMMA of different molecular weights (35, 200, 495, 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 1–1.5 × 106 spectra were taken for each sample.