Development characteristics of polymethyl methacrylate in alcohol/water mixtures: a lithography and Raman spectroscopy study
Nanotechnology | 15 Dec 2015
LE Ocola, M Costales and DJ Gosztola
Poly methyl methacrylate (PMMA) is the most widely used resist in electron beam lithography. This paper reports on a lithography and Raman spectroscopy study of development characteristics of PMMA in methanol, ethanol and isopropanol mixtures with water as developers. We have found that ethanol/water mixtures at a 4:1 volume ratio are an excellent, high resolution, non-toxic developer for exposed PMMA. We have also found that the proper methodology to use so that contrast data can be compared to techniques used in polymer science is not to rinse the developed resist but to immediately dry with nitrogen. Our results show how powerful simple lithographic techniques can be used to study ternary polymer solvent solutions when compared to other techniques used in the literature. Raman data show that both tightly bonded -OH groups and non-hydrogen bonded -OH groups play a role in the development of PMMA. Tightly hydrogen bonded -OH groups show pure Lorentzian Raman absorption only in the concentration ranges where ethanol/water and IPA/water mixtures are effective developers of PMMA, pointing to possible ordering or reduced amorphization due to the liquid state. The impact of understanding these interactions may open doors to a new developers of other electron beam resists that can reduce the toxicity of the waste stream.
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