Publications by Andrew Turberfield

The control of shrinkage and thermal instability in SU-8 photoresists for holographic lithography

Advanced Functional Materials 21 (2011) 1593-1601

RG Denning, CF Blanford, H Urban, H Bharaj, DN Sharp, AJ Turberfield

The negative-tone epoxy photoresist, SU-8, expands ≈1% by volume after postexposure baking. However, if the maximum optical fl uence is comparable to that at the insolubility threshold, as in a holographic exposure, the developed resist shrinks ( ≈35% by volume) due to the removal of light oligomers not incorporated into the polymeric network. IR spectroscopy shows that, at this level of exposure, only 15% of the epoxy groups in the insoluble polymer have reacted; consequently microstructural elements soften and collapse at > 100 °C. When the light oligomers are removed, the sensitivity of the resist is unchanged, provided that 5% (w/w) of a high-molecular-weight reactive plasticizer (glycidoxy-terminated polyethylene glycol) is added, but it shrinks less on development and, when used as a photonic crystal template, shows improved uniformity with less cracking and buckling. Reinforcing the polymer network by reaction with the polyfunctional amine (bis- N , N′ -(3-aminopropyl) ethylenediamine) increases the extent of cross-linking and the thermal stability, allowing inverse replicas of photonic crystal templates to be fabricated from both Al:ZnO and Zr 3 N 4 using atomic layer deposition at temperatures up to 200 °C. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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