Positive or negative tone resist for a T-NIL/UVL hybrid process

Abstract

In order to utilise both techniques in the best and easiest way, thermal nanoimprint (T-NIL) and optical/UV lithography (UVL) were combined in a hybrid process to pattern the same resist layer. Typically, T-NIL as the first step defines the small, submicron patterns, UVL as the second step the larger patterns, well above 1 μm. The hybrid process is performed with a conventional Si stamp for imprint and a conventional photomask for UVL and does not require any special infrastructure. Conventional, commercially available positive and negative tone resists were used, SU-8 and AR-P 3510. In the case of SU-8, a chemically amplified negative resist with low glass temperature, the imprint is uncritical and does not result in any optical degradation. However, the post exposure bake required to finalise the crosslink reaction has to be adapted and performed as a temperature ramp. In the case of AR-P 3510 the imprint step is critical, as the photoactive component is degenerated at suitable imprint temperatures. We found that at temperatures up to 130°C this degradation can be compensated by an increase of the exposure dose. Though more critical in processing, the positive tone resist features a better definition of the transition region between imprinted patterns and UV patterns.