Evaluation of a novolak based positive tone photoresist as NanoImprint Lithography resist

Motivated by the high etch selectivity obtained with novolak based UV photoresists masks in the pattern transfer to silicon, we have studied the conditions under which a novolak photoresist may be also patterned by NanoImprint Lithography (NIL). The present study is specifically carried out on MICROPOSIT S1800, for which we have identified a suitable NIL process window. The overall quality of the produced nanopatterns depends strongly on the thermal history of the photoresist film. In particular, residuals of solvent in the film are essential to obtain thin residual layers and to avoid cracks during stamp separation, which otherwise easily occur in fully dried material owing to an increase of brittleness. Infrared spectroscopy is applied to determine the relative amount of solvent for different processes and to correlate it to the optimal imprinting conditions. Finally, high-aspect-ratio pattern transfer has been demonstrated in an Inductively Coupled Plasma (ICP) etching system using NIL nanopatterned S1800 resist as a mask.