Vertical sidewalls in thick epoxy resists – a challenge for laser-based direct write lithography

Abstract

Straight, almost vertical sidewalls can be achieved in thick negative-tone resist using focused laser beam-based direct write lithography (DWL). This is possible despite beam divergence and Gaussian intensity distribution that cause non-homogeneous illumination over the resist thickness and non-sharp edges between exposed and non-exposed areas. Three write modes with different focal lengths, numerical apertures and resolutions were used in our DWL 66+ pattern generator from Heidelberg Instruments. By variation of dose, vertical adjustment of location of focus, and multipass exposure, up to 88° sidewalls were achieved in 60 μm high and 100 μm wide ridges. The results show the potential of DWL to achieve resist structures with larger height up to 200 μm, higher resolution down to 5 μm, aspect ratio of over 8 and defined sidewall shape.