Pushing deep greyscale lithography beyond 100-µm pattern depth with a novel photoresist

Abstract

Greyscale lithography for the manufacture of complex 2.5D and freeform microstructures in photoresists receives increasing attention from industry for the fabrication of advanced micro-optical elements. The thus obtained structures serve as master or template for different methods of pattern transfer into materials for final, permanent applications, such as refractive and diffractive lenses, blazed gratings, beam-shapers etc. However, many such applications require large structure heights beyond 100 μm which was not easily accessible until now. We present a novel photoresist, mr-P 22G_XP, enabling greyscale lithography of very deep patterns. Issues limiting the pattern depth caused by the photoresist chemistry were addressed. Greyscale pattern depths of 120 μm were possible with an easily accessible set-up with this prototype, with a well-considered choice of photoresist ingredients, and lithography process adjustments focusing on laser direct writing, with the prospect of even deeper patterns up to 140–150 μm.