Using megasonic development of SU-8 to yield ultra-high aspect ratio microstructures with UV lithography

SU-8 resist is commonly used to produce high aspect ratio microstructures in MEMS field. The resist is patterned using either ultraviolet (UV) or X-ray lithography and developed to produce structures ranging from 20 microns to 1.5 millimeters in height. Three processes are currently used to develop SU-8 resist: dip development with or without stirring and dip development with ultrasonic agitation. One difficulty associated with producing high aspect ratio microstructures lies in the development of open and closed fields evenly on the same substrate. To overcome this obstacle, we have applied megasonic agitation to the developer bath, which resulted in faster development rates, uniformed development, and the ability to produce structures with higher aspect ratios. To date, this process has been used to achieve 100:1 aspect ratio open field features and 45:1 intact cylinder arrays using a broadband optical contact aligner.