Novel microelectromechanical systems image reversal fabrication process based on robust SU-8 masking layers

Abstract

This paper discusses a novel fabrication process that uses a combination of negative and positive photoresists with positive tone photomasks, resulting in masking layers suitable for bulk micromachining high-aspect ratio microelectromechanical systems (MEMS) devices. Mi- croChem's negative photoresist Nano TM SU-8 and Clariant's image rever- sal photoresist AZ 5214E are utilized, along with a barrier layer, to effec- tively convert a positive photomask into a negative image. This technique utilizes standard photolithography chemicals, equipment, and processes, and opens the door for creating complementary MEMS structures without added fabrication delay and cost. Furthermore, the SU-8 masking layer is robust enough to withstand aggressive etch chemistries needed for fabrication research and development, bulk micromachining high-aspect ratio MEMS structures in silicon substrates, etc. This processing tech- nique was successfully demonstrated by translating a positive photomask to an SU-8 layer that was then utilized as an etching mask for a series of trenches that were micromachined into a silicon substrate. In addition, whereas the SU-8 mask would normally be left in place after process- ing, a technique utilizing Rohm and Haas Microposit TM S1818 as a re- lease layer has been developed so that the SU-8 masking material can be removed post-etching. C 2011 Society of Photo-Optical Instrumentation Engineers