Using Positive Photomasks to Pattern SU-8 Masking Layers for Fabricating Inverse MEMS Structures
Society of Photo-Optical Instrumentation Engineers (SPIE)
Proceedings of SPIE 7972, Advances in Resist Materials and Processing Technology XXVIII
This paper discusses a novel processing technique that uses a combination of negative and positive photoresists for use with positive photomasks, resulting in masking layers suitable for bulk micromachining in the fabrication of microelectromechanical systems (MEMS). MicroChem's negative photoresist Nano(TM) SU-8 and Clariant's image reversal photoresist AZ 5214E are utilized, along with a barrier layer, to effectively convert a positive photomask into a negative photomask. This technique allows for the use of positive photomasks with negative resists, which opens the door to the ability to create complementary mechanical structures without the fabrication delays and cost associated with having to obtain a negative photomask. Furthermore, the SU-8 mask created is robust enough to withstand the bulk micromachining and aggressive etch chemistries needed to create MEMS structures. This processing technique was successfully demonstrated by translating a positive photomask to an SU-8 layer that was then utilized as a mask to etch trenches and other features into a silicon substrate.