Abstract
Thick SU-8 photoresist has been a popular photoresist material to fabricate various mechanical, biological, and chemical devices for many years. The accuracy and precision of the ultraviolet (UV) lithography process of thick SU-8 depend on key parameters in the set-up, the material properties of the SU-8 resist, and the thickness of the resist structure. As feature sizes get smaller and pattern complexity increases, accurate control and efficient optimization of the lithography process are significantly expected. Numerical simulations can be employed to improve understanding and process design of the SU-8 lithography, thereby allowing rapid related product and process development. A typical comprehensive lithography of UV lithography of thick SU-8 includes aerial image simulation, exposure simulation, post-exposure bake (PEB) simulation, and development simulation, and this article presents an overview of the essential aspects in the comprehensive simulation. At first, models for the lithography process of the SU-8 are discussed. Then, main algorithms for etching surface evolvement, including the string, ray tracing, cellular automaton, and fast marching algorithms, are introduced and compared with each other in terms of performance. After that, some simulation results of the UV lithography process of the SU-8 are presented, demonstrating the promising potential and efficiency of the simulation technology. Finally, a prospect is discussed for some open questions in three-dimensional (3D) comprehensive simulation of the UV lithography of the SU-8.
Highlights
SU-8 is a negative, epoxy-type, ultraviolet (UV) photoresist based on EPON SU-8 epoxy resin from Shell Chemical, The Hague, The Netherlands, that has been originally developed, and patented (US Patent No 4882245 (1989)), by International Business Machines Corporation (IBM, Armonk, NY, USA) [1]
The first SU-8 products were reported by MicroChem Inc., [2]
Lithography process simulations of thick photoresist such as SU-8 cannot be accurately implemented by the software specified for thin photoresist, because there are some differences between these two lithography processes [28,29], such as nonlinear factors, the special exposure method for thick SU-8 lithography process, and so on
Summary
SU-8 is a negative, epoxy-type, ultraviolet (UV) photoresist based on EPON SU-8 epoxy resin from Shell Chemical, The Hague, The Netherlands, that has been originally developed, and patented (US Patent No 4882245 (1989)), by International Business Machines Corporation (IBM, Armonk, NY, USA) [1]. Lithography process simulations of thick photoresist such as SU-8 cannot be accurately implemented by the software specified for thin photoresist, because there are some differences between these two lithography processes [28,29], such as nonlinear factors, the special exposure method for thick SU-8 lithography process, and so on To overcome this problem, some specified researches for the UV lithography simulations of thick photoresists have been reported during the past several years [30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48]. Simulation Models for Ultraviolet (UV) Lithography Process of Thick SU-8 Photoresist
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