Simulation Of SU-8UV Lithography With3-D String Algorithm

MEMS(micro Electro Mechanical System) is a subject withmultidisciplinary areas. It has important applications in aerospace,automotive, biomedical, environmental monitoring and other areas.MEMS technology and MEMS simulation technology have experienced arapid development process over the past decades, the size of it’s structureand complexity have higher requests. Some2D simulations of MEMSetching process were reported[1-2]. However,3D surface simulation is stillfacing many challenges. Achieving faster and more accurate simulationwith low CPU and memory resources has become the need at present.SU-8photoresist’s application in the field of MEMS and othermicro-machining is increasing. In UV-LIGA technology, SU-8plastic hasits unique advantages, such as low-cost production, stable, hightemperature and so on. SU-8photoresist lithography is a MEMS-specificprocess. It can achieve the delicate structure with a lower cost that isdifficult to traditional process. The simulation of the lithography processincludes several steps such as exposure, after drying, developing or calledetching, in which photoresist developing process simulation is the mosttime-consuming one. At present, the photoresist etching processsimulation of cellular automata (CA)’s algorithm is slow and is notconducive to the growing importance of multi-step process simulation. Inorder to improve computational efficiency of the algorithm, this articleuses two-dimensional normal vector as component, calculates theweighted sum and then get the approximation of the unit normal vector onthe three-dimensional grid points, improves the classic2-dimensionalstring algorithm to three-dimensional form, and integrates the variouseffects of diffraction, absorption rate with the change of the photoresistdepth and cross-linked enhancement in SU-8photoresist lithographyprocess, uses3D string algorithm to build three-dimensional modeling ofthe SU-8chemical amplification plastic lithography process. On this basis,to discrete program each module with C language, and to mapping analyzethe program output data with MATLAB software to achieve the3D effect.As a micro-device fabrication plastic mold, SU-8photoresist’s lithography dimensional accuracy directly affects the dimensionalaccuracy of the micro-devices. Therefore, the requirements on the microsize of SU-8photoresist are becoming increasingly exigent. While thispaper gives the simulation results, it also considers the fact that thediffraction effect would make the side wall no longer vertical, and basedon the fact that the refractive index of glycerol is similar to that ofphotoresist, we can add glycerol in the gap between the mask and theSU-8photoresist in order to reduce the impact of the diffraction patternsize. In this article, the process has been simulated, and the simulationresults are accurate, which can be used to effectively predict the SU-8photoresist lithography simulation results in practical applications.