Study On Simulation Of UV-Lithography And Mask Optimization

With the rapid development and application of MEMS (Micro Electro Mechanical System) in the recent years, the micro-fabrication technology is improving. UV-LIGA technology is a micro fabrication technology derived from LIGA. Comparing with LIGA, UV-LIGA has notable characteristics of simple exposure process and low cost, and it attracts much attention and research.Being the pivotal and fundamental process of UV-LIGA, lithography technology and its simulation theory are the hotspot of research. With the requirement of complicated structure and high ratio aspect MEMS components, it is more important to research and develop computer simulation technology to reduce the cost of development, shorten research cycle and improve the quality of MEMS.In order to protect the valuable photo-mask, proximity lithography is used in exposure process of UV-LIGA. But diffraction effect caused by the little gap between photo-mask and the surface of photo-resist engenders graphics distortion both in contour and side will of 3D photo-resist structure.Pattern Transfer defect in proximity exposure caused by the diffraction effect is studied. The scalar diffraction and angular spectrum theory is adopted in this thesis to study the luminous intensity distribution on photo-resist and estimate the distortion. An angular spectrum method using FFT (Fast Fourier Transform) is presented to simulate the propagation of light in air and absorbing media. FFT method speeds up the progress of the lithography simulation. A preferable simulation result is achieved by choosing relevant parameters needed in calculation, a mathematical model is presented to describe the lithography process. The method provides feasibility for engineering application of the lithography simulation.With the mentioned simulation model, analysis and simulation of optical distribution are done for photo-resist structure with different line widths and shapes, and the contour and gradient errors of deep proximity lithography are studied. The fast angle spectrum simulation model agrees with the experiment very well and the defects are: line width becomes narrower and corner rounding. For the deep lithography, the structure becomes columned, diminishing in gradient and underexposure in the bottom, the comparison between simulation and experiment show the validity of the model.Based on a strategy of DFM (Design for Manufacture), an error compensation method is presented to optimize the pattern transfer in lithography. The strategy of the method is to modulate the optical distribution by adjusting the pattern of the photo-mask. Genetic Algorithm (GA) is adopted to study the approach, which is method to get an ideal shape of photo resist structure through changing the shape of the photo mask graphics. In the GA experiments, the optimum mask graphics and its exposure graphics are achieved. The simulation results show the distortion is reduced obviously. It gives a new way for the photo-mask design of MEMS components.For the deep lithography defect of SU-8 thick photo-resist, a similar GA optimization method is applied to optimize the specified cross section contour. Simulation of the compensated mask pattern shows the error of the contour reduces, and the optimization is also effective.This thesis systematically studies the fast angle spectrum method of proximity lithography in UV-LIGA. Detailed analysis about the light propagation of 2D on surface and 3D inside of photo-mask is studied. In order to reduce the defect in lithography, an optimization study on mask design is carried out. This research gives a guide to photo-mask design.