【作者】 李晓光；

【导师】 沈连婠；

【作者基本信息】 中国科学技术大学 ， 精密仪器及机械， 2007， 博士

【摘要】 近年来，微机电系统(MEMS，Micro Electro Mechanical System)研究及其应用的快速发展，推动着微细加工技术的不断改进和提高。UV-LIGA技术作为LIGA技术的一种派生技术，由于其光刻工艺中采用传统的紫外光源，与使用X射线的LIGA技术相比，尽管其制成的微结构质量和高宽比不及，但具有工艺简单，成本低廉的优势，因此受到广泛的关注和研究。由于光刻技术在UV-LIGA技术中的关键的基础地位，对于光刻的理论模拟研究一直都是热点。随着结构复UV-LIGA工艺主要采用接近式光刻，曝光时掩模和光刻胶间有一定的间隙以保护昂贵的掩模。在光刻过程中，由于间隙的存在，使得衍射效应明显，造成在光刻图形转移的过程中产生形状误差，这种形状误差随着掩模极限尺寸和光刻深度的不同而不同。本文就接近式光刻曝光工艺中因衍射效应产生的图形失真的机理开展了研究。结合光刻机的照明机理，根据光在空气和吸收介质中的标量衍射理论和角谱理论，本文提出了一种光刻传播光场分布角谱计算方法。角谱衍射计算中，选择快速傅立叶变换(FFT)技术进行仿真计算，通过适当选择FFT计算中的相关参数范围，确定较佳的FFT参数，在频域中建立了较为真实的描述接近式曝光过程的光刻数学模型。该仿真方法的特点是能够快速准确地对光刻胶表面及其内部的光场分布进行仿真计算，为光刻的仿真计算的工程实用提供了一种可行的方法。利用上述仿真模型，对不同线宽、不同形状特征的掩模在光刻胶表面和内部的衍射光场分布做了接近式光刻仿真，对衍射造成的二维图形和深度方向的误差分布和特点做了深入的分析研究。仿真及实验图形验证表明，该快速角谱仿真模型模拟得到的误差现象与实验结论较吻合，包括：在光刻胶表面，图形轮廓出现线宽变窄，拐角圆化等现象。而对于光刻胶深度方向，微结构出现了圆柱化，侧壁陡度变小，底部收缩等现象。实验对比在一定程度上证明了本模型的有效性。在光刻误差分析的基础上，本文基于可制造性设计(DFM，Design for Manufacture)对接近式光刻的图形进行优化仿真研究。借鉴投影式光刻掩模优化策略，本文对接近式光刻的优化方法是：基于掩模预补偿的思想，在引起衍射的掩模特征处，通过调整其分布，实现光刻胶表面的衍射光场调制。本文根据分段分类思想，运用遗传算法(GA，Genetic Algorithm)，对光刻掩模进行有限区域的搜索，寻找曝光图形最接近于理想图形的预补偿掩模。对得到的最优预补偿掩模仿真表明，优化后图形转移的质量大大提高，为接近式紫外光刻的掩模设计提供了新的思路。对于SU-8厚胶的深度光刻中的深度方向误差，运用同样的掩模重新分布的遗传算法搜索策略，针对光刻胶内特定深度截面的轮廓形状进行优化研究。对接近式深度光刻中的掩模进行了补偿优化搜索及其仿真表明，预补偿掩模在一定程度上降低了深度光刻中光刻胶内特定深度截面的图形误差。本文系统进行了UV-LIGA工艺中接近式紫外光刻的快速角谱仿真研究。对光刻薄胶到厚胶深度光刻，它们的二维和三维的光场分布都做了详细的仿真分析。为降低光刻中的误差，对薄胶和厚胶分别进行了掩模优化研究，对MEMS光刻掩模的设计提供了指导性的依据。更多还原

【Abstract】 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.更多还原