扫描干涉场曝光系统中干涉条纹周期测量误差对光栅掩模槽形的影响

Effect of Measured Interference Fringe Period Error on Groove Profile of Grating Masks in Scanning Beam Interference Lithography System

扫描干涉场曝光系统中干涉条纹周期的测量误差是影响曝光过程中相位拼接的主要因素。为制作符合离子束刻蚀要求的高质量光栅掩模,建立了条纹周期测量误差与扫描曝光对比度关系的数学模型,利用光刻胶在显影过程中的非线性特性,建立了扫描干涉场曝光光栅的显影模型,给出了光栅掩模槽形随周期测量误差的变化规律,并进行了实验验证。结果表明:周期测量误差不仅会使掩模槽形变差,还会引起槽形在空间上的变化。在周期测量的相对误差一定时,相位拼接误差与相邻扫描间的步进间隔成正比,与干涉条纹周期成反比。在显影条件一定、曝光光束束腰半径1mm、曝光步进间隔0.8mm、曝光线密度1800gr/mm时,周期测量误差控制在139ppm以内,理论上可以制作槽底洁净无残胶、槽形均匀的光栅掩模。

Measured interference fringe period error has a major effect on the phase stitching error in scanning beam interference lithography system. In order to make high quality grating masks which can meet the requirement of the ion beam etching, mathematical model of the relationship between measured fringe period error and dose contrast is established. Based on the photoresist nonlinearities in developing process, the developing model of grating masks made by scanning beam interference lithography system is built. According to this model, variation of groove profile with measured fringe period error is given. Experiments are done to verify this model. It shows that： measured fringe period error makes groove profile worse and varies in space domain. With a certain measured fringe period error, phase stitching error between scans is proportional to step over distance and inversely proportional to fringe period. When interference beam waist radius is 1 mm, step over distance is 0.8 mm and grating line density is 1800 gr/mm, with certain developing conditions, measured fringe period error must be less than 139 ppm to make grating masks with bottom clean without residue and groove uniform.