掩模分形提高光刻边缘锐度的研究

针对电寻址空间光调制器制作灰度掩模过程中，精缩透镜的低通滤波特性导致灰度掩模边缘锐度下降的问题，提出了掩模分形技术。对一幅高频灰阶掩模图形，按固定的或可变的低频采样。低频掩模的每个周期中，只包含原掩模图形多个周期中的一个抽样。通过实时掩模技术，将多个低频掩模按顺序曝光，从而恢复出原高频掩模图形。制作二元光栅时，分形掩模技术可使透镜造成的高频能量相对损失由35、23％降低至6．09％，同时，可将部分低频能量搬迁至中高频，较好地改善了灰阶掩模图形的边缘锐度。分形掩模还可以变多灰阶复杂掩模为简单的二元掩模，简化掩模的设计与实现，同时消除屏幕刷新率对掩模制作的影响。

Research of Mask Division for Improving the Edge Sharpness of Photolithography

A new technique of mask division for improving the sharpness of mask edge is put forward, which can be used to solve the lowpass filtering problem of the reduction lens in the system of mask fabrication with electrically addressed spatial light modulators. A mask image with high frequency is sampled with fixed or variable low frequency. In each period of the low frequency mask, only one part of the initial mask is included. Using real-time mask technique, multiple division masks are exposed sequentially and the high frequency mask is restored. For fabrication of binary grating, the relative lost efficiency caused by aperture limit of the lens can be decreased from 35.23% to 6.09%. And part of the low frequency energy is moved to the middle and high frequency. The sharpness of the mask edge is ameliorated evidently. Using division mask, complex shape mask or multi-level mask can be changed into binary mask, which is easy to be designed and realized. Moreover, the transition of multi-level gray to binary, that is, black and white, can eliminate the disturbing effect of the refresh rate of screen.