一种控制矩形光刻胶光栅槽深和占宽比的方法

利用光刻胶的非线性效应可以制作出了矩形的全息光栅。制作矩形光栅时，对槽形的控制被简化为对槽深和占宽比这两个参量的控制。首先借助实时潜像监测技术获得最佳曝光量，然后根据显影监测曲线的特征找出光栅槽底的残胶厚度为零的显影时刻，就能得到槽底干净的矩形光栅，同时保证槽深近似等于光刻胶的初始厚度；如果此后继续显影，就能适度减小占宽比。实验结果和理论分析都证实了这种控制方法的可靠性。对1200lp／mm的光栅，目前工艺能精确调控的最大槽深为1μm，占宽比在0．2～0．6范围内。实验还揭示，为了提高对光栅槽形的调控能力，必须首先提高干涉条纹的稳定性。

Method for Controlling Groove Depth and Duty Cycle of Rectangular Photoresist Gratings

Rectangular photoresist gratings can be fabricated by taking advantage of the nonlinearity of photoresist. For rectangular gratings the task of controlling groove profile is simplified to controlling the duty cycle and groove depth. By monitoring diffraction intensity of latent image in photoresist in real time, the optimal exposure dose can be determined. Then, by observing characteristic behavior of the development-monitoring curve, the development process can be stopped at the moment when photoresist at the groove troughs is completely etched away. Therefore, rectangular grooves with clean troughs can be obtained; meanwhile the groove depth is kept equal to the initial photoresist thickness. Further development will reduce the duty cycle. It has been proven reliable by experiments and theoretical analysis. For gratings with 1200 lp/mm groove spacing, the groove depth up to 1 μm has been controlled accurately in authors' present fabrication, and the duty cycle value obtained is in the range 0.2 to 0.6. The experimental results have also demonstrated that good controllability of groove profiles depends on good fringe stability of the laser interference patterns.