基于复合光栅的大范围高精度对准方法

High-Precision Alignment Technique with Large Measurement Range Based on Composite Gratings

提出一种基于复合光栅的对准方法,满足接近式光刻高精度、大范围对准需要。该复合光栅由周期具有微小差异的小周期光栅以及与之相正交的大周期小范围光栅组成。对准过程中,通过对叠栅条纹进行高精度相位解析,实现精对准;通过直接求取大周期光栅位置实现粗对准。由于两个方向上的光栅相互正交,傅里叶变换提取频谱时将不受影响。分别分析小周期光栅的叠栅条纹相位分布,以及大周期光栅的强度分布,实现大范围、高精度对准。推导了基片、掩模相对移动量与复合光栅变化之间的关系。通过计算机模拟对该对准方法进行了仿真分析,考虑噪声的基础上,对准精度可以达到16.5 nm;通过实验系统对该对准方法进行了验证与分析,对准精度可以达到30.19 nm。

In order to meet the demands of high-accuracy alignment with large measurement range in proximity lithography, a method based on composite gratings is introduced. The composite gratings consist of small-period gratings with slightly different periods and large-period gratings with small range which are orthogonal to the small- period ones. Fine alignment is realized by high-precision phase analysis on moire fringes while coarse alignment is achieved by obtaining the position of large-period gratings directly. Since the different-direction gratings are orthogonal to each other, there will be no influence on extracting frequency spectrum by applying Fourier transform. By analyzing the phase variations of small gratings＇ moire fringes and the intensity of large-period gratings, substrate and mask can be aligned with high accuracy and large measurement range. Furthermore, the relation between the offsets of substrate and mask and the position changes of the two composite gratings are derived. An analysis of the built model is performed via simulation to show that the accuracy can reach 16.5nm while considering the noises; and an experiment is also conducted to verify the effectiveness of the proposed method and the accuracy can reach 30.19 nm.