在纳米光刻中,采用周期相差不大的两光栅分别作为掩模和硅片上的对准标记。当对准光路通过这两个标记光栅时受到两次调制,发生双光栅衍射及衍射光的干涉等复杂现象,最后形成有规律、且呈一定周期分布的莫尔条纹。周期相对光栅周期被大幅度放大,条纹移动可表征两标记的相对位移,具有很高探测灵敏度,可用于纳米级高精度对准。从傅里叶光学角度分析推导了对准应用中,两频率接近的光栅重叠时莫尔条纹振幅空间近似分布规律。并设计了一组对准标记,能继续将灵敏度提高一倍。通过仿真分析,从大致上定量地验证条纹复振幅分布的近似数学模型以及光刻对准应用中的条纹对准过程。

In the application of nanometer lithography, two gratings with similar periods were chosen for alignment marks on the wafer and mask respectively. Then light was modulated by these two gratings when they traveled through two alignment marks, and some phenomenon such as diffraction and interference occurred so that regular and periodic-distributed moiré patterns were formed in the process of alignment. Because the fringe with magnified period versus periods of two gratings has high sensitivity to represent relative movement of two gratings on wafer and mask, it has a good prospect in the application of alignment of lithography. Theoretical analysis and deduction of the regularity of approximate spatial distribution of moiré patterns resulting from superposition of two proximity gratings with close frequencies were performed in the viewpoint of Fourier Optics. Furthermore, a set of alignment marks which could double the sensitivity were designed. Approximate mathematical model of complex amplitude of interferometric fringes and the process of alignment of lithography were verified through simulation.