提出一种新的步进扫描投影光刻机工件台方镜不平度测量方法。以方镜平移补偿量与旋转补偿量为测量目标,使用两个双频激光干涉仪分别测量工件台在x和y方向的位置和旋转量；将方镜不平度的测量按照一定的偏移量分成若干个序列,每一个序列包括对方镜有效区域的若干次往返测量；根据所有序列的测量结果计算出方镜的旋转补偿量；为每一个序列建立临时边界条件,并据此计算出每一序列所测得的方镜粗略平移补偿量；采用三次样条插值与最小二乘法建立每一个序列间的关系,以平滑连接所有测量序列得到精确的方镜平移补偿量。结果表明,该方法用于测量方镜平移补偿量,测量重复精度优于2.957 nm,测量旋转补偿量,测量重复精度优于0.102 μrad。

A novel in-situ non-flatness measurement method of wafer stage mirrors in a step-and scan lithographic tool is presented. According to the impact of mirror non-flatness on wafer stage′s positioning, the non-flatness of the mirror is expressed as translation compensation and rotation compensation usually. The double frequency laser interferometers are used to measure the horizontal positions and rotations of the wafer stage. The whole measurement is divided into several sequences. Each sequence includes a whole measurement of the valid area of the mirror. The rotation compensation of the mirror is calculated from each measured values of the wafer stage′s rotation. The coarse translation compensation of the mirror is calculated recursively by setting a temporary boundary condition in each sequence. The cubic spline interpolation method and least square method are used to smooth and connect all the coarse translation compensations of the mirror to calculate the accurate translation compensation of the mirror. Experiment results prove that by this method the measurement reproducibility of the translation compensation of mirror is better than 2.957 nm and the measurement reproducibility of the rotation compensation of mirror is better than 0.102 μrad.