提出一种步进扫描投影光刻机承片台不平度检测新技术。在晶圆与承片台存在不同偏移量时,利用线性差分传感器在线测量晶圆上不同点的局部高度;通过建立临时边界条件,以递推法消除晶圆面形影响,并逐行计算出承片台的相对不平度;通过逐行计算的结果递推相邻行之间的高度差,并将该高度差叠加到每一行,以消除临时边界条件的限制,得到处于同一高度上的承片台不平度;将计算的结果作为初始值,根据最小二乘原理,以邻近的四个测量点作为参考,逐步逼近得到承片台的真实不平度。计算机仿真结果验证了该检测方法的正确性,计算结果逐步收敛并逼近真实值.实验结果表明,该方法的计算结果较好地表示了承片台的真实不平度,重复精度优于0.3 nm;同时该方法也可用于晶圆表面面形的测量。

A novel in-situ non-flatness measurement method of wafer chuck in step-and-scan projection lithographic tool is presented. The local heights of wafer surface are measured by the linear variable differential transformer (LVDTs) when the different offsets between wafer and wafer chuck exist. A temporary boundary condition is built to calculate the relative non-flatness of wafer chuck line by line and eliminate the effect of the wafter surface shape with recursion formula. The height difference of the neighboring columns is calculated with recursion formula, which is added to each row to remove the temporary boundary condition limitation and the coarse non-flatness of wafer chuck with the same height is determined. According to the coarse result, the four neighboring points of the measured point are used as reference to approach the accurate non-flatness of wafer chuck with the least square method. Computer simulation and experimental results prove that the calculated result accords with the real non-flatness of wafer chuck well, and the reproducibility by this method is better than 0.3 nm. The method is also valid for measurement of wafer surface shape.