掩模位置误差对光刻投影物镜畸变的影响

Effect of alignment errors of reticle on distortion in lithographic projection lens

为使光刻投影物镜满足光刻工艺的要求,研究了掩模位置误差对光刻投影物镜引入的畸变。采用勒让德多项式描述光刻投影物镜的畸变,并应用勒让德多项式对光刻投影物镜进行了畸变分析及畸变补偿。利用以上方法,对一台工作波长为193 nm,数值孔径(NA)为0.75的光刻投影物镜进行了畸变分析。结果显示:当掩模面3个方向的平移公差为1.0μm,绕3个轴的转动公差为0.1 mrad时,光刻投影物镜标定前后的畸变分别为2 113.2 nm和10.0 nm。利用勒让德多项式进行了畸变拟合,获得了多项式中各项系数,并给出掩模面位置误差的畸变敏感度系数;然后利用畸变敏感度系数对掩模面的随机位置误差进行了公差分析和补偿。结果表明,将光刻投影物镜畸变控制在2 nm以内时,掩模面z方向的位置公差为±2.0μm,掩模面与x轴与y轴的倾斜公差分别为±22.3μmad和±55.3μmad。实验结果证明提出的方法适用于对掩模面引入的光刻投影物镜畸变进行有效分析及补偿。

To meet the requirement of lithographic tool for the distortion in a lithographic projection lens, the distortion of the optical lithography introduced by alignment errors of a reticle was researched. The Legendre polynomials were used to describe the distortion of lithographic projection lens, and then it was taken to analyze and compensate the distortion. Based on the proposed methods, a lithographic projection lens with a Numerical Aperture（NA） of 0.75 and the working wavelength of 193 nm was analyzed. The analysis results show that the combinational tolerances of the reticle tilt error in 1.0 μm and the reticle translation error in 0.1 mrad have aroused by uncalibrated distortions of 2 113.2 nm and 10.0 nm. The Legendre polynomial was used to fit the distortion to obtain the coefficients of the Legendre polynomial, and then to get the distortion sensitivity of the reticle alignment errors. The distortion sensitivity then was used to perform the tolerance analysis and compensation for the random position errors of the reticle. As the distortion was expected to be less 2 nm, the requirement of the reticle z-direction tolerance is ＋2.0 μm and those of the reticle x-tilt and y-tilt tolerances are ＋22.3μmad and ＋55.3txmad, respectively. The results demonstrate that the way proposed is suitable for analyzing and compensating the distortion introduced by reticle alignment errors in lithographic projection lenses.