相位光栅非对称性对位置测量精度的影响

Effect of Phase Grating Asymmetry on Position Measurement Accuracy

在相位光栅位置测量系统中,加工、后处理等工艺会导致光栅结构发生非对称性变形,增加了位置测量误差。因此,建立了非对称性光栅的衍射场理论模型,分析了光栅非对称性对位置测量精度的影响,并根据不同衍射级次对非对称性敏感度的差异提出了一种多衍射级次权重优化方法,以修正光栅非对称性变形引入的测量误差。实验结果表明,当光栅中心槽深为入射波长的1/4时,顶部倾斜非对称性和底部倾斜非对称性对测量精度的影响可以忽略;当占空比为0.5时,侧壁非对称性对测量精度的影响可以忽略。非对称性引入的位置误差,经多衍射级次权重优化法修正后可控制在0.05 nm以内。

In a position measurement system based on a phase grating, the grating undergoes asymmetric deformation during processing and post-processing, resulting in a position measurement error. Therefore, this paper established a theoretical diffraction field model of an asymmetric grating and analyzed the influence of grating asymmetry on position measurement accuracy. On this basis, it proposed a weight optimization method with multi-diffraction orders according to the different sensitivity of the diffraction orders to the grating asymmetry. The method is expected to correct the measurement error introduced by the asymmetrical grating deformation. The experimental results show that when the center groove depth of the grating is 1/4 of the incident wavelength, the influence of top tilt asymmetry and bottom tilt asymmetry on the measurement accuracy can be neglected. When the duty cycle is 0.5, the effect of sidewall asymmetry can also be neglected. The position error introduced by asymmetry can be kept within 0.05 nm by the weight optimization method with multi-diffraction orders.