扫描干涉场曝光系统中的干涉条纹周期是相位锁定系统的重要参数，其设定值与名义值之间的偏差会引起相邻扫描间的干涉条纹相位拼接误差。为获取以扫描曝光方式所制作光栅的衍射波前特征，根据步进扫描曝光的特点及动态相位锁定的工作原理，建立了扫描曝光的数学模型，给出了曝光刻线误差及曝光光栅周期的变化规律，并进行了相关实验验证。结果表明，相位锁定中周期设定误差会带来周期性的刻线误差。曝光光栅周期会随周期设定值的变化而改变，当周期设定误差较小时，曝光光栅周期等于周期设定值。对于曝光光斑束腰半径为0.9 mm、曝光步进间隔为0.6 mm、曝光条纹周期为555.6 nm的系统参数，周期设定的相对误差小于278×10-6时，周期性的刻线误差小于1 nm。若要求曝光对比度大于0.9，则周期设定的相对误差需要控制在92.6×10-6以内，周期设定值及曝光光栅周期的可变范围为102.8 pm。

Interference fringe period is a very important parameter of phase locking in scanning beam interference lithography system. The deviation between period setting value and nominal fringe period value will cause stitching error of interference fringe between adjoining scans. To get features of scanning lithography manufactured grating diffraction wavefront, according to the characteristics of step-and-scanning lithography and working principle of dynamic phase locking, the mathematical model of scanning beam interference lithography is built. According to this model, variations of printed error and lithography grating period are given. Experiments are done to verify this model. Results show that period setting error in phase locking system will cause periodic printed error. Periods of lithography grating vary with period settings. Lithography grating period is equal to period setting value with tiny period setting error. When interference beam waist radius is 0.9 mm, step over distance is 0.6 mm and fringe period is 555.6 nm, periodic printed error is less than 1 nm with period setting relative error less than 278×10-6. If the dose contrast is more than 0.9, period setting error must be controlled within 92.6×10-6. The variable range of period setting value and lithography grating period is 102.8 pm.