极紫外（EUV）投影光刻掩模在斜入射光照明条件下，掩模成像图形位置和成像图形特征尺寸（CD）都将随入射光方向变化，即存在掩模阴影效应。基于一个EUV掩模衍射简化模型实现了掩模阴影效应的理论分析和补偿，得到了掩模（物方）最佳焦面位置和掩模图形尺寸校正量的计算公式。掩模（物方）焦面位置位于多层膜等效面上减小了图形位置偏移；基于理论公式对掩模图形尺寸进行校正，以目标CD为22 nm的线条图形为例，入射光方向变化时成像图形尺寸偏差小于0.3 nm，但当目标CD继续减小时理论公式误差增大，需进一步考虑掩模斜入射时整个成像光瞳内的能量损失和补偿。

In extreme-ultraviolet (EUV) lithography with off-axis illumination, the mask shadowing effects occur such as the orientation dependent pattern shift and critical dimension (CD) variation. Based on a simplified mask diffraction model, a theoretical analysis of the mask shadowing effects is proposed. The calculation formulas for the best mask (object space) focal-plane position and the correct value of mask pattern size are derived and used to compensate the mask shadowing effects. When focal plane of the mask is positioned on the equivalent plane of the multilayer, the pattern shift amount is reduced. When the mask pattern size is corrected using the derived formula, taking lines with the target CD of 22 nm as an example, the imaging CD bias is below 0.3 nm. However, with the decrease of the target CD, the formula error increases. It is necessary to consider the compensation of energy loss within the whole pupil that is caused by the off-axis illumination.