System and method for focus determination using focus-sensitive overlay targets

A lithography mask is disclosed. The lithography mask includes at least one asymmetric segmented pattern element. A particular asymmetric segmented pattern element includes at least two segments witha separation distance between consecutive segments smaller than a resolution of a set of projection optics for generating an image of the particular asymmetric segmented pattern element on a sample such that the image of the particular asymmetric segmented pattern element is an unsegmented pattern image. A position of the unsegmented pattern image on the sample is indicative of a location of the sample along an optical axis of the set of projection optics. 本发明揭示种光刻掩模。所述光刻掩模包含至少个不对称经分段图案元素。特定不对称经分段图案元素包含至少两个分段，其中连续分段之间的分离距离比用于在样本上产生所述特定不对称经分段图案元素的图像的组投射光学器件的分辨率小，使得所述特定不对称经分段图案元素的所述图像为未经分段图案图像。所述未经分段图案图像在所述样本上的位置指示所述样本沿着所述组投射光学器件的光轴的位置。