Alignment method, method of measuring front to backside alignment error, method of detecting non-orthogonality, method of calibration, and lithographic apparatus

摘要

In a method of measuring front to backside alignment error according to one embodiment, a transparent substrate has a plurality of marks on both the front and backside. The relative location of the marks on the front and backside of the substrate is determined to calculate the front to backside alignment error for the whole substrate. In a further embodiment, the substrate is rotated by 180° within the plane of the substrate and the front relative location of the marks is again determined.