Measurement substrate, substrate table, lithographic apparatus, method of calculating an angle of an alignment beam of an alignment system, and alignment verification method

An alignment verification method for verifying a defined front-to-back-side alignment error in a lithographic apparatus comprising an alignment system, the method comprising:

• providing an alignment beam of radiation using an alignment system;
• providing a verification substrate that is transparent to the alignment beam of radiation;
• patterning the beam of radiation with a first pattern in its cross-section;
• projecting the first patterned beam of radiation onto a first side of the verification substrate to create a first verification mark;
• turning the verification substrate over;
• aligning the verification substrate;
• patterning the beam of radiation with a second pattern in its cross-section;
• projecting the second patterned beam of radiation onto a second side of the verification substrate to create a second verification mark;
• detecting the position of the first mark on the first side of the verification substrate using the alignment system;
• detecting the position of the second verification mark on the second side of the substrate using the alignment system, the verification substrate remaining stationary relative to a substrate table holding the verification substrate between the first detecting and the second detecting to measure a displacement between the first and the second verification mark in the plane of the substrate;
• and
• calculating an angle of the alignment beam of the alignment system according to a method comprising:
• arranging a plurality of alignment marks on a measurement substrate;
• covering less than all of the alignment marks with a transparent plate to provide a covered alignment mark and an uncovered alignment mark;
• measuring a first position of the uncovered alignment mark;
• measuring a first position of the covered alignment mark;
• calculating a first shift for the covered alignment mark between a first actual position and the first measured position of the covered alignment mark;
• calculating a first value for the angle, using the first shift for the covered alignment mark;
• and
• using the angle to correct the measured displacement in order to determine the front-to-back-side alignment error.