Alignment systems and methods for lithographic systems

A device manufacturing method comprising:

• projecting a patterned beam of radiation onto a substrate;
• and
• aligning the substrate so that the patterned beam of radiation is projected at desired locations on the substrate, the aligning comprising
• illuminating an alignment mark provided on the substrate with a radiation beam, the alignment mark including a first grating and a second grating that are each adapted to enhance a different diffraction order, each of the first and the second grating including a plurality of segments alternately repeated along a first direction, wherein at least one segment of each of the first and the second grating is divided to form sub-segments that are alternately repeated along a second direction that is different from the first direction;
• and
• detecting a signal resulting from an interaction between the alignment mark and the radiation beam.

A lithographic apparatus comprising:

• a patterning device support configured to support a patterning device, the patterning device adapted to pattern a beam of radiation to form a patterned beam of radiation;
• a substrate table configured to support a substrate;
• a projection system configured to project the patterned beam of radiation onto the substrate;
• and
• an alignment system configured to align the substrate in the lithographic apparatus, the alignment system comprising
• a source of radiation configured to illuminate an alignment mark provided on the substrate with a radiation beam, the alignment mark including a first grating and a second grating that are each adapted to enhance a different diffraction order, each of the first and the second grating including a plurality of segments alternately repeated along a first direction, wherein at least one segment of each of the first and the second grating is divided to form sub-segments that are alternately repeated along a second direction that is different from the first direction, and
• a first and a second detection channel, the first detection channel adapted to detect a signal resulting from an interaction between the first grating and the radiation beam and the second detection channel adapted to detect a signal resulting from an interaction between the second grating and the radiation beam.