Patent ID: 7781237

Claim:
An apparatus comprising: a first support structure configured to support an element, said element including a reflective alignment marker provided with at least one height difference; and an alignment sensor comprising: a light source configured to provide a light beam that illuminates the reflective alignment marker, wherein the light beam includes an angle of incidence and a principle angle of reflectance; imaging optics configured to selectively receive that fraction of the energy of the light beam reflected by at least one height difference of the reflective alignment marker; and at least one detector arranged to detect a location of the at least one height difference of the reflective alignment marker, based on the received fraction of the energy of the light beam, to enable an alignment of said element, and wherein a divergence of the light beam from the reflective alignment marker is larger than a numerical aperture of the imaging optics, such that an intensity distribution in a pupil of the imaging optics is uniform.