Patent ID: 7737566

Claim:
A substrate having at least one dual-period alignment mark, said at least one dual-period alignment mark comprising: a first periodic sequence of lines and spaces along a first direction of the substrate, said first periodic sequence having a first period; and a second periodic sequence of line segments and space segments arranged within said lines or within said spaces, said second periodic sequence being arranged along the first direction to form a grating that is periodic with a second period, wherein said second period is smaller than said first period and wherein said second periodic sequence is arranged so that, when the dual-period alignment mark is illuminated with radiation having a wavelength which is smaller than the first period and larger than the second period, an efficiency of the dual-period alignment mark on a per-phase-depth basis is different from an efficiency said dual-period alignment mark would exhibit if the dual-period alignment mark had been implemented as a single-period alignment mark that includes the first periodic sequence but does not include the second periodic sequence.