Patent ID: 7612882

Claim:
A method of aligning a lithography tool with a substrate, the method comprising: providing a substrate having at least one substrate alignment feature comprising a first optical grating, wherein the first optical grating is configured to have a plurality of alternating light and dark regions; providing a lithography tool having at least one tool alignment feature comprising a second optical grating, wherein the second optical grating is configured to have a plurality of alternating light and dark regions, the first optical grating and the second optical grating being configured to generate a Moiré pattern in a beam of electromagnetic radiation when the beam of electromagnetic radiation interacts with both the first optical grating and the second optical grating, the sensitivity of the Moiré pattern varying with the relative alignment between the substrate and the lithography tool; configuring the alternating light and dark regions of both the first optical grating and the second optical grating to have at least one of a width, a pitch, and a duty cycle that varies across each respective optical grating; positioning the lithography tool relative to the substrate and roughly aligning the tool alignment feature and the substrate alignment feature; causing a beam of electromagnetic radiation to interact with both the first optical grating and the second optical grating to generate a Moiré pattern; and adjusting the relative position between the substrate and the lithography tool to cause the Moiré pattern to approximate or match a predetermined pattern representing an acceptable degree of alignment between the lithography tool and the substrate.