Alignment of layers during manufacture of a multi-layer sample is controlled by applying optical measurements to a measurement site in the sample. The measurement site includes two diffractive structures located one above the other in two different layers, respectively. The optical measurements include at least two measurements with different polarization states of incident light, each measurement including illuminating the measurement site so as to illuminate one of the diffractive structures through the other. The diffraction properties of the measurement site are indicative of a lateral shift between the diffractive structures. The diffraction properties detected are analyzed for the different polarization states of the incident light to determine an existing lateral shift between the layers.
This is a continuation of application Ser. No. 11/271,773 filed Nov. 14, 2005, now allowed and about to issue as U.S. Pat. No. 7,122,817, itself a continuation of grandparent application Ser. No. 10/257,544 filed Feb. 6, 2003, now U.S. Pat. No. 6,974,962.
Lithography tools and substrates are aligned by generating geometric interference patterns using optical gratings associated with the lithography tools and substrates. In some embodiments, the relative position between a substrate and lithography tool is adjusted to cause at least one geometric shape to have a predetermined size or shape representing acceptable alignment. In additional embodiments, Moire patterns that exhibit varying sensitivity are used to align substrates and lithography tools. Furthermore, lithography tools and substrates are aligned by causing radiation to interact with optical gratings positioned between the lithography tools and substrates. Lithography tools include an optical grating configured to generate a portion of an interference pattern that exhibits a sensitivity that increases as the relative position between the tools and a substrate moves towards a predetermined alignment position.
