Patent ID: 7879682

Claim:
A method of controlling an alignment of layers in a multi-layered substrate having at least a first layer and a second layer, the second layer being formed over the first layer, the method comprising: providing at least two marker areas on the multi-layered substrate, in each marker area the first layer includes a first periodic structure and the second layer includes a second periodic structure, the second periodic structure being different from the first periodic structure, wherein placing the second periodic structure over the first periodic structure creates a diffractive structure in each of the marker areas, wherein the first and second periodic structures in a first marker area are shifted relative to each other in a first predetermined direction by a first predetermined amount, and wherein the first and second periodic structures in the second marker area are shifted relative to each other in a second predetermined direction by a second predetermined amount; illuminating each diffractive structure with electromagnetic radiation; detecting a signal strength of radiation diffracted from each of the diffractive structures; calculating a differential signal strength for each diffractive structure by comparing the detected signal strength of each diffractive structure with a maximum obtainable signal strength; employing a linearization technique for each diffractive structure to determine a relationship between the shift of the first periodic structure and the second periodic structure with respect to each other and the differential signal strength, based on the calculated values of differential signal strength for the corresponding diffractive structure and the corresponding predetermined shift direction and the predetermined shift amount; calculating, for each diffractive structure, a shift for which the differential signal strength reaches a maximum value, based on the determined relationship between the predetermined shift and the differential signal strength; and adjusting alignment settings to compensate for the calculated value for the shift in each diffractive structure.