Self-referencing and self-calibrating interference pattern overlay measurement

A method comprising:

• establishing a first target having a first pitch on a first optical mask;
• establishing a second target having a second pitch on the first optical mask, wherein the second target is adjacent to the first target;
• establishing a third target having the second pitch on a second optical mask;
• establishing a fourth target having the first pitch on the second optical mask, wherein the third target is adjacent to the fourth target, wherein the first target and the third target form first interference patterns, wherein the second target and the fourth target form second interference patterns, wherein the first interference patterns and the second interference patterns form a first pair of conjugated interference patterns, and wherein the first target, the second target, the third target, and the fourth target comprise a first set of targets;
• establishing a second set of targets identical to the first set of targets and inverted relative to the first set of targets on the first optical mask and the second optical mask to produce a second pair of conjugated interference patterns that is inverted relative to the first pair of conjugated interference patterns, wherein at least one of the first pitch and the second pitch are below a minimum optical resolution of a measurement system, and wherein the first pair of conjugated interference patterns and the second pair of conjugated interference patterns are above the minimum optical resolution;
• and
• outputting a design containing the first optical mask and the second optical mask, wherein the design is usable in the measurement system.

A structure comprising:

• a substrate including a first layer and a second layer overlaying the first layer;
• a first feature having a first pitch, wherein the first feature is in a first location of the first layer;
• a second feature having a second pitch different than the first pitch, wherein the second feature is in a second location of the first layer that is adjacent to the first location;
• a third feature having the second pitch, wherein the third feature is in a third location of the second layer that corresponds to the first location of the first layer;
• and
• a fourth feature having the first pitch, wherein the fourth feature is in a fourth location of the second layer that corresponds to the second location of the first layer,
• wherein the first feature and the third feature are structured to form first interference patterns, and the second feature and the fourth feature are structured to form second interference patterns,
• wherein at least one of the first pitch and the second pitch are below a minimum optical resolution of a measurement system, and
• wherein the first interference patterns and the second interference patterns are above the minimum optical resolution.