Optical devices and method of optical device metrology

An optical device, comprising:

• a substrate;
• and
• a plurality of structures disposed on a surface of the substrate of the optical device, the plurality of structures having critical dimensions less than one micron, the plurality of structures including one or more target features, wherein a ratio of one or more target features to the plurality of structures is between about 1:100,000 and about 1:1,000,000,000, the one or more target features are readable by metrology tools and include at least one of:
• one or more structures merged together;
• one or more structures merged together surrounded by one or more structures that have been removed;
• or
• one or more structures that have been removed having one or more profiles defined by adjacent structures to the target features.

A method, comprising:

• directing a measurement area of a metrology tool over an approximate first location of a surface of a substrate of an optical device;
• identifying a precise location of a first target feature of the optical device, the optical device comprising a plurality of structures disposed on the surface, the plurality of structures including one or more target features, wherein the one or more target features are readable by metrology tools and include at least one of:
• one or more structures merged together;
• one or more structures merged together surrounded by one or more structures that have been removed;
• or
• one or more structures that have been removed having one or more profiles defined by adjacent structures to the target features;
• determining one or more of critical dimensions, gaps, pitches, and peripheral distances of at least one of the plurality of structures based on the precise location within the measurement area;
• and
• repeating the steps of directing the measurement area of the metrology tool, identifying a target feature, and determining the one or more of critical dimensions, the gaps, the pitches, and the peripheral distances of at least one of the plurality of structures within the measurement area at one or more subsequent locations.