Method and apparatus for diffraction-based overlay measurement

A system for determining an overlay error, comprising:

• a processor coupled to an analyzer module;
• a reference pattern module comprising a first reference pattern and a separate second reference pattern;
• an optical system comprising:
• one or more light sources and configured to generate a first beam of light to radiate the first reference pattern of the reference pattern module and to radiate a first overlay measurement pattern disposed in a substrate and to generate a second beam of light to radiate the second reference pattern of the reference pattern module and to radiate a second overlay measurement pattern disposed in the substrate;
• and
• one or more light detectors, the one or more light detectors configured to receive a first combination of diffracted light from the first overlay measurement pattern and the first reference pattern and to receive a second combination of diffracted light from the second overlay measurement pattern and the second reference pattern;
• and
• the analyzer module is configured to receive detected signals associated with the first combination of diffracted light to determine a first overlay error between the first reference pattern of the reference pattern module and the first overlay measurement pattern of the substrate, to receive detected signals associated with the second combination of diffracted light to determine a second overlay error between the second reference pattern of the reference pattern module and the second overlay measurement pattern of the substrate, and to determine a total overlay error between the first and second overlay measurement patterns in the substrate based on the first and second overlay errors.

A system for determining an overlay error, comprising:

• a controller;
• a reference pattern module coupled to the controller, comprising a first reference pattern and a spaced-apart second reference pattern;
• and
• an analyzer module coupled to the controller, configured to:
• determine a first overlay error between the first reference pattern of the reference pattern module and a first overlay measurement pattern in a substrate,
• determine a second overlay error between the second reference pattern of the reference pattern module and a second overlay measurement pattern in the substrate, and
• determine a total overlay error between the first and second overlay measurement patterns in the substrate based on the first and second overlay errors.