Compressive sensing for metrology

A semiconductor metrology system, comprising:

• an illuminator for generating illumination;
• illumination optics for directing the illumination towards a target of interest on a semiconductor wafer;
• collection optics for directing a plurality of signals from the particular structure to a sensor in response to the illumination, wherein the collection optics comprise a spatial light beam controller for controlling a spatial profile of a pupil image of the metrology system;
• the sensor for collecting the plurality of signals from the target of interest;
• and
• a controller configured for performing the following operations:
• defining a plurality of collection patterns for the spatial light beam controller;
• for each collection pattern, collecting a signal from the sensor of the metrology tool, wherein each collected signal represents a combination of a plurality of signals that the spatial light beam controller samples, using each collection pattern, from a pupil image of the target of interest, wherein the collection patterns are selected so that the pupil image is reconstructable based on the collection patterns and their corresponding collection signals;
• and
• analyzing the collected signal for each of the collection patterns to determine a structure or process parameter value for the target of interest;
• obtaining a representative set of pupil images from a plurality of test structures that were fabricated or simulated with known process variations;
• extracting basis images for a plurality of possible collection patterns that are most related to the known process variations from a large set of basis images that are generated for the representative set of pupil images;
• and
• using the extracted basis images to define the collection patterns for the spatial light beam controller.

A method of determining a structure or process parameter value of a target of interest on a semiconductor water, the method comprising:

• defining one or more collection patterns for a spatial light beam controller positioned at a pupil image plane of a metrology tool, wherein each collection pattern is defined based on a plurality of coefficients of a model for predicting a corresponding structure or process parameter value for a target of interest;
• for each collection pattern, collecting a signal from a sensor of the metrology tool, wherein each collected signal represents a combination of a plurality of signals that the spatial light beam controller samples, using each collection pattern, from a pupil image of the target of interest;
• reporting a value of each collected signal for each of the collection patterns as a corresponding structure or process parameter value for the target of interest;
• obtaining a representative set of pupil images from a plurality of test structures that were fabricated or simulated with known process variations;
• extracting basis images for a plurality of possible collection patterns that are most related to the known process variations from a large set of basis images that are generated for the representative set of pupil images;
• and
• using the extracted basis images to define the collection patterns for the spatial light beam controller.