Method for evaluating microstructures on a workpiece based on the orientation of a grating on the workpiece

A system for evaluating parameters of a workpiece, comprising:

• means for measuring a periodic structure on the workpiece to produce image data;
• means for identifying an orientation of a feature in the image data produced by higher-order diffractions from the periodic structure;
• means for determining an orientation of the periodic structure, based on the orientation of the feature in the image data;
• and
• means for correcting for the orientation of the periodic structure to produce a correlation between the compared image data and simulated image data;
• and
• means for performing a comparison of the image data with the simulated image data to ascertain parameters of the periodic structure.

An apparatus for evaluating parameters of a microstructure on a workpiece, comprising:

• an irradiation source for producing a beam of radiation;
• an optical system aligned with a path of the beam for focusing the beam at a focal plane;
• a workpiece site for holding the workpiece with the microstructure positioned at the focal plane;
• a detector for receiving a scattered radiation distribution diffracted from the microstructure;
• a computer including a computer operable medium containing instructions for:
• identifying an orientation of a feature in image data produced by higher order diffractions from the microstructure;
• determining an orientation of the microstructure based on the orientation of the feature in the image data;
• and
• performing a comparison of the image data with simulated image data to ascertain parameters of the periodic structure, wherein the determined orientation of the periodic structure is used to produce a correlation between the compared image data and simulated image data.