Patent ID: 9625937
Date: 2017-04-18
CPC Classifications: G06E

Claim:
1. A method comprising: simulating a diffraction signal for a certain three-dimensional structure using a processing unit of an optical metrology system, the diffraction signal being calculated from a set of diffraction orders; prioritizing the diffraction orders, the set of diffraction orders representing a matrix of diffraction orders in a Fourier transformation, wherein a subset of the set of diffraction orders may be defined with a truncation schema having a basic schema shape; for each of a plurality of truncation schemas, each truncation schema having a basic non-rectangular schema shape, determining a difference between a result generated by the truncation schema and a result generated by a rectangular schema; comparing the difference for each of the plurality of truncation schemas to an error threshold; selecting a truncation schema of the plurality of truncation schemas for the three-dimensional structure that provides a best result based at least in part on the comparison of the difference for each of the plurality of truncation schemas to the error threshold; truncating the set of diffraction orders based on the selected truncation schema, wherein truncating the set of diffraction orders includes the processing unit retaining only diffraction orders presented in the matrix of diffraction orders that are within the selected truncation schema; determining the simulated diffraction signal based on calculations using the truncated set of diffraction orders; and comparing the simulated diffraction signal to a diffraction signal measured from the three dimensional structure using an optical metrology tool.