Numerical aperture integration for optical critical dimension (ocd) metrology

A method for generating simulated spectral information in optical critical dimension (OCD) metrology, the method comprising:

• receiving an intensity distribution function over a numerical aperture space for a target diffracting structure;
• generating points and weights for an interpolated function fitted to the intensity distribution function;
• and
• rigorously computing the simulated spectral information based on the set of generated points and weights.

An optical critical dimension (OCD) measurement apparatus, comprising:

• a light source;
• a detector to collect measured spectral information from the light source as diffracted by a target grating disposed on a substrate being measured by the apparatus;
• a simulated spectral information module to generate simulated spectral information by numerically integrating a non-linear transformed intensity distribution function by Gaussian quadrature using a set of weights and points that account for the effect of Wood anomalies on diffraction efficiency;
• and
• logic to compare the measured spectral information and the simulated spectral information and generate an estimate of a critical dimension of a feature in the target grating.