Rigorous coupled-wave analysis

A staircase approximation is needed for curved devices with properties such as dielectric permittivity graded along the z-direction.

The overall problem is solved by matching boundary conditions at each of the interfaces between the layers using a technique like scattering matrices.

Truncating the number of spatial harmonics can also slow convergence and techniques like fast Fourier factorization (FFF) should be used.

The difficulty with FFF in crossed grating devices is that the field must be decomposed into parallel and perpendicular components at all of the interfaces.

Almost without exception, however, the scattering matrices implemented for RCWA are inefficient and do not follow long standing conventions in terms of how S11, S12, S21, and S22 are defined.

This technique has been used to provide trench depth and critical dimension (CD) results comparable to cross-section SEM, while having the added benefit of being both high-throughput and non-destructive.

[citation needed] In order to extract critical dimensions of a trench structure (depth, CD, and sidewall angle), the measured polarized reflectance data must have a sufficiently large wavelength range and analyzed with a physically valid model (for example: RCWA in combination with the Forouhi-Bloomer Dispersion relations for n and k).