There are a number of possible sources of scattering in diffractive optics: sloping walls, pattern depth errors, line edge errors, quantization errors, roughness, and the step wise approximation to the ideal surface. These sources of scattering can be systematic (deterministic) or random. In this paper scattering formulas for both systematic and random errors are derived using Fourier optics. These formulas can be used to explain the results of scattering measurements and computer simulations.
D. W. Ricks,
"Scattering from diffractive optics", Proc. SPIE 10271, Diffractive and Miniaturized Optics: A Critical Review, 102710B (28 December 1993); doi: 10.1117/12.170184; https://doi.org/10.1117/12.170184