Scatterometry modeling for gratings with roughness and irregularities

A rigorous electromagnetic simulation method for grating diffraction is presented that concurrently enables appropriate roughness and irregularity modeling. The approach will it make possible for example to overlay surface roughness and or line edge roughness (LER) to regular patterns. In this way, a unique tool is provided to model diffraction and scattering at the same time. It is based on a combination of modal methods such as the RCWA or C-method with near field stitching and subsequent near-to-far field propagation. This paves the way to an efficient and accurate modeling of large scattering areas. Fields of applications are the design of spectrographic gratings as well as optical scatterometry or kindred optical metrology techniques. Examples are provided both for 2D line/space patterns with sinusoidal and blaze profiles and 3D line/space patterns possessing LER and line width roughness (LWR). First ideas are derived how to determine LER and LWR from scatterometric measurements.