Electromagnetic simulation for scatterometry

Scatterometry is a specific kind of ellipsometry for diffracting patterns: analyzing the change in polarization at diffraction on periodic structures, we get some information about the geometry or materials. Scatterometry is widely used in every subfields of microelectronics for fast and non-destructive inspection or process control.

This metrology technique relies on solving an inverse problem: from an ellipsometric signature, we are guessing information which cannot be directly derived from the measurements; we usually need to simulate a lot of responses from a variety of modelled shapes to approximate the actual diffracting pattern (fig.1).

In addition to general ellipsometry expertise, LTM uses and develops high-performance simulation codes for the direct problem (2D, 3D-RCWA, etc.). Those codes serve the inverse problem for simple to very challenging configurations where a high number of signatures are needed or where high-complexity geometry needs specifically optimized computing techniques (GPU, massive parallelization, memory management, etc.).

Our expertise is shared for industrial applications as well as for more fundamental research: the illustration bellow shows a 3D-RCWA simulation of Muller matrices (fig.2) for a periodic arrangement of nano-spirals. The objective was then to evaluate how cutting-edge scatterometry can measure circular dichroism.