Sensitivity analysis for the detection of pitchwalk in self-aligned quadruple patterning by GISAXS

Recent studies for profile reconstructions of nanostructures produced with self-aligned quadruple patterning (SAQP) indicate the limits for solving the inverse problem with a rigorous simulation. Using Monte Carlo methods for the theoretical investigation of the observed pitchwalk behaviour is not feasible due to the high computational cost of simulating GISAXS measurements by solving Maxwell's equations with an FEM approach for each proposed structural model. We will show that a surrogate model based on a polynomial chaos expansion is a versatile tool to reduce the computational effort significantly. The expansion provides not only a surrogate for the forward model, but also Sobol indices for a global sensitivity analysis. This enables the study of the sensitivities in GISAXS in detail.