Optical far field measurements applied to microroughness determination of periodic microelectronic structures

With device size reduction, variability induced by local micro roughness is becoming less and less negligible in terms of statistical control of critical dimensions (CD). We applied a recent approach developed at Fresnel Institute for the determination of micro roughness on periodic structures through optical far field characterization using an angle resolved scatterometer. Structure periodicity affects the diffraction orders, while roughness signature is mainly found between diffraction orders. Theoretical simulation was performed using two in-house computer codes based on differential method and on first order approximation. We will review the theoretical approach and show roughness data derived from measurement on glass gratings as well as poly silicon gate type structures.