Self-referenced and self-calibrated MoiréOVL target design and applications

This paper presents a new overlay metrology target design and scheme referred as MoiréOVLTM. It utilizes Moiré patterns of two overlapping gratings to amplify the kernel response to overlay misalignment and thereby has the potential to enhance kernel sensitivity, detectability and measurement accuracy. A Self-referenced (SR) MoiréOVL design scheme, which enables MoiréOVL to be measured with existing image-based overlay tools is proposed and evaluated on a contact layer. This paper demonstrated the feasibility of SR-MoiréOVL on existing IBO tools. When comparing to the reference SEM-based overlay, a magnification factor of 6.9X with an R² of 0.96 and a calibrated intercept of 0.34nm was observed on wafer. Comparison between MoiréOVL and POR IBO on TIS, residuals, precision and TMU is presented. Lastly we present the idea of a Self-calibrated (SC) MoiréOVL scheme to calibrate the magnification factor on the fly during measurement for enhanced usability.