Optical illumination optimization for patterned defect inspection

Rapidly decreasing critical dimensions (CD) for semiconductor devices drive the study of improved methods for the detection of defects within patterned areas. As reduced CDs are being achieved through directional patterning, additional constraints and opportunities present themselves in defect metrology. This simulation and experimental study assesses potential improvements in patterned defect inspection that may be achieved by engineering the light incident to the sample within a high-magnification imaging platform. Simulation variables include the incident angle, polarization, and wavelength for defect types common to directional device layouts. Detectability is determined through differential images between no-defect- and defect-containing images. Alternative metrologies such as interference microscopy are also investigated through modeling. The measurement of a 20 nm defect is demonstrated experimentally using 193 nm light. The complex interplay of unidirectional patterning and highly directional defects is explored using structured off-axis illumination and polarization.