The Limits and Extensibility of Optical Patterned Defect Inspection

New techniques recently developed at the National Institute of Standards and Technology using bright-field optical tools are applied to signal-based defect analysis of features with dimensions well below the measurement wavelength. A key to this approach is engineering the illumination as a function of angle and analysis of the entire scattered field. In this paper we demonstrate advantages using this approach for die-to-die defect detection metrology. This methodology, scatterfield optical microscopy (SOM), is evaluated for defect inspection of several defect types defined by Sematech on the Defect Metrology Advisory Group (DMAG) intentional defect array (IDA) wafers. We also report the systematic evaluation of defect sensitivity as a function of illumination wavelength. Theoretical simulations are reported that were carried out using a fully three-dimensional finite difference time domain (FDTD) electromagnetic simulation package. Comprehensive modeling was completed investigating angle-resolved illumination to enhance the detection of several defect types from the IDA wafer designs. The defect types covered a variety of defects from the IDA designs. The simulations evaluate the SOM technique on defect sizes ranging from those currently measurable to those the industry considers difficult to measure. The simulations evaluated both the 65 nm IDA metal-1 M1 trench and the polysilicon stack and more recent 13 nm linewidth logic cells.