Automatic Defect Review of a Patterned Wafer using Hybrid Metrology

The scaling trend toward under 5nm in semiconductor design requires tighter control over defects on wafers. To measure defects on wafer surfaces, several kinds of inspection and review tools can be employed—i.e., Surface Scanning Inspection Systems (SSIS), Scanning Electron Microscopy (SEM), or Transmission Electron Microscopy (TEM). Among the options, Atomic Force Microscopy (AFM) has proven particularly advantageous because it directly measures the dimensions (height and width) and physical properties of defects of interest and gives reference information for other characterization tools. At the same time, since the AFM measurement speed is relatively slow, it is unrealistic to find all defects on the wafer surface by using AFM alone. Therefore, we have introduced the hybrid metrological instrument by combining White Light Interferometer (WLI) to an industrial automated AFM platform. By utilizing the vibration-isolated platform and the low noise z scanner of AFM, the performance of WLI has significantly been improved, achieving unprecedented high z resolution. We introduce a method to identify the differences between wafers to locate the hot spots quickly and investigate the problems, thereby measuring many minor defects on the patterned wafer with higher throughput. The hybridization of WLI and AFM provides us new possibilities in semiconductor and other industrial applications.