Characterization of Multimodal Spot Scanning Imaging System for Wafer Defect Inspection

Abstract

Typical defects on unpatterned wafers include particles, residues, scratches, and cracks. Various dark-field scattering methods have been applied to detect unpatterned wafer surface defects. However, these methods have only one optical detection channel, making handling multiple types of wafer defects difficult. In response, the theory of multimodal defect inspection is improved, and a multimodal spot-scanning imaging system is developed. The laser beam is focused on the wafer surface, generating micron-level high-intensity focused spot illumination. Scattered light from the wafer surface is collected by the dark-field objective, and the intensity is measured by the photodiode. Reflected light from the wafer surface is collected by the bright-field objective. After polarization splitting, it is measured by two four-quadrant detectors to analyze the topography, film, and reflected signal. The turntable and linear guide drive the optical head and wafer, allowing the focused spot to scan along the wafer in a spiral trajectory, enabling fast and accurate detection. The defect inspection system has been verified through experiments. The minimum detectable PSL particle size is less than 200 nm, the minimum detectable scratch width is less than $1~\mu $ m, and the minimum detectable stain width is less than $20~\mu $ m.