Development of Particle Detection System using Subtracted Image Signal

Abstract

An automatic particle detection system for patterned wafers has been developed. The system consists of optical image processing and electrical signal processing that enable detection of much smaller particles. A specific area of the wafer is illuminated with 4-lasers at ± 45° diagonal in reference to an orientation-flat shaped on the wafer. The scattered light is detected by an objective lens. The images of the adjacent two-chips are detected with an image sensor. The subtracted signal of the two detected images is transformed into a binary signal with a threshold. This system is performed so as to detect 0.6 μm standard particles on a first photo-process wafer, and 1.0-1.5 μm standard particles on a latter photo-process wafer in 1.5 minutes on 5-inch-diameter wafers.