PARTICLE-DETECTION SYSTEM USING SUBTRACTED IMAGE SIGNAL

An automatic particle detection system for patterned wafers has been d eveloped. The system consists of optical image processing and electric al signal processing that enable detection of much smaller particles. A specific area of the wafer is illuminated with 4-lasers at +/-45-deg rees diagonal in reference to an orientation-flat shaped on the wafer. The scattered light is detected by an objective lens. The images of t he adjacent two-chips are detected with an image sensor. The subtracte d signal of the two detected images is transformed into a binary signa l with a threshold. This system is performed so as to detect 0.6 mum s tandard particles on a first photo-process wafer, and 1.0-1.5 mum stan dard particles on a latter photo-process wafer in 1.5 minutes on 5-inc h-diameter wafers.