Particle detection on a patterned or bare wafer surface

Abstract

A method and apparatus for predicting the number of contaminant particles in circuit area of a patterned semiconductor wafer having a number of reflective circuit areas. The method includes forming on a wafer in specified areas, a grating test pattern, such as a line grating. The grating patterns are formed at the same time and in the same manner that repetitive circuit patterns are formed on the wafer. The wafer is then scanned by a light beam. Since the diffraction pattern caused by the grating test patterns is known, it is possible to detect when the light beam is scanning one of the known grating patterns. The diffraction pattern may be inspected for fabrication derived variations. In response to detecting a known grating pattern, a detection mechanism is activated. Since the diffraction pattern is known it may be spatially separated. In this way only light scattered by particles or defects in the pattern are collected and detected. From the scattered light that is collected and detected, a particle count may be determined for the grating pattern area. From this particle count an accurate prediction of the number of particles in the circuit patterns may be made. The apparatus may also inspect bare areas. In this manner real time inspection may be performed on patterned wafers.