CIRCULAR SCANNING PATTERNS

A method to compare similar physical areas of an inspection area using a scanning arrangement. The inspection area has a periodic pattern having a repeat vector. The scanning arrangement has a stage, a drive mechanism and at least one circular scanner. The circular scanner has a scanning head and an axis of rotation about which the scanning head performs a circular scanning motion. The drive mechanism is configured to provide relative movement between the stage and the axis of rotation. The method includes the steps of: scanning the inspection area by a combination of circular scanning of the scanning head and by generating relative movement between the stage and the axis of rotation such that pairs of curved scanning paths are related by an integer multiple of the repeat vector; and comparing at least one of said pairs of the curved scanning paths by a pixel to pixel comparison.