Patent ID: 7397554

Claim:
An apparatus for examining features of a disk-shaped sample, said apparatus comprising: a) a stage for supporting said sample; b) an X-drive for moving said stage along an X s direction; c) a Y-drive for moving said stage along a Y s direction; d) a θ-drive for rotating said stage about a center of rotation substantially aligned with a center of said sample; e) a measurement assembly above said sample for examining said features; and f) a scheduling module for coordinating said X-drive, said Y-drive and said θ drive and said measurement assembly such that said sample is examined in an even number n of angular sectors defined by a sector angle Θ, where Θ=360°/n, and a multiple of Θ includes 90° and 180°, wherein said disk-shaped sample comprises a reference feature, and said apparatus further comprises: i) an image rotation module for rotating an image of said reference feature; and ii) a pattern matching module for performing a matching of said image of said reference feature with a stored image of said reference feature.