Apparatus and method for examining a disk-shaped sample on an X-Y-theta stage

A method for examining features of a disk-shaped sample on a stage, said method comprising:

• a) providing said stage with an Xs direction of motion, a Ys direction of motion and a θ rotation about a center of rotation;
• b) placing said sample on said stage such that a center of said sample is substantially aligned with said center of rotation;
• c) subdividing said sample into an even number n of angular sectors, each of said angular sectors having a sector angle Θ, where Θ=360°/n and a multiple of Θ includes 90° and 180°;
• d) examining said features with a measurement assembly in accordance with a schedule, whereby said stage is coordinated in said Xs direction, said Ys direction and said θ rotation to examine said sample by said angular sectors, 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.