An apparatus and method for examining features of a planar, disk-shaped samples on a stage that holdings the sample and has an X-drive, a Y-drive and a .theta.-drive for rotating the stage about a center of rotation defined in the stage coordinates. The sample is placed on the stage such that the center of the sample is substantially aligned with the center of rotation and a measurement assembly is located above the sample to examine the features optically. A scheduling module coordinates the X-drive, the Y-drive and the .theta.-drive with the measurement assembly such that the sample is examined in an even number n of angular sectors defined by a sector angle .THETA. that is the same for each sector. Specifically, the sector angle .THETA. is defined in terms of n as follows:.THETA..times..degree. ##EQU00001## where n=4m and m is an integer, such that a multiple of sector angle .THETA. always includes angles 90.degree. and 180.degree..

This invention relates to an apparatus and method for integrated measurement of a sample that has miniature features. The apparatus has an optical measuring unit for illuminating the sample with a global test radiation over an optical test region and obtaining an optical response, such as scattered or transmitted radiation from the optical test region. In addition, the apparatus has a local measuring unit for making a nanometer scale measurement of a local material parameter .rho. of the sample. The local parameter .rho. is determined with a mechanical, optical, magnetic, electric or other physical measurement performed in the nanometer range with a scanning probe tip at a test location lying within the optical test region. The material parameter .rho. is selected such that it is substantially constant or uniform over the illuminated area. A computational unit determines a property of the miniature features within the optical test region from the optical response supplemented with an adjustment derived from the local material parameter obtained by the local measuring unit.

A system and a method for optical characterization of a symmetric grating illuminated at off-normal incident angle are provided, where the plane of incidence is parallel to the grating lines. In this case corresponding positive and negative diffraction orders have the same intensity and phase. Several approaches for exploiting this symmetry are given. The first approach is a symmetric rigorous coupled wave analysis (SRCWA) adapted to the symmetric case, which accounts for N positive and N negative diffraction orders with M=N+1 space harmonics, without approximation. Various approximation methods are also given. Approximate versions of the RCWA (or SRCWA) can be developed by neglecting polarization coupling for small angles of incidence. A normal incident angle calculation can be used to approximate a situation with a small angle of incidence. Refinements to this approximation include revision of grating depth or refractive indices to improve accuracy. Methods other than the RCWA can also be symmetry simplified according to the invention.