Patent ID: 7970579

Claim:
Apparatus for determining information relating to a sample surface structure, the apparatus comprising: a light director operable to direct light along a sample path towards a region of a surface of a sample and along a reference path towards a reference surface such that light reflected by the region of the sample surface and light reflected by the reference surface interfere, the light director being capable of providing light having a point spread function with a spread at a sample surface greater than a pitch of surface structure elements providing a surface structure of the sample; a mover operable to effect relative movement along a measurement scan path between a sample and the reference surface; a sensing device operable to sense light representing interference fringes produced by a sample surface region during relative movement along the measurement scan path; a controller operable to carry out a measurement operation by causing the mover to effect relative movement while the sensing device senses light intensity at intervals to provide a series of intensity values representing interference fringes produced by a sample surface region during the relative movement; and a data processor operable to receive and process i) structure intensity data comprising a set of intensity values resulting from a measurement operation on a structure surface sample area using light with a point spread function having a spread at the sample surface greater than a pitch of surface structure elements providing the surface structure of the structure surface sample area, and ii)non-structure intensity data comprising a set of intensity values resulting from a measurement operation on a non-structure surface sample area not having the structure, the data processor comprising: a frequency transform ratio determiner operable to determine a frequency transform ratio corresponding to a ratio between the structure and non-structure intensity data; and a structure provider operable to relate the frequency transform ratio to a relationship involving a first structure measure representing a ratio between the width and pitch of the surface structure elements and a second structure measure representing the size of the surface structure elements in a direction transverse to the sample surface so as to enable determination of a value for at least one of said first and second structure measures.