Patent ID: 6816252
Filing Date: 2004-11-09
Classification: G01B,G01N,G03F

Abstract:
An apparatus for obtaining information on critical dimensions and overlay accuracy of features formed in a semiconductor structure, wherein the semiconductor structure includes a first diffracting pattern oriented with respect to a first direction and a second diffracting pattern oriented with respect to a second direction, the apparatus comprising:a light source for emitting at least one light beam; a first plurality of deflecting elements defining a first optical path in a first plane of incidence corresponding to the first direction, and a second plurality of deflecting elements defining a second optical path in a second plane of incidence corresponding to the second direction; a detector optically connectable to the first and second optical paths to receive a light beam diffracted by the first and the second diffracting patterns, respectively; and a first partially reflecting mirror directing a first portion of an incident light beam into the first optical path and directing a second portion of the incident light beam into the second optical path, wherein a common transmittance of the first partially reflecting mirror and of a transmissive element arranged in the second optical path is substantially equal to a reflectivity of the first partially reflecting mirror.