Patent ID: 9164397
Filing Date: 2015-10-20
Classification: G01N,G03F

Abstract:
1. An apparatus, comprising: an overlay metrology tool, the overlay metrology tool comprising: an illumination source configured to generate continuous illumination; a first beam splitter configured to direct a first portion of continuous illumination from the illumination source along a first optical arm and a second portion of continuous illumination along a second optical arm; at least one illumination symmetrization module (ISM) positioned in the first optical arm, the ISM including one or more optical elements configured to apply a symmetrization process on the first portion of continuous illumination from the illumination source; a second beam splitter configured to combine the first portion of continuous illumination from the first optical arm, following processing of the first portion of continuous illumination by the ISM, and the second portion of continuous illumination from the second optical arm to form a symmetrized continuous output beam such that tool induced shift of the optical metrology tool is at or below a selected level, wherein the second beam splitter is further configured to direct the symmetrized continuous output beam to a surface of one or more specimens; and a detector disposed along a primary optical axis of the overlay metrology tool, wherein the detector is configured to collect a portion of illumination reflected from the surface of the one or more specimens wherein the at least one ISM comprises: a 180 degree symmetrization module configured to perform a 180 degree rotational symmetrization transformation on the first portion of continuous illumination form the illumination source.