Overlay abnormality gating by Z data

A method of monitoring topography over a wafer, said method comprising:

• measuring a position and orientation of a plurality of first alignment shapes formed on a first layer disposed on a surface of a wafer comprising a plurality of fields, wherein the plurality of first alignment shapes are spaced over the surface of the wafer with a first resolution;
• defining a modeled topography of a topography over the surface of the wafer as a function of wafer position by subjecting the wafer to a set of symmetry operations comprising translation or rotation about orthogonal axes which:
• minimizes misalignment of one or more of a plurality of second alignment shapes formed on a patterning apparatus to one or more of the plurality of first alignment shapes;
• and
• maximizes a focus of radiation on the surface, wherein the radiation is provided by an exposure tool and filtered by the patterning apparatus;
• defining a measured topography by measuring the topography over the surface of the wafer without recognizing the plurality of first alignment shapes, and with a second resolution greater than the first resolution;
• and
• determining a first non-correctable error as a difference between the modeled topography and the measured topography.

A metrology system, comprising:

• an alignment stage configured to position a wafer relative to an exposure tool by subjecting the wafer to a set of symmetry operations comprising translation or rotation about orthogonal axes;
• a surface measurement tool configured to create a measured map by measuring a surface topography over the wafer as a function of wafer position and with a first resolution;
• a scanning tool configured to determine first locations of a plurality of first alignment shapes disposed over a surface of the wafer relative to second locations of a plurality of second alignment shapes formed on a patterning apparatus relative, and to direct a controller to position the alignment stage based upon the first and second locations, wherein the plurality of first and second alignment shapes are spaced with a second resolution less than the first resolution;
• and
• a computation unit configured to create a modeled map of the surface topography based upon the set of symmetry operations as a function of wafer position, and to determine a first non-correctable error as a difference between a modeled wafer topography and a measured wafer topography.