Patent ID: 9646896
Date: 2017-05-09
CPC Classifications: G01B,G03F,H01L

Claim:
1. A method of evaluating alignment of a feature or layer with a previously formed feature or layer on a face of a wafer, comprising: defining a plurality of fields on the face of the wafer, wherein each field includes a total predetermined number of alignment structure sites which are arranged in a predetermined pattern that is the same for each of the plurality of fields; organizing the plurality of fields into an orthogonal field structure and two or more continuous field structures, wherein the orthogonal field structure comprises fields which reside on first and second orthogonal axes and which are arranged near an outer edge of the wafer, and wherein each continuous field structure includes two or more adjacent fields that are separate from the orthogonal field structure and wherein the two or more continuous field structures are asymmetric about the first and second orthogonal axes; randomly selecting a first predetermined number of the alignment structure sites from the predetermined pattern within each field of the two or more continuous field structures, the first predetermined number being less than the total predetermined number; measuring a first number of alignment structure positions at the first predetermined number of alignment structure sites, respectively, within each field of the two or more continuous field structures; selecting a second predetermined number of alignment structure sites from the predetermined pattern within each field of the orthogonal field structure, the second predetermined number being greater than the first predetermined number; measuring a second number of alignment structure positions at the second predetermined number of alignment structure sites, respectively, within each field of the orthogonal field structure; and aligning the feature or layer to the previously formed feature or layer based upon the measured alignment structure positions of the two or more continuous field structures and the orthogonal field structure.