Patent Document ID: 5438413
Application ID: 08025435
Patent Status: 1

Claim One:
1. A method of inspecting a semiconductive wafer in process to determine the accuracy of alignment of one process layer to a subsequent process layer formed thereover, said subsequent layer having at least a second alignment attribute intended to have a predetermined registrational relationship to a corresponding first alignment attribute of said one layer, said first and second attributes each being defined by at least one edge of geometric bodies formed during fabrication of said one and said subsequent process layers, comprising the steps of: using an interference optical system including an object channel and a reference channel for simultaneously inspecting said wafer and a reflective reference surface, and developing a plurality of images formed by the interference between object wave energy, passing from said wafer and through said object channel to an image plane, and reference wave energy passing from said reference surface and through said reference channel to said image plane, each said image being formed in response to a change in axial position of either said wafer along the optical axis of said object channel or said reference surface along the optical axis of said reference channel; detecting for each image the magnitude of the mutual coherence between the object wave energy reflected from a portion of the surface of said wafer including said second attribute, and from a portion of said wafer including at least a vestige of said first attribute, and said reference wave energy; using the magnitude coherence data to generate synthetic image data representative of at least one edge of said first attribute and at least one edge of said second attribute; and using said synthetic image data to determine the relative alignment of said second attribute of said subsequent layer to said first attribute of said one layer.