Abstract The present invention is predicted upon the discovery by applicants that is scattered light from an etched workpiece is measured over many orders of diffraction, important characteristics of the etched workpiece can be correlated with the principal component content of the intensity characteristic. In accordance with the present invention, an etched workpiece is inspected by 1) exposing the workpiece to a beam of coherent light, 2) measuring the intensity of the light scattered from the workpiece over a range of spatial frequencies corresponding to a plurality of diffraction orders, 3) determining the principal component content of the tested workpiece intensity envelope, and 4) accepting or rejecting the workpiece in accordance with whether or not the principal component content satisfies predetermined criteria. In preferred embodiments the principal components are determined in relation to a plurality of reference measurements by singular value decomposition.
A method for optically inspecting workpieces comprising the steps of: determining by singular value decomposition a set of principal components for the intensity envelope of light scattered from one or more reference workpieces over a range of spatial frequencies corresponding to a plurality of diffraction orders, defining criteria for the acceptability or nonacceptability of a workpiece in accordance with the principal component content of the intensity envelope of the workpiece; exposing a workpiece to be tested to a beam of coherent light; measuring the intensity of the light scattered from said workpiece over a range of spatial frequencies corresponding to a plurality of diffraction orders, determining the principal component content of the intensity envelope of said workpiece to be tested for one or more principal components; and accepting or rejecting said workpiece in accordance with whether or not said principal component content satisfies said criteria.
Claim 2
Independent Claim
145 words
A method for optically inspecting workpieces comprising the steps of: determining by singular value decomposition a set of principal components for the intensity envelope of light scattered from one or more reference workpieces over a range of spatial frequencies corresponding to a plurality of diffraction orders, defining criteria for the acceptability or nonacceptability of a workpiece in accordance with the principal component content of the intensity envelope of the workpiece; exposing a workpiece to be tested to a beam of coherent light; measuring the intensity of the light scattered from said workpiece over a range of spatial frequencies corresponding to a plurality of diffraction orders, determining the principal component content of the intensity envelope of said workpiece to be tested for one or more principal components; and accepting or rejecting said workpiece in accordance with whether or not said principal component content satisfies said criteria.
Claim 3
Dependent Claim
38 words
The method according to claim 1 wherein the principal component content of the intensity envelope of said workpiece to be tested is determined by ascertaining the coefficients of said envelope with respect to one or more principal components.
Claim 4
Dependent Claim
32 words
The method according to claim 2 wherein said principal component content of said intensity envelope is determined by ascertaining the coefficients of said envelope with respect to the first two principal components.
Claim 5
Independent Claim
16 words
The method of claims 1, 2, or 3 wherein said workpiece is an etched semiconductor workpiece.
Claim 6
Independent Claim
41 words
The method of claims 1, 2, or 3 wherein said workpiece is an etched semiconductor workpiece containing a test grid of etched lines and said step of exposing said workpiece comprises directing a beam of coherent light onto said test grid.