Grating test patterns and methods for overlay metrology

Abstract

A metrology for determining bias or overlay error in lithographic processes. This metrology includes a set of diffraction test patterns, optical inspection techniques by using spectroscopic ellipsometer or reflectometer and a method of test pattern profile extraction. The invention uses a set of diffraction gratings as the test patterns, and thin film metrology equipment, such as spectroscopic ellipsometer or spectroscopic reflectometer. The profiles of the test patterns in the two successive layers are analyzed. Overlay information is obtained after processing the profile data. In a first aspect of the invention, a line-on-line overlay grating test patterns structure is disclosed in which a second layer mask is placed in the center of a clear line in a first layer mask. In a second aspect of the invention, a line-in-line overlay grating test patterns structure is disclosed in which a second layer mask is placed in the center of a dark line in the first mask.

Dependencies are inferred from the claim text.