Apparatus and methods for detecting overlay errors using scatterometry
First Claim
1. A method for determining an overlay error between at least two layers in a multiple layer sample, the method comprising:
- using an imaging optical system to measure a plurality of measured optical signals from a plurality of periodic targets on the sample, wherein the targets each have a first structure in a first layer and a second structure in a second layer, wherein there are predefined offsets between the first and second structures; and
using a scatterometry overlay technique to analyze the measured optical signals of the periodic targets and the predefined offsets of the first and second structures of the periodic targets to thereby determine an overlay error between the first and second structures of the periodic targets,wherein the scatterometry overlay technique is a phase based technique that includes representing each of the measured optical signals as a set of periodic functions having a plurality of known parameters and a plurality of unknown parameters that include an unknown overlay error parameter and analyzing the set of periodic functions to solve for the unknown overlay error parameter to thereby determine the overlay error, wherein the number of periodic targets equals the number of unknown parameters,wherein the imaging optical system is configured to have an illumination and/or collection numerical aperture (NA) and/or spectral band selected so that a specific diffraction order is collected and measured for the plurality of measured optical signals.
2 Assignments
0 Petitions
Accused Products
Abstract
Disclosed is a method for determining an overlay error between at least two layers in a multiple layer sample. An imaging optical system is used to measure a plurality of measured optical signals from a plurality of periodic targets on the sample. The targets each have a first structure in a first layer and a second structure in a second layer. There are predefined offsets between the first and second structures. A scatterometry overlay technique is then used to analyze the measured optical signals of the periodic targets and the predefined offsets of the first and second structures of the periodic targets to thereby determine an overlay error between the first and second structures of the periodic targets.
159 Citations
18 Claims
-
1. A method for determining an overlay error between at least two layers in a multiple layer sample, the method comprising:
-
using an imaging optical system to measure a plurality of measured optical signals from a plurality of periodic targets on the sample, wherein the targets each have a first structure in a first layer and a second structure in a second layer, wherein there are predefined offsets between the first and second structures; and using a scatterometry overlay technique to analyze the measured optical signals of the periodic targets and the predefined offsets of the first and second structures of the periodic targets to thereby determine an overlay error between the first and second structures of the periodic targets, wherein the scatterometry overlay technique is a phase based technique that includes representing each of the measured optical signals as a set of periodic functions having a plurality of known parameters and a plurality of unknown parameters that include an unknown overlay error parameter and analyzing the set of periodic functions to solve for the unknown overlay error parameter to thereby determine the overlay error, wherein the number of periodic targets equals the number of unknown parameters, wherein the imaging optical system is configured to have an illumination and/or collection numerical aperture (NA) and/or spectral band selected so that a specific diffraction order is collected and measured for the plurality of measured optical signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
-
-
15. A method for determining an overlay error between at least two layers in a multiple layer sample, the method comprising:
-
(a) using an imaging optical system to measure a plurality of measured optical signals from a plurality of periodic targets on the sample, wherein the targets each have a first structure in a first layer and a second structure in a second layer, wherein there are predefined offsets between the first and second structures; and (b) using a scatterometry overlay technique to analyze the measured optical signals of the periodic targets and the predefined offsets of the first and second structures of the periodic targets to thereby determine an overlay error between the first and second structures of the periodic targets, wherein the scatterometry overlay technique is a phase based technique that includes representing each of the measured optical signals as a set of periodic functions having a plurality of known parameters and an unknown overlay error parameter and analyzing the set of periodic functions to solve for the unknown overlay error parameter to thereby determine the overlay error, wherein the imaging optical system is configured to have an illumination and/or collection numerical aperture (NA) and/or spectral band selected so that a specific diffraction order is collected and measured for the plurality of measured optical signals, wherein the imaging optical system has a broadband source for generating an optical incident beam having multiple wavelengths, a detector for detecting a measured signal from the sample in response to the incident beam and a filter for selectively passing particular one or more wavelengths of the output signal to the detector, wherein using the imaging optical system includes directing at least one radiation beam towards each target to measure a plurality of measured signals from the periodic targets while adjusting the filter so as to pass a particular one or more wavelengths of the measured signals through the filter towards the detector in the form of a plurality filtered signals, wherein the analysis of the filtered signals and the predefined offsets includes obtaining an intensity from some or all of the pixels of an image of each target and combining the intensities of each target together to give an intensity value for each target at a particular setting of the filter. - View Dependent Claims (16, 17, 18)
-
Specification