Lithographic Metrology Correction for Field Non-Homogeneity
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Solution Overview
Problem
Lithographic metrology systems face challenges in accurately measuring parameters like overlay, focus, and dose due to measurement field non-homogeneity, which affects the accuracy and reliability of intensity measurements across different locations within the measurement field.
Innovation Solution
A method is introduced to determine a correction factor by performing first and second measurements of periodic structures, where the second measurement is taken at a shifted location relative to the measurement field, allowing for the correction of measurement field location dependence in intensity values, enabling more accurate monitoring and control of lithographic processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If intensity measurements are performed at different locations within the measurement field, then comprehensive process parameter monitoring is achieved, but measurement accuracy deteriorates due to measurement field non-homogeneity
Solution Approach 1:
The patent applies local quality by determining location-specific correction factors for different regions within the measurement field. Each location receives a tailored correction based on its specific non-homogeneity characteristics, allowing accurate measurements across the entire field while accounting for local variations in illumination and detection properties.
Solution Approach 2:
The patent changes the parameter of measurement location by performing measurements at multiple discrete locations throughout the measurement field. By systematically varying the measurement location parameter and applying location-dependent corrections, the system achieves comprehensive process monitoring while maintaining accuracy at each specific location.
2Measurement precision
If multiple measurements are performed at different locations to correct for non-homogeneity, then measurement accuracy improves, but measurement time increases
Solution Approach 1:
The patent applies preliminary action by performing a calibration measurement phase before actual production measurements. During calibration, the system measures intensity values at multiple locations and pre-determines correction factors that are then applied during subsequent measurements. This preliminary characterization of the measurement field non-homogeneity eliminates the need for repeated multi-location measurements during production, significantly reducing measurement time while maintaining accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves the accuracy of lithographic process parameters by correcting for measurement field non-homogeneity, leading to more reliable and consistent measurements across the measurement field, enhancing the precision of overlay, focus, and dose monitoring.
Implementation Method 1
measure one or more properties of the scattered radiation—e.g., intensity at a single angle of reflection as a function of wavelength; intensity at one or more wavelengths as a function of reflected angle; or polarization as a function of reflected angle—to obtain a diffraction 'spectrum' from which a property of interest of the target can be determined
Data Source
AI summary
Disclosed is a method of determining a correction for measured values of radiation diffracted from a target comprising a plurality of periodic structures, subsequent to measurement of the target using measurement radiation defining a measurement field. The correction acts to correct for measurement field location dependence in the measured values. The method comprises performing a first and second measurements of the periodic structures; and determining a correction from said first measurement and said second measurement. The first measurement is performed with said target being in a normal measurement location with respect to the measurement field. The second measurement is performed with the periodic structure in a shifted location with respect to the measurement field, said shifted location comprising the location of another of said periodic structures when said target is in said normal measurement location with respect to the measurement field.