Lithographic Overlay Metrology via Scatterometry and Asymmetry Modeling
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Solution Overview
Problem
Existing dark-field image-based overlay measurements in lithographic processes are inaccurate due to reliance on assumptions that overlay error is the sole cause of target asymmetry, failing to distinguish between overlay errors and structural asymmetries or sensor errors, leading to perturbed measurement results.
Innovation Solution
A method involving the use of a scatterometry model and an asymmetry model to determine a system of equations based on normal and complementary higher diffraction orders, allowing for the separation of measurement values and solving for the parameter of interest, thereby accounting for measurement system errors and structural asymmetries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If dark-field image-based overlay measurements are performed using conventional scatterometry, then measurement speed is improved, but measurement precision deteriorates due to inability to distinguish overlay errors from structural asymmetries and sensor errors
Solution Approach 1:
The measurement process is segmented into multiple measurements with different illumination conditions (different polarizations, wavelengths, or illumination angles). Each measurement provides partial information, and the combination of all measurements enables separation of overlay errors from structural asymmetries and sensor errors, thereby improving precision while maintaining speed.
Solution Approach 2:
The problem is extended from a single measurement dimension to multiple dimensions by varying illumination parameters (polarization, wavelength, angle). This multi-dimensional approach provides additional independent equations that enable the system to solve for multiple unknowns simultaneously, distinguishing overlay errors from other asymmetry sources without sacrificing measurement speed.
2Measurement precision
If multiple measurements with different illumination conditions are performed to distinguish overlay errors from other asymmetries, then measurement precision is improved, but measurement time increases
Solution Approach 1:
Multiple measurements with different illumination conditions are merged into a single integrated analysis process. The scatterometry model simultaneously processes all measurement data to solve for overlay parameters, structural asymmetries, and sensor errors in one computational step, eliminating the need for sequential processing and reducing total measurement time.
Solution Approach 2:
The system varies illumination parameters (polarization, wavelength, angle) to create diverse measurement conditions that provide independent information about different aspects of the target structure. These parameter changes enable the formation of a solvable system of equations that can distinguish overlay errors from other asymmetries while maintaining efficient measurement throughput.
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 provides a more direct and accurate measurement of overlay errors by distinguishing between overlay errors and other asymmetry contributions, enhancing the precision of lithographic process measurements.
Implementation Method 1
These devices direct a beam of radiation onto a target structure and measure one or more properties of the scattered radiation... to obtain a 'spectrum' from which a property of interest of the target can be determined
Data Source
AI summary
Disclosed is a method, and associated apparatuses, for measuring a parameter of interest relating to a structure having at least two layers. The method comprises illuminating the structure with measurement radiation and detecting scattered radiation having been scattered by said structure. The scattered radiation comprises normal and complementary higher diffraction orders. A scatterometry model which relates a scattered radiation parameter to at least a parameter of interest and an asymmetry model which relates the scattered radiation parameter to at least one asymmetry parameter are defined, the asymmetry parameter relating to one or more measurement system errors and/or an asymmetry in the target other than a misalignment between the two layers. A combination of the scatterometry model and asymmetry model is used to determine a system of equations, and the system of equations is then solved for the parameter of interest.