Lithography Metrology Target Reconstruction via Multi-Angle Diffraction
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Solution Overview
Problem
Metrology tools in lithographic processes face challenges in accurately measuring overlay and layer heights due to structural asymmetry caused by processing steps like etching and CMP, leading to measurement errors that affect throughput, flexibility, and accuracy, especially when dealing with small target structures that require dark-field techniques.
Innovation Solution
A method and apparatus that utilize measurement data from non-zeroth diffraction orders to reconstruct geometric parameters of targets formed in multiple layers on a substrate, minimizing differences between measurement and simulation data to directly determine variable geometric parameters, thereby improving overlay measurement accuracy and layer height estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional metrology methods are used to measure overlay, then measurement process is simple, but measurement precision deteriorates due to structural asymmetry errors
Solution Approach 1:
The patent segments the measurement process into multiple illumination settings, each capturing different aspects of the target structure. By dividing the measurement into separate angular measurements and combining them through optimization, the method isolates overlay information from structural asymmetry effects, improving precision without requiring hardware changes.
Solution Approach 2:
The patent changes measurement parameters by using multiple illumination settings (different angles and configurations) to probe the target structure. By varying the illumination parameters and optimizing the combination of measurements, the method extracts accurate overlay values while compensating for structural asymmetries.
2Measurement precision
If dedicated thin film targets are used for layer height measurement, then measurement accuracy is improved, but substrate area consumption increases
Solution Approach 1:
The patent makes the overlay target multi-functional by enabling it to serve both overlay measurement and layer height measurement purposes. Through optimized multi-parameter reconstruction from combined measurements, the same target structure provides information about both overlay and layer heights, eliminating the need for separate dedicated targets and saving substrate area.
Solution Approach 2:
The patent merges overlay measurement and layer height measurement into a single integrated process. By combining measurements from multiple illumination settings and using optimization to reconstruct both overlay and layer height parameters simultaneously, the method consolidates multiple measurement functions into one target and one measurement sequence.
3Measurement precision
If multiple measurement types are performed on separate targets, then measurement accuracy is maintained, but measurement time increases
Solution Approach 1:
The patent combines overlay measurement and layer height measurement into a single measurement sequence using the same target and the same metrology tool. By performing both measurements simultaneously through optimized multi-parameter reconstruction, the method eliminates the time required to switch between separate targets and measurement modes while maintaining accuracy.
Solution Approach 2:
The patent maintains continuous useful action by performing multiple measurement functions in a single uninterrupted measurement sequence. The optimized reconstruction process extracts multiple parameters (overlay, layer heights) from the same set of measurements without requiring intermediate steps or target changes, maximizing measurement efficiency.
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 enhances the precision and accuracy of overlay measurements by distinguishing between overlay and structural asymmetry effects, allowing for robust reconstruction of true overlay values and geometric parameters, improving both fabrication processes and production yield without requiring additional hardware or measurement tools.
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 'spectrum'
Data Source
AI summary
Disclosed herein is a metrology method, and an associated metrology apparatus, the metrology method includes measuring a target formed in at least two layers on a substrate by a lithographic process and capturing at least one corresponding pair of non-zeroth diffraction orders, for example in an image field, to obtain measurement data. A simulation of a measurement of the target as defined in terms of geometric parameters of the target, the geometric parameters including one or more variable geometric parameters, is performed and a difference between the measurement data and simulation data is minimized, so as to directly reconstruct a value for each of the one or more variable geometric parameters.