Metrology Correction for Asymmetric Deviations in Lithography
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Solution Overview
Problem
Metrology sensors in lithographic applications face challenges in accurately measuring structures with asymmetric deviations due to wavelength/polarization-dependent variations, requiring multiple measurements across different conditions to correct for these imperfections.
Innovation Solution
A method that calculates intensity asymmetry values and corresponding phase offset values to determine measurement corrections for asymmetric deviations, using dispersion models to convert intensity asymmetry into phase offsets, thereby improving measurement accuracy without the need for extensive training data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple measurements are performed under different wavelengths and polarizations to correct for asymmetric deviations, then measurement precision is improved, but measurement time and process complexity increase
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing correction values for asymmetric deviations in a lookup table during system setup or calibration. During actual measurements, the system determines the asymmetric deviation parameters and directly retrieves the corresponding correction values from the pre-computed table, avoiding the need to perform multiple measurements under different wavelengths and polarizations in real-time. This significantly reduces measurement time while maintaining correction accuracy.
Solution Approach 2:
The patent employs parameter changes by measuring asymmetric deviations at multiple wavelengths and polarizations during calibration to build a comprehensive correction model. The system then uses this model to predict correction values for any given measurement conditions, effectively transforming the correction process from requiring multiple actual measurements to using a single measurement with computational correction based on pre-established parameter relationships.
2Manufacturing precision
If multiple measurements under different illumination conditions are performed to correct asymmetric deviations, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent replaces the mechanical/optical complexity of performing multiple physical measurements under different wavelengths and polarizations with a computational system. The system uses a pre-computed lookup table and algorithmic processing to determine correction values, substituting complex measurement hardware operations with software-based correction that retrieves and applies predetermined correction parameters based on measured asymmetric deviation characteristics.
Solution Approach 2:
The patent applies preliminary action by pre-computing correction values for various asymmetric deviation scenarios and storing them in a lookup table during system calibration. This preliminary computation phase captures the effects of multiple wavelengths and polarizations, allowing the operational measurement system to use a single measurement and retrieve the appropriate correction from the pre-prepared table, thereby reducing device complexity during actual use.
3Measurement precision
If intensity asymmetry values are converted to phase offsets using dispersion models, then measurement accuracy is improved, but computational requirements increase
Solution Approach 1:
The patent applies preliminary action by pre-computing the complex dispersion model conversions and storing the results in lookup tables during system calibration. The computationally intensive conversion of intensity asymmetry to phase offset using dispersion models is performed once during setup, and the results are cached. During operational measurements, the system simply retrieves pre-computed phase offset values from the lookup table based on measured intensity asymmetry, dramatically reducing real-time computational requirements 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 enhances measurement accuracy by directly calculating phase offsets from intensity asymmetry, reducing the reliance on training data and improving the precision of position corrections in lithographic processes.
Implementation Method 1
at least one intensity asymmetry value comprising a metric related to a difference or imbalance between respective intensities or amplitudes of at least two diffraction orders of radiation diffracted by the structure
Data Source
AI summary
A metrology method relating to measurement of a structure on a substrate, the structure being subject to one or more asymmetric deviation. The method includes obtaining at least one intensity asymmetry value relating to the one or more asymmetric deviations, wherein the at least one intensity asymmetry value includes a metric related to a difference or imbalance between the respective intensities or amplitudes of at least two diffraction orders of radiation diffracted by the structure; determining at least one phase offset value corresponding to the one or more asymmetric deviations based on the at least one intensity asymmetry value; and determining one or more measurement corrections for the one or more asymmetric deviations from the at least one phase offset value.