Non-Iterative Metrology Field Reconstruction for Periodic Structures
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Solution Overview
Problem
Existing metrology methods struggle to accurately measure the full electric field, particularly in partial coherent illumination scenarios, due to computational demands and alignment requirements, limiting the effectiveness of phase retrieval and measurement precision.
Innovation Solution
A non-iterative metrology method that reconstructs the electric field using partial coherent illumination by selecting an appropriate wavelength-over-pitch ratio and defining a region of interest in the detection pupil plane, allowing for accurate phase retrieval without strict alignment with the mask edge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If holography tools are used to access the full electric field, then measurement capability is improved, but operation complexity and alignment requirements increase
Solution Approach 1:
The patent extracts only the necessary diffraction orders from the scattered radiation spectrum, specifically selecting those that contain information about the structure parameters of interest. This selective extraction eliminates the need for complex holographic interference patterns while still enabling full electric field measurement through non-iterative phase retrieval algorithms applied to the selected diffraction orders.
Solution Approach 2:
The patent changes the measurement approach by working in the diffraction order domain rather than requiring spatial interference patterns. By transforming the measurement parameters from spatial interference (holography) to spectral diffraction order analysis, the method achieves full electric field access with relaxed alignment requirements and simplified operation.
2Measurement precision
If iterative phase retrieval methods are used, then phase information can be recovered, but computational demand increases
Solution Approach 1:
The patent applies preliminary actions by pre-selecting specific diffraction orders that contain the necessary phase information before phase retrieval. By preparing the data set in advance through selective diffraction order extraction and applying appropriate weighting, the method enables direct non-iterative phase calculation using closed-form solutions, eliminating the need for computationally intensive iterative optimization loops.
Solution Approach 2:
The patent creates a simplified mathematical model (copy) of the scattering process that directly relates selected diffraction orders to structure parameters. This analytical model copy allows for direct calculation of phase information without requiring iterative numerical optimization, significantly reducing computational time while maintaining measurement precision.
3Measurement precision
If strict alignment with mask edge is required, then measurement accuracy is improved, but ease of operation deteriorates
Solution Approach 1:
The patent implements self-service by making the measurement method inherently insensitive to mask edge alignment errors. The non-iterative phase retrieval algorithm, when applied to selected diffraction orders, automatically compensates for misalignment artifacts without requiring precise manual alignment. The system serves itself by being robust to alignment variations, eliminating the need for operator skill in achieving strict alignment.
Solution Approach 2:
The patent converts the potentially harmful effect of misalignment artifacts into a benefit by using the specific angular distribution of diffraction orders. The method leverages the fact that misalignment affects different diffraction orders in predictable ways, allowing the selected orders to inherently reject alignment errors while maintaining sensitivity to structure parameters.
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
Enables precise measurement of structure parameters using partial coherent illumination, improving measurement accuracy and reducing computational complexity while maintaining robustness against misalignment artifacts.
Implementation Method 1
capturing the resultant scattered radiation from said periodic structure at a detection plane, said scattered radiation passing through at least one angularly resolved plane
Data Source
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Figure 5~6(b)
AI summary
Disclosed is a metrology method comprising: obtaining metrology data relating to a measurement obtained by illuminating a periodic structure comprising at least one pitch with partial coherent illumination comprising a wavelength and capturing the resultant scattered radiation from said periodic structure at a detection plane, said scattered radiation passing through at least one angularly resolved plane between said periodic structure and detection plane, said angularly resolved plane comprising at least one mask edge; non-iteratively reconstructing a field of said scattered radiation; using said reconstructed field to determine a parameter of interest of the structure; and in an initial step: selecting said wavelength and a maximum of said at least one pitch such that the wavelength-over-pitch ratio is greater than a first distance in said angularly resolved plane.