Phase-Modulated Optical Inspection for Sub-Diffraction Lithography Metrology
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Solution Overview
Problem
Current metrology techniques in lithographic processes face challenges in accurately measuring small product structures due to the use of larger metrology targets that do not suffer the same distortions as the actual product structures, leading to inaccurate measurement results and the need for time-consuming scanning electron microscopy.
Innovation Solution
A method and apparatus that modulate the phase of illuminating radiation after scattering by the object structure using a subadditive aberration function, allowing for the reconstruction of object structure data from intensity patterns captured at unique parameter values, enabling direct measurement of small features without the need for large targets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If optical metrology techniques are used to measure small product structures, then measurement speed is improved, but measurement precision deteriorates because the techniques cannot resolve features smaller than the optical resolution limit
Solution Approach 1:
The patent moves the measurement from real space to reciprocal space (diffraction space). By measuring the diffraction pattern of the object structure and retrieving phase information through iterative algorithms, the system achieves sub-diffraction-limit resolution. This dimensional transformation allows optical techniques to resolve features smaller than the conventional optical resolution limit while maintaining high measurement speed.
2Productivity
If large metrology targets are used for optical measurement, then measurement speed is improved, but measurement precision deteriorates because the targets do not suffer the same distortions as the actual small product structures
Solution Approach 1:
The patent extracts the essential measurement information directly from the small product structures themselves, eliminating the need for separate large metrology targets. By applying phase retrieval to the diffraction pattern of the actual object structure, the system obtains accurate measurements of overlay errors and critical dimensions that reflect the true distortions experienced by the product features during manufacturing.
Solution Approach 2:
Instead of using a simplified copy (large target) that doesn't represent the actual structure, the patent directly measures the diffraction pattern of the real object structure. The phase retrieval algorithm reconstructs the complex wavefield from intensity measurements, creating an accurate digital copy of the object structure's properties including all distortions, enabling precise measurement without requiring physical target copies.
3Measurement precision
If scanning electron microscopy is used to measure small product structures, then measurement precision is improved, but productivity deteriorates because the method is much more time consuming than optical measurements
Solution Approach 1:
The patent replaces the mechanical scanning process of SEM with a non-scanning optical diffraction measurement. By capturing the entire diffraction pattern in a single shot and using iterative phase retrieval algorithms to reconstruct the object structure, the system achieves SEM-level resolution without the time-consuming scanning process, dramatically improving measurement throughput while maintaining precision.
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 accurate and efficient method for measuring small product structures, improving the precision of lithographic process control by directly measuring object structures, reducing the reliance on indirect measurement techniques and increasing measurement speed.
Implementation Method 1
illuminating radiation; modulating the phase of said illuminating radiation after scattering by the object structure
Data Source
AI summary
Disclosed is a method of obtaining data describing an object structure. The method comprising the steps of: (a) illuminating the object structure with illuminating radiation; (b) modulating the phase of the illuminating radiation after scattering by the object structure, the modulation comprising applying a first phase factor dependent upon at least one controllable parameter and an aberration function having a form of a subadditive function of a vector norm; (c) capturing a plurality of intensity patterns, wherein each intensity pattern corresponds to a unique value of the at least one controllable parameter; and (d) reconstructing the data describing the object structure based on the plurality of intensity patterns. Also disclosed are corresponding inspection and lithographic apparatuses, a method of manufacturing devices and a computer program.