Multi-Electron Beam Imaging With Wien Filter Aberration Correction
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Solution Overview
Problem
Current electron beam systems face challenges in achieving high throughput and resolution due to issues like Coulomb interactions, source energy dispersion blurs, and astigmatism, particularly when increasing the number of beamlets to improve throughput, which leads to difficulties in maintaining image-forming uniformity across a large field of view.
Innovation Solution
The system employs a multi-electron beam setup with a Wien filter, transfer lens, and various optical components such as micro stigmator and deflector arrays to correct for source energy dispersion and astigmatism, while using a second Wien filter to compensate for energy dispersion, and an acceleration electrode to reduce Coulomb interactions, enabling the generation of hundreds of beamlets with improved resolution and uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of beamlets is increased to improve throughput, then productivity increases, but image-forming uniformity deteriorates due to off-axis aberrations, source energy dispersion blurs, optical astigmatisms, and Coulomb interaction influences
Solution Approach 1:
The patent divides the electron beam into multiple beamlets (hundreds of beamlets) that are spatially separated and can be independently controlled. This segmentation allows simultaneous processing of multiple locations on the wafer, achieving high throughput while maintaining image quality through individual beamlet optimization
Solution Approach 2:
The patent applies local quality by using micro stigmator arrays and micro deflector arrays that can independently adjust parameters for each beamlet or group of beamlets. This allows correction of off-axis aberrations and astigmatism locally for each beamlet, maintaining uniformity across the large field of view even with hundreds of beamlets
Solution Approach 3:
The patent changes physical parameters including beam energy (using acceleration electrodes), beam direction (using deflector arrays), and beam focus (using micro lens arrays) to optimize performance. By dynamically adjusting these parameters for each beamlet, the system maintains image-forming uniformity while operating with hundreds of beamlets for high throughput
2Productivity
If the number of beamlets is increased to improve throughput, then productivity increases, but resolution deteriorates due to strong Coulomb interaction influences from higher beam currents
Solution Approach 1:
The patent segments the total beam current into hundreds of individual beamlets, each carrying a fraction of the total current. This reduces the beam current density and minimizes Coulomb interactions within each beamlet, maintaining resolution while achieving high throughput through parallel processing
Solution Approach 2:
The patent introduces intermediate optical elements including micro lens arrays and micro stigmator arrays that act as mediators between the beam source and the wafer. These intermediaries correct beam distortions and focus each beamlet independently, compensating for resolution degradation caused by Coulomb interactions
3Measurement precision
If a Wien filter is used to separate secondary electron beams from primary electron beams, then measurement capability improves, but source energy dispersion blurs and optical astigmatism increase
Solution Approach 1:
The patent uses micro stigmator arrays positioned after the Wien filter to locally correct astigmatism for each beamlet. This allows the Wien filter to perform its separation function while the downstream micro stigmators compensate for the induced astigmatism, maintaining both detection capability and image quality
Solution Approach 2:
The patent implements feedback correction using micro stigmator arrays that can be dynamically adjusted based on detected beam characteristics. This feedback mechanism compensates for energy dispersion blurs and astigmatism introduced by the Wien filter, maintaining optimal beamlet focus and image quality
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 configuration significantly enhances the resolution and uniformity of the electron beam across a large field of view, allowing for higher throughput and accurate inspection of semiconductor wafers by minimizing optical aberrations and beamlet distortions.
Implementation Method 1
A cold field emission (CFE) source or a thermal field emission (TFE) source may be used as the electron beam source
Implementation Method 2
A transfer lens (TL) field focuses the beamlets to an optimal optical magnification
Implementation Method 3
An energy acceleration booster field reduces Coulomb interaction effects and improves resolutions of the beamlets
Implementation Method 4
A Wien filter with electrostatic and magnetic deflection fields can separate the secondary electron beam (SEB) or beams from the primary electron beam or beams
Implementation Method 5
A magnetic objective lens field images-form the multi-electron beams at a wafer with minimized optical aberrations
Data Source
AI summary
A multi-electron beam system that forms hundreds of beamlets can focus the beamlets, reduce Coulomb interaction effects, and improve resolutions of the beamlets. A Wien filter with electrostatic and magnetic deflection fields can separate the secondary electron beams from the primary electron beams and can correct the astigmatism and source energy dispersion blurs for all the beamlets simultaneously.