Charged Particle Beam Aberration Correction via Wien Filter
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Solution Overview
Problem
Existing charged particle beam apparatuses face challenges in accurately correcting off-axis chromatic aberration and deflection coma aberration during beam tilting, leading to increased complexity and difficulty in maintaining precision, especially at large tilt angles and with factors like axis deviation or assembling errors.
Innovation Solution
A charged particle beam apparatus comprising an objective lens and a tilting deflector, with a first optical element being an electromagnetic quadrupole to suppress dispersion and a second optical element, either a deflector or another electromagnetic quadrupole, to generate a different dispersion, allowing for simple adjustment and correction of aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If beam tilt is performed by the deflector, then three-dimensional observation capability is improved, but deflection coma aberration and off-axis chromatic aberration are generated
Solution Approach 1:
The patent introduces a Wien filter as an intermediary optical element between the deflector and the objective lens. This Wien filter generates chromatic dispersion that acts as a mediator to correct the off-axis chromatic aberration caused by beam tilting, thereby maintaining beam diameter precision while preserving three-dimensional observation capability
Solution Approach 2:
The patent extracts the aberration correction function from the objective lens system by introducing a separate Wien filter unit. This allows the deflector to perform beam tilting for three-dimensional observation while the Wien filter independently corrects the resulting aberrations, separating the observation function from the correction function
2Manufacturing precision
If a two-stage deflector is used to cancel off-axis chromatic aberration, then aberration correction is improved, but device complexity increases
Solution Approach 1:
The patent replaces the mechanical two-stage deflector system with an electromagnetic Wien filter that uses crossed electric and magnetic fields to achieve chromatic dispersion. This substitution simplifies the optical system structure while maintaining aberration correction capability
Solution Approach 2:
The Wien filter serves multiple functions simultaneously: it generates chromatic dispersion for aberration correction, enables beam tilting for three-dimensional observation, and maintains compatibility with the objective lens system. This multi-functionality reduces the need for separate correction components
3Adaptability or versatility
If large angle tilting is performed to achieve wide observation range, then adaptability is improved, but deflection coma aberration becomes apparent and resolution is degraded
Solution Approach 1:
The patent applies preliminary anti-action by using the Wien filter to generate chromatic dispersion that pre-compensates for the deflection coma aberration before it significantly degrades the beam. This allows large angle tilting to be performed while maintaining resolution through proactive aberration management
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 enables effective suppression of off-axis chromatic aberration and deflection coma aberration, maintaining precision and simplicity in the optical system, even at large tilt angles, and accommodating variations due to axis deviation or assembling errors.
Implementation Method 1
a first optical element includes an electromagnetic quadrupole which causes a dispersion to suppress the dispersion which is generated by the deflection by the tilting deflector
Implementation Method 2
a tilting deflector which is disposed between the charged particle source and the objective lens and tilts the charged particle beam
Implementation Method 3
an objective lens which focuses a charged particle beam emitted from a charged particle source to impinge a specimen
Data Source
AI summary
The present invention provides a charged particle beam apparatus which is provided with a tilting deflector which is disposed between a charged particle source and an objective lens and tilts a charged particle beam, wherein a first optical element includes an electromagnetic quadrupole which generates dispersion to suppress the dispersion which is generated by deflection by the tilting deflector, and a second optical element is composed of a deflector for deflecting the charged particle beam which enters the first optical element or an electromagnetic quadrupole which causes the charged particle beam to generate a dispersion different from the dispersion generated by the first optical element.