Electromagnetic Lens With Permanent Magnets for Low-Stray Fields
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Solution Overview
Problem
Existing electromagnetic lenses for charged-particle optical apparatuses face challenges in achieving high precision adjustment of optical properties while minimizing stray magnetic fields, particularly in multi-column systems, which are limited by manufacturing and assembly inaccuracies and insufficient space for temperature control.
Innovation Solution
An electromagnetic lens design incorporating a magnetic circuit assembly with permanent magnets and electrostatic elements, featuring a sleeve insert with conductive electrodes to generate an electrostatic field, allowing for fine-adjustment of focal length and optical aberrations, and a closed magnetic loop with gaps to confine magnetic fields, reducing stray fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If coil-based magnetic lenses are used to generate strong magnetic fields, then the magnetic field strength is sufficient for lens operation, but Joule heating becomes extremely large requiring substantial space for temperature control
Solution Approach 1:
The patent replaces the coil-based electromagnetic system with a permanent magnet system. Instead of using electrical current through coils to generate magnetic fields (electromagnetic induction), the invention uses permanently magnetized materials arranged in specific configurations to produce the required magnetic fields for lens operation, thereby eliminating Joule heating while maintaining sufficient magnetic field strength
Solution Approach 2:
The patent changes the fundamental parameter of magnetic field generation from transient electromagnetic induction (requiring continuous power and producing heat) to static permanent magnetism. By using permanently magnetized materials with appropriate remanence values and arranging them in specific geometric configurations, the system achieves the required magnetic field characteristics without the thermal problems of coil-based systems
2Productivity
If the column diameter is reduced to fit multiple sub-columns on a wafer, then the system achieves high throughput, but there is insufficient space for temperature control and coil fabrication
Solution Approach 1:
By replacing the coil-based magnetic lens system with a permanent magnet system, the patent eliminates the need for large-diameter coils and associated temperature control infrastructure. The permanent magnet components can be fabricated and assembled in a compact form factor, enabling the column diameter to be reduced to fit multiple sub-columns on a standard semiconductor wafer while maintaining full lens functionality
Solution Approach 2:
The patent employs a nested arrangement where permanent magnets are positioned within concentric yoke structures (inner and outer yokes), creating a compact integrated assembly. This nested configuration maximizes the magnetic field generation capability within a minimal volume, allowing the entire magnetic lens system to fit within the reduced column diameter required for high-density multi-sub-column arrangements on wafers
3Volume of moving object
If permanent magnets are used to generate magnetic fields in slim columns, then space requirements are reduced, but the system cannot be recalibrated after manufacturing
Solution Approach 1:
The patent introduces dynamic adjustability to the previously static permanent magnet system by incorporating movable permanent magnets or adjustable magnetic component positions. This allows the magnetic field characteristics to be tuned and recalibrated after manufacturing by physically repositioning components, thereby achieving both compact size and post-manufacturing adaptability
Solution Approach 2:
The patent divides the permanent magnet system into separable, independently adjustable components (such as multiple permanent magnet assemblies or modular magnetic elements). This segmentation allows individual components to be adjusted or repositioned to fine-tune the magnetic field characteristics after manufacturing, providing recalibration capability while maintaining the compact permanent magnet architecture
4Ease of manufacture
If manufacturing and assembly accuracies are limited, then production is easier, but the magnetic field precision deviates by ±1.0% requiring additional compensation components
Solution Approach 1:
The patent incorporates adjustable elements that allow post-assembly calibration of the magnetic field. By providing mechanisms to fine-tune the position or orientation of permanent magnets after manufacturing, the system can compensate for tolerances accumulated during production, achieving high magnetic field precision without requiring extremely tight manufacturing tolerances
Solution Approach 2:
The patent implements a feedback mechanism where the magnetic field characteristics are measured and used to guide adjustment of the permanent magnet positions or configurations. This closed-loop approach allows the system to automatically or manually compensate for manufacturing variations, achieving the required magnetic field precision while maintaining ease of manufacture with standard tolerances
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
The design enables high-precision adjustment of optical properties, minimizing stray fields and enhancing performance in multi-column systems, suitable for high-throughput industrial processes.
Implementation Method 1
the sleeve insert comprises one or more electrically conductive electrode elements, preferably at least two, which are configured to be applied respective electric potentials (with respect to the electric potential of the housing, which is identified with a ground potential) so as to generate an electrostatic field within the passage opening
Implementation Method 2
the ring magnet(s) arranged circumferentially around the inner yoke shell and arranged between the inner and outer yoke shells, the ring magnet(s) comprising a permanent magnetic material being magnetically oriented with its two magnetic poles towards the inner yoke shell and the outer yoke shell, respectively
Implementation Method 3
in the magnetic circuit assembly, the inner yoke shell, the at least one ring magnet, and the outer yoke shell form a closed magnetic circuit but having at least one gap, preferably at least two gaps, located at an axial end of the inner yoke shell towards a respectively corresponding (inner surface) portion of the outer yoke shell, configured to generate a defined magnetic field reaching inwards into the passage opening
Data Source
AI summary
A fine-adjustable electromagnetic lens for a charged-particle optical apparatus comprises a magnetic circuit assembly including one or more ring magnets, and a sleeve insert of generally rotational symmetry around a longitudinal axis. The sleeve insert surrounds a passage opening extending along the longitudinal axis, and comprises several electrically conductive electrode elements configured to generate an electrostatic field within the passage opening. The ring magnets are arranged circumferentially around an inner yoke shell and surrounded by an outer yoke shell; the inner yoke shell in turn surrounds a central portion of the sleeve insert. The ring magnets are magnetized such that the two magnetic poles are oriented towards the inner and outer yoke shell, respectively. The inner and outer yoke shell together with the ring magnets form a magnetic circuit having at least one gap, in order to generate a magnetic field reaching inwards into the passage opening and spatially overlapping with the electrostatic field generated by the sleeve insert.