Ferrite Core Auxiliary Lens for E-Beam Focus Tuning
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Solution Overview
Problem
Conventional methods for determining focus parameters in electron beam inspection are limited by low accuracy and require multiple scans, which are time-consuming and can contaminate the wafer surface, especially as feature sizes shrink in semiconductor devices.
Innovation Solution
A fast response auxiliary lens with a ferrite core is introduced below the aperture and above the in-lens detector, allowing for precise focus adjustment along the z-direction within ±3 to 5 μm, enabling accurate focusing within one 3D scan and integrating small-area focusing parameters for a larger field of view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional laser auxiliary focus is used, then the focusing system is simple, but the detecting accuracy is limited within 0.5 μm to 0.01 μm due to wafer surface pattern diffraction
Solution Approach 1:
An auxiliary lens with ferrite core is introduced as an intermediary component between the objective lens and the specimen. This auxiliary lens mediates the focusing process by providing additional magnetic field control, enabling sub-diffraction accuracy without replacing the entire focusing system.
Solution Approach 2:
The patent changes the magnetic properties of the auxiliary lens by using ferrite core material, which allows dynamic adjustment of the magnetic field strength and distribution. This parameter change enables precise control of electron beam focusing beyond the limitations of conventional optical methods.
2Measurement precision
If multiple e-beam images are taken for focusing, then the focusing accuracy can be improved, but the process takes a long time and may contaminate the processing wafer
Solution Approach 1:
The auxiliary lens with ferrite core performs preliminary focusing adjustment before the main imaging process. By pre-adjusting the focus to within ±3 to 5 μm range, the system eliminates the need for multiple iterative scans, achieving accurate focusing in a single scan.
3Measurement precision
If multiple e-beam images are taken for focusing, then the focusing accuracy can be improved, but the wafer surface may be contaminated
Solution Approach 1:
The auxiliary lens acts as an intermediary that enables accurate focusing measurement without direct multiple e-beam exposures to the wafer surface. The ferrite core auxiliary lens provides the necessary magnetic field modulation to achieve sub-diffraction accuracy while minimizing wafer exposure.
4Speed
If conventional focusing methods are used, then the system is stable, but the focus response speed is slow
Solution Approach 1:
The auxiliary lens with ferrite core introduces dynamic control capability to the focusing system. The ferrite material allows rapid adjustment of magnetic field parameters, enabling fast focus response while maintaining system stability through controlled magnetic field variations.
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 solution enables rapid and accurate focus tuning, reducing contamination risks and improving focus accuracy across the entire field of view, facilitating high-speed focusing without affecting the primary beam position.
Implementation Method 1
A fast response auxiliary lens with a ferrite core is introduced below the aperture and above the in-lens detector, allowing for precise focus adjustment along the z-direction within ±3 to 5 μm
Implementation Method 2
A fast response auxiliary lens with a ferrite core is introduced below the aperture and above the in-lens detector
Data Source
AI summary
This invention relates to apparatus and method to fast determine focus parameters in one pre-scan during an e-beam inspection practice. More specifically, embodiments of the present invention provide an apparatus and method that provide accurate focus tuning after primary focusing has been done.