Objective Lens Layout for Long-Working-Distance Beam Inspection
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Solution Overview
Problem
Charged particle beam inspection systems face challenges in achieving high image resolution and minimizing chromatic aberration due to the use of wide wavelength light sources, while also requiring a long working distance and large field of view to accommodate high-voltage components and vacuum conditions.
Innovation Solution
An optical imaging system with an objective lens comprising a first lens group having negative refractive power and a second lens group with positive refractive power, optimized for a narrow-band light source and designed for operation under vacuum conditions, providing a longer working distance and larger field of view, and minimizing chromatic aberration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional objective lens is used, then the structure is simple, but the image resolution is poor and chromatic aberration is high
Solution Approach 1:
The objective lens is divided into multiple lens groups (first lens group with negative refractive power, second lens group with positive refractive power, and third lens group) instead of using a single simple lens. This segmentation allows each group to contribute differently to the overall optical performance, improving image resolution and reducing chromatic aberration while maintaining a manageable structural complexity.
2Reliability
If the working distance is increased to accommodate high-voltage components and vacuum conditions, then the system can handle high-voltage components and maintain vacuum conditions, but the image resolution deteriorates
Solution Approach 1:
The patent optimizes specific parameters of the lens groups, including the effective focal lengths (EFL1, EFL2, EFL3) and spacing distances (d1, d2, d3), to achieve a balance between working distance and image resolution. By carefully controlling these parameters, the system maintains long working distance for high-voltage components and vacuum conditions while preserving high image resolution through precise optical design.
3Measurement precision
If a narrow-band light source is used, then chromatic aberration is reduced, but the illumination intensity decreases
Solution Approach 1:
The multi-group lens structure with different refractive powers allows the system to effectively utilize the available narrow-band light while correcting chromatic aberration. Each lens group contributes to focusing and correcting optical errors, enabling the system to maintain high image quality with reduced chromatic aberration even when using a narrow-band light source with limited intensity.
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 objective lens achieves improved image resolution and reduced chromatic aberration, with a longer working distance and larger field of view, suitable for charged particle beam inspection systems, enhancing the system's ability to handle high-voltage components and maintain vacuum conditions.
Implementation Method 1
a first lens group having negative refractive power, and a second lens group having positive refractive power
Data Source
AI summary
An objective lens for forming an image of an object. The objective lens includes, sequentially from an image side to an object side, a first lens group having negative refractive power, and a second lens group having positive refractive power.