Wafer Inspection Objective Lens Layout for High NA and Long Working Distance
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Solution Overview
Problem
Existing objectives for wafer inspection face challenges in achieving high resolution with a wide field of view and long working distance while effectively correcting aberrations, particularly spherical aberration and coma aberration, due to the limitations of existing lens configurations.
Innovation Solution
The objective design includes a first lens group with a meniscus lens having positive refractive power and a second lens group with negative refractive power, featuring a pair of meniscus lens components and multiple cemented lenses, configured to satisfy specific conditional expressions that enhance aberration correction, particularly through the use of achromatic lens components and optimized lens diameters and curvatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the numerical aperture is increased to achieve high resolution, then the resolution is improved, but the working distance becomes shorter and the field of view becomes narrower
Solution Approach 1:
The objective lens is divided into multiple lens groups (first lens group with positive refractive power, second lens group with negative refractive power, and third lens group) that can be independently designed and optimized. This segmentation allows each group to contribute differently to the overall optical performance, enabling high NA while maintaining long WD through coordinated design of divergent and convergent light paths
Solution Approach 2:
The patent employs specific parameter ranges for lens curvatures (R1, R2, R3, R4), thicknesses (d1, d2, d3), and refractive powers to achieve the desired balance. By carefully controlling parameters such as the ratio of lens curvatures and the distribution of refractive power across lens groups, the system achieves high resolution with maintained working distance
2Measurement precision
If the numerical aperture is increased to achieve high resolution, then the resolution is improved, but the field of view becomes narrower
Solution Approach 1:
The objective lens is divided into multiple lens groups (first lens group with positive refractive power, second lens group with negative refractive power, and third lens group) that can be independently designed and optimized. This segmentation allows each group to contribute differently to the overall optical performance, enabling high NA while maintaining long WD through coordinated design of divergent and convergent light paths
Solution Approach 2:
The patent employs specific parameter ranges for lens curvatures (R1, R2, R3, R4), thicknesses (d1, d2, d3), and refractive powers to achieve the desired balance. By carefully controlling parameters such as the ratio of lens curvatures and the distribution of refractive power across lens groups, the system achieves high resolution with maintained working distance
3Measurement precision
If conventional lens configurations are used to achieve high numerical aperture, then resolution is improved, but aberration correction becomes insufficient
Solution Approach 1:
The objective lens is divided into multiple lens groups (first lens group with positive refractive power, second lens group with negative refractive power, and third lens group) that can be independently designed and optimized. This segmentation allows each group to contribute differently to the overall optical performance, enabling high NA while maintaining long WD through coordinated design of divergent and convergent light paths
Solution Approach 2:
The patent uses cemented lens structures where lenses with different refractive indices and Abbe numbers are bonded together. Specifically, the first lens group includes a positive meniscus lens and a biconvex lens cemented together, and the second lens group includes negative meniscus lenses with specific glass material combinations. This composite approach enables sophisticated aberration correction through the complementary optical properties of different materials
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 achieves a high numerical aperture, wide field of view, and long working distance with improved aberration correction, particularly in the periphery of the field of view, ensuring high throughput and reduced manufacturing errors.
Implementation Method 1
a first lens group that has positive refractive power and converts divergent light from an object point to convergent light
Implementation Method 2
The objective includes three or more cemented lenses that are arranged closer to the object side than the pair of meniscus lens components
Data Source
AI summary
The objective includes a first lens group having positive power and a second lens group having negative power and including a pair of meniscus lens components having concave surfaces facing each other. The first lens group includes a first lens situated closest to an object side and has positive power with a concave surface facing the object side. The objective includes three or more cemented lenses arranged closer to the object side than the pair of meniscus lens components, and satisfies the following conditional expressions.2.6≤φL1/DL1≤16(1)0.1≤<semantics definitionURL="">❘<annotation encoding="Mathematica">"\[LeftBracketingBar]"</annotation></semantics>R212<semantics definitionURL="">❘<annotation encoding="Mathematica">"\[RightBracketingBar]"</annotation></semantics>/f≤3.5(2)Here, φL1 and DL1 are an outer diameter and a thickness of the first lens. R212 is a radius of curvature of a surface closest to the image side in a first meniscus lens component among the pair of meniscus lens components. f is a focal length of the objective.