High NA Objective Lens System with Segmented Groups
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Solution Overview
Problem
Current high NA objective lens systems for scatterometry suffer from limitations such as small working distance, restricted spectral bandwidth, chromatic aberrations, field curvature aberrations, and reduced light collection due to obscuration, leading to reduced accuracy in measurements.
Innovation Solution
An objective lens system configuration featuring a first lens group with positive meniscus lenses, a second lens group including a triplet lens, and a third lens group with a bi-concave lens and doublet lens, designed to correct field curvature and pupil aberrations, while maintaining high NA and wide spectral bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If current high NA refractive objective lens systems are used, then high NA is achieved, but working distance becomes small (less than 0.35 mm)
Solution Approach 1:
The objective lens system is divided into multiple lens groups (first lens group with positive meniscus lenses, second lens group with triplet lens, third lens group with bi-concave and doublet lenses). Each group contributes differently to the overall optical performance, allowing high NA to be achieved while maintaining adequate working distance through distributed optical power.
Solution Approach 2:
The system uses composite lens designs combining different lens types (meniscus lenses, triplet lens, doublet lens, bi-concave lens) with different optical properties. This composite approach allows optimization of both numerical aperture and working distance by combining the strengths of different lens configurations.
2Illumination intensity
If current high NA refractive objective lens systems are used, then high NA is achieved, but spectral bandwidth is restricted (450-700 nm)
Solution Approach 1:
The lens design incorporates specific parameter choices for each lens element (curvature radii, thicknesses, refractive indices) that are optimized to minimize chromatic aberrations across a broader spectral range. This allows the system to maintain high NA performance while extending operational bandwidth beyond the traditional 450-700 nm range.
Solution Approach 2:
The combination of different lens materials and designs in the multi-group configuration allows the system to handle multiple wavelengths effectively, extending the usable spectral bandwidth while maintaining high numerical aperture performance.
3Illumination intensity
If current high NA refractive objective lens systems are used, then high NA is achieved, but chromatic aberrations increase causing resolution loss
Solution Approach 1:
The objective lens is segmented into multiple groups with different optical characteristics. The first lens group with positive meniscus lenses, second lens group with triplet lens, and third lens group with bi-concave and doublet lenses work together to correct chromatic aberrations while maintaining high NA, thereby preserving resolution.
Solution Approach 2:
The multi-group lens configuration acts as an intermediary system that corrects chromatic aberrations introduced by high NA requirements. Each lens group serves as a corrective element that compensates for wavelength-dependent focal shifts, maintaining resolution across the spectral bandwidth.
4Illumination intensity
If catadioptric or reflective objective lens systems are used, then high NA is achieved, but field curvature aberrations and pupil aberrations increase
Solution Approach 1:
The refractive objective lens system is divided into multiple specialized lens groups that collectively correct field curvature and pupil aberrations. This segmentation allows each group to be optimized for specific aberration correction while maintaining high NA, avoiding the field curvature problems of catadioptric systems.
5Illumination intensity
If current high NA refractive objective lens systems are used, then high NA is achieved, but light collection is reduced due to obscuration
Solution Approach 1:
The composite lens design combines different lens types and configurations that optimize light transmission. The specific arrangement of positive meniscus lenses, triplet lens, and doublet lens groups minimizes obscuration effects while maintaining high numerical aperture, thereby improving light collection efficiency.
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 proposed configuration achieves a high NA without central obscuration, with a larger working distance and reduced optical aberrations, enabling accurate measurements across a broader spectral range without compromising optical performance.
Implementation Method 1
An objective lens system is disclosed that may be used for directing and/or focusing a radiation beam onto an object of inspection (e.g., a reticle, a target of a pattern on a surface of a substrate), and/or collecting and/or imaging light scattered by and/or reflected from the object of inspection
Data Source
AI summary
An objective lens system having a high numerical aperture, a large working distance, and low optical aberrations over a wide spectral band of wavelengths is disclosed. The objective lens system includes a first lens group, a second lens group, and a third lens group. The first lens group includes first and second positive meniscus lenses that are positioned at a distance from each other along an optical axis of the objective lens system. The distance may be dependent on a focal length of the objective lens system. The second lens group includes first and second meniscus lenses and a bi-convex lens. The third lens group includes a bi-concave lens and a doublet lens.