Objective Lens with Retrofocus Configuration for High NA Inspection

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Solution Overview

Problem

Existing objective lenses for semiconductor and flat panel display inspection devices face challenges in achieving high numerical aperture, long working distance, and short focal length while minimizing the number of lenses and avoiding cemented lenses to prevent damage from high-power laser light.

Innovation Solution

The objective lens is configured with a small number of single lenses made of synthetic quartz or fluorite, arranged in a retrofocus type configuration with a first afocal lens group and a second positive lens group, achieving a retro ratio of 1.5 or higher without cemented lenses.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If the number of lenses is reduced to improve light use efficiency and reduce damage risk, then light absorption loss decreases, but achieving high numerical aperture and long working distance becomes more difficult

Engineering Contradiction:

Improvelight absorption lossVSAvoidnumerical aperture and working distance

Core Design Contradiction:

Loss of energyVSManufacturing precision

Solution Approach 1:

The patent changes the material parameter by using synthetic quartz or fluorite with specific refractive indices and dispersion characteristics. By selecting materials with appropriate optical parameters, the lens system achieves high numerical aperture (0.75 or higher) and long working distance (1 mm or longer) while using only a small number of lenses, thus reducing light absorption loss.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If cemented lenses are used to improve aberration correction, then optical performance improves, but damage from high-power laser light increases

Engineering Contradiction:

Improveaberration correctionVSAvoidlaser light damage

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent extracts and eliminates the cemented lens structure from the optical system. By using only single lenses made of synthetic quartz or fluorite without cemented joints, the invention removes the vulnerable adhesive components that would be damaged by high-power laser light, while still achieving excellent aberration correction through precise lens design and material selection.

Inventive Principle:

Principle #2Taking out (Extraction)

3Length of moving object

If the focal length is shortened to reduce overall system length, then compactness improves, but working distance becomes harder to maintain

Engineering Contradiction:

Improveoverall system lengthVSAvoidworking distance

Core Design Contradiction:

Length of moving objectVSLength of stationary object

Solution Approach 1:

The patent employs asymmetric lens design where the positive and negative lens groups have different configurations and power distributions. This asymmetric arrangement allows the objective lens to achieve a short focal length (3 mm) for compactness while maintaining a long working distance (1 mm or longer) through optimized group spacing and individual lens curvatures.

Inventive Principle:

Principle #4Asymmetry

4Measurement precision

If high numerical aperture is achieved to improve resolution, then spatial resolution improves, but light absorption and damage risk increase

Engineering Contradiction:

Improvespatial resolutionVSAvoidlight absorption

Core Design Contradiction:

Measurement precisionVSLoss of energy

Solution Approach 1:

The patent uses composite material strategy by combining synthetic quartz and fluorite lenses in a multi-group configuration. Each material has complementary optical properties - fluorite has low dispersion and high transmission in UV range, while synthetic quartz provides mechanical strength and controlled refractive index. This composite approach enables high numerical aperture (0.75+) with reduced light absorption compared to single-material systems.

Inventive Principle:

Principle #40Composite 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

This configuration allows for a high numerical aperture, long working distance, and short focal length, effectively addressing the limitations of prior art designs while maintaining excellent aberration correction and preventing lens damage from high-power laser illumination.

Implementation Method 1

an objective lens which is configured by multiple lenses (L), each consisting of a single lens having no cemented surface

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 2

a retro ratio of 1.5 or higher, the retro ratio being a ratio of a working distance of the objective lens to a focal length of the objective lens

Methodology Applied

Scientific EffectDivergence:

Data Source

PatentUS12298594B2Objective lens

Publication Date: 2025.05.13 KYOCERA SOC CORP

AI summary

An objective lens configured by multiple lenses each consisting of a single lens has a retro ratio of 1.5 or higher. The multiple lenses configure a substantially afocal first lens group and a positive second lens group arranged in this order from a magnification side. The first lens group includes a 1a lens group having a negative power and a 1b lens group having a positive power which are arranged in this order from the magnification side. Provided that a focal length of the first lens group is represented by f(Gr1) and a focal length of a whole system of the objective lens is represented by f(total), a condition of |f(Gr1)/f(total)|>10 is satisfied. The second lens group includes a 2a lens group having a negative power and a 2b lens group having a positive power which are arranged in this order from the magnification side.