Catadioptric Illumination Relay for Lithography Aberration Control

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Solution Overview

Problem

Existing lithographic projection systems suffer from significant chromatic aberrations and impractical designs due to the use of dioptric illumination relays, leading to inefficient operation and high costs in correcting aberrations, especially when operating at high numerical apertures and large reduction ratios.

Innovation Solution

A projection optical system is designed with a catadioptric illumination relay and projection lens, where both portions are configured as catadioptric systems, forming an intermediate optical image, and the first portion acts as a dioptric system to transfer light to the image plane, satisfying specific magnification conditions to minimize aberrations and maintain practicality.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a dioptric illumination relay is used in the projection system, then the system structure is simpler, but chromatic aberrations increase significantly

Engineering Contradiction:

Improvesystem structureVSAvoidchromatic aberrations

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

A catadioptric illumination relay is introduced as an intermediary component between the light source and the projection lens. This relay includes a first negative lens and a concave mirror that work together to redirect and condition the light beam, effectively reducing chromatic aberrations while maintaining a practical system structure.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The illumination relay employs a composite optical system combining refractive elements (negative lenses made of optical glass) and reflective elements (concave mirror). This catadioptric combination leverages the complementary properties of refraction and reflection to correct chromatic aberrations that cannot be adequately addressed by dioptric systems alone.

Inventive Principle:

Principle #40Composite materials

2Measurement precision

If the projection system is designed for high numerical aperture and large reduction ratio, then imaging precision is improved, but chromatic aberrations and distortion increase

Engineering Contradiction:

Improveimaging precisionVSAvoidchromatic aberrations and distortion

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The system operates at high numerical aperture (NA≥1.0) and large reduction ratio (≥50×) by carefully selecting and optimizing optical parameters. The catadioptric illumination relay is designed with specific focal lengths and curvatures that enable high-precision imaging while compensating for the increased chromatic aberrations and distortion that naturally occur at these extreme parameters.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces complex mechanical adjustment mechanisms with an optimized optical design. The catadioptric illumination relay provides inherent aberration correction through its optical geometry, eliminating the need for complex mechanical correction systems that would be required to achieve the same imaging precision.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Object-affected harmful factors

If complex aberration correction is implemented, then chromatic aberrations are reduced, but system complexity and cost increase

Engineering Contradiction:

Improvechromatic aberrationsVSAvoidaberration correction complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The aberration correction function is extracted from the main projection lens and implemented in a separate catadioptric illumination relay. This modular approach isolates the complex aberration correction mechanisms in a dedicated subsystem, making the overall system more manageable and potentially reducing costs by allowing independent optimization of each module.

Inventive Principle:

Principle #2Taking out (Extraction)

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 system effectively reduces chromatic aberrations and maintains operational efficiency at high numerical apertures and large reduction ratios, ensuring negligible distortion and high Strehl ratios across spectral bandwidths, thus improving image quality and reducing correction costs.

Implementation Method 1

the second portion is configured as a catadioptric optical system designed to form an intermediate optical image

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 2

the first portion is configured as a dioptric optical system disposed to transfer light

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS10488638B2Catadioptric imaging systems for digital scanner

Publication Date: 2019.11.26 NIKON CORP

AI summary

Projection optical system for forming an image on a substrate and including an illumination relay lens and a projection lens each of which is a catadioptric system. The projection lens may include two portions in optical communication with one another, the first of which is dioptric and the second of which is catadioptric. In a specific case, the projection optical system satisfies4<βIβT<30,where βI and βT are magnifications of the first portion and the overall projection lens. Optionally, the projection lens may be structured to additionally satisfy6<βIIβT<20,where βII is a magnification of the second portion. A digital scanner including such projection optical system and operating with UV light having a spectral bandwidth on the order of 1 picometer. Method for forming an image with such projection optical system.