Optical Element Protective Cover for Microlithography

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Solution Overview

Problem

In microlithographic projection exposure apparatuses, hydrogen radicals can enter the substrate and cause blister formation and loss of reflectivity due to the lack of suitable light-transmissive refractive materials, especially at the edges of reflective optical components where the reflection layer system is interrupted or damaged.

Innovation Solution

An optical element with a protective cover extending over the edge regions, featuring a narrow and long gap between the cover and the layer system to promote hydrogen radical recombination into molecular hydrogen, and using materials like copper or silver for the cover to enhance this recombination, thereby preventing ingress into the layer system.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a protective cover is added to prevent hydrogen radical ingress, then reliability is improved, but device complexity increases

Engineering Contradiction:

Improveprevent hydrogen radical ingressVSAvoidstructure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent employs a protective cover in the form of a thin film or shell structure that extends over the edge region of the optical element. This cover acts as a physical barrier to prevent hydrogen radicals from reaching the layer system, while maintaining optical transparency. The thin film nature minimizes added complexity while providing effective protection against hydrogen radical ingress that causes blister formation and reflectivity loss.

Inventive Principle:

Principle #30Flexible shells and thin films

2Reliability

If the protective cover is placed close to the layer system, then protection effectiveness is improved, but the risk of scratching the layer system increases

Engineering Contradiction:

Improveprotection effectivenessVSAvoidscratch risk

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent introduces a cushioning layer or protective interface between the protective cover and the layer system. This intermediate structure serves as a buffer that prevents direct contact between the cover and the sensitive layer system, thereby eliminating scratch risk while maintaining the protective barrier function against hydrogen radicals. The cushioning layer is designed to be transparent and non-interfering with the primary protection mechanism.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Object-affected harmful factors

If hydrogen gas is used for purging, then contamination prevention is improved, but hydrogen radical formation increases

Engineering Contradiction:

Improvecontamination preventionVSAvoidhydrogen radical formation

Core Design Contradiction:

Object-affected harmful factorsVSObject-generated harmful factors

Solution Approach 1:

The patent utilizes the hydrogen radicals formed from hydrogen gas purging not as harmful contaminants but as beneficial cleaning agents. The hydrogen radicals react with and remove carbon-containing contaminants from the optical surface, a process known as hydrogen termination or hydrogen cleaning. By controlling the purging conditions and using the protective cover to direct the hydrogen flow, the system converts the potentially harmful hydrogen radicals into a useful contamination removal mechanism that maintains optical surface purity.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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

Significantly reduces hydrogen radical ingress and blister formation, maintaining reflectivity and mechanical protection against scratches, while ensuring effective purging in other regions.

Implementation Method 1

featuring a narrow and long gap between the cover and the layer system to promote hydrogen radical recombination into molecular hydrogen

Methodology Applied

Scientific EffectRadical recombination:

Implementation Method 2

using materials like copper or silver for the cover to enhance this recombination

Methodology Applied

Scientific EffectCatalysis: Catalysis

Implementation Method 3

thereby preventing ingress into the layer system

Methodology Applied

Scientific EffectPhysical barrier protection: Physical Containment

Data Source

PatentUS10578974B2Optical element, in particular for a microlithographic projection exposure apparatus

Publication Date: 2020.03.03 CARL ZEISS SMT GMBH

AI summary

The disclosure relates to an optical element, in particular for a microlithographic projection exposure apparatus. The optical element has an optical effective surface. The optical element includes a substrate, a layer system that is present on the substrate, and a protective cover extending over an edge region of the optical element that is adjacent to the optical effective surface. During operation of the optical element, the protective coating reduces an ingress of hydrogen radicals into the layer system in comparison with an analogous design without the protective cover, wherein a gap is formed between the protective cover and the layer system.