EUV Optic RF Plasma Cleaning via Back Surface Electrode

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Solution Overview

Problem

The challenge in EUV light sources is the contamination of EUV optics due to plasma erosion and unvaporized target material, which reduces reflectivity and requires effective cleaning methods without compromising the EUV collection angle or introducing additional components that cause debris scattering.

Innovation Solution

An electrically conductive surface on the EUV optic is used as an electrode to generate a capacitively coupled RF plasma for cleaning, utilizing an electrode plate that spans the optic surface except for a central aperture, allowing RF power to be coupled and contaminants to be removed efficiently.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a plasma cleaning system is introduced to clean EUV optics, then cleaning effectiveness is improved, but device complexity increases and may cause debris scattering

Engineering Contradiction:

Improvecleaning effectivenessVSAvoidsystem complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent combines the cleaning function with the existing EUV optic structure by using the optic's back surface as the RF electrode. This integration eliminates the need for separate cleaning components while maintaining effective plasma cleaning capability, thus improving reliability without increasing device complexity.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The EUV optic serves dual functions: it acts as both the optical element for EUV light collection and as the RF electrode for plasma generation. This multi-functionality allows the same component to perform both optical and cleaning roles, reducing overall system complexity while maintaining cleaning effectiveness.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

If additional components are added for plasma cleaning, then cleaning capability is improved, but EUV collection angle is reduced

Engineering Contradiction:

Improvecleaning capabilityVSAvoidEUV collection angle

Core Design Contradiction:

ReliabilityVSArea of moving object

Solution Approach 1:

The cleaning system is merged with the EUV optic structure itself, using the back surface of the optic as the RF electrode. This approach requires no additional components in the EUV collection path, thereby preserving the full EUV collection angle while providing effective cleaning capability.

Inventive Principle:

Principle #5Merging (Combining)

3Reliability

If additional components are added for plasma cleaning, then cleaning capability is improved, but debris scattering is introduced

Engineering Contradiction:

Improvecleaning capabilityVSAvoiddebris scattering

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

By integrating the RF electrode function into the existing EUV optic structure, the invention eliminates additional components that could generate debris. The optic's back surface serves as the electrode, ensuring cleaning capability is achieved without introducing new sources of debris scattering.

Inventive Principle:

Principle #5Merging (Combining)

4Reliability

If RF plasma is generated near the EUV source, then cleaning effectiveness is improved, but space constraints are violated

Engineering Contradiction:

Improvecleaning effectivenessVSAvoidspace availability

Core Design Contradiction:

ReliabilityVSVolume of stationary object

Solution Approach 1:

The invention merges the RF electrode with the EUV optic structure, utilizing the back surface of the optic as the electrode. This integration eliminates the need for separate RF electrode components and associated spacing requirements, enabling effective plasma cleaning within the constrained space of the EUV light source.

Inventive Principle:

Principle #5Merging (Combining)

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 method effectively cleans the EUV optic surfaces without adding extra components, maintaining the EUV collection angle and preventing debris scattering, thus ensuring continuous optimal performance of the EUV light source.

Implementation Method 1

the electrically conductive surface and the electrically conductive member being arranged with respect to each other such that a plasma is produced when RF power is supplied to the electrically conductive member

Methodology Applied

Scientific EffectCapacitively coupled RF plasma: Plasma

Implementation Method 2

The electrically conductive member is in sufficient proximity to the electrically conductive surface so as be able to couple RF energy to the electrically conductive surface

Methodology Applied

Scientific EffectRF energy coupling: Electromagnetic Induction

Implementation Method 3

the plasma being capable of removing contaminants from at least a portion of the electrically conductive surface

Methodology Applied

Scientific EffectPlasma cleaning: Plasma

Data Source

PatentUS10493504B2Apparatus for and method of active cleaning of EUV optic with RF plasma field

Publication Date: 2019.12.03 ASML NETHERLANDS BV

AI summary

Apparatus for and method of cleaning an electrically conductive surface of an optical element in a system for generating extreme ultraviolet radiation in which electrically conductive surface is used as an electrode for generating a plasma which cleans the surface.