Reflective Element Mounting for EUV Illumination Mode Switching

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Solution Overview

Problem

Existing lithographic apparatuses face challenges in achieving efficient operation with extreme ultraviolet (EUV) radiation due to the absorption of EUV radiation by refractive materials, which limits the intensity of the radiation beam and necessitates the use of spatial filters that block a significant portion of the beam, reducing efficiency.

Innovation Solution

An array of reflective elements is mounted on a flexible sleeve system, allowing for adjustable orientation and movement to create various illumination modes without blocking the radiation beam, including dipole and annular modes, using a combination of primary and secondary reflective elements that can rotate between specific orientations to direct radiation effectively.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If spatial filters are used to create illumination modes, then the desired illumination pattern is achieved, but a considerable proportion of the radiation beam is blocked, reducing beam intensity

Engineering Contradiction:

Improveradiation beam intensityVSAvoidillumination mode control

Core Design Contradiction:

Illumination intensityVSEase of operation

Solution Approach 1:

The illumination system is segmented into multiple independent reflective elements (first and second reflective components with multiple reflective elements each) that can be individually oriented. This segmentation allows different portions of the beam to be directed to different locations without blocking, achieving illumination mode control while maintaining beam intensity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of using transmissive spatial filters that block unwanted portions of the beam, the invention uses reflective elements that actively direct the beam to desired locations. This inversion from passive blocking to active directing maintains beam intensity while achieving the same illumination mode control function.

Inventive Principle:

Principle #13The other way round (Inversion)

2Illumination intensity

If refractive optical components are used to create illumination modes, then the illumination pattern can be controlled, but EUV radiation is strongly absorbed, reducing beam intensity

Engineering Contradiction:

ImproveEUV radiation intensityVSAvoidillumination mode capability

Core Design Contradiction:

Illumination intensityVSAdaptability or versatility

Solution Approach 1:

The invention replaces refractive optical components (which rely on material properties that absorb EUV radiation) with reflective mechanical elements. The reflective components use mechanical orientation and positioning to achieve illumination mode control, eliminating the absorption problem inherent in refractive materials for EUV wavelengths.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The invention changes the fundamental optical parameter from refraction to reflection. By using reflective surfaces instead of refractive materials, the system maintains EUV radiation intensity while achieving the necessary illumination mode versatility through controlled reflection angles and element positioning.

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If multiple independently movable refractive components are used, then zoom-axicon functionality is achieved, but the system is not suitable for EUV radiation due to strong absorption

Engineering Contradiction:

Improveillumination mode variabilityVSAvoidEUV radiation intensity

Core Design Contradiction:

Adaptability or versatilityVSIllumination intensity

Solution Approach 1:

The invention replaces the refractive zoom-axicon mechanism with a reflective element array system. Multiple reflective elements can be independently oriented and positioned to achieve variable illumination modes (including annular, dipole, and other patterns) without the EUV absorption problems of refractive materials, maintaining both versatility and intensity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 solution enhances the efficiency of EUV lithographic apparatuses by maintaining high radiation intensity while allowing for rapid switching between different illumination modes, improving the quality and efficiency of pattern projection onto substrates without the need for substantial beam blocking.

Implementation Method 1

the sleeve including a first resiliently flexible portion which is configured to bend in order to allow the movement of the second end of the rod to take place

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 2

an array of reflective elements, at least one of the reflective elements being mounted on a mounting which comprises a rod

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS8757823B2Mountings for rotation of array of reflective elements and lithographic apparatus incorporating same

Publication Date: 2014.06.24 ASML NETHERLANDS BV

AI summary

An array of reflective elements in which at least one of the reflective elements is mounted on a mounting which comprises a rod at least partially located within a sleeve. A first end of the rod is fixed to a first end of the sleeve and a second end of the rod is moveable, the sleeve including a first resiliently flexible portion which is configured to bend in order to allow the movement of the second end of the rod to take place, wherein the reflective element is mounted at the first end of the sleeve such that bending of the sleeve causes rotation of the reflective element.