EUV Optical Element Mounting Pin Stiffness and Damping

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Solution Overview

Problem

EUV projection exposure apparatuses face instability due to undesirable transverse resonances, which are not effectively controlled by existing systems, leading to amplitude magnification and potential control loop instability.

Innovation Solution

A mechanical coupling system with a pin having high axial stiffness and low lateral stiffness, combined with a damping element that provides at least 1% critical damping in the lateral direction to suppress transverse resonance magnification while maintaining axial resonance, using materials like fluoro rubbers and arranging the damping element to minimize additional stiffness and maximize damping effect.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a pin with high axial stiffness and low lateral stiffness is used to couple the actuator to the optical element, then the axial resonance is maintained and transverse resonances are reduced, but transverse resonances still occur and can cause amplitude magnification and control loop instability

Engineering Contradiction:

Improvecontrol loop stabilityVSAvoidtransverse resonance amplitude magnification

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent converts the harmful transverse resonances into a beneficial effect by introducing damping elements that specifically target and dampen the transverse vibration modes. The damping elements transform the harmful resonance amplification into controlled energy dissipation, stabilizing the control loop while preserving the desired axial resonance characteristics for positioning accuracy.

Inventive Principle:

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

Solution Approach 2:

The patent applies different stiffness characteristics to different directions of the pin coupling. The pin is designed with high stiffness in the axial direction (for precise positioning) and low stiffness in the lateral direction (to reduce transverse resonances). This anisotropic stiffness distribution, combined with localized damping elements, resolves the contradiction by making the system directionally selective in its mechanical properties.

Inventive Principle:

Principle #3Local quality

2Reliability

If damping elements are added to suppress transverse resonances, then control loop stability is improved, but the device complexity increases

Engineering Contradiction:

Improvecontrol loop stabilityVSAvoidmounting arrangement complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent merges the damping function with existing structural elements of the mounting arrangement. The damping elements are integrated into the pin coupling or the actuator-optical element interface, combining the mechanical coupling function with vibration suppression in a single integrated design. This reduces the overall device complexity compared to adding separate, standalone damping systems.

Inventive Principle:

Principle #5Merging (Combining)

3Object-affected harmful factors

If the pin stiffness in lateral direction is reduced to minimize transverse resonances, then transverse vibration is reduced, but the mechanical coupling stability may be compromised

Engineering Contradiction:

Improvetransverse resonanceVSAvoidmechanical coupling stability

Core Design Contradiction:

Object-affected harmful factorsVSStability of the object's composition

Solution Approach 1:

The patent introduces damping elements as intermediary components between the pin and the actuator/optical element interface. These damping elements act as mediators that allow the low-stiffness pin design to suppress transverse resonances while the damping provides additional stabilization, compensating for the reduced lateral stiffness and maintaining overall mechanical coupling stability.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 solution stabilizes the positioning of optical elements by preventing amplitude magnification from transverse resonances, ensuring the axial natural vibration behavior is maintained, and effectively filtering out undesirable frequencies, thus enhancing the system's stability and control loop performance.

Implementation Method 1

fitting to an optical element in a projection exposure apparatus at least one additional element which brings about an energy dissipation of the vibration energy of the optical element by means of friction

Methodology Applied

Scientific EffectFriction damping: Friction

Implementation Method 2

at least one damping element which brings about a damping of a natural vibration form of the pin in a lateral direction

Methodology Applied

Scientific EffectViscous damping: Viscous Damping

Data Source

PatentUS9410662B2Arrangement for mounting an optical element, in particular in an EUV projection exposure apparatus

Publication Date: 2016.08.09 CARL ZEISS SMT GMBH

AI summary

The invention relates to an arrangement for mounting an optical element, in particular in an EUV projection exposure apparatus, comprising at least one actuator which exerts a controllable force on the optical element; wherein between the actuator and the optical element a mechanical coupling in the form of a pin is embodied in such a way that, relative to the drive axis of the actuator, the ratio of the stiffness of the mechanical coupling in an axial direction to the stiffness in a lateral direction is at least 100; and at least one damping element which brings about a damping of a natural vibration form of the pin in a lateral direction.