Active-Isolation Mounts for Optical Elements Using Non-Contacting Actuators

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Solution Overview

Problem

Piezoelectric transducer (PZT) actuators in EUV microlithography systems face challenges such as high stiffness, continuous energization leading to vibration transmission, and introduction of additional vibrational modes, making it difficult to isolate optical elements from high-frequency disturbances.

Innovation Solution

The use of non-contacting electromagnetic actuators like voice-coil motors and EI-core actuators, combined with displacement sensors and a servo-control loop, allows for precise movement of optical elements relative to the frame without physical contact, thereby isolating them from vibrations and eliminating additional vibrational modes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If piezoelectric transducer actuators are used to mount optical elements, then precise positioning control is achieved, but high stiffness and continuous energization cause vibration transmission to the optical element

Engineering Contradiction:

Improvepositioning precisionVSAvoidvibration transmission

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent replaces piezoelectric transducer actuators with electromagnetic actuators (voice coil motors or EI-core actuators). This substitution changes the actuation mechanism from piezoelectric expansion/contraction to electromagnetic force generation, eliminating the stiffness and continuous energization issues while maintaining precise positioning control through servo feedback

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The electromagnetic actuators are energized only when correction is needed, rather than continuously as with piezoelectric transducers. The servo control system activates the actuators periodically or intermittently based on feedback from displacement sensors, reducing vibration transmission while maintaining positioning precision

Inventive Principle:

Principle #19Periodic action

2Measurement precision

If piezoelectric transducer actuators are used, then positioning control is provided, but additional vibrational modes are introduced that interfere with optical element stability

Engineering Contradiction:

Improvepositioning controlVSAvoidvibrational modes

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the fundamental operating parameters of the actuator system by switching from piezoelectric materials to electromagnetic actuators. This parameter change eliminates the introduction of additional vibrational modes while preserving positioning control capabilities through the servo system

Inventive Principle:

Principle #35Parameter changes

3Stability of the object's composition

If rigid mounting is used to hold optical elements, then stable positioning is achieved, but vibration isolation from the support structure is reduced

Engineering Contradiction:

Improvepositioning stabilityVSAvoidvibration transmission

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The patent transitions from rigid static mounting to dynamic active isolation mounting. The electromagnetic actuators continuously adjust the optical element's position based on feedback from displacement sensors, providing both stability and vibration isolation by actively compensating for disturbances rather than passively resisting them

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent introduces active isolation mounts as an intermediary between the optical element and the support structure. These mounts include electromagnetic actuators and displacement sensors that mediate the connection, allowing the optical element to be isolated from vibrations while maintaining stable positioning through active control

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

This solution effectively reduces the transmission of disturbances to optical elements, improving image quality by maintaining precise positioning and reducing vibrational interference, even at high frequencies.

Implementation Method 1

non-contacting electromagnetic actuators like voice-coil motors and EI-core actuators

Methodology Applied

Scientific EffectElectromagnetic force: Lorentz Force

Implementation Method 2

At least one displacement sensor is associated with each respective location on the optical element. The displacement sensors are sensitive to displacements of the respective locations

Methodology Applied

Scientific EffectDisplacement sensing: Accelerometer

Data Source

PatentUS7989756B2Active-isolation mounts for optical elements

Publication Date: 2011.08.02 NIKON CORP

AI summary

Disclosed are, inter alia, optical components that include an optical element (e.g., mirror) and at least three active-isolation mounts mounting the optical element to a frame (e.g., optical barrel or optical frame). An active-isolation mount has a non-contacting actuator connecting a respective location on the optical element to the frame and provides movability of the respective location relative to the frame in at least one direction. At least one displacement sensor is associated with each respective location on the optical element. The displacement sensors are sensitive to displacements of the respective locations in at least one respective direction and reference the displacements to an absolute reference. The actuators and sensors are connected to a servo control loop to provide feedback control.