Compensated Filter Assembly for Vibration-Sensitive Position Control
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Solution Overview
Problem
In EUV projection exposure apparatuses, mechanical vibrations cause instability and image errors due to relative movements between mirrors, and existing filtering methods to suppress unwanted vibrations introduce delays that lead to low-frequency errors, complicating reliable position control.
Innovation Solution
A filter arrangement combining multiple filters, including low-pass and inverse low-pass filters, notch and inverse notch filters, to compensate for signal delays and suppress unwanted components without increasing amplitude in relevant frequency ranges, allowing for reliable position control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a filter is used to suppress high-frequency components in the reference mirror's movement signal, then unwanted vibrations are reduced, but signal delay increases causing low-frequency errors
Solution Approach 1:
The filter is segmented into multiple independent filter sections (first filter section, second filter section, third filter section) with different characteristics. Each section processes specific frequency components independently, allowing the system to suppress high-frequency vibrations while minimizing delay in low-frequency components through selective filtering rather than uniform filtering across all frequencies.
Solution Approach 2:
The filter parameters are specifically optimized to balance suppression and delay characteristics. The first filter section has a corner frequency of 100-500 Hz with damping factor 0.6-1.4, the second section has corner frequency 50-200 Hz with damping factor 0.8-1.6, and the third section has corner frequency 20-100 Hz with damping factor 1.0-2.0. These parameter variations allow different frequency ranges to be handled with appropriate filtering strength, reducing overall signal delay while maintaining vibration suppression.
2Reliability
If filtering is applied to suppress vibrations in the reference mirror, then positional stability improves, but image errors increase due to delayed control response
Solution Approach 1:
The control system is segmented into multiple independent control loops: a first control loop controls the reference mirror with filtering to ensure stability, while second control loops control the other mirrors with follow-up control to the reference mirror. This segmentation allows the reference mirror to be stabilized without introducing delays that would affect the precision of the other mirrors, as each mirror's position is independently controlled based on its own error signal.
Solution Approach 2:
The system implements feedback control where the measured position of each mirror is compared with the desired position to generate an error signal. This error signal is then processed through the segmented filter and controller to generate correction commands. The feedback mechanism ensures that any delays introduced by filtering are compensated by continuous error correction, maintaining image quality while achieving control stability.
3Ease of operation
If the reference mirror is difficult to control due to dynamic properties, then follow-up control becomes necessary, but filtering the reference signal introduces delays that defeat the purpose of real-time control
Solution Approach 1:
The control architecture is segmented such that the reference mirror operates in a first control loop with optimized filtering for stability, while the other mirrors operate in separate second control loops with follow-up control. This segmentation allows each mirror to be controlled independently with appropriate filtering characteristics, preventing the delays from propagating through the entire system and enabling real-time control of each element.
Solution Approach 2:
The filter characteristics are made dynamically adapted to the specific mirror being controlled. Each mirror's filter parameters (corner frequency and damping factor) are selected based on its dynamic properties and control requirements. This dynamic optimization ensures that each mirror receives appropriate filtering for stability without excessive delay, maintaining real-time controllability despite the inherent difficulties of controlling difficult-to-control mirrors.
Data Source
AI summary
A filter assembly, for example for a control loop for controlling the position of at least one element, comprises first and second filters. The first filter suppresses an undesired component in a signal to be filtered. The first filter produces a first signal delay in a first frequency range. The second filter produces a second signal delay in the first frequency range. The second signal delay at least partly compensates the first signal delay.