Mirror Tilting Regulation via High-Frequency Modulation
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Solution Overview
Problem
Existing optical components with displaceable mirrors face challenges in efficiently regulating tilting movements, leading to mechanical excitation and noise interference, particularly when dealing with large numbers of mirror elements in projection exposure systems for microlithography.
Innovation Solution
A high-frequency modulation signal is applied to the mirror or actuator electrodes, decoupling mechanical excitation and improving signal-to-noise ratios by using a signal generator connected to actuator electrodes, which also function as sensors, allowing for negligible mechanical excitation and enhanced capacitive detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a modulation signal is applied to actuator electrodes for regulating mirror tilting, then the signal-to-noise ratio of capacitive detection is improved, but mechanical excitation of the mirror element increases
Solution Approach 1:
The patent applies a modulation signal with frequency above the resonant frequency of the mirror element (at least one decade above) to the actuator electrodes. This parameter change in signal frequency improves the signal-to-noise ratio of capacitive detection while minimizing mechanical excitation, as the high-frequency signal does not resonate with the mirror's natural frequency.
Solution Approach 2:
The patent uses periodic modulation signals (sinusoidal or square wave) applied to the actuator electrodes for capacitive detection. This periodic action at high frequency enables reliable detection of mirror position and disturbances while the symmetry of application to opposing electrodes ensures mechanical excitations cancel out.
2Stability of the object's composition
If two actuator electrodes are connected in parallel to reduce mechanical excitation, then symmetry with respect to tilting axis is improved, but device complexity increases
Solution Approach 1:
The patent employs a symmetric arrangement of actuator electrodes with respect to the tilting axis, with two electrodes positioned symmetrically on opposite sides of the axis. This symmetric configuration ensures that mechanical excitations from the modulation signal cancel out, minimizing mirror element vibration while maintaining simple control circuitry.
3Measurement precision
If high-frequency modulation signal is used for capacitive detection, then detection precision is improved, but energy consumption increases
Solution Approach 1:
The patent uses high-frequency modulation signals (at least one decade above resonant frequency, e.g., 100 Hz to 50 kHz or higher) for capacitive detection of mirror position and disturbances. This high-frequency parameter change significantly improves the signal-to-noise ratio and detection precision while the symmetric electrode configuration minimizes energy waste through canceling mechanical excitations.
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 approach reduces mechanical excitation and enhances the signal-to-noise ratio, enabling precise regulation of mirror tilting with minimal disturbance, particularly suitable for large arrays of mirror elements in projection exposure systems.
Implementation Method 1
The signal-to-noise ratio of a capacitive detection of disturbances of the tilting of the mirror element can be considerably improved by means of the high-frequency modulation signal. In this case, the invention makes use of the fact that the capacitive reactance decreases as the frequency increases.
Implementation Method 2
The modulation signal has a frequency above a resonant frequency of the mirror element. It has, in particular, a lower limit frequency which lies at least one decade, in particular at least two decades, above the resonant frequency of the mirror element. Such frequencies are also designated hereinafter as high-frequency. This ensures that the modulation signal leads at most to a negligible mechanical excitation of the mirror element.
Data Source
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AI summary
An optical component (25) comprises a carrying structure (19), at least one mirror element (23) which is mounted in a tiltable manner relative to the carrying structure (19) by an actuator system and which comprises at least one mirror electrode (22; 37), at least one local regulating device (30) for regulating the tilting of the mirror element (23), having at least one capacitive sensor and at least one actuator electrode (24) for tilting the mirror element (23), and a signal generator (39) for generating a modulation signal, having a frequency above a resonant frequency of the mirror element (23), wherein the signal generator (39) is connected in a signal-transmitting manner to the at least one mirror electrode (22; 37).