MEMS Mirror Tilt Sensing With Opposite-Polarity Capacitive Signals
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Solution Overview
Problem
The emission of electrons from MEMS mirrors in EUV lithography apparatuses due to EUV radiation causes temporally and spatially varying current flows, significantly disturbing the monitoring of the tilt angle of the mirrors, which affects the precision of the control loop for micromirrors.
Innovation Solution
A lithography apparatus with a capacitive sensor having four sensor units per tilt axis, where two pairs of sensor units are excited with opposite polarity signals, and a differential evaluation unit subtracts these signals to cancel out disturbances, allowing precise determination of the mirror's position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If MEMS mirrors are used in EUV lithography apparatus, then installation space is reduced, but measurement precision of tilt angle deteriorates due to disturbing current flows
Solution Approach 1:
The patent converts the harmful photoelectric effect into a beneficial measurement mechanism. By using the EUV radiation-induced current flows as the measurement signal itself in a capacitive sensor, the disturbing effect becomes the basis for precise tilt angle detection. The evaluation unit processes these current flows to determine mirror position, transforming the disturbance into useful information.
Solution Approach 2:
The patent introduces a capacitive sensor with electrode structures as an intermediary between the MEMS mirror and the measurement system. This sensor mediates the measurement of tilt angles by detecting changes in capacitance caused by mirror displacement, providing precise measurement without direct interference from the photoelectric current flows on the mirror surface.
2Device complexity
If conventional capacitive sensors are used on MEMS mirrors, then device complexity is reduced, but measurement precision deteriorates due to radiation-induced current disturbances
Solution Approach 1:
The patent transforms the harmful radiation-induced current flows into the measurement mechanism itself. The capacitive sensor electrodes are designed to detect these current flows and convert them into useful measurement signals for determining mirror tilt angle, making the previously disturbing effect the basis for precise measurement.
Solution Approach 2:
The patent changes the measurement parameter from direct capacitance measurement to current flow detection. By monitoring the radiation-induced current flows in the capacitive sensor electrodes and processing these signals through an evaluation unit, the system achieves precise tilt angle measurement while maintaining simple device structure.
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 significantly reduces disturbances caused by EUV radiation, enabling more precise control of the micromirrors and improving the control loop for MEMS mirrors.
Implementation Method 1
a capacitive sensor having a number of electrodes for capturing the tilt angle
Implementation Method 2
The photons from the EUV radiation source in the lithography apparatus may trigger the emission of electrons from the mirror surfaces of the MEMS mirrors as a result of the photoelectric effect
Data Source
AI summary
A lithography apparatus comprises: a radiation source for creating radiation with a specific repetition frequency; and a MEMS mirror which is displaceable through a tilt angle in at least two tilt axes and serves to guide the radiation in the lithography apparatus. The mirror comprises a capacitive sensor comprising electrodes that capture the tilt angle. Four sensor units are provided per tilt axis for capturing a respective measurement signal from the capacitive sensor. A first pair of the sensor units excites the capacitive sensor with a first excitation signal and receives as a response a respective measurement signal. A second pair of the sensor units excites the capacitive sensor with a second excitation signal and receives as a response a respective measurement signal. The first and second excitation signals have opposite polarities. An evaluation unit determines the position of the MEMS mirror using the measurement signals.