MEMS Mirror Shielding Plate for Accurate Tilt Angle Sensing
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Solution Overview
Problem
The use of MEMS mirrors in EUV lithography apparatuses is hindered by temporally and spatially varying current flows due to electron emission from mirror surfaces, which disturb the monitoring of tilt angles and affect the precision of micromirror positioning.
Innovation Solution
Incorporating an electrically conductive shielding plate under the mirror plate to reduce capacitive coupling between the mirror plate and the capacitive sensor, along with dedicated grounding to manage electron discharge, thereby improving the precision of tilt angle detection and control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitive sensor with electrodes is used to detect the tilt angle of the mirror plate, then the tilt angle can be monitored, but electron-induced current flows disturb the measurement precision
Solution Approach 1:
A capacitive sensor with multiple electrodes is introduced as an intermediary measurement device to detect the tilt angle of the mirror plate without direct electrical contact. The sensor measures changes in capacitance caused by mirror displacement, thereby avoiding direct interference from electron-induced currents while still enabling precise tilt angle monitoring
Solution Approach 2:
The harmful electron-induced current flows are extracted and separated from the measurement circuit by using the capacitive sensor's electrodes as distinct measurement points. The current disturbances are isolated to specific regions while the capacitance measurement remains unaffected, allowing accurate tilt detection despite the presence of electron currents
2Manufacturing precision
If the mirror plate is made manipulable in six degrees of freedom for precise positioning, then positioning accuracy is improved, but device complexity increases
Solution Approach 1:
Multiple actuators for controlling six degrees of freedom are integrated into a unified MEMS structure where the mirror plate, carrier plate, and actuators form a single manufactured component. This merging reduces assembly complexity while maintaining the capability for precise six-degree-of-freedom positioning
Solution Approach 2:
A capacitive sensor system with multiple electrodes provides real-time feedback on the mirror plate's position and tilt angle. This feedback enables closed-loop control of the six actuators, allowing the system to achieve and maintain precise positioning despite the increased complexity of having multiple degrees of freedom
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
Enhances the precision of micromirror positioning by minimizing disturbances from electron-induced current flows, allowing for more accurate control of MEMS mirrors in EUV lithography systems.
Implementation Method 1
a capacitive sensor having a number of electrodes for detecting the tilt angle of the mirror plate
Implementation Method 2
an electrically conductive shielding plate is arranged under the mirror plate in order to reduce a capacitive coupling between the mirror plate and the electrodes of the capacitive sensor
Implementation Method 3
radiation (also referred to as operating light, for example EUV light) is incident on the surface of the micromirror and is reflected there
Implementation Method 4
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 MEMS mirror for a lithography system, comprising: a mirror plate which can be displaced about a tilt angle; a carrier plate for carrying the mirror plate; a base plate; a solid-body joint, coupling the base plate and the carrier plate, for tilting the mirror plate; and a capacitive sensor having a number of electrodes for detecting the tilt angle of the mirror plate. An electrically conductive shield plate for reducing a capacitive coupling between the mirror plate and the electrodes of the capacitive sensor is arranged under the mirror plate.