Capacitive Sensor Thin Film Guard Electrode Design
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Solution Overview
Problem
Existing capacitive sensors for lithography machines are large, leading to positioning errors and reduced spatial resolution due to their size, requiring complex and costly manufacturing processes, and necessitate frequent recalibration due to wiring capacitance issues.
Innovation Solution
A capacitive sensing system with a thin film structure, where each sensor has a separate sensing electrode and a back guard electrode formed in the same plane, eliminating the need for separate side guard electrodes and simplifying the manufacturing process, and utilizing a triaxial cable for electrical connections to reduce capacitance interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional capacitive sensors with side guard electrodes are used, then the electric field can be confined within the sensing area, but the sensor height and width increase to about 20 mm, causing positioning errors and reduced spatial resolution
Solution Approach 1:
The patent moves the guard electrode from the front surface to the back surface of the insulating layer, utilizing the third dimension (depth/thickness) to resolve the contradiction. This allows the guard electrode to surround the sensing electrode's projection area without increasing the sensor's front-facing height or width, thereby maintaining positioning accuracy while reducing the dimensions that cause manufacturing and alignment errors.
Solution Approach 2:
The patent uses a thin insulating layer (25-100 μm thick) to separate the sensing electrode from the back guard electrode. This thin film structure enables the guard electrode to be positioned on the back surface while maintaining effective electric field confinement, significantly reducing the sensor's overall height compared to conventional designs that require side guard electrodes extending from the front surface.
2Ease of manufacture
If sensors are spaced further apart to accommodate their size, then manufacturing and assembly become easier, but spatial resolution decreases and measurement speed reduces
Solution Approach 1:
The thin film construction (25-100 μm insulating layer) enables compact sensor design with reduced dimensions. Multiple sensors can be densely spaced on the substrate without overlapping, allowing high spatial resolution while maintaining ease of manufacture through simple lamination processes. The thin structure facilitates close spacing of multiple sensors to achieve high measurement speeds across large wafer surfaces.
Solution Approach 2:
The patent divides the measurement function into multiple independent sensor elements that can be arranged in arrays. Each sensor is a simple two-electrode unit (sensing electrode on front, back guard electrode on back), allowing modular assembly and dense packing. This segmentation enables parallel measurement across multiple locations, significantly increasing productivity while keeping individual sensor manufacturing simple.
3Reliability
If complex wiring connections are made to connect sensing and guard electrodes, then electrical connectivity is achieved, but capacitance interference increases requiring frequent recalibration
Solution Approach 1:
The patent combines the sensing electrode and back guard electrode into a single integrated sensor unit manufactured on one side of the substrate. This merging eliminates the need for complex wiring connections between separately mounted components. The electrical connections are made to adjacent contact pads on the same substrate, minimizing parasitic capacitance and eliminating the need for frequent recalibration due to wiring interference.
Solution Approach 2:
The patent extracts the guard electrode function from the front surface assembly and places it on the back surface of the substrate. This separation allows the sensing electrode to have direct, simple electrical connections without requiring wiring to reach around to guard electrodes. The back guard electrode is independently connected to the signal processing system, eliminating capacitance interference from complex inter-electrode wiring.
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
The solution results in a more accurate, compact, and cost-effective capacitive sensor system with reduced calibration needs, improving spatial resolution and measurement speed, and minimizing errors caused by sensor positioning variations.
Implementation Method 1
capacitive sensor for measuring distance... measures the height of the wafer surface, e.g. the distance between the projection lens and the wafer surface
Implementation Method 2
The guard electrode 3 is set at the same potential as the sensing electrode to confine the electric field within the sensing area to generate a relatively uniform electric field between the sensing electrode 2 and the target 9
Data Source
Figure 1A~2
Figure 3~5
Figure 6A~6D
AI summary
A capacitive sensing system, comprising a sensor (30) having thin film structure, the thin film structure comprising a sensor having a first insulating layer (34) and a first conductive film comprising a sensing electrode (31) formed on a first surface of the first insulating layer (34) and a second conductive film comprising a back guard electrode (35). The back guard electrode may be formed in a single plane and comprise a peripheral portion in the same plane, and is disposed on a second surface of the first insulating layer (34) and a first surface of a second insulating layer (43) or protective layer (38). The peripheral portion of the back guard electrode may extend beyond the sensing electrode (31) to form a side guard electrode which substantially or completely surrounds the sensing electrode.