Eddy Current Sensor Core Layout for Wafer Edge Film Thickness
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Solution Overview
Problem
Existing eddy current sensors face challenges in accurately measuring film thickness at the edges of semiconductor wafers due to their elongated rectangular shape, which makes it difficult to enter and exit the wafer perpendicularly, leading to inaccurate detection signals and reduced detection accuracy in the edge regions.
Innovation Solution
The design incorporates a core with a base portion and outer legs where the length in one direction is not less than the length in a direction orthogonal to it, allowing for a shorter path when entering or exiting obliquely, and an E-shaped core with a middle leg and side legs to enhance detection accuracy by intensifying the magnetic field and reducing the distance required for signal rise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the outer diameter of the eddy current sensor is reduced to enhance detection accuracy in edge regions, then the moving distance required for the sensor to enter/exit the wafer is shortened, but the detection output of the eddy current is reduced due to smaller sensor area
Solution Approach 1:
The patent applies this principle by using a ferrite core (magnetic material) combined with a coil structure. The ferrite core concentrates and intensifies the magnetic field generated by the coil, thereby enhancing the eddy current detection output without requiring a larger sensor outer diameter. This composite structure allows the sensor to maintain small size for accurate edge region detection while achieving sufficient detection signal strength through magnetic field intensification.
2Shape
If the sensor enters the wafer obliquely due to elongated rectangular shape, then the sensor cannot be perpendicular to the wafer surface, but the distance required for the sensor to fully enter/exit the wafer increases
Solution Approach 1:
The patent applies this principle by designing the ferrite core with an asymmetric cross-sectional shape where one dimension (width) is smaller than the other dimension (length). By orienting the smaller dimension perpendicular to the wafer surface, the sensor achieves proper perpendicular alignment during oblique entry/exit motion. This asymmetric geometry reduces the effective moving distance required for the sensor to fully enter or exit the wafer compared to a symmetric elongated rectangular shape.
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 configuration improves the detection accuracy of film thickness in the edge regions by shortening the distance needed for signal rise and reducing the range of inaccurate detection, allowing for more precise polishing control.
Implementation Method 1
an excitation coil that is arranged on the core and forms an eddy current in the conductive film
Implementation Method 2
a detection coil that is arranged on the core and detects the eddy current formed in the conductive film
Implementation Method 3
it is effective to increase the outer diameter of the eddy current sensor so that a large eddy current is generated in the conductive film to increase the detection output of the eddy current
Data Source
AI summary
The eddy current sensor for measuring the film thickness of a conductive film formed on a substrate includes a core made of a magnetic material that has a base portion, and outer legs provided to the base portion at both end portions in a first direction of the base portion respectively, an excitation coil that is arranged on the core and forms an eddy current in the conductive film, and a detection coil that is arranged on the core and detects the eddy current formed in the conductive film. The length of the base portion in the first direction is not less than the length of the base portion in a second direction that is substantially orthogonal to the first direction.