Eddy Current Sensor Placement for Wafer Edge Thickness Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional eddy current sensors have limitations in measuring film thickness in narrow ranges due to wide spot diameters and weak magnetic flux, making it difficult to accurately control film thickness, especially near the edges of semiconductor wafers, where film thickness variations are common.
Innovation Solution
The polishing apparatus incorporates an eddy current sensor arranged inside a projection member on the polishing table, reducing the distance to the wafer and minimizing interference with the polishing pad, allowing for precise film thickness measurement in narrower ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional eddy current sensor with a large sensor coil diameter is used, then the magnetic flux is strong enough to form eddy currents on the substrate, but the spot diameter becomes wide (not less than approximately 20 mm), making it difficult to measure film thickness in narrow ranges and reducing detection accuracy at edge portions
Solution Approach 1:
The patent applies local quality by creating a non-uniform magnetic flux distribution through the specific coil configuration. The coil is designed with multiple turns having different diameters and positions, creating a concentrated magnetic flux path that generates a small spot diameter (less than 20 mm) while maintaining sufficient flux density for accurate eddy current formation and film thickness measurement at specific locations including edge portions
2Area of stationary object
If the sensor coil diameter is reduced to measure film thickness in narrow ranges, then the spot diameter becomes smaller for better edge portion detection, but the distance from the sensor to the film becomes too small, making it difficult to form eddy currents due to the polishing pad thickness
Solution Approach 1:
The patent resolves this contradiction by transitioning from a single-plane coil design to a three-dimensional coil structure with multiple turns at different heights and radial positions. This dimensional approach allows the magnetic flux to penetrate through the polishing pad thickness effectively while maintaining a concentrated spot diameter, enabling reliable eddy current formation at the substrate surface despite the reduced sensor-to-film distance
3Reliability
If the distance from the eddy current sensor to the film is increased to accommodate the polishing pad thickness, then eddy currents can be formed on the substrate, but the magnetic flux spreads out and the spot diameter becomes larger, reducing detection accuracy
Solution Approach 1:
The patent applies segmentation by dividing the coil into multiple discrete turns with different diameters and positions. This segmented structure creates multiple concentrated magnetic flux paths that collectively form a small spot diameter on the substrate. The segmentation allows the magnetic flux to maintain its concentration throughout the polishing pad thickness, preventing flux spreading while ensuring reliable eddy current formation
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 enhances the detection accuracy of film thickness in narrow ranges, improving the ability to detect residual films and control film thickness variations near the edges of semiconductor wafers, reducing the need for height adjustments during pad changes and maintaining consistent sensitivity.
Implementation Method 1
an eddy current type end point detection sensor (hereinafter, referred to as an 'eddy current sensor')
Data Source
AI summary
The polishing apparatus has: a polishing pad that has a polishing surface to polish a semiconductor wafer; a polishing table to which a back surface of the polishing pad on an opposite side of the polishing surface can be attached; a top ring that is opposed to the polishing surface, and can hold the semiconductor wafer; and an eddy current sensor that is arranged in the polishing table, and detects an end point of polishing. The polishing table has on an attachment surface a projection member projecting from the attachment surface to which the polishing pad is attached. The back surface of the polishing pad has a concave portion in a portion opposed to the projection member, and at least a part of the eddy current sensor is arranged inside the projection member.