Melt Surface Distance Measurement Using Magnetic Damping and Image Segmentation
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Solution Overview
Problem
Existing methods for determining the distance between a reference member and a melt surface in the Czochralski process struggle with precision due to surface vibration and brightness fluctuations, especially when growing large-diameter silicon crystals, leading to inaccurate control of the crystal temperature gradient and increased defects in silicon wafers.
Innovation Solution
Applying a magnetic field to reduce melt surface vibration, processing separate images of the reference member and its reflection to set optimal binarization levels, and calculating the relative distance between the reference member and the melt surface using a detector and calculator, allowing for precise control of the distance between the reference member and the heat insulating member.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a magnetic field is applied to reduce melt surface vibration, then measurement stability is improved, but device complexity increases
Solution Approach 1:
A magnetic field is introduced as an intermediary to suppress melt surface vibration. The magnetic field acts as a mediator between the melt surface and the measurement system, stabilizing the surface without direct mechanical contact. This resolves the contradiction by using a field-based intermediary to improve measurement stability while avoiding complex mechanical vibration control mechanisms.
2Measurement precision
If separate image processing is used to set optimal binarization levels, then measurement accuracy is improved, but processing complexity increases
Solution Approach 1:
The image processing is segmented into separate handling of the reference member image and its reflection image. Each image is processed independently with its own optimized binarization level, allowing precise distance measurement. This segmentation approach improves accuracy by treating each image component separately while the modular processing structure manages complexity systematically.
Solution Approach 2:
The binarization levels are made dynamic and adaptive rather than fixed. The system automatically determines optimal binarization levels for each image based on actual image characteristics, allowing the processing parameters to adapt to varying conditions. This dynamic adjustment improves measurement accuracy across different operating conditions.
3Manufacturing precision
If the distance between melt surface and heat insulating member is controlled with very high precision, then crystal quality is improved, but control difficulty increases
Solution Approach 1:
A feedback control system is implemented using optical measurement of the distance between the melt surface and heat insulating member. The measured distance is fed back to automatically adjust the crucible position, maintaining the optimal distance without manual intervention. This feedback mechanism achieves high precision control while simplifying operation by automating the adjustment process.
Solution Approach 2:
Manual or mechanical distance adjustment is replaced with an automated control system based on optical measurement and automatic positioning. The mechanical control difficulty is substituted with an automated system that uses optical feedback to maintain precise distance control, improving both precision and ease of operation.
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 method stabilizes the determination of the melt surface location and maintains precise control of the distance, resulting in improved crystal quality and reduced defects by accurately controlling the axial temperature gradient during silicon single crystal growth.
Implementation Method 1
pulling the silicon single crystal applying a magnetic field
Implementation Method 2
the vibration of the melt surface can be sufficiently reduced
Implementation Method 3
a picture of a real image of the reference member and a mirror image of the reference member reflected on the melt surface is taken
Data Source
AI summary
The present invention is a method for determining a relative distance between a reference member placed above a melt surface and the melt surface upon pulling a silicon single crystal out of a raw material melt in a crucible by a CZ method characterized by at least: pulling the silicon single crystal applying a magnetic field; taking a picture of a real image of the reference member and a mirror image of the reference member reflected on the melt surface with a detector; processing the picture taken of the real image and the mirror image of the reference member as different pictures by separating the picture taken; and calculating the relative distance between the real image and the mirror image of the reference member from the processed pictures to determine the relative distance between the reference member and the melt surface. This provides a method for determining the distance between the reference member and the melt surface that makes it possible to determine the relative distance between the reference member and the melt surface more stably and more accurately.