Liquid Level Measurement in Czochralski Crystal Pulling
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Solution Overview
Problem
Existing methods for measuring the liquid level in a Czochralski method-based single crystal pulling apparatus face challenges in selecting the optimal reflection method due to varying gaps between the single crystal and the heat shield, affecting beam reception probability and requiring either high laser power or increased influence from the inclined portion of the melt surface.
Innovation Solution
A method that determines the gap between the single crystal and the heat shield, selects an optimal reflection method from multiple options based on pre-created information associating each gap with suitable reflection methods, and adjusts the measurement accordingly to ensure reliable and stable liquid level measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gap between the single crystal and the heat shield is large, then the beam reception probability is improved, but the measurement precision deteriorates due to increased influence from the inclined portion of the melt surface
Solution Approach 1:
The system dynamically selects between direct reflection method and return reflection method based on the real-time gap value. When the gap is large, direct reflection method is selected to maintain measurement precision. When the gap is small, return reflection method is selected to improve beam reception probability. This dynamic adaptation resolves the contradiction by optimizing the measurement method according to operating conditions.
Solution Approach 2:
The invention changes the measurement parameter (reflection method) based on the gap parameter. By establishing a relationship between gap size and optimal reflection method, the system can adaptively adjust the measurement approach to maintain both beam reception probability and measurement precision across different operating conditions.
2Measurement precision
If the gap between the single crystal and the heat shield is small, then the measurement precision is improved, but the beam reception probability deteriorates
Solution Approach 1:
The system dynamically switches between direct reflection method and return reflection method based on the gap value. When the gap is small, the return reflection method is selected which uses the heat shield rim as an intermediate reflection surface, thereby improving beam reception probability while maintaining acceptable measurement precision through the triangulation principle.
Solution Approach 2:
The heat shield rim acts as an intermediary reflection surface in the return reflection method. The laser beam reflects from the melt surface to the heat shield rim and then to the detector, which improves beam reception probability when the gap is small by providing an additional stable reflection path that is less sensitive to melt surface inclination.
3Reliability
If the laser power is increased to improve beam reception probability, then the reliability is improved, but the energy consumption increases
Solution Approach 1:
Instead of changing laser power, the invention changes the measurement method parameter (reflection type) to optimize beam reception. By selecting appropriate reflection method based on gap conditions, the system achieves reliable measurement without increasing energy consumption, thus resolving the contradiction between reliability and energy use.
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
Enables reliable and stable measurement of the liquid level by selecting the optimal reflection method based on the determined gap, improving beam reception probability and reducing the impact of the inclined portion, thus ensuring accurate control of the single crystal growth process.
Implementation Method 1
a laser beam emitted by a laser beam source is projected onto a melt surface, the laser beam reflected on the melt surface is received, and the liquid level of the melt surface is measured based on the principle of triangulation
Data Source
AI summary
Provided is a method for reliably and easily measuring a liquid level by selecting an optimal reflection method from among a plurality of reflection methods, depending on growing conditions of a pulled single crystal. The method comprises: setting a plurality of measuring methods having different ways of determining the liquid level; creating, in advance, information that associates with a gap between the outer peripheral face of the single crystal and a predetermined position located between a heat shield and the outer peripheral face of the single crystal; determining the gap in accordance with manufacturing conditions; selecting a measuring method associated to the determined gap, on the basis of the information; and measuring the liquid level of a melt surface in use of the selected measuring method.