Heat Shield Gap Measurement for Czochralski Silicon Melt Control
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Solution Overview
Problem
Existing methods for measuring and controlling the distance between the lower end surface of a heat shielding member and the surface of a raw material melt in the Czochralski method are inaccurate, especially under conditions of strong radiant light or melt surface vibration, leading to inconsistent crystal quality and productivity.
Innovation Solution
A method involving a heat shielding member with a through-hole is used to measure the distance by observing the mirror image of the through-hole with a fixed point observation apparatus, allowing for precise measurement and control of the distance between the heat shielding member and the melt surface, even under strong radiant light conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a criterion reflector is provided to measure the distance between the heat shielding member and melt surface, then the distance measurement precision is improved, but the measurement reliability deteriorates under strong radiant light conditions
Solution Approach 1:
The invention applies a reflective tape (criterion reflector) with high reflectivity to the heat shielding member. The reflector creates a bright mirror image against the dark background of the melt surface, enabling clear detection even under strong radiant light conditions. The high reflectivity of the tape ensures that the mirror image remains distinguishable from surrounding elements despite the intense thermal radiation environment.
Solution Approach 2:
The invention introduces a magnetic field as an intermediary to suppress melt surface vibration. By applying a magnetic field to the conductive melt, the surface tension is enhanced and vibrations are damped, creating a more stable mirror image for measurement. This intermediary field resolves the contradiction by stabilizing the measurement reference without affecting the optical detection capability.
2Ease of operation
If the melt surface position is allowed to vary naturally, then the ease of operation is improved, but the manufacturing precision deteriorates
Solution Approach 1:
The invention implements a feedback control system where the distance between the heat shielding member and melt surface is continuously measured using the mirror image method. The measured distance is fed back to the control system, which automatically adjusts the heat shielding member position to maintain the predetermined optimal distance. This feedback mechanism enables precise distance control while maintaining operational simplicity through automation.
Solution Approach 2:
The invention replaces manual mechanical adjustment of the heat shielding member position with an automated control system. The control system uses optical measurement (mirror image detection) and automatic actuation to maintain the predetermined distance, eliminating the need for manual intervention while achieving higher precision than manual methods could provide.
3Productivity
If the crystal growth rate is increased, then the productivity is improved, but the manufacturing precision of crystal quality deteriorates
Solution Approach 1:
The invention uses feedback control to maintain the optimal distance between the heat shielding member and melt surface throughout the crystal growth process. This precise distance control ensures a stable temperature gradient at the crystal-melt interface, allowing faster growth rates while preventing defects that would normally occur at higher growth speeds. The feedback system dynamically adjusts parameters to maintain quality standards even at increased productivity levels.
Solution Approach 2:
The invention optimizes the distance parameter between the heat shielding member and melt surface to achieve the best balance between growth rate and crystal quality. By precisely controlling this distance parameter, the temperature gradient is optimized to support faster crystal growth while maintaining the conditions necessary for defect-free crystal formation. This parameter optimization enables higher productivity without sacrificing manufacturing precision.
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 enables stable and accurate measurement and control of the distance, resulting in precise control of the crystal axis temperature gradient and high-quality silicon single crystal production at high productivity.
Implementation Method 1
when a silicon single crystal is pulled by the Czochralski method while a magnetic field is applied to the raw material melt in a crucible
Implementation Method 2
forming a through-hole in the lower end surface of the heat shielding member; actually measuring the distance between the lower end surface of the heat shielding member and the surface of the raw material melt, and observing a position of a mirror image of the through-hole with a fixed point observation apparatus
Data Source
AI summary
A method for measuring distance between lower end surface of heat shielding member and surface of raw material melt, the method including providing the member being located above the melt, when a silicon single crystal is pulled by the Czochralski method while a magnetic field is applied to the melt in a crucible, the method including: forming a through-hole in the member; measuring distance between the member and the melt surface, and observing position of mirror image of the through-hole with fixed point observation apparatus, the mirror image being reflected on the melt surface; then measuring a moving distance of the mirror image, and calculating distance between the member and the melt surface from a measured value and the moving distance of the mirror image, during the pulling of the crystal. The distance between the member and the melt can be precisely measured by the method.