Silicon Melt Level Measurement via Mirror Image
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Solution Overview
Problem
Conventional silicon single crystal pull-up apparatuses face challenges in precisely measuring the liquid surface level of silicon melt due to distortion caused by the cylindrical purging tube, which affects the stability of dopant concentration and resistivity distribution in the pull-up direction.
Innovation Solution
A silicon single crystal pull-up apparatus that includes a camera to photograph the mirror image of a thermal radiation shield reflected on the silicon melt through a purging tube, with a liquid surface level calculator using a conversion table to accurately determine the liquid surface level, minimizing distortion influence and enabling precise control of the crucible height.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a cylindrical purging tube is used to straighten the purge gas flow, then the gas straightening effect is improved, but the image distortion increases making liquid surface level measurement difficult
Solution Approach 1:
A flat plate is introduced as an intermediary component at the observation position of the purging tube. This flat plate serves as a reference object that reflects light from the liquid surface, allowing the camera to capture the liquid surface image through the purging tube without being affected by the tube's cylindrical distortion. The flat plate mediates between the distorted optical path and the measurement requirement.
Solution Approach 2:
The invention uses optical reflection properties (analogous to color changes) by utilizing the flat plate's reflective surface to create a clear optical path. The flat plate reflects light from the liquid surface in a controlled manner, enabling the camera to capture undistorted or correctable images of the liquid surface level despite viewing through the cylindrical purging tube.
2Speed
If the distance between the thermal radiation shield and melt liquid surface is set small to control purge gas flow rate, then the gas straightening effect is improved, but the measurement complexity increases
Solution Approach 1:
The flat plate acts as a mediator that simplifies the measurement system by providing a stable reference point. Instead of directly measuring the liquid surface through the distorted cylindrical tube, the system measures the flat plate's position and uses it to calculate the liquid surface level, reducing measurement complexity.
Solution Approach 2:
The invention replaces direct optical measurement through the distorted tube with an indirect measurement system using the flat plate as a reference. This substitution allows for simpler image processing and calculation algorithms to determine the liquid surface level.
3Stability of the object's composition
If the purging tube is provided inside the thermal radiation shield to improve dopant evaporation control, then the resistivity distribution stability is improved, but the liquid surface level measurement accuracy deteriorates due to image distortion
Solution Approach 1:
The flat plate is positioned within the thermal radiation shield's observation area, serving as an intermediary reference object. It allows the system to maintain the purging tube inside the thermal radiation shield for dopant control while simultaneously enabling accurate liquid surface level measurement by providing a distortion-corrected reference point for the camera.
Solution Approach 2:
The measurement system is segmented into two independent functions: the purging tube handles gas flow control and dopant evaporation management, while the flat plate handles optical reference for liquid surface level measurement. This segmentation allows both functions to operate effectively without interfering with each other.
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 allows for precise measurement and control of the liquid surface level, improving the stability of dopant concentration and resistivity distribution in the silicon single crystal, ensuring consistent resistivity along the pull-up axis.
Implementation Method 1
a camera (18) for photographing a mirror image of the radiation heat shield (16) shown in an image photographed by the two-dimensional CCD camera (18)
Data Source
AI summary
A silicon single crystal pull-up apparatus is provided with a chamber into which an inert gas is introduced; a crucible that supports a silicon melt within the chamber; a heater that heats the silicon melt in the crucible; a lifting device for lifting and lowering the crucible; a thermal radiation shield disposed above the crucible; a cylindrical purging tube that is provided inside the thermal radiation shield so as to straighten the inert gas; a CCD camera that photographs the mirror image of the thermal radiation shield reflected on the liquid surface of the silicon melt through the purging tube; a liquid surface level calculator that calculates the liquid surface level of the silicon melt from the position of the mirror image photographed by the camera; and a conversion table creator that creates a conversion table representing a relationship between the liquid surface level of the silicon melt and the mirror image position obtained. The liquid surface level calculator calculates the liquid surface level based on the conversion table.