Optical Melt Level Control for Single Crystal Pulling
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Solution Overview
Problem
Conventional methods for controlling the melt level in single crystal pulling apparatuses, such as the Czochralski method, face challenges in accurately setting and maintaining the melt surface position due to errors in rod and seed crystal lengths, camera mounting issues, and high equipment costs associated with methods like laser triangulation.
Innovation Solution
The use of an optical recording device and processing unit to photograph and analyze the real and reflected images of furnace internal structural objects, allowing for precise control of the melt surface position by calculating relationships between image distances and movements, enabling accurate adjustment of the melt level without modifying the furnace body.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional methods (non-combustible rod or seed crystal contact) are used to verify melt surface position, then the melt level can be controlled, but measurement precision deteriorates due to errors in rod/seed crystal length and contact verification
Solution Approach 1:
The patent uses optical imaging to create a visual copy/reflected image of the melt surface and furnace internal structural object. By capturing and analyzing these optical images, the system measures the distance between the reflected image and the structural object without physical contact, eliminating measurement errors associated with physical rods or seed crystals while maintaining high precision and reliability
Solution Approach 2:
The patent replaces the mechanical measurement system (physical rods or seed crystals that require contact verification) with an optical measurement system. The optical recording device captures images and the processing device calculates distances based on image analysis, substituting mechanical contact-based measurement with non-contact optical measurement to improve both precision and reliability
2Measurement precision
If laser triangulation method is used to measure melt surface position, then measurement precision improves, but device complexity and equipment costs increase
Solution Approach 1:
The patent utilizes the existing camera in the single crystal pulling apparatus for its original purpose of monitoring crystal growth, and simultaneously employs it for melt surface position measurement. The same optical recording device serves multiple functions, eliminating the need for separate complex measurement equipment like laser triangulation systems while maintaining measurement precision
Solution Approach 2:
The system uses optical image copying and analysis rather than complex physical measurement systems. By capturing reflected images and analyzing their geometric relationships through image processing, the patent achieves precise measurement without requiring expensive and complex laser triangulation equipment
3Ease of manufacture
If camera-based image comparison method is used to control melt level, then equipment costs reduce, but measurement precision deteriorates due to camera mounting position errors
Solution Approach 1:
The patent introduces a furnace internal structural object as an intermediary reference element with a known, fixed position relative to the melt surface. By measuring the distance between this intermediary object and its reflected image in the melt, the system establishes a reliable reference that compensates for camera mounting position errors, maintaining measurement precision while using simple camera equipment
Solution Approach 2:
The system continuously captures optical images of the furnace internal structural object and its reflected image, calculates the distance between them, and uses this feedback information to determine and control the melt surface position. This closed-loop feedback mechanism maintains measurement precision despite variations in camera mounting position
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 approach allows for easy and accurate adjustment of the melt surface position, reducing errors and equipment costs, and maintaining the melt level consistently during single crystal pulling, improving the quality of silicon single crystals.
Implementation Method 1
an optical recording device which obtains image information by photographing a real image of a furnace internal structural object and a reflected image of the furnace internal structural object that is reflected on the melt surface
Data Source
AI summary
This mechanism for controlling a melt level includes: an optical recording device by which a real image of a furnace internal structural object and a reflected image reflected on the melt surface; and a processing device which, taking a value based on the real image as a reference value, controls the position of the melt surface based on a relationship of a position or a size of the reflected image, a distance between the reflected image and the real image, or amounts of changes thereof to the position of the melt surface. This mechanism for adjusting a melt level includes: the above mechanism for controlling a melt level; and a lifting mechanism which is controlled by the mechanism for controlling a melt level and adjusts the melt surface to the set position.