Eddy Current Thickness Measurement for Melt-Grown Silicon Sheets
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Solution Overview
Problem
Current methods for producing silicon wafers, such as sawing and cleaving, result in significant material waste and increased costs due to kerf losses and temperature gradients, which limit the efficiency and quality of solar cells, and there is a need for a method to measure the thickness of sheets formed from a melt without being hindered by high temperature environments.
Innovation Solution
A sheet-forming apparatus and measurement method using a cooling plate and eddy current measurement system, where an exciting coil and sensing coil generate a time-varying magnetic field to measure the thickness of the sheet by detecting the difference in conductivity between the solid and liquid phases, allowing for real-time monitoring and process control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If sawing is used to produce silicon wafers, then wafers can be manufactured, but significant material waste occurs due to kerf losses
Solution Approach 1:
The patent replaces the mechanical sawing process with a magnetic field-based eddy current measurement and control system. By using electromagnetic induction to measure thickness in real-time and control the solidification process, the system eliminates the need for subsequent mechanical sawing and kerf loss, achieving waste-free wafer production from the melt
Solution Approach 2:
The patent implements real-time feedback control by continuously measuring sheet thickness during solidification using eddy current sensors. The measurement signal is fed back to control the cooling rate and solidification process, ensuring precise thickness control without post-processing removal, thereby eliminating material waste
2Productivity
If vertically-pulled silicon ribbon is used, then sheets can be produced from melt, but temperature gradient causes poor crystal quality
Solution Approach 1:
The patent inverts the conventional vertical pulling approach by implementing horizontal sheet solidification. The melt is solidified horizontally across a cooling surface, which distributes temperature more uniformly and eliminates the severe vertical temperature gradient that causes thermal stress and poor crystal quality in vertically-pulled ribbons
Solution Approach 2:
The patent changes the geometric parameters of the solidification process from vertical to horizontal orientation. This parameter change fundamentally alters the temperature distribution pattern, reducing thermal gradients and improving crystal structure quality while maintaining high production efficiency
3Measurement precision
If conventional thickness measurement devices are used, then thickness can be measured, but they cannot withstand high temperature environment of the melt
Solution Approach 1:
The patent replaces conventional mechanical or contact-based thickness measurement devices with an eddy current measurement system. This non-contact electromagnetic measurement method uses magnetic field induction to measure thickness through the sheet, allowing operation in high-temperature environments without physical contact with the hot material
Solution Approach 2:
The patent introduces a magnetic field as an intermediary for thickness measurement. The eddy current sensors generate and detect magnetic fields that penetrate the sheet material, allowing indirect measurement of thickness without physical contact. This intermediary approach enables measurement in extreme temperature conditions where direct contact sensors would fail
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 enables the production of sheets with controlled thickness, reducing material waste and improving crystal quality, while withstanding high temperatures, thus addressing the inefficiencies of existing methods and enabling more cost-effective and efficient solar cell production.
Implementation Method 1
An exciting coil and a sensing coil are downstream of the cooling plate. A power source is connected to the exciting coil
Implementation Method 2
The thickness of the sheet is measured using an eddy current
Data Source
AI summary
A sheet of a material is disposed in a melt of the material. The sheet is formed using a cooling plate in one instance. An exciting coil and sensing coil are positioned downstream of the cooling plate. The exciting coil and sensing coil use eddy currents to determine a thickness of the solid sheet on top of the melt.