Active Edge Control for Crystalline Sheets on Melt Surfaces
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Solution Overview
Problem
Existing methods for producing large single-crystal silicon wafers face challenges in maintaining stability and uniform thickness during the ribbon growth process, leading to uncontrolled narrowing and instability due to lateral heat diffusion at the ribbon edge.
Innovation Solution
An apparatus and method utilizing optical sensors to detect the edge of the crystalline ribbon, combined with a segmented thinning controller, adjust cooling and heating units to stabilize the ribbon width and thickness, and a controlled melt-back process to achieve uniform thinning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a segmented thinning controller with active edge control is used to maintain uniform ribbon thickness, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The thinning controller is divided into multiple independent heating zones along the ribbon width, with each zone controlled by separate power supply circuits. This segmentation enables localized thickness adjustment at different positions of the ribbon, allowing precise control of thickness uniformity while managing the complexity through modular zone control
Solution Approach 2:
Different sections of the ribbon receive different heating intensities based on their specific thickness requirements. The edge regions receive higher heating power to counteract lateral heat diffusion and narrowing, while the center region receives lower power to prevent excessive thinning, achieving local optimization of thickness control
2Productivity
If heating is applied to thin the ribbon through melt-back, then productivity is improved by achieving target thickness, but lateral heat diffusion causes ribbon narrowing and instability
Solution Approach 1:
The heating system is divided into multiple independent zones along the ribbon width, allowing differential heating control. Edge zones receive higher power to maintain width stability against lateral heat diffusion, while center zones receive lower power for controlled thinning, thus maintaining ribbon stability during productive thinning
Solution Approach 2:
The heating power distribution is non-uniform across the ribbon width, with elevated power at edges to counteract narrowing tendencies and reduced power at the center for effective thinning. This local quality differentiation enables simultaneous achievement of productivity (through center thinning) and stability (through edge maintenance)
3Manufacturing precision
If optical sensors are used to detect ribbon edge for active control, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
Optical sensors continuously detect the ribbon edge position and thickness profile, feeding this information back to the segmented thinning controller. The controller adjusts heating power in real-time based on the feedback signals, creating a closed-loop control system that maintains precise thickness uniformity while managing complexity through automated feedback regulation
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 the production of stable, uniformly thick crystalline ribbons and wafers with controlled thickness profiles, reducing the risk of instability and defects, and facilitating the production of larger, high-quality silicon wafers for solar and semiconductor applications.
Implementation Method 1
The local cooling may be accomplished by employing a device that rapidly removes heat above the region of the melt surface where crystallization is initiated
Implementation Method 2
optical sensors configured to detect a difference in emissivity between the melt and a solid ribbon on the melt
Implementation Method 3
This may be accomplished by heating the ribbon over a region of a crucible containing the melt as the ribbon is pulled in a pulling direction. As the ribbon is drawn through the region while the ribbon is in contact with the melt, a given thickness of the ribbon may melt back
Implementation Method 4
a portion of a melt surface is cooled sufficiently to locally initiate crystallization with the aid of a seed
Data Source
AI summary
An optical sensor is configured to detect a difference in emissivity between the melt and a solid ribbon on the melt, which may be silicon. The optical sensor is positioned on a same side of a crucible as a cold initializer. A difference in emissivity between the melt and the ribbon on the melt is detected using an optical sensor. This difference in emissivity can be used to determine and control a width of the ribbon.