Directional Solidification Gas Flushing Device for Silicon Purity Control
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Solution Overview
Problem
The production of multicrystalline silicon by directional solidification often results in increased carbon and oxygen concentrations due to contamination from furnace components and handling processes, which affects the quality and usability of the material for solar cells.
Innovation Solution
A device with a gas flushing system featuring a stamp-shaped body with adjustable gas outlets positioned close to the melt surface, allowing for controlled gas flow and high velocities to effectively remove carbon and oxygen impurities, and a graphite-free design to prevent contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a gas flushing device with a fixed central tube is used, then the device structure is simple, but the gas flow does not cover the entire melt surface and backflow effects occur transporting carbon and oxygen to the melt
Solution Approach 1:
The gas flushing device is segmented into multiple gas outlets arranged around the crucible perimeter rather than a single central tube. This segmentation allows gas flow to cover the entire melt surface effectively, preventing backflow effects while maintaining reasonable structural complexity.
Solution Approach 2:
An inert gas atmosphere is introduced as an intermediary between the melt and the surrounding environment. This gas layer acts as a protective barrier that prevents carbon and oxygen from furnace components and handling processes from contaminating the melt, while the multi-point gas outlets ensure uniform distribution of this protective atmosphere.
2Device complexity
If gas outlets are positioned far from the melt surface, then the device structure is simpler, but gas velocities are too low to effectively remove impurities
Solution Approach 1:
The gas outlets are positioned locally close to the melt surface at specific strategic locations around the crucible perimeter. This local positioning creates high-velocity gas jets that directly interact with the melt surface, effectively removing carbon and oxygen impurities without requiring complex overall device structure.
3Ease of manufacture
If graphite components are used in the furnace, then the device structure is simple and durable, but carbon contamination of the melt is inevitable
Solution Approach 1:
An inert gas atmosphere (such as argon or nitrogen) is maintained throughout the crucible and furnace chamber. This inert environment prevents oxidation of graphite components and eliminates carbon contamination of the melt, while allowing graphite components to be used where structurally necessary. The inert gas acts as a protective medium that decouples the structural needs of graphite components from the purity requirements of the melt.
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
The solution enables precise control of carbon and oxygen content in the crystalline material, improving the homogeneity of dopants and impurities distribution, resulting in higher quality multicrystalline silicon with reduced contamination levels.
Implementation Method 1
A well-known way of influencing the carbon and oxygen concentration in the silicon is to implement a suitable gas flow over the melt surface, via which substances containing carbon and oxygen are transported away.
Implementation Method 2
The gas outlet is formed by one or more openings in a lower stamp surface of a stamp-shaped body... allowing at least partial insertion of the stamp-shaped body into the crucible... The gas flushing device and/or the support surface are arranged or mounted so that they can be adjusted in an axial direction in order to enable an adjustment or change in a vertical distance between the support and the plunger-shaped body.
Implementation Method 3
The process is also used to purify metallurgical silicon by utilizing the segregation effect.
Data Source
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AI summary
The invention relates to a device and a method for producing crystalline bodies by directional solidification. The device comprises a melting furnace (11) having a heating chamber (12) in which at least one supporting surface (13) for a crucible (8) and at least one gas purging device arranged above the supporting surface (13) and having a gas outlet facing the supporting surface (13) are defined. An embodiment of the device is characterized in that the gas outlet is defined by one or more openings in a lower plunger surface of a plunger-shaped element (2) which has a geometry adapted to the inner shape of the crucible (8), said shape allowing an at least partial insertion of the plunger-shaped body (2) into the crucible (8). The gas purging device and/or the supporting surface (13) comprise an adjusting mechanism or are designed to be adjustable in such a manner that they allow an adjustment of a perpendicular distance between the supporting surface (13) and the plunger-shaped body (2). The device and the corresponding method allow carbon- and oxygen-containing materials to be discharged from the melt more efficiently and in a controlled manner. The device and the method thus allow - within certain limits - a specific adjustment of the carbon and oxygen content of the crystalline bodies.