Gas Conduit for Silicon Ingots
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Solution Overview
Problem
The challenge in manufacturing crystalline silicon ingots for photovoltaic applications is maintaining the purity of molten silicon during directional solidification, as existing methods fail to adequately control gas flow, leading to carbon contamination and deterioration of furnace components, resulting in reduced efficiency and increased costs due to SiC impurities and premature wear of graphite elements.
Innovation Solution
A gas conduit arrangement is implemented, featuring a continuous peripheral opening between upper and lower shield elements, with a flow constriction to prevent backflow of SiO-gas and fumes, directing them out of the compartment, thereby protecting the silicon melt and furnace components from contamination and deterioration, while reducing purge gas consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If higher amounts of purge gas flow are used to prevent carbon contamination and remove SiO-gas, then the purity of molten silicon is improved, but the silicon nitride coating deteriorates leading to sticking of silicon to silica crucible walls and loss of ingots
Solution Approach 1:
The gas flow path is segmented into multiple zones: a first gas flow path for purge gas to protect the melt surface, and a second gas flow path for inert gas to protect the coating. This segmentation allows different gas flows to serve different protective functions without interfering with each other, resolving the contradiction between preventing carbon contamination and protecting the coating.
Solution Approach 2:
A second inert gas flow is introduced as an intermediary protective layer between the purge gas and the silicon nitride coating. This intermediary gas flow prevents direct contact between the high-velocity purge gas and the coating, thereby protecting the coating while still allowing the purge gas to effectively remove SiO-gas and prevent carbon contamination.
2Manufacturing precision
If higher amounts of purge gas flow are used to prevent back flow of CO and remove SiO-gas, then carbon contamination is reduced, but the service life of graphite components is reduced due to increased gas flow erosion
Solution Approach 1:
The gas flow system is divided into two separate flow paths: one optimized for contaminant removal (purge gas) and another for component protection (inert gas). The inert gas flow specifically protects graphite components from erosion by the purge gas, extending their service life while maintaining the effectiveness of carbon contamination prevention.
Solution Approach 2:
A second inert gas flow is introduced to create a protective inert atmosphere around graphite components. This inert environment shields the graphite from direct exposure to high-velocity purge gas, reducing mechanical erosion and extending the service life of graphite heating elements and insulation while maintaining the purge gas effectiveness for contaminant removal.
3Reliability
If low purge gas flow is used to preserve coating integrity, then coating deterioration is reduced, but carbon contamination increases due to insufficient removal of SiO-gas and back flow of CO
Solution Approach 1:
The protective gas system is segmented into two functional streams: a first purge gas flow optimized for contaminant removal with sufficient velocity, and a second inert gas flow optimized for coating protection with lower velocity. This segmentation allows each gas flow to be optimized for its specific function without compromise.
Solution Approach 2:
The second inert gas flow acts as an intermediary protective barrier that allows the first purge gas flow to maintain higher velocity for effective contaminant removal. The intermediary gas layer prevents direct interaction between the high-velocity purge gas and the coating, enabling both high purity and coating stability.
4Manufacturing precision
If purge gas is flushed onto the surface of silicon to protect against gaseous contamination, then purity is improved, but SiC deposits form on carbon-containing furnace elements reducing their service time
Solution Approach 1:
The gas protection system is segmented into two zones: a first zone with purge gas for melt protection where SiO-gas is removed, and a second zone with inert gas for component protection where SiC deposition is prevented. This spatial segmentation prevents SiC deposits on heating elements while maintaining high purity silicon production.
Solution Approach 2:
A second inert gas flow serves as an intermediary protective layer between the SiO-gas environment and carbon-containing furnace elements. This intermediary gas prevents direct reaction between SiO-gas and graphite components, eliminating SiC deposit formation and extending heating element service life while maintaining the first gas flow's effectiveness for purity control.
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 solution effectively reduces carbon contamination of silicon ingots, minimizes SiC formation, and extends the service life of furnace components, enhancing the quality and yield of photovoltaic cells by maintaining a cleaner environment within the furnace.
Implementation Method 1
a gas conduit formed by a continuous peripheral opening between an upper shield element placed at a distance above the crucible and which covers the horizontal cross-section area of the compartment to separate it in two overlaid sub-compartments
Implementation Method 2
a flow constriction located in the gas conduit or the one or more outlet(s) providing a cross-section area, A, in the gas conduit or one or more outlet(s) where A = P·d
Implementation Method 3
an upper shield element placed at a distance above the crucible and which covers the horizontal cross-section area of the compartment to separate it in two overlaid sub-compartments
Data Source
Figure 1
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AI summary
The present invention relates to an arrangement for manufacturing crystalline silicon ingots by directional solidification, where the melt and carbonaceous structural parts of the crystallisation furnace is protected from the fumes of the melt by applying a gas conduit which leads the fumes directly out of the directional solidification compartment of the furnace.