Continuous Annealing of Granular Silicon for Hydrogen Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing methods for producing polysilicon through pyrolytic decomposition of silicon-bearing gases result in granular silicon with high hydrogen content, which needs to be reduced to meet electronic-grade standards, and there is a need for a continuous annealing process to achieve this.
Innovation Solution
An annealing device and method that includes a shell with heating zones, inert gas circulation, and a metering system to control the flow of granular silicon, allowing for continuous reduction of hydrogen content by maintaining the silicon at high temperatures for sufficient residence times, with optional vibratory forces to prevent agglomeration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If granular silicon is produced by pyrolytic decomposition of silicon-bearing gas, then production efficiency and mass transfer are improved, but hydrogen content increases to 10-20 ppmw which exceeds electronic-grade requirements
Solution Approach 1:
The patent implements continuous annealing of granular silicon through a fluidized bed reactor system where silicon particles continuously flow through heated zones. The system maintains continuous operation with silicon feed rate controlled at 400-600 kg/hr, ensuring uninterrupted dehydrogenation process that reduces hydrogen content to ≤5 ppmw while sustaining high productivity
Solution Approach 2:
The patent changes physical parameters including heating the granular silicon to temperatures of 900-1400°C in the annealing zone, controlling residence time of 30-120 minutes, and adjusting fluidizing gas flow rates. These parameter changes enable effective hydrogen removal while maintaining continuous production efficiency
2Manufacturing precision
If heat treatment is applied to reduce hydrogen content, then hydrogen diffusion is enhanced, but processing time increases and continuous operation becomes difficult
Solution Approach 1:
The patent transforms batch heat treatment into continuous annealing operation. Granular silicon is continuously fed into the fluidized bed reactor and passes through the heated zone without interruption. The system achieves hydrogen content reduction to ≤5 ppmw with residence times of only 30-120 minutes, eliminating the time losses associated with batch loading, heating, holding, and unloading operations
Solution Approach 2:
The patent replaces traditional mechanical batch heating systems with a fluidized bed system where gas flow suspends and circulates silicon particles through the heated zone. This substitution enables continuous processing and efficient heat transfer, reducing processing time while achieving the required hydrogen content reduction
3Manufacturing precision
If high temperature annealing is performed, then hydrogen diffusion rate increases, but energy consumption and risk of agglomeration increase
Solution Approach 1:
The patent implements continuous annealing where granular silicon flows continuously through the heated zone at controlled rates of 400-600 kg/hr. This continuous operation allows optimization of energy input, maintaining temperatures of 900-1400°C only for the necessary residence time of 30-120 minutes, thereby reducing total energy consumption compared to prolonged batch heating while achieving hydrogen content ≤5 ppmw
Solution Approach 2:
The patent applies mechanical vibration to the reactor system to prevent agglomeration of granular silicon particles during high-temperature annealing. The vibration keeps particles separated and in constant motion, ensuring uniform heating and preventing particle fusion even at temperatures of 900-1400°C, thus enabling effective hydrogen removal without the harmful effect of agglomeration
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 process effectively reduces hydrogen content in granular silicon to 5 ppmw or less, enabling the production of electronic-grade polysilicon in a continuous and efficient manner, capable of processing over 400 kg per hour.
Implementation Method 1
each tube comprising a heating zone... a heat source for heating the heating zones of the tubes
Implementation Method 2
an inert gas source in fluid communication with the interior of a lower portion of the shell and, thereby, the open lower end of each tube
Implementation Method 3
hydrogen diffuses out of the silicon
Implementation Method 4
a vibrator positioned to apply a vibratory force to the one or more tubes when the annealing device is in operation
Data Source
AI summary
This disclosure concerns embodiments of an annealing device and a method for annealing flowable, finely divided solids, such as annealing granular silicon to reduce a hydrogen content of the granular silicon. The annealing device comprises at least one tube through which flowable, finely divided solids are flowed downwardly. The tube includes a heating zone and (i) a residence zone below the heating zone, (ii) a cooling zone below the heating zone, or (iii) a residence zone below the heating zone and a cooling zone below the residence zone. An inert gas is flowed upwardly through the tube. The tube may be constructed from two or more tube segments. The annealing device may include a plurality of tubes arranged and housed within a shell. The annealing device and method are suitable for a continuous process.