Silicon Seed Rods with Flat Cross-Section and Low Resistivity
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Solution Overview
Problem
The Siemens process for manufacturing high-purity polycrystalline silicon suffers from slow deposition rates due to small surface area and high resistivity of silicon seed rods, requiring expensive pre-heating and potential contamination from metal core rods.
Innovation Solution
The method involves manufacturing long silicon seed rods with a flatter cross-sectional shape and lower resistivity by doping the silicon melt with oxygen, forming a silicon dioxide film, and using a growth reactor with an inductor heater and cooling fluid, allowing for semi-continuous or continuous rod production and reducing the need for pre-heating and welding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional silicon seed rods with slender diameter (around 5 mm) are used, then the rod structure is simple and easy to manufacture, but the surface area available for deposition is small resulting in slow deposition rate
Solution Approach 1:
The patent changes the geometric parameters of the silicon seed rod by introducing a flatter cross-sectional shape with increased width and reduced thickness, transforming the traditional cylindrical shape into a plate-like structure. This parameter change increases the surface area from the conventional slender cylindrical surface to a larger flat surface, directly improving the deposition rate while maintaining structural integrity through controlled dimensions
2Use of energy by moving object
If high-resistivity silicon rods (1 kiloohm-cm or higher) are used, then the material purity is maintained, but it is difficult to pass current through the rod at room temperature requiring expensive pre-heating devices and consuming large amounts of electric energy
Solution Approach 1:
The patent modifies the electrical parameter of the silicon rod by controlling the oxygen content during crystal growth. By optimizing the oxygen concentration in the silicon lattice, the resistivity is reduced from the conventional 1 kiloohm-cm or higher to a lower value that allows sufficient current passage at room temperature, eliminating the need for expensive pre-heating devices and reducing energy consumption
3Stability of the object's composition
If metal core rods (Mo, W, Ta, Nb) with high recrystallization temperature are used instead of silicon seed rods, then the rod structural stability is improved, but the core part must be removed after reaction and metals cause diffusion into the deposited silicon
Solution Approach 1:
The patent applies homogeneity by using pure silicon material throughout the entire rod structure without metal cores or composite materials. The silicon seed rod is manufactured as a homogeneous single-material structure through controlled crystal growth, eliminating the heterogeneity introduced by metal cores while maintaining structural stability through optimized silicon crystal orientation and purity control
4Ease of manufacture
If short silicon seed rods are manufactured by hewing out from long silicon rods, then the manufacturing process is simple, but the silicon seed rods become shorter after every manufacturing cycle requiring periodic manufacturing from long rods
Solution Approach 1:
The patent enables continuous production of long silicon seed rods through optimized crystal growth processes that can sustain extended growth cycles without interruption. The continuous availability of long rods eliminates the periodic need to manufacture new rods from shorter ones, maintaining manufacturing simplicity while ensuring continuous supply of full-length rods for production
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 enhances the deposition rate and stability, reduces production costs, and prevents contamination, enabling the production of high-purity silicon seed rods with controlled parameters and improved efficiency.
Implementation Method 1
an inductor heater providing a silicon melt column above a die
Implementation Method 2
cooling the silicon columnar rods in a fluid bath
Implementation Method 3
forming a film of silicon dioxide on the silicon rod... the reaction between the silicon melt and oxygen
Data Source
AI summary
A method and apparatus for manufacturing high-purity long silicon seed rods with controlled resistivity for Siemens and similar processes with using a film of silicon dioxide, wherein a film of silicon dioxide is formed on the seed rod in the course of a reaction between a silicon melt and oxygen. The rod is formed with a quartz die and cooled by direct immersion into a cooling fluid, such as de-ionized water and/or by cooling fluid vapor in the gas cooling zone.