Refining of Silicon: Removal of Boron, Enhancement

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David Lynch
Professor, Mining & Geological Engineering
Managed By
Robert Sleeper
Licensing Manager (520) 626-4604

Title: Refining of Silicon: Removal of Boron Using ZrN 

Invention: A new, low cost silicon refinement process which results in purity levels ideal for use in silicon-based solar cells. This method does not release toxic chlorosilanes commonly created during silicon refinement, while increasing the production of high grade polysilicon.

Background: The demand for polycrystalline silicon to manufacture solar cells increases with every year, while the availability of high-grade silicon for such uses is rapidly decreasing. It is therefore imperative to develop ways in which lower grade silicon can be purified for such applications. The most common purification method for silicon is the Siemens process, but has some major problems such as production of toxic chlorosilanes, high cost, and low productivity. This technology offers an alternative method for the removal of boron, a common silicon impurity, which does not have the drawbacks of the Siemens process. Zirconium nitride (ZrN) is used as the refining agent within an oxi-nitride slag, a system which acts as a chemical sink for boron. The presence of Zr remaining after purification can affect the efficiency of final solar cell products, but such a impurity can be greatly reduced through Silgrain processing and oxidative refining (both silicon purification techniques) to the point where the final polycrystalline silicon product can be efficiently used for photovoltaic manufacture. This process has the potential to increase fabrication of solar-grade silicon, thereby decreasing overall production costs.

 

Applications:

● Production of high purity polycrystalline silicon for use in photovoltaics

● Reducing costs of solar-grade polycrystalline silicon

● Reducing overall cost of silicon based solar cells

 

Advantages:

● Low-cost alternative to the Siemens refining technique, thus reducing the production cost of silicon-based solar cells

● Increase manufacture efficiency of solar-grade silicon and silicon-based solar cells

● Does not evolve toxic chlorosilanes that are prevalent in common silicon refinement processes

● Can remove impurities (including Zr) to the point where they do not effect solar cell efficiency

 

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Bob Sleeper, http://techlaunch.arizona.edu/people/bob-sleeper

RobertS@tla.arizona.edu

520-626-4604