Many PV manufacturers use the Siemens process. Other choices are Fluid Bed Reactors (FBR) or Upgraded Metallurgical Grade (UMG) silicon – I’ll talk about these other techniques later in the next slide.For the many years that I worked at Texas Instruments, we sold our scrap silicon crystal tops and tails to the solar industry. That has changed in the last few years as rapid growth in PV has created a tremendous opportunity for a new technology. Cost is a very significant enabler in the PV business. Only 10% of the cost of a semiconductor device is the cost of the silicon. 50% of a solar cell cost for the eighty percent of the PV market supplied by crystalline silicon is the cost of the silicon.
The reduction of silicon tetrachloride by hydrogen is proven science. it was explored thoroughly as reported from the literature by Sirtl et. al. in the early 70’s since it was a major byproduct of the pyrolysis of trichlorosilane in the Siemens process. My research at Texas Instruments provides the basis for this technology, but has never been reduced to practice for several reasons.High purity silicon nitride containment materials or liners are not available commercially. All commercially available silicon nitride has substantial additives that make it not useful for high purity silicon processing.Our proven concept is based on our fabrication and understanding of our proprietary silicon nitride materials technology.
– my brief introduction will introduce the commercial model. Dave will discuss the technology in detail The building block for the line is a hot wall reactor
The major findings of our Proof-of-Concept project were carried out at Clemson University in the Advanced Materials Research Laboratory (photo) in the past few months. This lab specializes in advanced materials development including chemical vapor deposition of silica from the oxidation of silicon tetrachloride. We leveraged Clemson’s experience with gas bubblers to setup our sources for the reduction of silicon tetrachloride with hydrogen at high temperatures in our proprietary silicon nitride containment materials.
The process and materials concept works.Our advanced development reactor design will trade off reaction residence time versus deposition surface area of a packed silicon nitride particle bed. We retained Dr. Phillip Spencer, the world’s expert in the thermo-chemistry of silicon. He optimized the Siemens process. As he worked on our materials system he wondered why this process was not already being used to make silicon from silicon tetrachloride. Our short experiments with reduction of silicon tetrachloride by hydrogen in quartz containers near the melting point of silicon exhibited rapid erosion and etching and devitrification. Our silicon nitride materials have shown great resistance to chlorine chemistry.
This slide lists some of the principal reactions used in refining and depositing silicon.The next slide explores some of the Thermo-chemistry of the Anaxtal Silicon process for the reduction of silicon tetrachloride by hydrogen.
A optimum silicon yield with a ratio of 0.031 moles of silicon tetrachloride to one mole of hydrogen is predicted by the thermochemical model.
This slide shows the constituents of the reactor gas versus STC concentration at 1415o C.
Solubility of hydrogen, carbon and nitrogen in silicon below and above the melting point.Note the large supersaturation of nitrogen in the melt on freezing establishes crystal growth of beta silicon nitride on the silicon nitride liner.
Show the quartz reaction tube.
Show the graphite susceptor.Show the liner sections.
The ANAXTAL Silicon concept includes both innovative processes and materials. A multi-zone reactor permits both deposition and melting process cycles near the melting point of silicon as well as extraction of the molten silicon product. Read slide points. Not shown in this sketch is a silicon nitride liner and the silicon nitride particles in the packed bed.Scale up of this technology from our current single zone laboratory reactor will require sensors and controls technology – development to begin the prototype stage.We have considered the Siemens SIMATIC PLCs for our initial effort in Advanced Development.
The assembly is shown here with lab jacks to adjust the vertical position of the susceptor within the fixed coil.
In contrast to the loss of silica vapor from quartz, silicon nitride crystals are added to our crucibles in the ANAXTAL Silicon process. Sensors and controls will be added to our reactor to establish a nitrogen mass balance on the reactor to permit our containment material to last for thousands of hours of continuous operation.
Granular silicon will be the first product since that market exists for the semi-continuous crystal growth processes like EDFG (Tyco), string ribbon, Solaicx, Semi-Materials and Confluence Solar. BUT… this technology provides many additional opportunities for development of game-changing(leading) products…Read the rest. Our proprietary materials will also enable direct melt transfer to all crystal growth processes as well as more durable crucibles.
Very conservative estimate for the main inputs: STC and H.We feel there is a significant opportunity to reduce cost below what is shown in this slideCost of production: “all in” cost – inc’l direct cost, depreciation (10 year SL) and service contract.Siemens process capex at ~$130/kg for “average” project.
Very conservative estimate for the main inputs: STC and H.We feel there is a significant opportunity to reduce cost
ANAXTAL Silicon, LLC INTRODUCTION February 2, 2012 David E. Witter, CTO
Overview• Proven concept of patent pending technology to produce silicon engineered for solar photovoltaic (PV) applications.• Product cost based on the Siemens process silicon tetrachloride byproduct is lower than current industry average.• Proprietary molten silicon containment material enables direct melt transfer from silicon synthesis to crystal growth or direct wafer process. ANAXTAL Silicon
Background• Semiconductor grade silicon from the Siemens process supplies the PV industry Fluid bed reactor silicon is in production Alternate methods are in development• Cost of silicon is a key component in solar photovoltaic devices• Growth of the PV industry provides opportunity for a new production model or paradigm ANAXTAL Silicon
Opportunity• The chemistry is proven: Reduction of silicon tetrachloride (STC) with hydrogen• What has been lacking are the materials to enable the process – proprietary silicon nitride reactor liner• Anaxtal Silicon has the breakthrough technology• Materials development is the core of our intellectual property ANAXTAL Silicon
Technology Overview• Hot wall reactor concept – 100 tonne annual capacity• Typical line will consist of 5 reactors: 500 tonne annual capacity• Silicon supply for a 60 MW cell line• The line can be scaled up or down to meet customer requirements• Line to include ancillary equipment for feedstock supply and off-gas processing ANAXTAL Silicon
Proof of Concept• Lab scale reactor with packed particle bed• Thermochemical model SiCl4 + 2 H2 >> Si + 4 HCl @ 1415o C• Silicon nitride liner• Produced silicon pellets: > 10 grams.• Demonstrated an extended lifetime of containment vessel compared to quartz. ANAXTAL Silicon
US 4,710,260• Anaxtal Silicon will provide cost savings from dramatically reduced energy and capital requirements• Primary feedstock is a byproduct of the chemical industry ANAXTAL Silicon
Process Chemistry• MG Silicon SiO2 + 2C -> Si + 2CO• Siemens Process Si + 3HCl -> SiHCl3 + H2 SiHCl3 + H2 -> Si + 3HCl 2SiHCl3 -> Si + SiCl4 + 2HCl 4SiHCl3 -> Si + 3SiCl4 + 2H2• AS Solar Silicon Process SiCl4 + 2H2 -> Si + 4HCl (1400 C) SiCl4 + SiH4 -> 2Si + 4HCl * TCS is trichlorosilane (SiHCl3) ** STC is silicon tetrachloride (SiCl4) ANAXTAL Silicon
Thermochemical Model• Silicon nitride and graphite are compatible up to 1441 oC, then form silicon carbide.• Predicted optimum silicon yield with a ratio of 0.031 moles of silicon tetrachloride to one mole of hydrogen.• Constituents of the reactor gas versus STC concentration at 1415o C.• Solubility of hydrogen, carbon and nitrogen in silicon below and above the melting point. ANAXTAL Silicon
Approach – Laboratory• Built STC bubbler cabinet and gas manifold• Used oxy-hydrogen burner with quartz reaction tubes• Used resistance heated Vertical Tube Furnace (VTF) with quartz envelopes and silicon nitride reaction tubes to drip silicon.• Used Horizontal Tube Furnace (HTF) to fabricate silicon nitride liners. ANAXTAL Silicon
Approach – Laboratory• Used graphite susceptors with RF generator to heat gases from bubbler cabinet to deposit and melt silicon for production of 10 grams of silicon granules.• Analyzed the liners to determine their potential lifetime for continuous operation of the reactor for thousands of hours of silicon production. ANAXTAL Silicon
Technology• Feedstocks cracked at high temperature to create high purity silicon• Enabled by proprietary silicon nitride liner technology• Reactor liner created in place for purity and durability
Additional Opportunities• Direct melt transfer• Silicon spheres for flexible solar panels• Improved cell efficiencies with reduction of oxygen precipitates• Pre-doped silicon• Silicon nitride liners for crucibles and crystal growth• SiGe alloys ANAXTAL Silicon
Commercial Model - Customer• Annual silicon output – 500 tonnes• Estimated cost of production: $18.00 / kg• Capital cost (per kg of silicon): $4.00 / kg 70% less than Siemens process technology• Total “All in” cost: $22.00 / kg• Annual savings: $14,000,000 Based on silicon market price of $50 / kg• Estimated payback: 1.4 years ANAXTAL Silicon
Commercial Model - Customer• Silicon cost savings• Control of a critical raw material• Freedom from the commodity cycle of silicon• Shortened lead time - ability to quickly respond to additional capacity requirements
Support Network• SC Launch – State agency to foster and support advanced materials companies• SCRA – South Carolina Research Authority• Clemson University: Lab space and facilities support Analytical resources Chemical engineering department• Clemson University Research Foundation Business incubator space ANAXTAL Silicon
Intellectual Property• Extensive search done on prior art• U. S. provisional patent filed March 2009• Full patent filed in March 2010: United States International PCT needed• Additional IP is expected for controls and sensors ANAXTAL Silicon
AbstractMETHODS FOR MAKING SILICON NITRIDE ARTICLES AND SILICONThe present invention provides methods for making silicon nitridearticles and methods for making silicon using those articles.Unexpectedly, Applicant has found that high purity silicon nitride canbe deposited from molten silicon. In certain conditions, β-phasesilicon nitride is deposited. Given nitrogen’s relatively low solubilityin silicon, such silicon nitride articles such as crucibles are verydesirable for manufacturing high purity silicon. Moreover, β-phasesilicon nitride is less soluble in molten silicon than α-phase siliconnitride, allowing the β-phase silicon nitride articles to last longer.Applicant has also invented methods to maintain and grow siliconnitride liners, including β-phase silicon nitride liners, during the siliconmanufacturing process. The disclosed embodiments provide a viablealternative to quartz crucibles and other materials that are quicklyconsumed during silicon manufacturing and crystal pullingoperations. ANAXTAL Silicon
Conclusion• Investment and collaboration has significant benefits for expanding your renewable energy portfolio• Expands your reach in the solar PV value chain• Excellent model to expand the industry by enabling regionalization of the entire production cycle• Outstanding financial returns ANAXTAL Silicon