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Schumacher Bromosilane Process
Schumacher Bromosilane Process Background The Schumacher Bromosilane Process ("SBP") was initially conceived and developed by Dr. John Schumacher while he was President and Chief Executive Officer of J.C. Schumacher Company. Ten years and over $25 million was invested in designing and operating lab and larger scale facilities utilizing the process. Valuable "know-how" was gained regarding production of electronic grade ("EG") polycrystalline silicon by means of the bromosilane process, during this period.
The work included the operation of a mini-plant that covered all major process features, and successfully produced very pure pellet material shown above that meets the purity requirements of the solar electricity ("SE") generation industry as seen in the following Table.
Previous work also included both design and construction of a 40 MTPY pilot plant based on the mini-plant experimental data, so that the true costs for plant construction at this scale are known. J.C. Schumacher Company plans to commercialize the Schumacher Bromosilane Process were abandoned when Air Products and Chemicals acquired the Company’s principal business of electronic chemical and equipment manufacturing in 1987. In the ensuing 20 years since the commercialization project was shut down, several factors have come to light that confirm that the SBP is the safest, most reliable process to produce low cost EG polysilicon. They explain why bromosilane and only bromosilane can make the spherical beads wanted for continuous pulling, why silane always has to be diluted, and why bromosilane reactors are easier to operate for longer periods of time than silane or chlorosilane alternatives. Technology SBP poly, seen above, meets all the requirements for mass deployment of solar electric ("SE") generation. Its purity allows for high efficiency conversion of sunlight into electricity. Its projected cost elements are significantly below those upon which silicon prices paid by the industry today are based. Finally, its dense spherical bead form factor and uniform particle size distribution make it the ideal feedstock for the continuous high volume substrate manufacturing processes fundamental to forecasted demand expansion and price reduction. The SBP process change from conventional polysilicon approaches is from an open-loop, batch, high temperature process, to a closed-loop (environmentally friendly), continuous, low temperature process. This innovation is accomplished by changing the silicon chemistry from a chlorine base to a bromine base (tribromosilane or "TBS"), and use of a "fluid bed" ("FB") deposition reactor with continuous recycle of by-products. No material availability constraints on production volume of the process exist because silicon is the second most plentiful element in the earth’s crust, and according to the US Geological Survey Mineral Commodity Summaries "resources of bromine are virtually unlimited." Competitive Advantage Factors demonstrating the technical and economic superiority of the SBP have come to light as a result of continued study of EG silicon technology over the past 20 years. The following paragraphs list a number of significant differences between the SBP and TCS/Silane approaches that contribute to high cost, low reliability and quality, and difficulty in downstream processing into SE and IC substrates, of the latter.
Bromosilanes obviously are the best way to low cost high-grade silicon. The Schumacher process that uses undiluted ("TBS") tribromosilane with silicon tetrabromide ("STB") recycle to a hydrogenation reactor possesses significant advantages. Process Development Project A flexible plan has been developed for commercializing the Schumacher Bromosilane Process. Earlier process designs will be examined to identify areas where meaningful cost reduction is possible, if done without sacrificing process operability, product quality or safety. The dramatically improved modeling tools now available will be used to reduce the capital costs of the facility. Potential modifications to the system will be analyzed by use of the available detailed design information, by use of scale factors of the pilot plant and commercial plant costs, and by use of standard factors for material of construction changes which are available in chemical engineering literature. Schumacher’s unique tribromosilane ("TBS") based fluid bed ("FB") poly seen above, meets all the requirements for mass deployment of SE. Its high purity provides high conversion efficiency of sunlight directly into electricity. The cost is significantly below competing means of producing high-quality silicon. Minimum energy investment pay-back time is insured by the small total heat load compared to alternate technologies. Finally, its dense spherical bead form factor and uniform particle size distribution make it the ideal feedstock for continuous substrate manufacturing processes.
Pilot scale production will first be carried out at a greenfield site in south central Oregon. Since the process is portable, large scale production facilities can then be
constructed anywhere in the world. It should also be noted that the costliest
process component, bromine, is available in large quantities at low cost, from many
sources
throughout the world.
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