High-Purity Highly Enriched Silicon
Development of the Plasma-Chemical Method for Direct Production of Highly Enriched Silicon Isotopes from SiF4 Gas
Tech Area / Field
- CHE-IND/Industrial Chemistry and Chemical Process Engineering/Chemistry
8 Project completed
Senior Project Manager
van der Meer A
Russian Academy of Sciences / Institute of Applied Physics, Russia, N. Novgorod reg., N. Novgorod
- Institute of Physics of Microstructures, Russia, N. Novgorod reg., N. Novgorod
- Keio University / Faculty of Science and Technology, Japan, Yokohama\nEuropean Commission / Joint Research Center / Institute for Reference Materials and Measurements, Belgium, Geel\nInstitute of Crystal Growth, Germany, Berlin\nKorea Research Institute of Chemical Technology, Korea, Taejon\nSimon Fraser University, Canada, Burnaby\nPhysikalisch-Technische Bundesanstalt / Braunschweig Branch, Germany, Braunschweig\nVITCON Projectconsult GmbH, Germany, Jena
Project summaryThe proposed work refers to conversion activities of the IAP RAS and IPM RAS and is devoted to the development of a new technology for production of highly enriched silicon isotopes (silicon-28 – 99.9995%, silicon-29- 99.97%, and silicon-30-99.97%) for use in metrology, spintronic (development of a quantum computer), and solid-state physics.
During the preceding ISTC Projects #1354, 2630, and 2980p, a demonstration monoisotopic silicon technology with a Si-28 productivity of ~5 kg/year was developed and tested. The following sequence of work was used: production of silicon in the form of SiF4, enriched by the given isotopes → conversion of SiF4 into monosilane using metal hydrides or alumohydrides → pyrolytic decomposition of monosilane with the production of polycrystalline silicon. Samples of polycrystalline silicon-28 with isotopic concentration 99.994% and high chemical purity were obtained by this “silane” method. However, this record isotopic enrichment turned out to be insufficient for preparation of the silicon synthetic isotopic mixtures required for calibration of analytical methods of high-precision determination of silicon-28 single-crystal isotopic composition for Avogadro project as well as for the development of a quantum computer.
Production of silicon-28 with an order of magnitude greater enrichment using the conventional silane method is not possible because of the isotopic dilution equal to 0.005% at all steps of chemical treatment and purification. Besides, elaboration of the direct method of production of high-purity silicon isotopes immediately from enriched SiF4, which is more efficient from both technical and economic viewpoints, is very attractive and topical. This problem can be solved by using the method of plasma enhanced chemical vapor deposition (PECVD) which is used at present for producing very thin polycrystalline silicon films of natural isotopic composition.
The principal objectives of the project are as follows. Development of the technology of direct production of high-purity and highly enriched silicon from a silicon tetrafluoride gas in the form of films and bulk polycrystals using the plasma-enhanced chemical vapor deposition (PECVD) method. Production of samples of finished product, first of all silicon-28, at a rate of several grams per hour with given parameters of isotopic and chemical purity (silicon-28 – 99.9995%, silicon-29 -99.97% and silicon-30 – 99.97%), and maximum yield (85-90%). Issue of recommendations for the promising large-scale production of silicon isotopes and isotopes of other elements having highly enriched fluoride precursors at a rate of several hundreds of grams per hour.
The submitted project implies the following main activities:
- Preliminary experiments on plasma-chemical decomposition of silicon tetrafluoride (of natural composition and enriched) and production of films and bulk silicon using a conventional commercial setup for plasma-chemical deposition equipped with capacitively coupled and inductively coupled reactor units. The task of this study is to work out the main experimental conditions and issue recommendations for creating a specialized laboratory setup for decomposition of a volatile precursor and silicon deposition with the conservation of isotope purity.
- Development and creation of a specialized laboratory setup for plasma-chemical decomposition of silicon tetrafluoride. Selection of decomposition mode based on the maximum yield and on isotopic and chemical purity of silicon.
- Development of the plasma-chemical method of production of bulk silicon samples using a specialized laboratory setup. Production of demonstration samples of highly enriched polycrystalline silicon deposited on a plane graphite or silicon substrate, the tube fabricated from refractive metal (e.g., Mo), the rod fabricated from graphite, and highly enriched silicon itself.
- Development of a chemical model of the SiF4 plasma based on the methods of thermodynamics and quantum chemistry.
- Development of diagnostics of a plasma based on silicon tetrafluoride and hydrogen.
- Development of methods of isotopic and chemical analysis of silicon tetrafluoride, exhaust gases, and polycrystalline silicon.
- Development of optical and electro-physical methods of diagnostics of polycrystalline and grown on its base single-crystal highly-enriched silicon.
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