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Optimization of Monoisotope Silicon Technology


Optimization of the Test Technology of Production of Highly Enriched Silicon Isotopes for Semiconductor Quality Crystal Growth

Tech Area / Field

  • CHE-IND/Industrial Chemistry and Chemical Process Engineering/Chemistry
  • FIR-ISO/Isotopes/Fission Reactors
  • MAT-OTH/Other/Materials
  • PHY-SSP/Solid State Physics/Physics

8 Project completed

Registration date

Completion date

Senior Project Manager
Kulikov G G

Leading Institute
TsKBM, Russia, St Petersburg

Supporting institutes

  • Russian Academy of Sciences / Physical Technical Institute, Russia, St Petersburg\nInstitute of Chemistry of High Purity Substances, Russia, N. Novgorod reg., N. Novgorod\nKhlopin Radium Institute, Russia, St Petersburg


  • Physikalisch-Technische Bundesanstalt / Braunschweig Branch, Germany, Braunschweig\nEuropean Commission / Joint Research Center / Institute for Reference Materials and Measurements, Belgium, Geel\nVITCON Projectconsult GmbH, Germany, Jena\nFreie Universität Berlin / Institut fur Experimentalphysik, Germany, Berlin\nInstitute of Crystal Growth, Germany, Berlin

Project summary

The proposed work is related to the conversion activity of CENTROTECH, RI, IChPS, PhTI, PNPI, and is devoted to the optimization of the technology of production of chemically pure monoisotopic silicon and study of its properties.

During the Project МSTC #1354 performance, we designed and tested the demonstration monoisotopic silicon technology with a productivity Si-28 ~0.5 kg/year, using the following chain of works: production of the isotopically enriched silicon in the form SiF4, enriched in the given isotopes conversion of SiF4 into the monosilane using metal hydrides or aluminium hydrides pyrolytic decomposition of the monosilane with the production of a polycrystalline silicon. Samples of the polycrystalline silicon-28 with isotopic concentration more than 99.98%, Si-29, Si-30 with the isotope content more than 99% were obtained. Using that material project collaborator in Germany has grown the monocrystals Si-28, Si-29, Si-30 for the first time in the world. Epitaxial layers of the monocrystal silicon-28, silicon-30 and heterostructures Si-28/Si-30 were grown and examined in PhTI. In PNPI a transmutation neutron doping of the epitaxial layers samples of Si-30 and heterostructures Si-28/Si-30 was carried out for the first time in the world.

Actual directions of application of this technology are:

– creation of the mass standard on the basis of the monoisotopic perfect crystals of the highly enriched Si-28 (99.98 %) and Si-30 (99.5%) (Project of precise definition of the Avogadro constant);

– monochromators of the synchrotron radiation based on the crystals Si-28;
– production of the monocrystalline and polycrystalline materials on a basis of Si-29 for the research related to the Quantum computing;
– production of isotopic heterostructures on the basis of Si-30 and Si-28 for the investigations in the area of solid state microelectronics, design of microelectronic circuits and basic elements of integrated schemes, in particular, isotopic superlattices Si-28/Si-30.

The programs of realization of works in these directions have started in the EU countries, USA, Japan and other countries. In particular, in April 2002 taking into account the results of ISTC Project 1354, it was decided to starts the works on Project Avogadro. The project proposed by ISTC supplements the NIMIS international project on the Avogadro constant performed within the framework of 6-frame programme, however, it presents an independent value.

The total demands of silicon isotopes for these programs are up to 10 kg of Si-28/year and hundreds of grams of the isotopes Si-29, Si-30 per year. On the basis of investigations of the silicon isotopes produced during the works on the Project #1354 in Russia and abroad, the technical requirements of the isotopic and chemical purity of isotopes Si-28, Si-29, Si-30 are now specified.

The basic scientific and technical problem for the use of the developed technologies in the specified directions is the increase of the chemical purity of the produced polycrystalline monoisotopic silicon in relation to the content of oxygen, carbon, boron impurities up to a level relevant to the requirements of the mass standard in the Project "AVOGADRO" and for a microelectronics - less than 1-3·1015 atoms/cm3 for the O, C impurities and less than 1·1015 atoms/cm3 for В.

Besides, the chemical purification of the isotope polycrystalline silicon during its production, and also during growing of the perfect silicon isotopes monocrystals at an existing level of technology results in essential losses of the isotopic enriched silicon - more than 50%, that is unacceptable.

These factors are critical for the prospects of the large-scale manufacture of the silicon isotopes and for the determination of the economic prospective of the technology. That is why additional scientific investigations and technologies development for the increase of the chemical (100 times higher) and isotopic purity (up to >99.985%) of the silicon isotopes are required as well as an increase of a utilization factor of the isotopic enriched silicon up to 80% during its processing into monocrystals with simultaneous ~10 times increase of the achieved productivity.

The principal objective of the Project is the improvement of the technology of production of the high-enriched silicon isotope in the form of the pure polycrystals with the impurity concentrations matching the requirements of the AVOGADRO project, and for the realization of the modern investigations of new physical properties of such materials.

The basic proposed activities are:

– development of the advanced technology of the silicon isotopes separation in the form of SiF4, providing the decrease of the impurities content and concentrations of isotopes Si-28 (99.99 %), Si-29, Si-30 (> 99%) with productivity of Si-28 (99.99%) up to 5-7 kg per one year (CENTROTECH),

– manufacturing the pilot samples of 28SiF429SiF430SiF4 for subsequent chemical transformation into SiH4, Si02 and polycrystalline silicon with the purpose of improvement of technology of manufacturing of large lots of isotopic silicon with isotopic and chemical cleanliness matching the AVOGADRO project, and for growing of the epitaxial layers of the monoisotopic silicon and analytical investigations (CENTROTECH),
– improvement of the RI technology of production of silicon isotopes in the form of the polycrystals with the purpose of decrease of the content of the carbon and oxygen impurities down to the requirements of the Project Avogadro. Manufacturing of the samples of all isotopes in the form of SiH4 and polycrystalline silicon for the realization of works on improvement of the analysis methods, growing of the epitaxial layers of the silicon monoisotopes and 28Si monocrystals (for initial growing rods - ”slimrods”), with the amount of isotopes 28Si (RI) - hundreds of grams.
– improvement of the IChPS technology of silicon-28 isotopes production in the form of the rod polysilicon-28 with enlarged installations productivity up to 5 kg of 28Si per year and decrease of the carbon and oxygen impurities content down to the requirements of the Project Avogadro. Manufacturing of the pilot lots of the polycrystalline 28Si in amount of some hundreds grams with a quality matching the requirements of the AVOGADRO project (IChPS),
– improvement of the methods of the analysis of a chemical and isotope composition of silicon in the form of SiF4, SiH4, polycrystalline Si with a limit of detection of the critical impurities at the level that 2-10 times lower, than the requirements of the Project Avogadro, and measurement accuracy for the concentration of the isotope 28Si (99.99 %) in these forms less then 0.005%. Analytical determination of the isotope and chemical compositions of the final and intermediate products (IChPS, PhTI, RI, CENTROTECH),
– optimization of isotope heterostructures growing technology using gas-phase and molecular-beam epitaxy methods and investigation of their properties. At growing of layers of the super-lattices 28Si/30Si and layers Si-29 for the quantum computer works the content of the electrically active microimpurities B, Р, Аl is provided at a level less than 1014-1015 atoms/cm3 by means of the improved technology and by the use of the isotope silicon materials with the low impurities content (PhTI),
– improvement of the technology of a neutron doping of the isotopic heterostructures 28Si/30Si and epitaxial layers 30Si providing the given doping level. Investigation of neutron irradiation influence on the layers of the isotopically pure 28Si, 29Si and 30Si (PhTI, PNPI)
– investigation of the semiconductor properties of the isotopic heterostructures, super-lattices and other samples, made of the silicon monoisotopes (PhTI).


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