The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Iron Gettering in Silicon Using Doped Layers and Bulk Defects

Heli Talvitie

Doctoral dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the School of Electrical Engineering for public examination and debate in the Large Seminar Hall of Micronova at the Aalto University School of Electrical Engineering (Espoo, Finland) on the 2nd of December 2011 at 12 noon.

Overview in PDF format (ISBN 978-952-60-4357-9)   [1859 KB]
Dissertation is also available in print (ISBN 978-952-60-4356-2)

Abstract

The removal of iron impurities to desired regions in silicon wafers has been studied using phosphorus and boron doped layers and bulk defects as gettering sites. Techniques to remove metal impurities, so-called gettering techniques, are needed for improving the performance of both the microelectronic and photovoltaic silicon devices, although the desired location of impurities may be different in various applications. In this work, both separate and simultaneous influences of the doped layers and bulk defects on the gettering behaviour of iron, e.g. the gettering efficiency and gettering mechanisms, were investigated.

The phosphorus diffusion gettering studies at low temperatures enabled the determination of a more accurate segregation coefficient for iron between a phosphorus diffused layer and bulk silicon. Comparison between the phosphorus diffusion gettering experiments and similar experiments with boron showed that boron diffusion gettering can in some cases be nearly as effective as the phosphorus diffusion gettering.

The gettering studies with implanted boron layers revealed that the gettering occurs also by precipitation, not only by segregation. Competitive gettering between an implanted boron layer and bulk defects was investigated using specially designed gettering anneals. It was found that depending on the desired location of iron in silicon wafers in different applications, iron can be collected either to the doped layers or the bulk defects. The gettering anneals were also applied to a microelectronic device process and their effect on the electronic device parameters was evaluated.

These results contribute to the understanding of iron behaviour in silicon. Thus, they can help when designing the gettering anneals both for microelectronic and photovoltaic fabrication processes.

This thesis consists of an overview and of the following 6 publications:

  1. H. Talvitie, V. Vähänissi, A. Haarahiltunen, M. Yli-Koski, and H. Savin. 2011. Phosphorus and boron diffusion gettering of iron in monocrystalline silicon. Journal of Applied Physics, volume 109, number 9, 093505, 5 pages. © 2011 American Institute of Physics (AIP). By permission.
  2. A. Haarahiltunen, H. Talvitie, H. Savin, M. Yli-Koski, M. I. Asghar, and J. Sinkkonen. 2008. Modeling boron diffusion gettering of iron in silicon solar cells. Applied Physics Letters, volume 92, number 2, 021902, 3 pages. © 2008 American Institute of Physics (AIP). By permission.
  3. A. Haarahiltunen, H. Talvitie, H. Savin, O. Anttila, M. Yli-Koski, M. I. Asghar, and J. Sinkkonen. 2008. Gettering of iron in silicon by boron implantation. Journal of Materials Science: Materials in Electronics, volume 19, supplement 1, pages S41-S45.
  4. Heli Talvitie, Marko Yli-Koski, Antti Haarahiltunen, Ville Vähänissi, Muhammad Imran Asghar, and Hele Savin. 2011. Experimental study of iron redistribution between bulk defects and boron doped layer in silicon wafers. physica status solidi (a), volume 208, number 10, pages 2430-2436.
  5. H. Talvitie, A. Haarahiltunen, H. Savin, M. Yli-Koski, M. I. Asghar, and J. Sinkkonen. 2009. Effect of internal gettering of iron on electrical characteristics of devices. Materials Science and Engineering B, volume 159-160, pages 269-273.
  6. H. Talvitie, A. Haarahiltunen, M. Yli-Koski, H. Savin, and J. Sinkkonen. 2008. Effect of transition metals on oxygen precipitation in silicon. Journal of Physics: Conference Series, volume 100, number 7, 072045, 4 pages.

Errata of publications 2, 3 and 5

Keywords: silicon, iron, gettering, boron, phosphorus, bulk defects

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© 2011 Aalto University

Last update 2012-07-23