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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Heterogeneous Precipitation and Internal Gettering Efficiency of Iron in Silicon

Antti Haarahiltunen

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Electrical and Communications Engineering for public examination and debate in Large Seminar Hall of Micronova at Helsinki University of Technology (Espoo, Finland) on the 23rd of March, 2007, at 12 noon.

Overview in PDF format (ISBN 978-951-22-8684-3)   [751 KB]
Dissertation is also available in print (ISBN 978-951-22-8683-6)

Abstract

In this thesis the heterogeneous iron precipitation was studied in silicon using oxide precipitates and related defects as precipitation sites. The motivation of the theoretical work is to find a model which quantitatively describes internal gettering results of iron under various supersaturation levels. The experimental work is used to verify the model.

The results of this thesis indicate that the initial iron concentration level has a major impact on gettering efficiency and a high supersaturation ∼0.34 eV is needed before significant nucleation of iron precipitates can occur. The internal gettering of iron at low levels of initial iron concentration (<1×1012 cm−3) is practically impossible to achieve by cooling. The low temperature nucleation anneal is needed to induce a significant number of iron precipitates which then grow and getter iron at higher temperatures. For optimal internal gettering the proper combination of nucleation and growth steps of iron precipitates must be found. The optimal place for two step gettering is after the last high temperature anneal in which all iron precipitates are dissolved, if it is assumed that device performance is mainly determined by the final concentration of metal precipitates and dissolved iron concentration in the device layer.

A model is presented for the heterogeneous precipitation of iron to oxygen-related defects in silicon during thermal processing. In the model we use special growth and dissolution rates, which are inserted into a set of modified Chemical Rate Equations or into the Fokker Planck Equation, to simulate time evolution of iron precipitates. This approach allows us to calculate the size distribution of iron precipitates and the residual iron concentration. By comparing the simulated results with numerous experimental results, it is proved that this model can be used to estimate the internal gettering efficiency of iron under a variety of processing conditions.

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

  1. A. Haarahiltunen, M. Yli-Koski, H. Väinölä, M. Palokangas, E. Saarnilehto, and J. Sinkkonen, Experimental study of internal gettering efficiency of iron in silicon, Physica Scripta T114, 91-93 (2004). © 2004 Institute of Physics Publishing. By permission.
  2. A. Haarahiltunen, H. Väinölä, M. Yli-Koski, E. Saarnilehto, and J. Sinkkonen, Detection of iron contamination in internally gettered p-type silicon wafers by lifetime measurements, The Electrochemical Society Proceedings Vol. 05, High purity silicon VIII, Editors: C. L. Claeys, M. Watanabe, R. Falster and P. Stallhofer, p 135-145 (2004). © 2004 The Electrochemical Society (ECS). By permission.
  3. H. Väinölä, A. Haarahiltunen, E. Saarnilehto, M. Yli-Koski, J. Sinkkonen, and O. Anttila, Enhancement of internal gettering efficiency of iron by low temperature nucleation, The Electrochemical Society Proceedings Vol. 05, High purity silicon VIII, Editors: C. L. Claeys, M. Watanabe, R. Falster and P. Stallhofer, p 160-164 (2004). © 2004 The Electrochemical Society (ECS). By permission.
  4. A. Haarahiltunen, H. Väinölä, O. Anttila, E. Saarnilehto, M. Yli-Koski, J. Storgårds, and J. Sinkkonen, Modeling of heterogeneous precipitation of iron in silicon, Applied Physics Letters 87, 151908 (2005). © 2005 American Institute of Physics. By permission.
  5. A. Haarahiltunen, H. Väinölä, O. Anttila, M. Yli-Koski, and J. Sinkkonen, Experimental and theoretical study of heterogeneous iron precipitation in silicon, Journal of Applied Physics 101, 043507 (2007). © 2007 American Institute of Physics. By permission.
  6. A. Haarahiltunen, H. Väinölä, O. Anttila, M. Yli-Koski, and J. Sinkkonen, Modeling and optimization of internal gettering of iron in silicon, ECS Transactions Vol. 3 (4), Editors: C. L. Claeys, M. Watanabe, R. Falster and P. Stallhofer, p 273-284 (2006). © 2006 The Electrochemical Society (ECS). By permission.

Keywords: silicon, iron, internal gettering, precipitation, oxide precipitates

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© 2007 Helsinki University of Technology

Last update 2011-05-26