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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Optical Activation of Copper in Silicon Studied by Carrier Lifetime Measurements
Marko Yli-Koski
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 Auditorium S4 at Helsinki University of Technology (Espoo, Finland) on the 12th of November, 2004, at 12 o'clock noon.
Dissertation in PDF format (ISBN 951-22-7234-2) [506 KB]
Dissertation is also available in print (ISBN 951-22-7233-4)
Abstract
In this work copper in silicon is studied by means of the microwave photoconductive decay technique. The motivation of this work is to develop a solution for the quantitative measurement of trace copper contamination in silicon using charge carrier lifetime measurements. The goal of this work is to study the influence of corona charge, oxygen defects and light intensity on the recombination activity of copper and the formation of copper precipitates at room temperature.
The results of this thesis indicate that the optical activation of copper takes place under high excess charge carrier conditions when boron-doped silicon contains interstitial copper atoms. Due to the positive charge state of interstitial copper atoms, a positive corona charge on the silicon dioxide layer prevents interstitial copper diffusion from p-type bulk silicon to the silicon surface. Interstitial copper is shown to exist in boron-doped bulk silicon after long storage periods. It is suggested that the main reason for the optical activation of copper is the decrease in the precipitation barrier of copper due to the change in the charge state of copper precipitates. The recombination activity of copper after a long optical activation time is independent of light intensity. The density of growing copper precipitates increases when the light intensity, the density of oxygen defects or the density of interstitial copper is increased. The quantitative detection limit of copper is shown to be about 3×1012 cm−3 in boron-doped silicon without oxygen defects. However, oxygen defects increase the recombination activity of copper. It is estimated that a copper concentration of 5×1010 cm−3 is quantitatively measurable, if the bulk silicon contains small oxygen defects at high density.
Keywords: silicon, copper, photoconductivity, corona charge, carrier lifetime, optical activation, precipitation
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© 2004 Helsinki University of Technology
Last update 2011-05-26