Optical activation of copper in silicon studied by carrier lifetime measurements
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Doctoral thesis (monograph)
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Date
2004-11-12
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en
Pages
75
Series
Reports in electron physics, 31
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.Description
Keywords
silicon, copper, photoconductivity, corona charge, carrier lifetime, optical activation, precipitation