Diffusion and Defects in Elementary and Compound Semiconductors
Copper related diffusion phenomena in germanium and silicon
Today an increasing interest in the properties of native point defects (vacancies and self-interstitials) and
foreign-atoms in Ge and SiGe alloys exists. This renewed interest in Ge and SiGe arises from their promising
applications in Si-based integrated circuit technology. With the advanced development of epitaxial deposition
techniques the former obstacles which strongly limited the use of Ge as the base material for electronic devices
no longer seriously exists. Using Ge or SiGe epitaxial layers instead of Si one can take advantage of the higher
carrier mobility in the Ge-rich layer. In the past 10 years the use of Cu as interconnection metal in the
ultra large-scale integration era of Si integrated circuits was extensively investigated. Compared to Al, which has
been the interconnect material for about 30 years, Cu possesses a lower resistivity and higher
electromigration resistance than Al. These advantageous properties of Cu, which also hold in comparison with
other possible metals, make this material highly suitable for the interconnection metal. This work concerns
diffusion related properties of Cu in Ge and Si. In Ge, Cu prefers to occupy a substitutional lattice site whereas
Cu in Si is mainly dissolved on an interstitial position. This difference in the lattice site occupancy is also
reflected in the diffusion behaviour. Whereas Cu diffusion in Ge is accurately described on the basis of the
dissociative mechanism, which involves Ge vacancies for the conversion of Cu from interstitial to substitutional
sites, the diffusion of Cu in Si is mainly mediated by the direct interstitial mechanism. The specific diffusion
behaviour of Cu in Ge and Si as well as its electronic properties strongly affect other diffusion related
phenomena such as the precipitation and gettering of Cu. Detailed understanding of the latter processes are of
fundamental technological significance to keep the contamination of electronic devices during processing to a
harmless level. The various aspects of Cu in Ge and Si, which are the result of former and recent experiments,
were reviewed in this work.
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