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B8.10.1

Diffusion of ion-implanted Boron and Silicon in Germanium Suresh Uppal, A. F. W. Willoughby, J. M. Bonara , N. E. B. cowernb , R. J. H. Morrisc and M. G. Dowsettc Material Research Group, School of Engineering Sciences, a Department Electronics and Computer Science, University of Southampton, Southampton SO17 1BJ, United Kingdom b Advance Technology Institute, University of Surrey, Guildford, Surrey GU2 7XH, United Kingdom c Physics Department, University of Warwick, Coventry, CV4 7AL, United Kingdom

ABSTRACT The diffusion of B and Si in Ge is studied using implantation doping. Concentration profiles after furnace annealing in the temperature range 800–900 ◦ C were obtained using high resolution secondary ion mass spectroscopy (SIMS). Diffusion coefficients are calculated by fitting the annealed profiles. For B, we obtain diffusivity values which are two orders of magnitude slower than previously reported in literature. An activation energy of 4.65(±0.3) eV is calculated for B diffusion in Ge. The results suggest that diffusion mechanism other than vacancy should be considered for B diffusion in Ge. For Si diffusion in Ge, the diffusivity values calculated in the temperature range 750–875 ◦ C are in agreement with previous work. The activation energy of 3.2(±0.3) eV for Si diffusion is closer to that for Ge self-diffusion which suggests that Si diffusion in Ge occurs via the same mechanism as in Ge self-diffusion.

INTRODUCTION With the scaling of Si based Complementary Metal Oxide Semiconductor (CMOS) devices reaching its limits, new materials are being considered which could synchronize with the running CMOS technology. Among these new materials SiGe and pure Ge layers grown on Si have the advantage that they can be easily incorporated in the existing Si technology. The success of the application of high-κ gate dielectrics have offered new paths for CMOS device realization on Ge substrates [1]. However, dopant diffusion in these materials need to be well characterized in order to utilize their full potential. Boron diffusion studies in Ge are about 40–50 years old in which electrical methods like pn-junction were used to quantify diffusion. Deposition of B on Ge substrates [2] and B doped Ge powder [3] were used as dopant sources for diffusion in earlier studies. With the advancement in technology, new and more accurate methods have become available for dopant introduction and profile measurement. Therefore, there exist a requirement to study B diffusion in Ge using state of the art methods. Investigations on Si diffusion in Ge have also been limited. Methods of introduction of Si in Ge included implantation [4, 5] and sputter deposition of Si directly on Ge substrates [6]. The concentration profiles have been measured using (p-γ) resonance [4], sputtering [5] and Secondary Ion Mass Spectroscopy (SIMS) [6]. In the present work, we have utilized a combination of ion-implantation and SIMS to investigate B and Si diffusion in Ge.

B8.10.2

EXPERIMENTAL PROCEDURE Ge wafers, supplied with low dislocation den