(Invited) On the Manipulation of Phosphorus Diffusion as Well as the Reduction of Specific Contact Resistivity in Ge by Carbon Co-Doping
Authors: Luo Jun , Liu Jinbiao , Simoen Eddy , Wang Guilei , Mao Shujuan , Radamson Henry H , Duan Ningyuan , Li Junfeng , Wang Wenwu , Chen Dapeng , Zhao Chao , Ye Tianchun 
Published: February 2020

Thanks to its intrinsic high mobilities for carriers i.e. 3900 and 1900 cm2V-1s-1 for holes and electrons respectively, Ge has resurged as an alternative channel material for metal-oxide-semiconductor field-effect transistors (MOSFETs) [1]. To realize the-state-of-the-art high-performance Ge devices, the formation of highly activated shallow junctions especially n-type junction as well as the large contact specific contact resistivity (ρc), however, are still great challenges remained to be resolved, in spite of numerous efforts spent in the past decade [2, 3]. Impurity species such as carbon (C), nitrogen (N) and fluorine (F) are utilized to suppress the rapid diffusion of phosphorus in Ge by trapping vacancies [4, 5], while at the expense of a reduced activation level usually. Specifically, in this paper, the impact of C implantation parameters (energy and dose) on the diffusion and activation of P in Ge pre-amorphized (PAI) germanium epitaxial layers on Si (100), is systematically explored. All samples received a Ge PAI at 20 keV, 6×1014
at/cm2, followed by C implantation at different energies ranging from 3 keV to 20 keV and doses varying from 5×1014 to 2×101
5 at/cm2. P was implanted with a fixed condition using an energy of 5 keV and dose of 2×101
5 at/cm2 and was completely contained in the amorphous Ge layer. During annealing, to prevent out-diffusion of the implanted dopants, all samples were capped with a 20 nm thick SiO2 deposited by plasma enhanced chemical vapor deposition (PECVD) at 280 oC. The annealing process was carried out in N2 ambient at 600 oC for 60 s. It is illustrated in Fig. 1a that the shallowest N-type junction occurs for C implantation at 8 keV with a dose of 1×1015 cm-2. This optimum condition can be ascribed to the carbon distribution shown in Fig. 1b that carbon atoms straddles the amorphous/crystal (a/c) interface. As a result, both the diffusion of P in the amorphous layer and in the Ge virtual substrate beyond the a/c interface can be effectively suppressed. Except the control of P diffusion, the specific contact resistivity (ρc) between NiGe and n-Ge by the presence of C is also investigated. As illustrated in Fig. 2, the thermal stability of NiGe films is obviously enhanced by the presence of C and this can be inferred by the decreasing sheet resistance till 600 oC and the pretty smooth NiGe/Ge interface for samples with C. At 500 oC germanidation temperature, the rc values are reduced from 1.1×10-4 Ω-cm2 and 2.9×10-5 Ω-cm2 for NiGe/n- and p-Ge contacts without carbon to 7.3×10-5 Ω-cm2 and 1.4×10-5 Ω-cm2 for their counterparts with carbon, respectively, as illustrated in Fig. 3 and 4.

References

[1] Y. Kamata, Mater. Today, vol. 11, issue 1-2, pp. 30-38, Jan. 2008
[2] J. Vanhellemont and E. Simoen, Mater. Sci. Semicond. Process., vol.15, 642 (2012).
[3] M. Shayesteh, C. L. L. M. Daunt, D. O¢Connell, V. Djara, M. White, B. Long, and R. Duffy, IEEE Trans. Electron Devices, vol. 58, no. 11, pp. 3801-3807, Nov. 2011
[4] E. Simoen, M. Schaekers, J. Liu, J. Luo, C. Zhao, K. Barla and N. Collaert, to be published in E-MRS proc., 2016.
[5] J. B. Liu, J. Luo, E. Simoen, Y. X. Niu, F. Yang, G. L. Wang, W. W. Wang, D. P. Chen, J. F. Li, C. Zhao, and T. C. Ye, ECS J. Solid State Science and Techno., vol. 5, no. 6, pp. 315-319, 2016.

Figure 1