Pushing the doping limit for future FETs


Pushing the doping limit for future FETs

Zhou, S.

In recent years, small-sized transistors including FinFETs or Nanowire FETs (or Gate-all-around FETs) have been manufactured to reduce the voltage and power consumption of devices. When CMOS transistors are scaled down below the 10 nm technology node, the effect of contact resistance on power consumption increases because the contact area decreases for smaller transistors. For nodes of <7 nm, the metal–semiconductor contact resistance become a dominant contributor to the total parasitic resistances of the transistor [1, 2]. To solve the problem, n- or p-type impurities were introduced at the alloy concentration in Si and SiGe [1, 2]. However, due to the self-compensation via defect complexes at high impurity concentration, the free carrier concentration saturates. In this talk, I will discuss our approaches to tackle this challenge. One is the use of deep level impurities for doping Si, for instance, chalcogen Te [3]. Contrary to general expectations, we find that with increasing Te doping concentration its interstitial fraction decreases and substitutional Te dimers become the dominant configuration. As shown by first-principle calculations, these Te dimers have the lowest formation energy and donate two electrons each to the conduction band. Another approach is to play with different annealing time scale. We find that by millisecond flash lamp annealing the dead P-dopants can be deliberated [4, 5]. Positron lifetime measurements indicate the dissolving of single vacancies. Therefore, we trace the origin of the unprecedented electron concentrations in Si and in Ge to the atomistic scale. Our results have fundamental implications in semiconductor physics as well as to the source/drain applications for future FETs.
[1] Z. Ye, et al., Applied Materials, ECS Trans. 98, 239 (2020).
[2] G. Rengo, et al., IMEC, ECS Trans. 98, 27 (2020).
[3] M. Wang, et al., Phys. Rev. Appl. 11, 054039 (2019), arXiv:1809.06055
[4] S. Prucnal, et al., Phys. Rev. Appl. 10, 064055 (2018), arXiv:1901.01721
[5] S. Prucnal, et al., New J. Phys., in press (2020).

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