Enhancing the thermal stability of NiGe by prior-germanidation fluorine implantation into Ge substrate

Abstract

Thanks to its low resistivity (22 µΩ cm), low formation temperature (300-500 °C) and low Ge consumption, NiGe is deemed as a promising candidate as source/drain contact material. However, the agglomeration of NiGe films at high temperature hinders their extensive applications in Ge-based devices. In this work, prior-germanidation fluorine implantation is employed to improve the thermal stability of NiGe films, as well as to form a shallow n-Ge junction simultaneously. As-formed NiGe films with and without fluorine were characterized by means of sheet resistance measurement, X-ray diffraction (XRD), scanning electron microscopy (SEM), and secondary ion mass spectrometry (SIMS). It is found that compared to NiGe films without fluorine, the thermal stability of NiGe films with fluorine can be improved by approximately 50 °C. Moreover, the junction depth of n-Ge with fluorine is approximately 8 nm shallower than that without fluorine. The aggregation of fluorine atoms at NiGe grain boundaries and at the NiGe/Ge interface is thought to be responsible for enhanced thermal stability, as well as the increase in sheet resistance of as-formed NiGe films.

Role of Carbon Pre-Germanidation Implantation on Enhancing the Thermal Stability of NiGe Films Below 10 nm Thickness

“…From the point of view of thermodynamics, segregated C atoms at both the grain boundaries and the NiGe/Ge interface lead to reduced interface energies. 16,17,25,28 Once the total energy of NiGe films is lowered by the introduction of C atoms, the NiGe films can be stabilized at high germanidation temperature. On the other hand, in view of kinetics, the diffusion of Ni and Ge atoms at high temperature could be hindered or slowed down by segregated C atoms at the grain boundaries and at the NiGe/Ge interface, which also gives rise to improved thermal stability in terms of delayed NiGe agglomeration similar to NiSi case.…”

“…Therefore, various methods have been proposed to improve the thermal stability of NiGe films, for example, adding a capping layer, 11 alloying Ni with high melting metals like Ta, Zr and Pt, [12][13][14] nitrogen plasma pre-treatment 10 and introducing impurities by implantation. [15][16][17][18][19] Among them, the introduction of carbon prior to Ni silicidation or germanidation has been proved to effectively suppress the agglomeration of NiSi [20][21][22] and NiSiGe, 23,24 as well as to improve the thermal stability of NiGe films. 16,25 However, in previous work, the thickness of deposited Ni films was generally large e.g.…”

Ti Interlayer Mediated Uniform NiGe Formation under Low-Temperature Microwave Annealing

“…However, one major drawback of Ni x Ge y is its rough interface due to polycrystalline grains and agglomeration at high annealing temperatures (500-550 • C). It was reported that the thermal stability of Ni x Ge y on bulk Ge could be improved by pre-germanidation implantation [6], prior-germanidation fluorine implantation into Ge substrate [7], dopant segregation [8], or introducing other elements, such as titanium (Ti) [9], platinum (Pt) [10], tungsten (W) [11], tantalum (Ta) [11,12], cobalt (Co) [13], ytterbium (Yb) [14], and so on.…”