Low‐Temperature Selective Growth of Heavily Boron‐Doped Germanium Source/Drain Layers for Advanced pMOS Devices

• Published in: Physica status solidi. A, Applications and materials science Applications and materials science, 2020-02, Vol.217 (3), p.n/a
• Main Authors: Porret, Clement, Vohra, Anurag, Nakazaki, Nobuya, Hikavyy, Andriy, Douhard, Bastien, Meersschaut, Johan, Bogdanowicz, Janusz, Rosseel, Erik, Pourtois, Geoffrey, Langer, Robert, Loo, Roger
• Format: Article
• Language: English
• Subjects: Boron; Carrier density; Chemical vapor deposition; Contact resistance; contact resistivity; Deactivation; Doping; Electric contacts; Electrical resistivity; First principles; Germanium; germanium pMOS; Hall effect; Low temperature; low-temperature selective epitaxial growth; Material properties; Organic chemistry; Performance degradation; source/drain materials; Transmission lines
• ISSN: 1862-6300; 1862-6319
• DOI: 10.1002/pssa.201900628

The peculiarities of heavily boron‐doped germanium, selectively grown at low temperature by means of a cyclic deposition and etch chemical vapor deposition process, are investigated through the analysis of the structural and electrical material properties. The incorporation of B in Ge can exceed 6 × 1020 cm−3, close to a factor 100 above the solubility limit, without any significant degradation of the Ge:B crystalline quality, although high B‐doping induces an unwanted contraction of the Ge lattice. Micro‐Hall effect measurements and the multiring circular transmission line method are used to evaluate the active carrier concentrations and resistivities of Ti/Ge:B contacts. Even though the resistivity of as‐grown layers saturates for chemical B concentrations approaching 1 × 1021 cm−3 and increases beyond that level, a contact resistivity below 3 × 10−9 Ω cm2 is obtained for the highest active doping concentration, showing that a compromise must be found to decrease the total contact resistance. Finally, first principles simulations are used to understand dopant deactivation mechanisms in the Ge:B system. In conclusion, the formation of boron‐interstitial clusters is most likely the cause for electrical performance degradation at high doping values. The peculiarities of heavily boron‐doped germanium, selectively grown at low temperature by means of a cyclic deposition and etch chemical vapor deposition process, are investigated through the analysis of the structural and electrical material properties. The experimental studies are supported by first principles simulations which are used to understand dopant deactivation mechanisms in the Ge:B system.