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Source-Drain Contact Engineering

For nanometer scale transistors reduction of source/drain (S/D) series resistance is most essential. The silicide layer used as the S/D contact should be thin and its contact resistance to the highly doped Si, SiGe or Ge should be very small. This holds, especially for devices fabricated on ultra thin SOI substrates in order to achieve a low S/D series resistance.

Ultra-thin silicides/germanides formed on Si, SiGe and Ge, which have a high thermal stability, low sheet resistance and low contact resistivity, and are uniform in morphology, are of our main interest.

We have successfully formed high quality single crystalline NiSi2 layers on Si and strained Si substrates. The results showed:
• Very low contact resistivity on n+ and p+ doped Si,
• Well controlled alignment to the gate without encroachment,
• Very high thermal stability which allows variable thermal treatments for junction formation.

Epitaxial NiSi2 S/D contacts have been used in 20nm SOI MOSFETs. Ion implantation into epitaxial-NiSi2 and dopant segregation at low temperatures allow formation of very steep tunnel junctions, significantly improving the tunneling currents in Si nanowire tunnel FETs (TFETs) (L. Knoll et al, IEEE Electron Device Letter. VOL. 34, NO. 6, pp.813-815, 2013).

Very homogeneous thin NiSiGe layers have been achieved on both, strained and relaxed SiGe substrates. The development is of high interest for pMOS FDSOI at 14nm.

Source-Drain ContactsFig.1: Single crystalline NiSi2 formed on SOI substrate (left); NiSi2 nanowire contact to strained Si nanowire tunnel FETs.

Source-Drain ContactsFig.2: single crystalline Ni(Al)SiGe contact on SiGe

Recent publications

Linjie Liu, Lei Jin, Lars Knoll, Stephan Wirths, Alexander Nichau, Dan Buca, Gregor Mussler, Bernhard Holländer, Dawei Xu, Zeng Feng Di, Miao Zhang, Q.T. Zhao, and Siegfried Mantl,
“Ultrathin highly uniform Ni(Al) germanosilicide layer with modulated B8 type Ni5(SiGe)3 phase formed on strained Si1xGex layers”.
Applied Physics Letters 103, 231909 (2013); doi: 10.1063/1.4838695

Q.T. Zhao, L. Knoll, B. Zhang, D. Buca, J.-M. Hartmann, Siegfried Mantl,
„Ultrathin epitaxial Ni-silicide contacts on (100) Si and SiGe: Structural and electrical investigations”,
Microelectronic Engineering. 03/2013; 107:190-195.

B. Zhang, W. Yu, Q.T. Zhao, D. Buca, U. Breuer, J.-M. Hartmann, B. Holländer, S. Mantl, M. Zhang, X. Wang, “Effects of C+ ion implantation on electrical properties of NiSiGe/SiGe contacts „ Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 10/2013; 307:408–411.

J. L. Padilla, L. Knoll, F. Gámiz, Q.T. Zhao, A. Godoy, and S. Mantl,
“Simulation of Fabricated 20-nm Schottky Barrier MOSFETs on SOI: Impact of Barrier Lowering”,
IEEE Transactions on Electron Devices , 59(5), pp.1320-1327, 2012.

Q.T. Zhao, L. Knoll, A. Schäfer, S. Trellenkamp, K. K. Bourdelle, and S. Mantl, (invited)
”Planar and Nanowire Schottky Barrier MOSFETs on SOI with NiSi and Epitaxial NiSi2 Contacts”
2012 12th International Workshop on Junction Technology Extended Abstracts, 2012, Shanghai, China

Q.T. Zhao, L. Knoll, S. Richter, S. Trellenkamp, A. Schäfer, K. K. Bourdelle and S. Mantl (invited),
“Si Nanowire Tunnel FETs with Epitaxial NiSi2 Source/Drain and Dopant Segregation”,
IEEE International Conference on Solid-State and Integrated Circuit Technology (ICSICT), 2012