Characterisation of nickel germanide formed on amorphous and crystalline germanium

Algahtani, F 2014, Characterisation of nickel germanide formed on amorphous and crystalline germanium, Doctor of Philosophy (PhD), Electrical and Computer Engineering, RMIT University.


Document type: Thesis
Collection: Theses

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Title Characterisation of nickel germanide formed on amorphous and crystalline germanium
Author(s) Algahtani, F
Year 2014
Abstract Germanium offers unique properties as a semiconductor materials for complementary metal–oxide–semiconductor (CMOS) devices with nearly four times the hole mobility and two times the electron mobility of silicon resulting in higher currents. However, two essential requirements in the application of Ge for CMOS technology are the formation of shallow junctions and the formation of ohmic metal contacts with low resistance.

High diffusivity of dopants in crystalline germanium is a problem when forming shallow junctions. However, amorphisation of crystalline germanium where dopant implants are to occur leads to shallow junctions. In this work both amorphous and crystalline germanium (a-Ge and c-Ge) are investigated. Nickel germanide (NiGe) formed on a-Ge and c-Ge is investigated for material and electrical properties. NiGe has been reported as a suitable germanide for low resistance ohmic contacts on c-Ge. The crystal quality of films formed is poorer for the germanides formed on a-Ge but there is only a slight increase in sheet resistance. The grains of NiGe formed on a-Ge show a growth that is hexagonal like, extending into the substrate further than germanides grains formed on crystalline germanium.

The NiGe formed on c-Ge has a much more uniform thickness and uniform grain size and shape. Thin films of nickel germanide conveniently form at the relatively low temperature of 300C in a matter of minutes and at even lower temperatures over a longer time. This thesis reports on the formation of NiGe on c-Ge substrates at low temperatures (less than 300°C). Ni films deposited on Ge substrates formed NiGe by heating the samples in an atmosphere VI nearly void of oxygen. Ni films of thickness 50 to 400 nm were deposited on c-Ge and heat treatments undertaken on samples for time durations of 5 minutes to 12 hours at different temperatures.

It was found that thickness of 25nm to 100 nm was not a significant factor and that NiGe formed in a few minutes on c-Ge for this thickness of Ni heated at 300°C. The temperature of formation for 400 nm reacting with germanium was longer. For all thickness of Ni, long durations were required for the lowest temperature of formation which were between 225°C and less than 300°C. The sheet resistances of NiGe on a-Ge and c-Ge are suitably low for use in CMOS technology. Metal contacts to NiGe were investigated and low resistance contacst were obtained. The contacts to c-Ge were significantly better. Improvements in processing is required for suitably low resistance contacts to be obtained for metal to NiGe formed on aGe, but results obtained here are promising and further investigation is warranted. NiGe on a-Ge shows poorer grain crystal quality and improvements in this are likely to lead to contacts with lower specific contact resistivity.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Electrical and Computer Engineering
Keyword(s) Nickel germanide
Electrical Characterization
Amorphous and Crystalline gemanium
Characterization Processes
Sheet Resistance
Ion Implantation
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