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Ion Beam Applications in Silicidation Processes of Si1-xGex Layers.

Curello, Giuseppe. (1998) Ion Beam Applications in Silicidation Processes of Si1-xGex Layers. Doctoral thesis, University of Surrey (United Kingdom)..

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Si6-xGex/Si system is expected to play a major role in Si-based advanced microelectronic and optoelectronic devices. Knowledge of metallizations to the SiGe alloy is required for device applications. In this work we have studied the feasibility and characteristics of Ir and Co silicidation processes of Si1-xGex alloy layers and compared these with the correspondent silicidation process of Si. Ir and Co were chosen for their diversity in both device applications and properties. Si-xGex alloy layers were both uniform composition Molecular Beam Epitaxy (MBE) grown and graded composition Ion Beam Synthesised (IBS). The silicidation processes used exploited the use of ion beams both in the synthesis of the Si1-xGex substrates and buried Co silicides, as well as in the modification of Ir silicides/SiGe interfaces. The silicides/SiGe structures were characterized by Rutherford Backscattering-ion Channeling, Cross-sectional Transmission Electron Microscopy and Four Point Probe. Thermal reaction of Ir films with SiGe substrates has been found to follow the same phase growth sequence of the Ir/Si system, with diffusion controlled phases (1:1, 1:1.75) formed at low temperatures (450°C - 650°C) and a nucleation controlled phase (1:3) formed at temperatures higher than 900°C. Remarkably, during annealing, Ir/SiGe structures preferentially react to form silicides, with Ge being piled up at the reacting-layer/SiGe interface. This effect has been explained by thermodynamic considerations (Heat of Formation) and has been exploited in the fabrication of silicide/SiGe structures where the SiGe layers were produced by high dose Ge+ implantation into Si followed by Solid Phase Epitaxy (SPE). The optimum implantation conditions for the fabrication of such SiGe layers have been determined by an extensive study on Ge+ ion beam power and dose effect on the crystalline quality of the SPE grown layers. The crystallographic defects produced have been classified and methods to reduce these to a minimum have been developed. Ion beam mixing of the Ir/SiGe structures has shown to produce a more uniform interface as consequence of the removal of Ir grain boundaries at the reacting interface. This process however allowed a higher degree of Ge incorporation in the reacted layer to occur. Similarly to Ir, Co preferentially reacts with Si rather than with Ge. Heat of formation data confirm this experimental evidence. Ion beam synthesis of almost stoichiometric buried CoSi2 in SiGe has been demonstrated despite the high Ge concentration (36 at. %) of the Co+ implanted MBE grown SiGe layer. Co diffusion and precipitation at the SiGe/Si interface was found to occur despite the use of RTA.

Item Type: Thesis (Doctoral)
Divisions : Theses
Authors : Curello, Giuseppe.
Date : 1998
Additional Information : Thesis (Ph.D.)--University of Surrey (United Kingdom), 1998.
Depositing User : EPrints Services
Date Deposited : 30 Apr 2019 08:07
Last Modified : 20 Aug 2019 15:32

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