Formation of Metal Silicide and Metal Germanosilicide Contacts to Si[subscript 1-x]subscript Ge[subscript x] Alloys

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Title: Formation of Metal Silicide and Metal Germanosilicide Contacts to Si[subscript 1-x]subscript Ge[subscript x] Alloys
Author: Burnette, James E. Jr.
Advisors: Dale Sayers, Committee Member
Robert Nemanich, Committee Member
Gregory Parsons, Committee Member
David Aspnes, Committee Member
Abstract: The goals of this research were to study the phase stability and formation of Ti-Si[subscript 1-x]Ge[subscript x] and Co-Si[subscript 1-x]Ge[subscript x] thin film reactions. The Ti-Si[subscript 1-x]Ge[subscript x] and Co-Si[subscript 1-x]Ge[subscript x] solid phase reactions result in the formation of precipitates within the grain boundaries of the films thus formed. The precipitates are either Ge or a Si-Ge compound, depending on the type of metal used in the reaction. The formation of Ti(Si[subscript 1-y]Ge[subscript y])₂ thin films on Si[subscript 1-x]Ge[subscript x] has been examined. It has been found that the generation of Ge-rich Si-Ge precipitates which form in the Ti-Si[subscript 1-x]Ge[subscript x] solid phase reaction could be reduced or eliminated by the insertion of an amorphous Si layer before the metallization step. A Gibbs free energy model, which was parameterized in terms of Ge concentration by atomic percentage was used to determine stability between the Ti(Si[subscript 1-y]Ge[subscript y])₂ layer and the Si[subscript 1-x] Ge[subscript x] substrate. The films in this study were characterized using x-ray diffraction (XRD) to investigate phase formation, stability, and the composition of the Ti(Si[subscript 1-y]Ge[subscript y])₂ layer. Scanning electron microscopy (SEM) was used to determine the surface morphology and phase stability. It was found that amorphous Si layers of a certain thickness could prevent precipitate formation, depending on the composition of the underlying Si[subscript 1-x] Ge[subscript x] layer. The formation of CoSi₂ on Si[subscript 1-x]Ge[subscript x] was also examined. The solid phase reaction of Co and Si[subscript 1-x]Ge[subscript x] results in the formation of a poly-crystalline CoSi₂ layer, and the occurrence of a Ge precipitate. The TIME (Titanium Interlayer Mediated Epitaxy) process has been used in the formation of epitaxial CoSi₂ on Si (100). A Ti layer of varying thicknesses, which serves as a barrier to retard the diffusion of Co atoms was deposited on a c-Si/Si[subscript 1-x]Ge[subscript x] substrate pseudomorphically strained to Si (100), before the final Co metallization step. The films in this study were characterized using x-ray absorption fine structure (XAFS) to determine the short-range crystalline order, XRD to determine phase formation and long-range crystalline order, Auger electron spectroscopy (AES) to determine surface chemistry, and SEM to determine the surface morphology. This work shows that the formation of epitaxial CoSi₂ on Si[subscript1-x]Ge[subscript x] can be achieved, depending on the thickness of the diffusion barrier. In addition, the optimal diffusion barrier thickness has been determined for the Co layer thickness used in these studies.
Date: 2004-04-20
Degree: PhD
Discipline: Physics
URI: http://www.lib.ncsu.edu/resolver/1840.16/4004


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