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

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.