B.A. Julies

A study of the NiSi to NiSi2 transition in the Ni–Si binary system

Abstract The growth mechanisms of the transition from polycrystalline NiSi to single-crystal NiSi2 have been investigated. Samples were prepared by depositing Ni on 〈100〉 Si substrates by ultra high vacuum electron-beam deposition followed by vacuum annealing to form a silicide. Experiments were carried out at the transition temperature of 750°C for different annealing times. Rutherford backscattering spectroscopy (RBS), cross-sectional transmission electron microscopy (XTEM), scanning electron microscopy (SEM), Auger emission spectroscopy (AES) and X-ray diffraction (XRD) were employed with special emphasis placed on scanning and transmission electron microscopy. Cross-sectional examination in the transmission electron microscope reflects the coexistence of nickel monosilicide and nickel disilicide for samples annealed at 750°C. Scanning electron microscopy shows interesting surface morphology of samples in which island-like NiSi2 growth takes place in an NiSi thin film. Grain boundaries in the initial and final stages of NiSi2 formation are characterized by holes which extend from the surface to the silicon substrate. A mechanism is proposed to account for these observations by involving the following: lattice diffusion of Ni into the Si substrate, the conversion of NiSi grains to NiSi2 via nucleation and diffusion processes and lateral grain growth resulting in accumulation of vacancies on grain boundaries resulting in holes.

Corrosion of titanium-nitride encapsulated silver films exposed to a H2S ambient

Abstract Annealing of a Ag(19 at.% Ti)/SiO 2 /Si(100) structure in a flowing NH 3 ambient resulted in the encapsulation of a silver film by a surface TiN of ∽20 nm and an interfacial TiO/Ti 5 Si 3 bilayer. TiN is formed by the reaction of the segregated Ti and the NH 3 ambient. The interfacial structure is a result of the dissociation of SiO 2 into free O and Si followed by the reaction of it with Ti. To evaluate the effectiveness of the TiN encapsulation to protect the Ag against corrosion, the encapsulated silver films were annealed in a severe H 2 S ambient for 30 min, at temperatures ranging from 100–500°C. At temperatures ≥300°C silver diffuses to the surface to react with the H 2 S to form a non-uniform layer of rhombic and cubic Ag 2 S crystallites. The unprotected Ag(Ti) alloys and pure Ag on SiO 2 corroded at 100°C, when annealed under the same conditions.

The effect of metals (Au, Ag) and oxidizing ambient on interfacial reactions in Au/Si and Ag/Si systems

Deposited metal layers on single crystal silicon can react at low temperature in an oxidizing ambient to produce silicon oxide. Akio Hiraki carried out the pioneering work in the early 1970s at California Institute of Technology. In this study Au/Si is revisited and compared with the Ag/Si system. Under oxidizing ambient conditions where oxide layers are formed in the Au/Si, no detectable oxide layers are formed in the Ag/Si system. The Ag layers agglomerates into a discontinuous film.

Amorphous and nc-Si:H Intrinsic Thin Films for Solar Cells Applications

This contribution discusses the deposition process and properties of intrinsic silicon thin films processed by the hot wire chemical vapour deposition technique. We review some fundamental characterization techniques that are used to probe into the quality of the material and thus decide its susceptibility to be used as the intrinsic layer in solar cells industry. This paper covers the optical, structural and electrical properties of the material. Results from UV-visible and IR spectroscopy, XRD and Raman scattering, X-section TEM as well as dark and photo-currents are given. It is shown that the thermal activation energy is a good measure of the quality of the sample.