This work reports on the morphological and electrical properties of Ni-based back-side Ohmic contacts formed by laser annealing process for SiC power diodes. Nickel films, 100 nm thick, have been sputtered on the back-side of heavily doped 110 mu m 4H-SiC thinned substrates after mechanical grinding. Then, to achieve Ohmic behavior, the metal films have been irradiated with an UV excimer laser with a wavelength of 310 nm, an energy density of 4.7 J/cm(2) and pulse duration of 160 ns. The morphological and structural properties of the samples were analyzed by means of different techniques. Nanoscale electrical analyses by conductive Atomic Force Microscopy (C-AFM) allowed correlating the morphology of the annealed metal films with their local electrical properties. Ohmic behavior of the contacts fabricated by laser annealing have been investigated and compared with the standard Rapid Thermal Annealing (RTA) process. Finally, it was integrated in the fabrication of 650V SiC Schottky diodes.

Nickel-silicon compounds, as most of the transition metal silicides, show peculiar thermodynamic and kinetic behaviours. The reason resides in the metastability of a rich variety of different phases, which are frequently favoured by the interaction with the substrate or by the limited amount of atoms available during the reactions (thin films). The large effort devoted to the comprehension of the phenomena governing Ni-Si interaction from the very beginning of the reaction process testifies the widespread interest in the field and it is driven by the need to push as far forward as possible the scaling down of micro/nano-electronics devices. Here, we provide a review on the crucial role of the early stages of the Ni-Si atomic interaction to show how this interaction has a huge impact on the reaction process and on the structural properties of the reaction products. The formation of a Ni-Si mixed layer at the deposition stage, its structure and its role in the further evolution of the reaction couple are discussed on [001] Si and amorphous Si substrates. Controlling the mixed layer properties becomes extremely important in a regime wherein kinetics upsets thermodynamic stability, i.e., in thin films interactions, and during low temperature and/or ultra-rapid thermal processes, as required by the scaling down of the devices. In the review, it is highlighted how the opportunity to control thickness and composition of the mixed (precursor) layer opens the field to tailor new materials possessing intriguing properties, such as the case of transrotational Ni-silicides. Compared to standard poly-Ni silicides, they offer large chemical and structural stability windows as well as a promising electrical behaviour

Nickel silicide is widely used to realize contact terminals of integrated circuits and is usually formed by ex-situ heating treatments. In-situ reactions during sputter depo- sition of a Ni layer onto a HF p-type [001] Si substrate have been investigated in this work, by means of trans- mission electron microscopy, X-ray diffraction and X-ray reflectivity analyses. A thin layer of polycrystalline sili- cide, with extremely flat interfaces and in fiber texture with the Si substrate, has been obtained by introducing a sputter etching step just before Ni deposition and prop- erly modulating its duration. The work has also been aimed to decouple the thermal impact of sputter etching from its effect on surface cleaning, disclosing its key role in the whole reaction process. Cross-sectional TEM analysis of a nickel silicide layer, formed by in-situ solid-state reaction, showing an ex- tremely flat interface with the Si substrate.

In this work we study the phase transition of 14 and 7 nm thin Ni layers grown on standard silicon and silicon on insulator (SOI) wafers implanted with As. We investigate the thermal stability of the NiSi phase using spike thermal processes which are widely used to preserve shallow junction from dopant diffusion during electrical activation. Nickel reaction has been performed in nitrogen ambient in the temperature range from 450 to 1125 oC and has been characterised by electrical and structural analyses. In spite of the thin layers used, spike annealing processes extend the stability window up to 900 oC preserving the NiSi layer from structural degradation. Moreover, the use of SOI substrates has a favourable impact on the silicide structure that prevents agglomeration and hole formation.

The formation of nickel silicide induced by thermal annealing of Ni/SiC samples was studied by means of Rutherford backscattering spectrometry (RBS) and S-Ray diffraction (XRD). Nickel silicide (Ni(2)Si) could be observed already after 20 minutes annealing at 600 degreesC, even RES analysis showed a thin layer of non-reacted Ni on the top of the sample at this temperature. On the other hand, annealing at higher temperature (800 degreesC) led to the complete reaction of the deposited film. Analytical transmission electron microscopy (EDX) showed that carbon was almost uniformly distributed inside the Ni(2)Si laver. RES and Transmission Electron Microscopy (TEM) analysis showed a rough interface between the silicide and the underlying SiC. Ar(+)-irradiation of the as-deposited samples and subsequent annealing at 600 and 800 degreesC resulted in the improvement of the silicide/SiC interface with respect to the non-irradiated samples. This effect can be ascribed to the radiation induced damage in the crystalline SiC substrate, which improves the adhesion of the deposited film and enhances the mobility of Ni atoms.