The thermal stability of reactively sputtered tungsten–nitrogen alloy thin films is investigated for the application as diffusion barriers in silicon contact metallizations. The composition of W–N barriers is varied over a wide range including pure W. Aluminum, gold, and silver are used as low resistivity overlayers. Metallurgical interactions at temperatures ranging from 500 to 900 °C are studied. Incorporating nitrogen into tungsten advantageously stabilizes all three systems. The overall failure takes place rapidly above critical temperatures that depend on both the metal overlayer and the microstructure of the barrier. In some cases, W–N alloys can effectively prevent interdiffusion at temperatures as high as 800 °C for 30 min.

Thin films of W-N alloys have been prepared by reactive rf sputtering from a W target.Alloy compositions up to about 65at.%N can be achieved by this method.

Epitaxial and polycrystalline silicon layers on sapphire have been annealed with Q-switch pulses from a Nd : YAG laser irradiated on the Si surface. Time-resolved optical reflectivity measurements have been performed. The annealing process is shown to be induced by melting and subsequent epitaxial regrowth. The best results were obtained if the whole Si layer was melted, thus allowing the (11̄02) oriented sapphire substrate to act as a seed for recrystallization. In this case commercially available Si-on-sapphire (SOS) wafers with additional Si implantation as well as polycrystalline layers of low-pressure chemical vapor deposited (LPCVD) Si on sapphire could be epitaxially regrown. The same material deposited on amorphous SiO2 did not show epitaxial regrowth, however an increase in size of randomly orientated grains from 60 nm to 1 μm could be achieved.

The moving species during the formation of Pt2Si, Ni2Si, and CrSi2 by both ion mixing with 300–600 keV Xe ions and thermal annealing is identified with inert markers using backscattering spectrometry. Samples of metal-on-silicon and silicon-on-metal have been used, evaporated on SiO2 substrates with two very thin markers (Mo for Pt2Si, W for Ni2Si and CrSi2) placed at the metal–silicon interface, and at the bottom interface with the SiO2 substrate. Monitoring the separation of the two markers as a function of the amount of silicide formed determines the ratio of atomic transport through the growing silicide layer. The results establish that the dominant moving species in both silicide formation processes is the same for the refractory metal-silicide CrSi2, e.g., Si, whereas different atomic transport ratios are found in the case of the near-noble metal silicides Pt2Si and Ni2Si. This outcome is discussed in terms of high-temperature effects during thermal formation of transition-metal silicides.

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