الفهرس 
THEORETICAL BACKGROUND and LITERATURE RECIEWOnly 14 pages are availabe for public view
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Abstract
SUMMARY
Ag/Sn thin film system is one of the lead-free interconnection technologies which attract growing interest to protect the environment, particularly due to the harmful effect of lead and the use of toxic fluxes chlorofluorocarbon (CFC) for conventional soldering. In this work, our main interest is investigating the solid-state reaction and diffusion intermixing processes in nanostructured Ag/Sn thin films system at room temperature. A set of thin films of Ag/Sn system [Ag(50nm)/Sn(50nm), Ag(150nm)/Sn(50nm), Ag(100nm)/Sn(50nm), and Ag(200nm)/Sn(100nm)] have been deposited by DC magnetron sputtering onto silicon nitride substrates at room temperature (at about 298K). The sputtering rates have been calculated from the layer thickness measured by the profilometer technique.
The solid-state reactions in this system for all thicknesses have been investigated by means of Secondary Neutral Mass Spectrometry (SNMS) depth profiling technique. As it has been confirmed by X-ray diffraction (XRD) too, the reaction and diffusion between the two layers of Ag and Sn started already in the as-deposited sample.
XRD patterns for the as-deposited studied samples showed that besides those of Ag and Sn, the reflections of Ag3Sn can be observed. Thus it was confirmed that Ag reacts with Sn at room temperature to form Ag3Sn phase. The average grain size for Ag, Sn and Ag3Sn was estimated for studied samples using the Debye-Scherrer’s formula.
The SNMS profiles have been measured for the as-deposited investigated samples and at different ageing times at room temperature. The SNMS profile proved that the reaction started in the as-deposited sample which is in a good agreement with the XRD measurements and also with the previous studies. Since the bulk diffusion not occurs at room temperature, the diffusion starts from the interface of the two films and spreads rapidly through the grain boundaries. Consequently the Ag3Sn phase was formed along the grain boundaries (GBs), gradually consuming the interior of grains, and was grown perpendicular to the GBs. This means that the diffusion along grain boundaries is accompanied with the Diffusion-induced grain boundary motion/GB diffusion-induced solid-state reaction mechanism [DIGM/GBDIREAC].
At the same time formation and growth of a small compact reaction layer near the interface was observed and the shift of the bordering parallel interfaces was controlled by grain boundary diffusion, thickness of which gradually increases with increasing the ageing time. This can be the effect of Diffusion-induced recrystallization (DIR) mechanism: nearby the original interface the stress accumulation can be strong enough to initiate the formation of small new grains with Ag3Sn composition.
Of course, after long time, we reach the full homogenization of the Ag3Sn layer. SNMS profile for the full reacted sample showed that the sample transferred to Ag3Sn phase. This would be explained by a good kinetics. from the kinetics of the diffusion process in the above two mechanisms both the interface velocity in the (DIGM) regime as well as the coefficient of parabolic growth in the planar growth regime were determined.
from these studies, it can be concluded that the diffusion process in Ag/Sn system was surprising fast because of the nanocrystallinity. Therefore, the solid-state reactions in nanostructured Ag/Sn system is important in the field of soldering process for nanotechnology applications and the study of the growth kinetics of the intermetallic phases formed in the connection area is of vital interest for the selection of appropriate conditions to get stable interconnection.