Abstract
The influence of a Nb layer between Si and Ti on the formation of TiSi2 in small-feature contacts and of the substrate doping level has been studied using transmission electron microscopy in combination with convergent-beam electron diffraction. For an As dose of 2.5×1016 cm−2, a mixture of C49 and partially agglomerated C54 TiSi2 grains was found in some of the 5×5 μm2 contact windows, while only C49 existed in the 0.7×0.7 μm2 windows. Agglomeration is shown to lead to possible C49−C54 coexistence, as well as erroneous interpretation of the C54 nucleation density. Decreasing the As dose to 5×1015 cm−2 leads to a thicker TiSi2 layer, but does not have a major influence on phase formation in the small windows, although only C54 TiSi2 was found in the large ones. In the presence of a thin Nb layer between Ti and poly-Si, C40 (Ti,Nb)Si2 was consistently found in all contacts, indicating that formation does not depend on the contact size at least down to 0.5 μm2. Surprisingly, Ti was found on both sides of the (Ti,Nb)Si2 layer and the silicide near the interface to Si was relatively rich in Ti instead of Nb.
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