is a film deposited between the
silicide layer (which is formed over the silicon substrate as an
interconnection path or contact) and the metallization layer.
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The high diffusivity
of silicon through silicide layers can be a problem in silicon-silicide-metal
systems since, with heat treatment, these can exhibit excessive
interdiffusion between the metal and the silicon through the silicide
layer. This silicon-metal interdiffusion can result in loss of
system integrity. Barrier layers are therefore used in preventing this
excellent interdiffusion barrier properties, films used as a barrier layer
between the metal layer and the silicide/silicon layers must exhibit
excellent adhesion to both the metal layer and the silicide layer.
Furthermore, a barrier layer must have low electrical resistivity, and
must be compatible with the wafer fabrication process.
Metals alloys are often used
as barrier metals in wafer fabrication. One commonly used metal
alloy for this purpose is that of titanium (Ti) and tungsten (W), i.e.,
10 wt.% Ti, which exhibits a resistivity of 50-80 micro-ohm-cm. In
this alloy, W acts as the barrier itself while Ti just serves as a
Ti-W barrier metal is usually formed by single-target
sputtering, a process that's also
compatible with the formation of the silicide film used as contact
layer. Ti-W barriers can withstand thermal processing at 400-500
deg C for 30 minutes. The typical thickness for such barriers ranges
from 450 to 1,800 angstroms.
explored for use as barrier layer include metal nitrides, carbides, and
Titanium nitride has recently been confirmed to be
superior to the Ti-W barrier metal. Titanium
nitride can exist either as Ti2N
or TiN. Stoichiometric TiN exhibits low electrical resistivity
(50-100 ohm-cm) and very good barrier properties. Tungsten nitride
films, on the other hand, have been found to be excellent barriers to
interdiffusion between GaAs and metals such as gold, silver, and
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