Gold Catalyzed Nickel Disilicide Formation: A New
Solid–Liquid–Solid Phase Growth Mechanism
- Publication date
- Publisher
Abstract
The
vapor–liquid–solid (VLS) mechanism is the predominate
growth mechanism for semiconductor nanowires (NWs). We report here
a new solid–liquid–solid (SLS) growth mechanism of a
silicide phase in Si NWs using in situ transmission electron microcopy
(TEM). The new SLS mechanism is analogous to the VLS one in relying
on a liquid-mediating growth seed, but it is fundamentally different
in terms of nucleation and mass transport. In SLS growth of Ni disilicide,
the Ni atoms are supplied from remote Ni particles by interstitial
diffusion through a Si NW to the pre-existing Au–Si liquid
alloy drop at the tip of the NW. Upon supersaturation of both Ni and
Si in Au, an octahedral nucleus of Ni disilicide (NiSi<sub>2</sub>) forms at the center of the Au liquid alloy, which thereafter sweeps
through the Si NW and transforms Si into NiSi<sub>2</sub>. The dissolution
of Si by the Au alloy liquid mediating layer proceeds with contact
angle oscillation at the triple point where Si, oxide of Si, and the
Au alloy meet, whereas NiSi<sub>2</sub> is grown from the liquid mediating
layer in an atomic stepwise manner. By using in situ quenching experiments,
we are able to measure the solubility of Ni and Si in the Au–Ni–Si
ternary alloy. The Au-catalyzed mechanism can lower the formation
temperature of NiSi<sub>2</sub> by 100 °C compared with an all
solid state reaction