Growth of Nickel Silicides in Si and Si/SiOx Core/Shell Nanowires

Abstract

We exploited the oxide shell structure to explore the structure confinement effect on the nickel silicide growth in one-dimensional nanowire template. The oxide confinement structure is similar to the contact structure (via hole) in the thin film system or nanodevices passivated by oxide or nitride film. Silicon nanowires in direct contact with nickel pads transform into two phases of nickel silicides, Ni31Si12 and NiSi2, after one-step annealing at 550 °C. In a bare Si nanowire during the annealing process, NiSi2 grows initially through the nanowire, followed by the transformation of NiSi2 into the nickel-rich phase, Ni31Si12 starting from near the nickel pad. Ni31Si12 is also observed under the nickel pads. Although the same phase transformations of Si to nickel silicides are observed in nanowires with oxide confinement structure, the growth rate of nickel silicides, Ni31Si12 and NiSi2, is retarded dramatically. With increasing oxide thickness from 5 to 50 nm, the retarding effect of the Ni31Si12 growth and the annihilation of Ni2Si into the oxide confined-Si is clearly observed. Ni31Si12 and Ni2Si phases are limited to grow into the Si/SiOx core-shell nanowire as the shell thickness reaches 50 nm. It is experimental evidence that phase transformation is influenced by the stressed structure at nanoscale.

Silicide formation in contacts to Si nanowires

“…The identification of NiSi 2 is consistent with work by Lin et al [55] and Ogata et al [56], who studied silicide formation using [111] SiNWs and in situ TEM. However, Lin et al additionally saw the growth of a more Ni-rich silicide immediately adjacent to the Ni pad after the NiSi 2 segment began to grow.…”

“…The sample geometries have included Ni contact pads on SiNWs [11,[51][52][53][54][55][56][57], point contacts between NiNWs and SiNWs [58,59] and even reactions with polycrystalline SiNWs [60]. Using the same approach described in earlier sections in our studies of other metals, we have reported phase formation and growth kinetics of Ni-silicides as a result of solid-state reaction of Ni contact pads with SiNWs [11,61].…”

“…Several authors have noted that silicidation is slowed with increasing oxide shell thickness (for Si/SiO 2 core/shell nanowires) [55,56] or when a carbonaceous shell surrounds the nanowire [65]. Compressive stress builds up as Ni atoms diffuse into the nanowire to form a Ni-silicide without the shell expanding sufficiently to make room for them, slowing diffusion.…”

Phase-controlled synthesis of nickel silicide nanostructures

“…Recently, various strategies have been developed for the growth of nickel silicide nanostructures involving about six stable nickel silicide phases, such as Ni 3 Si NWs [14], Ni 31 Si 12 NWs [15], Ni 2 Si NWs [11,16], Ni 3 Si 2 NWs [17], NiSi NWs [9,12,13], and NiSi 2 NWs [18], some of which have been successfully applied to nanoscale devices [19,20]. Generally, the method to synthesize different phases and morphologies of nickel silicides can be divided into two routes: delivery of Ni precursors to silicon and deposition of silicon sources on Ni film, both of which are based on the fundamental and crucial process of Ni-diffusion in silicon [9,12,13,21,22]. Particularly, the CVD growth of 1D nickel silicide nanostructures using SiH 4 as the precursor gas is widely adopted because it can offer practical advantages to produce singlecrystalline nanostructures and may be integrated into Si-based semiconductor devices.…”

Birth of silicon nanowires covered with protective insulating blanket

“…[6] Different phases by phase formation of silicide NWs were recognized by capping NWs with a SiO x shell that provided improved understanding of the growth mechanism. [7] Due to the high surface defects exhibited by SiNWs, there is a need for a surface passivation before incorporating NWs in electronic devices. High chemical stability and better compatibility without causing any stress to SiNWs, SiO x is the best candidate as a protective shell.…”