Orientation dependence of nickel silicide formation in contacts to silicon nanowires

Abstract

The orientation dependence of Ni silicide phase formation in the silicidation of silicon nanowires (SiNWs) by Ni has been studied. SiNWs with a [112] growth direction contacted by Ni pads form θ-Ni2Si for annealing conditions from 350 to 700 °C for 2 min. The θ-Ni2Si has an epitaxial orientation of θ-Ni2Si[001]∥Si[111¯] and θ-Ni2Si(100)∥Si(112) with the SiNW. On the other hand, SiNWs with a [111] growth direction react with Ni pads to form NiSi2 with an epitaxial orientation of NiSi2[11¯0]∥Si[11¯0] and NiSi2(111)∥Si(111) after annealing at 450 °C for 2 min. The [111] SiNWs were also silicided at 700 °C for 2 min, forming the low-resistivity NiSi phase. The epitaxial phases identified in the reactions of Ni films with SiNWs suggest that lattice matching at both the silicide/Si growth front and the surface of the original SiNW may play a significant role in determining the first silicide segment to grow.

Silicide formation in contacts to Si nanowires

“…The epitaxial orientation relationship between the h-Ni 2 Si and SiNW is found to be h-Ni 2 Si[001]//Si [11 " 1] and h-Ni 2 Si(100)//Si(112). This epitaxial relationship develops because of the good lattice match between these planes matching at the silicide/SiNW interface as well as the initial Ni/Si interface on the surface of the SiNW, as described previously [11], and low-interfacial energy is believed to play a large role in the formation of this phase. Neither we nor other researchers have observed h-Ni 2 Si when SiNWs with growth directions other than [112] are silicided.…”

“…However, in the case of the [111] oriented SiNWs, the silicide phase is identified as NiSi 2 by SAED. In this case, NiSi 2 forms because of lattice matching between the surface and interface planes present on the SiNWs with [111] growth directions [11]. Figure 16 shows an HRTEM image of a silicided SiNW with insets of digital Fourier transforms (FTs) from the silicide segment and the SiNW.…”

“…The SiNWs that were oxidized were [112] ntype SiNWs and they were oxidized in O 2 in a furnace at 900°C for 15 min with the addition of TCA. In the following section, our previously published results on Nisilicide formation in contacts to SiNWs [11,62] will be reviewed so that it can be compared with the other metals.…”

“…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]. These studies will be summarized briefly and discussed in light of other work with similar sample geometries in which researchers have examined lateral silicide growth from Ni contact pads on SiNWs.…”

“…Samples to study the solid-state reaction between Ti contact pads and SiNWs were fabricated by a method described elsewhere [11], with the exception being that Ti is used as the contact metal and e-beam evaporated to a thickness of 80 nm. The SiNWs were grown via the vaporliquid-solid growth technique [12] using gold as a catalyst.…”