@article{75fa279c55524cb2ae9c095890d4fc11,
title = "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 -Ni2 Si for annealing conditions from 350 to 700 °C for 2 min. The θ -Ni2 Si has an epitaxial orientation of θ -Ni2 Si [001] Si [11 1-] and θ -Ni2 Si (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 [1 1- 0] Si [1 1- 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.",
author = "Dellas, {N. S.} and Liu, {B. Z.} and Eichfeld, {S. M.} and Eichfeld, {C. M.} and Mayer, {T. S.} and Mohney, {S. E.}",
note = "Funding Information: The authors are grateful for financial support from the ARO (Contract No. W911NF0510334) and NSF (Contract No. ECS-0609282) and the use of facilities at the PSU NSF NNIN site under Grant No. 0335765. They also appreciate helpful suggestions of Professor Elizabeth Dickey and the Si nanowires provided by Professor Joan Redwing. FIG. 1. Schematic diagram of process flow used to fabricate TEM samples. The process begins with (a) a Si wafer coated with 100 nm of SiN x . (b) Ag electrodes are then patterned and deposited for electrofluidic alignment of the SiNWs. (c) The Ag alignment pads are etched away, and (d) Ni pads are patterned and deposited to contact the aligned SiNWs. Finally, (e) a window is RIE etched in the back side of the wafer, and (f) the Si is etched through with KOH to the front side SiN x layer. FIG. 2. (a) TEM image showing sample annealed at 400 ° C for 2 min and (b) SAED patterns from samples annealed at 400 ° C for 2 min identified as θ -Ni 2 Si by the [201] and (c) [001] zone axis diffraction patterns. FIG. 3. TEM image showing samples annealed at 300 ° C for 2 min and then 450 ° C for 2 min, with an epitaxial relation of θ -Ni 2 Si [ 001 ] ∥ Si [ 11 1 ¯ ] and θ -Ni 2 Si ( 100 ) ∥ Si ( 112 ) . The nanowire is split into three regions: region I is the original SiNW, region II is θ -Ni 2 Si , and region III is an unidentified Ni-rich silicide phase. FIG. 4. (a) TEM image showing overview of a sample annealed at 700 ° C for 2 min and (b) higher magnification image. Diffraction patterns (c) and (d) from the main silicide segment (trunk), where (c) and (d) show extra spots from microtwinning and (e) shows the diffraction pattern from a branch, showing that the branch is the same θ -Ni 2 Si phase as the main part of the nanowire, but without the extra spots from the microtwins. FIG. 5. (a) Ni-silicided [111] oriented SiNW after annealing at 450 ° C for 2 min and (b) HRTEM image of silicide/SiNW interface. The inset FTs are identified as the [ 1 1 ¯ 0 ] NiSi 2 zone axis and the [ 1 1 ¯ 0 ] Si zone axis with epitaxial relations of NiSi 2 [ 1 1 ¯ 0 ] ∥ Si [ 1 1 ¯ 0 ] and NiSi 2 ( 111 ) ∥ Si ( 111 ) . FIG. 6. EELS spectra showing the Ni L 2 , 3 edge for pure Ni; θ -Ni 2 Si and NiSi 2 showing a shift from pure Ni at the lowest energy to higher energy from θ -Ni 2 Si and NiSi 2 at the highest energy. FIG. 7. TEM image of SiNW silicided by Ni pad at 700 ° C for 2 min. Inset shows SAED pattern of the NiSi [103] zone axis. ",
year = "2009",
doi = "10.1063/1.3115453",
language = "English (US)",
volume = "105",
journal = "Journal of Applied Physics",
issn = "0021-8979",
publisher = "American Institute of Physics Publising LLC",
number = "9",
}