Towards Reconfigurable Electronics: Silicidation of Top-Down Fabricated Silicon Nanowires

We present results of our investigations on nickel silicidation of top-down fabricated silicon nanowires (SiNWs). Control over the silicidation process is important for the application of SiNWs in reconfigurable field-effect transistors. Silicidation is performed using a rapid thermal annealing process on the SiNWs fabricated by electron beam lithography and inductively-coupled plasma etching. The effects of variations in crystallographic orientations of SiNWs and different NW designs on the silicidation process are studied. Scanning electron microscopy and transmission electron microscopy are performed to study Ni diffusion, silicide phases, and silicide–silicon interfaces. Control over the silicide phase is achieved together with atomically sharp silicide–silicon interfaces. We find that {111} interfaces are predominantly formed, which are energetically most favorable according to density functional theory calculations. However, control over the silicide length remains a challenge.

Phase equilibrium and mechanical properties of Cr-Mo-Nb-Si-B alloys Composed of BCC and T2-silicide phase

ABSTRACTA new class of high-temperature materials based on refractory elements was investigated with an aim to improve the energy efficiency of thermal power plants. Alloys based on Nb and Mo composed of BCC solid solution (BCCss) (Nb-Mo) and T2-silicide (Nb,Mo)5(Si,B)3 are promising candidates as high-temperature materials. Further investigation on the alloy phase equilibria of this system is required to improve the mechanical properties and oxidation resistance through optimization of the phase compositions. Cr is one candidate to modify the properties of the alloy because Cr is expected to stabilize the T2 compound phase along with B. Here, the phase equilibria among BCCss and the T2 compound are widely investigated in the Cr-Mo-Nb-Si-B system, and a BCCss-T2 two-phase microstructure is found in Mo-rich alloys. The B/Si ratio in the T2 phase increases with the Cr content, while almost no B solubility was found in BCCss. As the Si content increases in alloys, the A15 silicide phase ((Cr, Mo, Nb)3Si) and/or Laves phase appear.Nanoindentation tests were conducted to investigate the mechanical properties of the BCCss phase of the alloys in the Cr-Mo-Nb-Si-B system. The nanohardness and reduced elastic modulus of these alloys tended to be higher with an increase in Cr.

Formation of Ohmic Contacts to n-Type 4H-SiC at Low Annealing Temperatures

The formation of Ohmic contacts to n-type 4H-SiC layers at low annealing temperature using dopant segregation technique is reported. n-SiC epilayer was implanted with phosphorous and subsequently activated at 1700 °C. Ni metal contacts fabricated on phosphorous implanted and annealed epilayers produced Ohmic contacts with a specific contact resistivity (ρc) of ~7.2x10-5 Ω.cm2 at an annealing temperature of 550 °C. ρc decreased with further annealing temperature reaching a value of ~2.1x10-5 Ω.cm2 at 1000 °C. XRD analysis showed that nickel silicide phase was formed at both 550 °C and 1000 °C.

Demonstrating the Instability of SiC Ohmic Contacts and Drain Terminal Metallization Schemes Aged at 300 °C

The long-term thermal stability of the drain contacts of three different commercially available SiC MOSFET devices has been determined at a storage temperature of 300 °C. Existing literature suggests that, at this temperature, the nickel silicides associated with ohmic contact creation should be stable, but this was found not to be the case. Our TEM and EDX work revealed silicide phase transformations, further silicide growth and severe thermally-driven degradation of the drain contact metallization stack on top of the silicide layers. We attribute this instability and growth of the silicides to the high storage temperature and large supply of nickel atoms available from the metal stack. The nickel atoms diffuse and decompose the original silicides to enable the formation of a new low temperature Ni32Si12 phase, and slowly decompose the SiC substrate to form additional nickel silicide.