Correlation between the performance and microstructure of Ti/Al/Ti/Au Ohmic contacts to p-type silicon nanowires.

Understanding the electrical and microstructural aspects of contact formation at nanoscale is essential for the realization of low-resistance metallization suitable for the next generation of nanowire based devices. In this study, we present detailed electrical and microstructural characteristics of Ti/Al/Ti/Au metal contacts to p-type Si nanowires (SiNWs) annealed at various temperatures. Focused ion beam cross-sectioning techniques and scanning transmission electron microscopy (STEM) were used to determine the microstructure of the source/drain metal contacts of working SiNW field-effect transistors (FETs) annealed for 30 s in the 450-850 °C temperature range in inert atmosphere. Formation of titanium silicides is observed at the metal/semiconductor interface after the 750 °C anneal. Extensive Si out-diffusion from the nanowire after the 750 °C anneal led to Kirkendall void formation. Annealing at 850 °C led to almost complete out-diffusion of Si from the nanowire core. Devices with 550 °C annealed contacts had linear electrical characteristics; whereas the devices annealed at 750 °C had the best characteristics in terms of linearity, symmetric behavior, and yield. Devices annealed at 850 °C had poor yield, which can be directly attributed to the microstructure of the contact region observed in STEM.