Ti/AlNi/W and Ti/Ni2Si/W Ohmic Contacts to P-Type SiC
AlNi and Ni2Si based ohmic contacts to p-type 4H-SiC have been produced using low energy ion implantation, a Ti contact layer, and sequential anneals. Low resistivities were promoted by degenerately (>1020 cm-3) doping the surface region of 4H-SiC epilayers via Al+ implantation. High acceptor activation and improved surface morphology was achieved by capping the samples with pyrolized photoresist and using a two-step anneal sequence in argon. Ti/AlNi/W and Ti/Ni2Si/W stacks of varying Ti and/or binary layer thickness were compared at varying anneal temperatures. AlNi based samples reliably and repeatedly achieved specific contact resistivities as low as 5.5 x10-5 ohm-cm2 after annealing at temperatures of 700-1000°C. For the Ni2Si samples, resistivities as low 4.5x10-4 ohm-cm2 were reached after annealing between 750 and 1100°C. Similarly, a set of Ti/AlNi/Au samples, with or without Ge as an additional contact layer, were prepared via the same procedures. In this case, specific contact resistivities as low as 5.0 x10-4 ohm-cm2 were achieved after annealing the Ti/AlNi/Au samples between 600 and 700°C for 30 minutes in a dynamic argon atmosphere or under high vacuum. The lowest resistivities were realized using thicker (~ 40 nm) Ti layers. I-V analysis revealed superior linear characteristics for the AlNi system, which also exhibited a more stable microstructure after anneal. SIMS and RBS were used to analyze the stability of the stacks subsequent to thermal treatment. AFM analysis demonstrated the superiority of photoresist capping over alternatives in minimizing surface roughness. Linear ohmic behavior after significantly reduced anneal temperature is the main observation of the present study.
Robert P. Devaty, David J. Larkin and Stephen E. Saddow
B. H. Tsao et al., "Ti/AlNi/W and Ti/Ni2Si/W Ohmic Contacts to P-Type SiC", Materials Science Forum, Vols. 527-529, pp. 903-906, 2006