AFRL-PR-WP-TR-2007-2065 POWER AND THERMAL TECHNOLOGY FOR AIR AND SPACE–SCIENTIFIC RESEARCH PROGRAM Delivery Order 0003: Electrical Technology Component Development

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 (>10 cm) doping the surface region of 4H-SiC epilayers via low energy Al+ implantation. High acceptor activation and improved surface morphology was achieved by capping the samples with pyrolized photoresist prior two 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 different anneal temperatures. For this set of AlNi based samples, specific contact resistivities as low as 5.5 x10 ohm-cm were reliably and repeatedly achieved after annealing at temperatures of 700-1000°C for 2 minutes in a high purity argon atmosphere. For the Ni2Si samples, resistivities as low 4.5x10 ohm-cm 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 procedure as those above. In this case specific contact resistivities as low as 5.0 x10 ohm-cm 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. Additional sets of Ti/AlNi/Au or W samples were later produced in order to confirm previous results and to demonstrate the effects of thermal aging. In all cases, 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. AFM analysis demonstrated the superiority of photoresist capping over alternatives in minimizing surface roughness. SEM and optical microscopy illustrated microstructure evolution with temperature. SIMS and RBS were used to analyze the stability of the stacks subsequent to thermal treatment. Linear ohmic behavior after significantly reduced anneal temperature is the main observation of the present study. Also, 2D and 3D thermal and mechanical models of multilayer electronic packages have been developed using finite element analysis. The temperature and stress distributions from this work generally agree with theoretical predictions.