Low Energy Ion Implantation and Annealing of Au/Ni/Ti Contacts to n-SiC
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Low Energy Ion Implantation and Annealing of Au/Ni/Ti Contacts to n-SiC Neelu Shrestha1, Martyn H. Kibel2, Patrick W Leech1, Anthony S Holland1, Geoffrey K Reeves1, Mark C Ridgway3, Phillip Tanner4 1
School of Engineering, RMIT University, Melbourne, Victoria, 3001, Australia Centre for Materials and Surface Science, Department of Chemistry and Physics, La Trobe University, Melbourne, Victoria, Australia. 3 Electronic Materials Engineering, Australian National University, Canberra, ACT, Australia. 4 Griffith University, Queensland Microtechnology Facility, Brisbane, Australia. 2
ABSTRACT The electrical characteristics of Au/Ni/Ti/ n-SiC contacts have been examined as a function of implant dose (1013-1014 ions/cm2) at 5 KeV and temperature of annealing (750-1000 °C). Measurements of specific contact resistance, ρc, were approximately constant at lower implant doses until increasing at 1 x 1015 ions/cm2 for both C and P ions. Annealing at a temperature of 1000 °C has reduced the value of ρc by an order of magnitude to ~1 x 10-6 Ω.cm2 at implant doses of 1013-1014 ions/cm2. Auger Electron Spectroscopy (AES) has shown that annealing at 1000 °C resulted in a strong indiffusion of the metallization layers at the interface. INTRODUCTION SiC has become an important semiconductor in devices operating at high power and elevated temperatures. A critical requirement in the realization of these devices has been the formation of ohmic contacts with low specific contact resistance, ρc, and strong mechanical adhesion at the metal/ SiC interface. For n-SiC, the most commonly used ohmic contact has been the metal Ni for which annealing at 900-1000 °C was required in order to obtain a minimum in ρc [1]. However, the formation of Ni2Si phase during annealing at 900-1000 °C has been accompanied by a segregation of carbon, the generation of interfacial voids and a roughening of the surface morphology of the metal [2]. These defects have acted to degrade the mechanical adhesion of the metal/n-SiC interface. To reduce the presence of excess carbon, the carbide forming element Ti has been incorporated into Ti/Ni multilayered contacts [3-5]. The reduction in excess carbon through the presence of TiC phase during annealing has resulted in an increased mechanical adhesion in comparison with Ni films [4]. In addition, the formation of TiSi2 at the interface during annealing of the contacts at >700 °C has resulted in a minimum in ρc [6]. An alternative method of forming ohmic contacts to n-SiC as reported by Grodzicki et al. has been the pre-treatment of the substrate with low energy ions [7]. In Cr/ n-SiC contacts, the bombardment of n-SiC with low energy Ar ions has resulted in a transition from a non-linear to a linear current/ voltage response [7]. In another study, the implantation of n-SiC with P or C ions at low energy has resulted in an increase in ρc in as-deposited contacts of Ti/Ni/Au [8]. The bombardment of polycrystalline layers of n-SiC with low energy Ar ions has shown a reduction in the surface energy and internal stress in the
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