Effect of Low Energy Implantation on the Properties of Ti/Ni/Au Contacts to n-SiC
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Effect of Low Energy Implantation on the Properties of Ti/Ni/Au Contacts to n-SiC Patrick W Leech1, Anthony S Holland1, Geoffrey K Reeves1, Yue Pan1, Mark Ridgway2, Phillip Tanner3 1 School of Electrical and Computer Engineering, RMIT University, Melbourne, Victoria, 3001, Australia 2 Electronic Materials Engineering, Australian National University, Canberra, ACT, Australia. 3 Griffith University, Queensland Microtechnology Facility, Brisbane, Australia. ABSTRACT The effect of low energy implantation of P or C ions in 3C-SiC on the properties of Ti/Ni/Au contacts has been examined for doses in the range 1013-1015 ions/cm2. Measurements of specific contact resistance, ρc, were performed using the two-contact circular test structure. The magnitude of ρc for the Ti/Ni/Au contacts on unimplanted SiC was 1.29 x 10-6 Ω.cm2. The value of ρc increased significantly at an implant dose of 1 x 1015 ions/cm2. The dependence of ρc on ion dose has been measured using both C and P implant species. INTRODUCTION The semiconductor SiC has shown exceptional properties in devices used in harsh environments such as at elevated temperatures and high power levels. Recent developments in the growth of high quality epitaxial layers of 3C and 6H-SiC on Si substrates have enabled the large-scale fabrication of these devices. An important requirement in the realization of high power devices on SiC has been the ability to form ohmic contacts with characteristics of low resistivity and high thermally stability. The most commonly used ohmic contacts to n-SiC have consisted of the deposition of a layer of metal (Ni, Ti, Co, Pd or Pt [1]) or carbon [2] followed by annealing at ~1000 °C. However, the high temperatures required for the localized formation of metal silicides or carbides at the interface has resulted in a degradation of the underlying SiC and a roughening of the metal surface [1]. Ion implantation has previously been used in the heavy doping of SiC below the contact although very high temperatures (~1500 °C) have been required for activation [3]. An alternative method of modifying the interfacial properties of SiC without the use of heavy impurity doping and high temperatures has been the prior implantation with low energy ions. The bombardment of polycrystalline SiC with low energy Ar ions at 330, 450 and 540 eV has been reported to reduce both the surface energy and internal stress within the layer [4]. In Cr/ n-SiC contacts, Grodzicki et al. have shown a transition from a non-linear to a linear current/ voltage response following the bombardment of n-SiC with Ar ions at 1.2 keV [5]. In this paper, we examine the effect of prior implantation of n-SiC with low energy ions on the electrical characteristics of Ti/Ni/Au contacts. Variation in the implant species (C and P) and dose (1013-1015 ions/cm2) were used in investigating for the first time the properties of these contacts. The interfacial layer of Ti was selected because of the ability of this metal to form ohmic contacts on n-SiC at a relatively lower annealing temperature than a
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