Annealing Study of Ga Implanted p-Type 6H-SiC for Ohmic Contact Metallizations
- PDF / 387,646 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 26 Downloads / 130 Views
Annealing Study of Ga Implanted p-Type 6H-SiC for Ohmic Contact Metallizations M. Prenatt1,3, A. A. Iliadis1, R. D. Vispute2, M. C. Wood3, M. Derenge3, B. Geil3, and K. A. Jones3 1 Electrical and Computer Engineering Department, University of Maryland, College Park, Maryland 20742 2 Center for Superconductivity Research, Physics Department, University of Maryland, College Park, Maryland 20742 3 Army Research Laboratory, 2800 Powder Mill Road, Adelphi, MD 20783 ABSTRACT Shallow implantations of Ga ions were performed on p-type 6H-SiC by conventional broad area implantation, and the physical and electrical properties of the Ga-SiC system upon high temperature annealing were examined, in order to understand the role of Ga in ohmic contact formation. The shallow implantation depth (30 nm) and high Ga doses ranging between 1x1015 and 1x1016 cm-2, resulted in heavy surface damage as observed by atomic force microscopy surveys. Samples annealed using a sacrificial SiC wafer as a capping layer, showed no improvement in surface roughness for annealing up to 1300 °C, while at 1500 °C, surface roughness was markedly changed. At 1600 °C the surface re-crystallized back to the stepped terraced morphology of the un-implanted surface but with significantly larger step and terrace size. At this annealing temperature, heavy Ga loss from the surface was observed. Samples annealed at 1500 °C using an AlN capping layer, showed significant outdiffusion of Si into the AlN layer, and redistribution of Ga within the SiC surface. The contact resistance of as-implanted and annealed samples using the sacrificial SiC wafer, were measured by the TLM method. Although contact resistance was found to decrease with increasing annealing temperature, sheet resistance increased, and contact resistance values were higher than expected, indicating that the heavy loss of Ga atoms contributed to the increased levels of contact resistance. INTRODUCTION The development of high quality ohmic metallization on p-type SiC is of critical importance to the performance of high temperature/high power SiC devices. Previous work indicated that the use of Gafocused ion beam (FIB) technology reduced contact resistance in p-type SiC by modifying the surface and incorporating high doses (1x1016 to 1x1017 cm-2) of Ga atoms within the top 30 nm of the SiC surface [1][2]. Ga can be considered to be a potential p-type dopant for SiC as indicated by photoluminescence [3] and deep implantation [4] experiments, and such high doses of Ga within a shallow surface layer, can result in a heavily modified surface layer, that may improve ohmic contact formation either by enhancing tunneling through high doping and/or interface states, or by reducing the barrier through the formation of a Si(Ga)C layer [2]. Generally high temperature annealing can be used to activate the implants, provided some precaution is taken to preserve the stoichiometry of the surface, such as Si overpressure [5], or other encapsulation methods. In the case of shallow high dose implantations, where the top surf
Data Loading...
