Multilayer antidiffusion barrier schemes for Schottky and ohmic contact metallisations to InAlN/GaN HEMTs
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Multilayer antidiffusion barrier schemes for Schottky and ohmic contact metallisations to InAlN/GaN HEMTs Eliana KamiĔska1, Iwona Pasternak1, Michaá A. Borysiewicz1, Marek Guziewicz1, Anna Piotrowska1, ElĪbieta Dynowska1,2, Rafaá Jakieáa2, Valery Kolkovski2, Marie-Antoinette di Forte-Poisson3 1
Institute of Electron Technology, Al. Lotników 32/46, 02-668 Warsaw, Poland Institute of Physics, PAS, Al. Lotników 32/46, 02-668 Warsaw, Poland 3 Alcatel-Thales III-V Lab, Route de Nozay, 91461 Marcoussis cedex-France 2
ABSTRACT The reported work focuses on developing antidiffusion barriers capable to increase the thermal stability of metal contacts above 700oC. In the chosen approach, such an antidiffusion barrier consists of several bilayers of materials with different crystalline structures. It has been demonstrated that an interface between such materials effectively blocks the atomic interdiffusion. In this work the following groups of materials were used as the bilayers: ZrB2 and ZrN and TaSiN and TiN. The materials were deposited by means of room temperature sputtering from elemental and compound targets in inert Ar and reactive Ar+N2 atmospheres. The structures were characterised using secondary ion mass spectroscopy depth profiling and scanning electron microscopy cross sectional imaging directly after deposition and after degradation. I-V characteristics were measured and contact resistivities were determined from the circular transmission line method. INTRODUCTION Power III-N high electron mobility transistor (HEMT) devices that operate at high frequencies require that the metallization schemes applied for Schottky and ohmic contacts be stable at temperatures elevated due to heating from power dissipation. One of the issues of this stability is to inhibit the interdiffusion between the contact layer and the Au (Cu) overlayer introduced for bonding and interconnection purposes. The most common solution to this problem is to deposit a thin-film antidiffusion barrier in-between the main contact and mounting layers. Among the materials used for antidiffusion barrier applications refractory metals and their nitrides are common. In particular TaN and TiN films in ohmic contact metallisation systems to Si have been proved stable after annealing at temperatures up to 750oC [1] and 800oC [2] respectively. The failure mechanism observed in both cases was the migration of Cu from the mounting layer to the Si substrate which can be assigned to diffusion through grain boundaries of the nitride films. The application of the TaN, TiN and ZrN films as antidiffusion barriers to Ti/Al based ohmic contacts to n-GaN have been reported by Voss et al [3]. The Auger spectroscopy depth profiles presented therein clearly demonstrate an outdiffusion of Al from the contact metallisation to the mounting layer via the nitride films after a 30 second long annealing process performed at 600oC. It is therefore clear that in order to obtain a higher thermal stability of the contact metallisations required for thermally stable GaN-based material
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