Structural Characterization of Alloyed Al/Ti and Ti Contacts on SiC

Abstract

Al-rich Al/Ti contacts on p-type SiC show good ohmic behaviour for a wide range of doping density after high temperature (> 950°C) post deposition annealing independently of the 4Hand 6H-SiC polytype [1, 2] employed. This ohmic contact behaviour appears to be closely related to the high Al content of the deposited metal layers. Several hypotheses have been proposed to explain the role of Al in such Al/Ti alloyed contacts mainly based on the doping effect of this element in SiC. However, Al/Ti-SiC alloyed contacts constitute a complex quaternary system where the formation and spatial distribution of different phases as well as loss of volatile Al could strongly affect the contact electrical characteristics. From recent structural investigations, two main experimental results deserve attention. On one hand, some of the phases expected from quaternary phase diagram based predictions have been identified in Al-rich Al/Ti-SiC alloyed contacts [3]. On the other hand, metallization spikes have been detected in this system. A high density of these metallic intrusions in the semiconductor is apparently bound to the ohmic behaviour and to the good contact-to-contact reproducibility observed [4]. Despite these experimental evidences several questions concerning the composition and the electrical behaviour of these contact regions are still open. Among these questions are the Al behaviour during the reaction that is not understood and the composition of the observed metallic spikes, suspected to enhance field emission, that is unknown. Additional structural investigations are thus needed to shed light upon these points. In this way, we report in this work a structural and chemical investigation of Al-rich Al/Ti-SiC alloyed contacts based on the Rutherford Back Scattering technique in the channeling mode (RBS-C) and Cross-Sectional Transmission Electron Microscopy (XTEM) in various analysis modes. These results are compared with those obtained from a preliminary structural investigation of Ti-SiC contacts.