Influence of Carbon Layer on the Properties of Ni-Based Ohmic Contact to n-Type 4H-SiC

Nickel-based contacts with additional interfacial layer of carbon, deposited on n-type 4H-SiC, were annealed at temperatures ranging from 600 to 1000°C and the evolution of the electrical and structural properties were analyzed by I-V measurements, SIMS, TEM, and Raman spectroscopy. Ohmic contact is formed after annealing at 800°C and minimal specific contact resistance of about ？？？cm2 has been achieved after annealing at 1000°C. The interfacial carbon is amorphous in as-deposited state and rapidly diffuses and dissolves in nickel forming graphitized carbon. This process activates interfacial reaction between Ni and SiC at lower temperature than usual and causes the formation of ohmic contact at relatively low temperature. However, our results show that the specific contact resistance as well as interface quality of contacts was not improved, if additional layer of carbon is placed between Ni and SiC. 1. Introduction Owing to its excellent intrinsic properties such as high thermal conductivity, high electric field breakdown strength, and high saturation, electron silicon carbide (SiC) is well recognized as an attractive material for application in high-power devices operating in high-temperature environment [1]. Much effort has been undertaken to master the SiC growth, both in form of ingots and of the epitaxial thin films, and important progress has been made in these fields during last two decades. However, in order to fully exploit this potential it is still necessary to overcome several technical issues related to the semiconductor processing and fabrication of power electronic devices; development of reliable ohmic contacts is one of the key problems in this respect [2]. The fabrication of ohmic contacts to SiC may be achieved by using various metallization schemes; as for the n-type SiC, Ni, and Ni-based contacts are the most commonly used ones. They are formed by high temperature annealing at temperatures in the range 950–1050°C for time of 2–15 minutes [3–6]. Although many experimental works have been performed in order to understand the mechanism of ohmic contact formation and different models were proposed to explain Schottky to Ohmic transition, the final picture is still far from completeness. There is no doubt that Ni very easily react with SiC forming the whole spectrum of nickel silicides, depending on details of ohmic contact fabrication. On the other hand there is a strong evidence that fabrication of silicides, via contact reaction of Ni with SiC or via deposition of the specific silicide does not provide solely an ohmic contact with