On the Ti₃SiC₂ Metallic Phase Formation for Robust p-Type 4H-SiC Ohmic Contacts

Abstract

This paper presents a detailed physical and electrical analysis of 4H-SiC ohmic contacts to p-type material, the main aim being to examine their ruggedness under high temperature conditions. XRD, FIB-TEM and SEM are techniques that have been utilized to examine the microstructure and interface properties respectively. A detailed physical study revealed the presence of a crystalline hexagonal Ti layer orientated in the same direction as the 4H-SiC epitaxial layer. This factor seems to be important in terms of electrical performance, having the lowest measured specific contact resistivity of 1x10-6Ωcm2. We attribute this to the optimized formation of Ti3SiC2at the metal/SiC interface. An initial high temperature study shows thermionic emission occurring across the metal/semiconductor junction.

Introductory Chapter: Need of SiC Devices in Power Electronics - A Beginning of New Era in Power Industry

“…Hence, more energy is needed to electrically activate them. Even at present, various research groups are working on p-type ohmic contacts [51][52][53][54][55][56]. Also, high temperature and special metallization processes are necessary to form ohmic and Schottky contacts on SiC.…”

Main Differences in Processing Si and SiC Devices

“…To compensate this, after metal deposition on even very highly doped SiC films, extra annealing step (1000-1200°C) is usually required to form a homogeneous silicide or carbide layer at the contact interface, which further lowers the Schottky barrier height, leading to a lower contact resistance. For N-type ohmic contact, nickel-based alloys are typically used, and resultant silicides are Ni 2 Si [35], while for P-type, Ti/Al alloys are common, leading to the formation of TiC or Ti 3 SiC 2 [36] at the interface after the contact anneal. The complete story behind the rapid thermal anneal for SiC ohmic contact is still not clear; apart from the silicide reaction, which had been consistently observed and confirmed, local carbon clusters [37,38] enriched at close to the contact interface, potentially providing more free carriers, were also often discussed and may have played a part, too.…”

“…The complete story behind the rapid thermal anneal for SiC ohmic contact is still not clear; apart from the silicide reaction, which had been consistently observed and confirmed, local carbon clusters [37,38] enriched at close to the contact interface, potentially providing more free carriers, were also often discussed and may have played a part, too. Specific contact resistance as low as 1 × 10 −6 Ω cm 2 [9,39] can be obtained on N-type SiC ohmic contact, and for the more difficult P-type due to deeper acceptor level, a higher value around 1 × 10 −4 Ω cm 2 is typical [12,36,40].…”

Ti/Al-based contacts to p-type SiC and GaN for power device applications

“…Several works have been reported on p‐type doped SiC, where metal layers based on Ti and Al are typically subjected to thermal treatments above 800 °C in order to obtain Ohmic contacts . In the contact formation, the role of the Ti 3 SiC 2 phase is continuously under discussion . However, these Al‐containing systems exhibit often of a poor morphology due to the tendency of Al to ball‐up during annealing .…”

“…However, these Al‐containing systems exhibit often of a poor morphology due to the tendency of Al to ball‐up during annealing . Hence, alternative solutions are under investigation, based on the introduction of additional elements in the stack, either acting as capping layers (e.g., Ti/Al/NiV , Ti/Al/Si , …) or stabilizing the Ti/Al system during high temperature annealing (e.g., Ni/Al/Ti ).…”