Interfacial stability of titanium, chromium, cobalt, and platinum contacts to gallium nitride and silicon carbide

Thermally stable contacts to gallium nitride (GaN) or silicon carbide (SiC) that also have desirable electrical characteristics are required for the further development of optoelectronic and high-temperature devices based on the GaN or SiC substrates. Metallization schemes used in semiconductor contact technology show various degrees of failure when subjected to elevated temperatures during device processing. The contact degradation is usually in the form of extensive interdiffusion, interfacial reaction, and interphase growth, accompanied by increase in contact resistivity. In this study, the interfacial microstructure and chemistry of the titanium nitride (TiN) contacts to GaN, gold (Au)-titanium (Ti) bilayer contacts to GaN, chromium (Cr) contacts to SiC, and chromium boride (CrB_x, 1 < x < 2) contacts to SiC in the as-deposited and annealed conditions were examined using transmission electron microscopy, scanning electron microscopy, Rutherford backscattering spectroscopy, and Auger electron spectroscopy. The results revealed that the nitrogen atoms in the GaN diffused into the Ti layer and formed TiN after annealing at 800°C for 30 seconds, and carbon atoms in the SiC diffused into the CrB_x layer and formed chromium carbide (Cr₇C ₃) after annealing at 1000°C for 120 seconds. No interfacial reaction was observed in the TiN-GaN contact system after annealing through 900°C and in the Cr-SiC contact system after annealed at 1000°C for 300 seconds. The ternary phase diagrams of titanium-gallium-nitrogen and several metal-silicon-carbon systems were estimated to provide an insight to the thermal stability of these contact systems. These phase diagrams suggested that titanium contacts to GaN, chromium, titanium, platinum, hafnium, or cobalt contacts to SiC are not thermally stable at the desired annealing temperature, and the results were also compared with experimental data. Finally, the consideration to predict the reaction products and evolution of interface morphology for ternary metal-semiconductor systems was discussed, along with the relation between interface morphology and metal species in the metal-SiC systems.