TiW/TiWN/Pt Ohmic Contacts ton-Type 3C-SiC

Abstract

TiW(40 nm)/TiWN(80 nm)/Pt(500nm) was investigated as a new high-temperature compatible contact stack to 3C-SiC for harsh environment applications. Performance of TiW/TiWN/Pt contacts deposited on unintentionally doped (8.85×10¹⁸ cm⁻³) 3C-SiC grown by LPCVD to a thickness of ~1µm on (100) Si are reported. The linear transmission line method was used to determine specific contact resistance (ρ_c) at room temperature and for long-term tests at 300 °C. As deposited contacts were Ohmic with a ρ_c range of 1×10⁻⁴ to 1×10⁻³ Ωcm². These contacts were annealed for five minutes in forming gas (8% H2 92% Ar), at temperatures from 450 to 950 °C and all retained Ohmic character. Annealing samples at 450, 550 and 950 °C decreased ρ_c while anneling between 650 and 850 °C generally increased ρ_c.

Auger Electron Spectroscopy (AES) analysis was performed on a sample annealed at 750 °C. The as-received surface was composed of Si and O; after a brief sputter etch a characteristic Pt peak became visible and the O peak decreased substantially. Depth profiles detected Si throughout the Pt capping layer but not in the TiW layers. We suspect that Si diffuses from the SiC substrate into the Pt capping layer and surface Si also reacts with O₂ to from an oxide. These reactions, in combination with incomplete SiC/TiW interface reactions, are suspected to cause the increase of ρ_c for samples annealed between 650 and 850 °C. Annealing at 950 °C gave the lowest contact resistance of 2.3×10⁻⁵. Long-term testing at 300 °C for 190 hours, in atmosphere, was performed on contacts annealed at 450 °C. When heated, the contacts initial ρ_c of 2.1×10⁻⁴ Ωcm² increased to ~4×10⁻³ Ωcm² which remained stable for the test duration. After long-term testing the sample ρ_c measured at room temperature decreased to 9.8×10⁻⁵ Ωcm².