Ti and Ni-based BEOL CMOS-compatible P+-InGaAs ohmic contacts for the future of wireless communications

We report the electrical results of scaled Ti and Ni-based P⁺-InGaAs (:C) ohmic contacts integrated with a CMOS-compatible flow on 200 mm Si substrates. To evaluate contact performance as well as thermal stability, Transfer Length Method (TLM) measurements were first conducted after rapid thermal annealing (RTA). The targeted temperatures are relevant to the typical Si-CMOS Back End Of Line (BEOL) thermal budgets. The issue of acceptor passivation, resulting from hydrogen exposure of the InGaAs layer during CMOS-compatible process, is then emphasized. The etching of the contact cavities was identified as being the root cause. Finally, a previously developed TLM-based numerical extraction method was employed to achieve a more precise assessment of the resistivity parameters. Specific contact resistivity values as low as 5 × 10⁻⁷ and 3 × 10⁻⁶ Ω*cm² were respectively extracted from scaled Ti-based and Ni-based contacts. The 5 × 10⁻⁷ Ω*cm² value approaches the required magnitude of 10⁻⁸ Ω*cm² for the base contact in a Heterojunction Bipolar Transistor (HBT) in order to reach THz performance, which is crucial for future 6G/sub-millimeter Wave (sub-mmW) applications.