High-Fidelity TiN Processing Modes for Multigate Ge-Based Quantum Devices

Charge or spin-qubits can be realized by using gate-defined quantum dots (QDs) in semiconductors in a similar fashion to the processes used in CMOS for conventional field-effect transistors or more recent fin FET technology. However, to realize a larger number of gate-defined qubits, multiples of gates with ultimately high resolution and fidelity are required. Electron beam lithography (EBL) offers flexible and tunable patterning of gate-defined spin-qubit devices for studying important quantum phenomena. While such devices are commonly realized by a positive resist process using metal lift-off, there are several clear limitations related to the resolution and the fidelity of patterning. Herein, we report a systematic study of an alternative TiN multigate definition approach based on the highest resolution hydrogen silsesquioxane (HSQ) EBL resist and all associated processing modes. The TiN gate arrays formed show excellent fidelity, dimensions down to 15 nm, various densities, and complexities. The processing modes developed were used to demonstrate applicability of this approach to forming multigate architectures for two types of spin-qubit devices prototypic to (i) NW/fin-type FETs and (ii) planar quantum well-type devices, both utilizing epi-grown Ge device layers on Si, where GeSn or Ge is the host material for the QDs.