Highly conductive and stable CoS thin films by atomic layer deposition: from process development and film characterization to selective and epitaxial growth.

CoS is an interesting sulfide material with metallic conductivity that has shown promise for various energy applications. Herein, we report a new atomic layer deposition process producing crystalline, pure, and highly conductive CoS thin films using CoCl(TMEDA) (TMEDA = ,,','-tetramethylethylenediamine) and HS as precursors at 180-300 °C. The lowest resistivity of 80 μΩ cm, best uniformity, and highest growth rate are achieved at 275 °C. Area-selective deposition is enabled by inherent substrate-dependency of film nucleation. We show that a continuous and conductive CoS film can be prepared on oxide-covered silicon without any growth on Si-H. Besides silicon, CoS films can be grown on a variety of substrates. The first example of an epitaxial CoS film is shown using a GaN substrate. The CoS films are stable up to 750 °C in N, 400 °C in forming gas, and 225 °C in O atmosphere. The reported ALD process offers a scalable and cost-effective route to high-quality CoS films, which are of interest for applications ranging from electrocatalysis and rechargeable batteries to metal barrier and liner layers in microelectronics and beyond.