Low temperature hot filament chemical vapor deposition of Ultrananocrystalline Diamond films with tunable sheet resistance for electronic power devices

This paper describes the results from systematic experiments performed to investigate the influence of different substrate-filaments distances, surface-substrate temperatures and reaction of precursors during the growth of Ultrananocrystalline Diamond (UNCD) films via the hot filament chemical vapor deposition (HFCVD) process. The experimental results provide valuable information to understand the important role of key molecules (CH_x, x = 1, 2, 3) and atoms (H), resulting from the cracking of precursor molecules (CH₄, H₂) on the hot surface of the filaments, and the contribution of argon (Ar) inert gas atoms, all interacting on the surface of the substrates when using different filaments-substrate distances to produce films with different structures and properties. The interaction of the cracked molecular and atomic species at different filaments-substrate distances, play a critical role in the nucleation and growth of films with different structures, as observed by complementary analytical techniques. Films grown at 5, 15, and 30 mm filaments-substrate distances exhibit graphite-disordered graphene phases, while those grown at 20 mm distances exhibit mixed large UNCD-minor graphite mixed phases, and those grown at 25 and 35 mm distances exhibit pure UNCD phase. UNCD films grown at ~ 600 °C exhibit grain boundaries with sp² and Trans-Polyacetylene (T-PA) dangling chemical bonds and low sheet resistance (~ 5 Ω), while UNCD films grown at relativity low temperature (~ 490 °C) exhibit high sheet resistance (~ 8 MΩ) and more T-PA dangling bonds. The results presented in this paper indicate that UNCD and mixed UNCD/disordered graphene/graphite films can be grown with tailored resistivity enabling potential applications in electronic power devices.