Atomic layer deposition of chromium oxide—An interplay between deposition and etching

Atomic layer deposition (ALD) of chromium oxide (Cr2O3) thin films is investigated in a custom built hot wall viscous flow reactor configuration at 300 °C. Chromium(III) 2,4-pentanedionate [Cr(acac)3] and ozone (O3) are employed as the metal and the oxygen sources, respectively. In situ quartz crystal microbalance (QCM) and ex situ x-ray reflectivity studies are utilized as the two complementary techniques to monitor the growth mechanism and self-limiting deposition chemistry during Cr2O3 ALD. In situ QCM studies reveal a negligible nucleation period on the previously grown Al-OH* terminated surface before revealing the perfectly linear growth mechanism at 300 °C. The saturated growth rate is found to be ca. 0.28 A/cycle. In addition, excessive O3 exposure also reveals an alternative, controlled, and spontaneous etching pathway of the growing film as a result of the partial surface oxidation of Cr2O3. The as-deposited thin films are found to exhibit a polycrystalline rhombohedral structure without any preferential orientation. X-ray photoelectron spectroscopy studies reveal uniform distribution of Cr and O throughout the stack of ca. 40 nm film with minimum C impurities. High resolution scans of Cr 2p core level also confirm the presence of Cr in the +3 oxidation state with the corresponding multiplet spectrum.