Vacuum Ultraviolet-Enhanced OxidationA Route to the Atomic Layer Etching of Palladium Metal

• Published in: Chemistry of materials Vol. 32; no. 14; pp. 6035 - 6042
• Main Authors: Coffey, Brennan M, Nallan, Himamshu C, Engstrom, James R, Lam, Chon Hei, Ekerdt, John G
• Format: Journal Article
• Language: English
• Published: American Chemical Society 28-07-2020
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/acs.chemmater.0c01379

Low-temperature, plasma-free atomic layer etching (ALE) of Pd0 is explored. A vacuum ultraviolet (VUV) light source (115 < λ < 400 nm) is used in conjunction with a controlled O2 gas exposure to produce PdO x at 100 °C. The amount of PdO x that forms is dependent on the duration of coexposure of O2 at 1 Torr and VUV irradiation. A minimum coexposure time of 1 min is required to partially oxidize 2 nm Pd while 3 min is required for 20 nm Pd films, which is verified in situ using X-ray photoelectron spectroscopy (XPS). Formic acid vapor is used to complete the etch cycle, which does not etch Pd0 and only removes the PdO x that forms. Repeated etch cycles on a ∼20 nm Pd thin film yield an etch rate of 2.81 Å/cycle, which is characterized in situ using XPS and ex situ using X-ray reflectivity. The morphology of the Pd0 surface does not change appreciably with etching. The only observed effect of repeated ALE cycles is a reduction in the roughness of the Pd film, which is measured using atomic force microscopy.