Operando XPS for Plasma Process Monitoring: A Case Study on the Hydrogenation of Copper Oxide Confined under h-BN

Here, we demonstrate that ambient pressure x-ray photoelectron spectroscopy (APXPS) can be used for in situ studies of dynamic changes in surface chemistry in a plasma environment. This opens a new and vast application space for XPS and greatly complements modern spectroscopy techniques to probe plasma-solid/liquid interactions relevant to process monitoring in the semiconductor industry, bio-medical plasma applications and plasma remediation technologies. Hexagonal boron nitride (h-BN) grown on Cu was used in this study as a well-defined model system for plasma process monitoring and because of its unique chemical, optical and electrical properties that make it a prospective material for advanced electronics. To better understand the stability and surface chemistry of h-BN during plasma assisted processing, we track in real time the plasma-induced chemical state changes of B, N and the underlying Cu substrate using APXPS equipped with an AC discharge plasma source operating at 13 Pa. Residual gas analysis (RGA) mass-spectra were concurrently collected during plasma-XPS to track reaction products formed during plasma exposure. A clear reduction of Cu_xO is seen, while an h-BN layer remains intact, suggesting hydrogen radical (H^•) species can attack the exposed and h-BN covered Cu oxide patches and partially reduce the underlying substrate without significantly damaging the overlaying h-BN, which is of practical importance for development of h-BN encapsulated devices and interfaces. In addition to demonstration of plasma-XPS capabilities we discuss the observed challenges (e.g., parasitic plasma-chamber walls reactions and charging effects) and propose potential solutions.. Authors: Diulus, J. Trey [National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)] (ORCID:0000000186758581); Naclerio, Andrew E. [Vanderbilt Univ., Nashville, TN (United States)]; Boscoboinik, Jorge Anibal [Brookhaven National Laboratory (BNL), Upton, NY (United States)] (ORCID:0000000250907079); Head, Ashley R. [Brookhaven National Laboratory (BNL), Upton, NY (United States)] (ORCID:0000000187330165); Strelcov, Evgheni [National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)]. DOE Contract: SC0012704; SC0022915. Subjects: 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; APXPS; boron nitride; plasma; surface science