Operando Plasma-XPS for Process Monitoring: Hydrogenation of Copper Oxide Confined Under h-BN Case Study

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. Hexagonal boron nitride (h-BN) was used in this study as a model system since it exhibits a wide array of 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 used polycrystalline Cu foils with single-layer h-BN, grown via chemical vapor deposition (CVD), and tracked in real-time the plasma-induced reduction of the underlying Cu oxide using APXPS equipped with 22 kHz 75 W 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 CuxO is seen, while an h-BN layer remains intact, suggesting H radical species can attack the exposed and h-BN-covered Cu oxide patches and partially reduce the underlying substrate. In addition to the demonstration and discussion of plasma-XPS capabilities, our results indicate the h-BN encapsulated metallic Cu interface might be repaired without significantly damaging the overlaying h-BN, which is of practical importance for the development of h-BN encapsulated devices and interfaces