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, biomedical 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 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 mass-spectra were concurrently
collected during plasma-XPS to track reaction products formed during
plasma exposure. A clear reduction of Cu
x
O is seen, while an h-BN layer remains intact, suggesting that 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
wall reactions and charging effects) and propose potential solutions.