Operando XPS in Reactive Plasmas: The Importance of The Wall Reactions

TL;DR

This paper demonstrates the use of operando ambient pressure XPS to study real-time plasma-surface interactions, emphasizing the critical role of wall reactions in understanding plasma-assisted surface processes in microelectronics.

Contribution

It introduces a novel plasma-XPS technique that captures in-situ surface and gas-phase chemistry during plasma exposure, revealing the importance of wall reactions.

Findings

Wall reactions significantly influence plasma-surface chemistry.

Real-time monitoring links surface changes with gas-phase species.

Plasma-XPS offers comprehensive insights into plasma processes.

Abstract

Advancements in differential pumping and electron optics over the past few decades have enabled x-ray photoelectron spectroscopy (XPS) measurements at (near-)ambient pressures, bridging the pressure gap for characterizing realistic sample chemistries. Recently, we demonstrated the capabilities of an ambient pressure XPS (APXPS) setup for in-situ plasma environment measurements, allowing plasma-surface interactions to be studied in operando rather than using the traditional before-and-after analysis approach. This new plasma-XPS technique facilitates the identification of reaction intermediates critical for understanding plasma-assisted surface processes relevant to semiconductor nanomanufacturing, such as physical vapor deposition, etching, atomic layer deposition, etc. In this report, we apply the plasma-XPS approach to monitor real-time surface chemical changes on a model Ag(111) single crystal exposed to oxidizing and reducing plasmas. We correlate surface-sensitive data with concurrent gas-phase XPS measurements and residual gas mass-spectra analysis of species generated during plasma exposure, highlighting the significant role of plasma-induced chamber wall reactions. Ultimately, we demonstrate that plasma-XPS provides comprehensive insights into both surface and gas-phase chemistry, establishing it as a versatile and dynamic characterization tool with broad applications in microelectronics research.