Impact of Oxygen Plasma Surface Treatment on Photoresist Adhesion in BaTiO3-Based Photonic Device Fabrication

Abstract

Oxygen-plasma pre-cleans are routine before fabrication, but on BaTiO3 thin films we observed catastrophic photoresist lift-off during mild rinsing and sonication. To explain the failure, we combined optical microscopy, EDS, and XPS. EDS showed no meaningful bulk stoichiometry change, whereas XPS revealed a nanometer-scale, plasma-induced shift in surface chemistry: hydroxylation and carbonate formation consistent with a BaCO3-rich interphase at the resist/BaTiO3 boundary. This chemically weak interphase, recreated upon each plasma step and removable by simple solvent cleaning, provides the mechanism for delamination. The key takeaway for practitioners is process guidance: avoid uncritical O2-plasma use on BTO; if cleaning is required, use alternative chemistries (e.g., UV-ozone) or carefully tuned plasma windows that preserve adhesion. More broadly, the study illustrates how lightweight analytics at the surface (correlative microscopy + surface spectroscopy) can pinpoint the root cause of yield-limiting defects in oxide photonics and translate directly into higher-reliability process recipes.