The erosion behaviors of Y₂O₃ and YF₃ coatings under fluorocarbon plasma

We deposited Y₂O₃ and YF₃ coatings using the electron beam evaporation method and investigated their erosion behavior under fluorocarbon plasma at various bias voltages. TEM analysis revealed that the Y₂O₃ coating was strongly fluorinated under the plasma, and the thickness of the fluorinated layer was increased up to a few hundred nm with bias voltage. XPS analysis also confirmed a significant Y-F bonding on the surface and showed fluorine content at a maximum on the surface, decreasing with the depth from the surface. The etch rate increased with bias voltage and it was slightly higher in YF₃ coating, implying that the etch rate depends on the surface fluorination and its removal by incident ions. Without applying bias voltage, the chemical reaction with the fluorocarbon plasma dominated, resulting in the formation of fine fluoride particles on the Y₂O₃ surface, but the YF₃ coating was intact and clean for the same condition. These results indicate that the YF₃ coating may be a new plasma-facing material that produces fewer contamination particles.