Etching characteristics of LiNbO3 crystal by fluorine gas plasma reactive ion etching

Etching characteristics of a LiNbO3 single crystal have been investigated using plasma reactive ion etching (RIE) method with mixture gases of CF4/Ar/H2. The etching rate of LiNbO3 with mixture gases of CF4/Ar/H2 was evaluated. The etching surface was evaluated by atomic force microscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy methods. The in situ surface temperature of the sample during RIE was measured. The surface temperature increased with increase of the etching time between 0 and 5 min and then became constant. The surface morphology of the etched LiNbO3 changed with the increase of the H2 gas flow ratio. The surface profile became flat similar to the surface of nonetched LiNbO3, upon optimizing the etching conditions. The XRD peak for LiNbO3 etched using the mixture gas of CF4 and Ar gases did not appear, because a noncrystalline layer was formed. It was found that the crystallinity of the surface was dependent on both the flow rate of H2 gas and the etching time. F atoms exist in the contamination layer, such as sediments, on the sample surface etched using the mixture gases of CF4, Ar, and H2 gases. Optimum etching conditions, considering both the surface flatness and the crystallinity, was determined.