Surface precipitates on single crystal LiNbO₃ after dry-etching by CHF₃ plasma

The CHF₃ electron cyclotron resonance (ECR) plasma etched LiNbO₃ (LN) surface was analyzed chemically and crystallographically to investigate the dry-etch machining process for LN crystal, which was recently needed to obtain broader-band optical modulators. The etched surface was entirely covered with amorphous-like precipitates having ~70 nm diameter. These precipitates (or a part of them) were thought to be LiF from Auger electron and x-ray photoelectron spectroscopy. The results indicated that the LiF was formed and remained on the etched surface while the Nb was almost completely removed.