Reactive ion etching of Ti-diffused LiNbO3slab waveguides

Reactive ion etching (RIE) of LiNbO3 (LN) in SF6 plasma atmosphere was studied for optimizing the preparation conditions for LN ridge waveguides. The samples to be etched are Ti-diffused LN slab waveguides overlaid with a chromium film mask that has a Mach-Zehnder interferometer (MZI) array pattern. The experimental results indicate that the LN-etching rate (RLN) and the Cr-etching rate (RCr) as well as the rate ratio RLN/RCr increase with either increasing the radio-frequency (RF) power at a given SF6 flow rate or increasing the SF6 flow rate at a fixed RF power. The maximum values of RLN = 43.2 nm/min and RLN/RCr = 3.27 were achieved with 300 W RF power and 40 sccm SF6 flow. When the SF6 flow rate exceeds 40 sccm, an increase in the flow rate causes the etching rates and the rate ratio to decrease. The scanning electron microscope images of the LN ridge prepared after ∼ 20 min etching show that the ridge height is 680 nm and the sidewall slope angle is about 60°.