Electroplated Ni mask for plasma etching of submicron-sized features in LiNbO3

We here report on the fabrication of electroplated nickel (Ni) masks for dry etching of sub-micron patterns in lithium niobate (LiNbO3). This process allows obtaining 350-nm thick Ni masks defining high air filling fraction holey arrays (e.g. openings of 1800 nm in diameter with inter-hole spacing of 300 nm, or 330 nm diameter holes spaced by 440 nm). The mask profile is perfectly vertical (angle ≈ 90°). The obtained metallic masks are used to realise photonic and phononic crystals. High aspect ratio and dense arrays of holey patterns were defined and transferred into LiNbO3 through RIE (Reactive Ionic Etching) in sulphur hexafluoride (SF6) chemistry. Nanometric holes exhibiting sidewall slope angles of the order of 60° have in this way been etched in LiNbO3. The LiNbO3/Ni selectivity is close to 6 and the etch rate around 6 nm/min.

Graphical abstractSEM pictures (tilt: 40° and 20°) before and after LiNbO3 etching: (a) metallic mask in electroplated Ni (b) RIE (SF6) etching.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Electroplated Ni has been chosen to make high-aspect ratio metallic masks featuring sub-micron patterns. ► Ni masks are used for dry etching of sub-micron patterns in lithium niobate (LiNbO3). ► The plasma etching (RIE) is performed with sulphur hexafluoride (SF6) chemistry. ► The obtained results open interesting prospects for the realisation of photonic, phononic crystals, or optical Bragg gratings.