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

SEM pictures (tilt: 40° and 20°) before and after LiNbO3 etching: (a) metallic mask in electroplated Ni (b) RIE (SF6) etching. [Display omitted] ► 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. 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 1800nm in diameter with inter-hole spacing of 300nm, or 330nm diameter holes spaced by 440nm). 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 6nm/min.