Highly selective electroplated nickel mask for lithium niobate dry etching

Abstract

International audienceA sulfur hexafluoride based reactive ion etching process allowing to etch several micron deep holes with diameters of the order of a few microns in lithium niobate is reported. Etching of deep structures with aspect ratios up to 1.5 was made possible through the use of an electroplated nickel mask exhibiting a selectivity as high as 20 with respect to lithium niobate. Several crystallographic orientations were investigated, although particular interest was paid to Y-axis oriented substrates. Photoresist as well as metal masks were also tested and their selectivity was compared. The influence of process parameters such as applied rf power or operating pressure on the sidewall slope angle of the etched patterns was investigated. The technique has been successfully applied to the fabrication of phononic crystals consisting of periodical arrays of 9 µm diameter, 10 µm deep holes, with a 10 µm period, and presenting sidewall angles as high as 73° etched in Y-axis oriented lithium niobate

Design and Fabrication of S₀ Lamb-Wave Thin-Film Lithium Niobate Micromechanical Resonators

“…The wafer is then flip-bonded to the LN carrier wafer using glue, and ground down to 1um thickness. Traditionally, reactive ion etching (RIE) is used for anisotropic etching of LN [8], [15], where metal or oxide hard mask and very high RF power are used. However, it is very hard to achieve >80 degrees side-wall verticality due to the re-deposition of lithium compound [16].…”

Investigation of fabricating a LiNbO<inf>3</inf> ultrasonic phased array transducer of more than 100 MHz

“…The aspect ratio of the large kerf (≥ 10 μm) etching is up to 1.3, while for the smaller kerf it decreases gradually. As the aspect ratio reduces to about 1 [19], it has been suggested that the etching rate begins to be limited by transport of etch gases into the kerf and etch products out of the kerf. For closely spaced structures, this would result in profile angles less than 60°, which is unacceptable for fabricating high-frequency arrays.…”

“…An ICP reactive ion etching system (from Surface Technology System company) with multiplex AOE reactor was used, which employed CF 4 based chemistry, for the etching process. At 750 W of ICP power, a DC bias voltage of 200 V, 20 sccm of He, and 60 sccm CF 4 , operating pressure of 0.2 Pa, the etching rate of LiNbO 3 film was 8 μm/hr, the selectivity of electroplated Ni with respect to lithium niobate is about 20 [19]. In an ideal case the kerf etching with high aspect ratio (h/d > 33 μm/7.5 μm) is required for a 100 MHz full-kerfed array.…”

Towards a SAW based phononic crystal sensor platform

“…It is far less developed for piezoelectric materials and typically based on reactive ion etching (RIE) [e.g. [6][7][8][9]. LiNbO 3 is the more appropriate material from the electroacoustic point of view; however, it is more challenging than quartz.…”