High quality surface micromachining of LiNbO 3 by ion implantation-assisted etching Simone Sugliani a , Pietro De Nicola a , Giovanni Battista Montanari a , Alessio Nubile a , Angela Menin a , Fulvio Mancarella b , Paolo Vergani c , Andrea Meroni c , Marco Astolfi c , Marco Borsetto c , Guido Consonni c , Roberto Longone c , Marco Chiarini a,d , Marco Bianconi a,b and Gian Giuseppe Bentini a,b a Laboratory of Micro and Submicro Enabling Technologies of Emilia-Romagna region S.c.r.l. (MIST E-R S.c.r.l.), Bologna, I-40129 Italy; b Institute for Microelectronics and Microsystems, National Research Council (CNR-IMM), Bologna, I-40129 Italy; c Oclaro North America Inc. – San Donato Office, San Donato Milanese (MI), I-20097 Italy; d CGS S.p.A. – Bologna Office, Bologna, I-40129 Italy ABSTRACT A surface micromachining technique of LiNbO 3 substrates, based on an improved implantation-assisted wet etching process, will be presented and discussed. 2.3 μm high relief structures with optical quality surfaces were fabricated on LiNbO 3 by 5 MeV Cu ion implantation through an SU-8 10 μm thick photoresist masking layer patterned by a standard photolithographic process. The LiNbO 3 regions amorphized by implantation were etched in a 49% HF aqueous solution at a rate of 100 nm/s exploiting the high differential etching rate between damaged and undamaged LiNbO 3 (100 nm/s against 1 nm/s). The process can be repeated to obtain higher aspect ratios. In this work the results of both single and double step processes will be presented. The sidewalls morphology of the microstructures will be also discussed. Both the surface quality and features of the manufactured structures make this technology highly promising for integrated optics and acousto/opto-fluidics. Keywords: Lithium Niobate, SU-8, Ion Implantation, surface micromachining 1. INTRODUCTION Lithium Niobate (LiNbO 3 ) is an extensively studied material mainly due to its piezo-electrical and electro-optical properties. It is a well-established material for acoustic and optical signal processing and it has recently attracted a renewed interest in the emerging field of acousto-fluidics 1,2 . The complexity of LiNbO 3 manufacturing, mainly related to its hardness and chemical inertia, has so far limited the use in commercial devices of surface engineered microstructures despite their great potential. The micro-fabrication of structures with optimized shape and roughness on a wafer scale could provide new opportunities for LiNbO 3 -based devices improving their performances. Several micromachining techniques have been reported in the last decade including dry etching methods (such as RIE or ICP-RIE with 3,4 or without 5 proton exchange, mechanical dicing 6 , femtosecond laser machining 7 ) and wet etching methods usually based on HF or HF/HNO 3 mixtures (selective etching of Z - face 8,9 , selective etching improved by proton exchange 10 ). Other wet etching methods like focused ion beam (FIB) milling 11,12,13,14 and ion implantation 15,16 exploit the damage induced by ions beams in the exposed LiNbO 3 to increase the etching selectivity between irradiated and virgin material. The maximum differential etching ratio is obtained through the complete amorphization of the damaged regions. Bianconi et al. 15 proposed an ion implantation-assisted wet-etching technique based on high energy and high fluence Cu ion implantation able to produce a fully amorphized LiNbO 3 over the whole ions range. In this way it is possible to induce a very high differential etching rate (100 nm/s in 49% HF aqueous solution) almost constant in the damaged layer. Cu ion was chosen because it represents a good trade-off between penetration depth (considering the available implantation energies) and the damage efficiency (stopping power). Moreover, it was demonstrated that by Micromachining and Microfabrication Process Technology XVIII, edited by Mary Ann Maher, Paul J. Resnick, Proc. of SPIE Vol. 8612, 86120E · © 2013 SPIE · CCC code: 0277-786X/13/$18 · doi: 10.1117/12.2002095 Proc. of SPIE Vol. 8612 86120E-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 04/29/2013 Terms of Use: http://spiedl.org/terms