Batch process for the fabrication of LiNbO3 photonic crystals using proton exchange followed by CHF3 reactive ion etching

Abstract

We report a simple process for the batch fabrication of photonic crystals in lithium niobate substrates. By means of proton-exchange (PE) followed by CHF 3 reactive ion etching (RIE) we have achieved structures with a diameter of 400 nm and an aspect ratio (depth-to-diameter) of 3:1. Sub-micrometric structures have been fabricated with an 85°angle between the walls and the plane of the substrate. We provide the optimized parameters -and their influence on the aspect ratio, the etching rate and the verticality of the walls. Transversal cross-section micrographs of the etched patterns, for both X-cut and Z-cut substrates, are shown as a clear evidence of the capability developed.

Fabrication of free-standing lithium niobate nanowaveguides down to 50 nm in width

“…In contrast to other lithography-based patterning schemes of LiNbO 3 , this approach allows one to design through the simulation tool and fabricate the sidewall shape and steep edges of the nanowaveguides. For comparison, the dry etching method results in strongly inclined sidewalls that prohibit any high aspect ratio patterns [37][38][39][40][41]. It is further unique to the presented approach that the resulting nanowaveguide structures are free-standing and can be easily detached from the substrate.…”

“…These methods use low energy ions and cause less damage to the crystal structure. However, the shapes of the resulting patterns are very limited due to their strongly inclined sidewalls [37][38][39][40][41] that originate from the isotropic etching behavior. A more suitable pattern transfer technique is ion-beam enhanced etching (IBEE) [42], which was specifically developed for high aspect ratio nanostructures in LiNbO 3 [43,44].…”

Analysis of linear and nonlinear optical properties of diffraction gratings inscribed on the surface of single crystals of the KTiOPO 4 family

“…Despite the interest that these synergetic structures can show, only a few works analyzed these effects on the literature. Photonic structures on nonlinear optical materials have been fabricated by field poling techniques 15 , ion etching 16 , electron beam lithography 17 , liquid phase epitaxy 18 , etc. Remarkably, it can be a promising approach to fabricate 1D and 2D photonic structures or grating by means of femtosecond laser ablation which has become increasingly important in the last few years as a result of the large amount of practical applications in surface modification or micro-structuring of dielectric materials.…”

Highly selective electroplated nickel mask for lithium niobate dry etching

“…RIE is in itself a highly controllable and versatile dry process involving both physical and chemical effects to achieve directive and anisotropic material removal. It has already been demonstrated that lithium niobate can be dry etched using fluorine-based chemistries, [14][15][16][17] and ICP-RIE has previously been used on X-or Z-axis crystallographic orientations of lithium niobate to successfully fabricate ridge waveguides or photonic crystals, usually after proton exchange [18][19][20] but there is no report of any specific process allowing to dry etch structures that are several microns in depth in lithium niobate. The fabrication of very deep or very high aspect ratio structures is actually seriously impaired by the formation of lithium fluoride ͑LiF͒ compounds during the etching process that are relatively nonvolatile, leading to redeposition phenomena impeding the material removal.…”