Patterning of wave guides in LiNbO3 using ion beam etching and reactive ion beam etching

Abstract

A number of current and future optoelectronic components require the creation of waveguides in LiNbO3. In order to accomplish this, trenches between one and ten microns deep must be patterned into the LiNbO3 substrate. We have demonstrated the formation of near-vertical, smooth-walled trenches up to ten microns deep using Ar ion beam etching (IBE) and Ar/CHF3 reactive ion beam etching (RIBE) processes. Both Ar IBE and Ar/CHF3 RIBE processes can achieve etching rates of up to 100 nm/minute. Our patented RIBE process [K. E. Williams, et al. U.S. Patent No. 6,238,582 (29 May 2001)] has the additional advantage of providing up to a 5:1 selectivity for etching the LiNbO3 over a photoresist mask. The collimated beam available with IBE and RIBE allows control over feature profiles and redeposition removal. Using a combination of RIBE and a multiangle process, the sidewall angle and smoothness of the mask have been transferred into LiNbO3 substrates to depths between one and ten microns. This depth range can be expanded in either direction if an appropriate mask can be fabricated.

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].…”