Surface precipitates on single crystal LiNbO₃ after dry-etching by CHF₃ plasma

Abstract

The CHF3 electron cyclotron resonance (ECR) plasma etched LiNbO3 (LN) surface was analyzed chemically and crystallographically to investigate the dry-etch machining process for LN crystal, which was recently needed to obtain broader-band optical modulators. The etched surface was entirely covered with amorphous-like precipitates having ~70 nm diameter. These precipitates (or a part of them) were thought to be LiF from Auger electron and x-ray photoelectron spectroscopy. The results indicated that the LiF was formed and remained on the etched surface while the Nb was almost completely removed.

Surface roughness of Ti:LiNbO3 etched by Ar∕C3F8 plasma and annealing effect

“…[4][5][6] The etching gas in the process chamber and the metal mask deposited on the LiNbO 3 for the etching process consisted of a C 3 F 8 /Ar gas mixture and a nickel film, respectively. Z-cut LiNbO 3 wafers, 1 mm in thickness and 3 in.…”

“…The thickness of the Ti layer was about 100 nm. 4,7 The influence of the annealing of the etched ridge structure waveguide is shown in Figs. The Ti diffusion temperature was 1050°C.…”

Challenges in electron cyclotron resonance plasma etching of LiNbO3 surface for fabrication of ridge optical waveguides

“…The origin for the extrinsic contaminants was previously investigated and found to be precipitation of LiF and polymers, possibly due to the etching gases ͑CHF 3 and CF 4 ͒. 8,9 In particular, the LiF precipitates were found to be crystalline in the CF 4 etching, while amorphous in the CHF 3 etching. 9 Presumably, the ex- istence of such plasma species as HF in the ECR plasma affects the structure of the deposits.…”

“…Generation of LiF precipitates on the etched surface, as recently reported by us, may have been the cause of the problem in the device fabrication processes. 8,9 The purpose of this article is to investigate and clarify such problems occurring in the fabrication of high speed LN modulators with ridge waveguides. A possible solution can be proposed for some of these problems.…”

An optical grating filter dry-etched on a LiNbO3 substrate

“…Finally, we removed the resist and Ti film using RIE. Fluorocarbons, such as CF 4 and CHF 3 , are generally used as etching gasses for LN etching [5], but the etching rate of LN is lower than ≈ 100 nm/min, due to the deposition of lithium fluoride (LiF) or carbon precipitates on the etched surface during the process [6]. We used a C 4 F 8 /Ar gas mixture for the etching [7,8].…”