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<reference>
(PDF) Plasma etching of proton-exchanged lithium niobate

Plasma etching of lithium niobate with fluorine gases is limited by the redeposition LiF. This results in a low etch rate and nonvertically etched walls. Etching of proton-exchanged lithium niobate can prevent the LiF deposition to a large extent

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Plasma etching of proton-exchanged lithium niobate

Alexey Milenin
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2006
https://doi.org/10.1116/1.2207150͔
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Abstract
Plasma etching of lithium niobate with fluorine gases is limited by the redeposition LiF. This results in a low etch rate and nonvertically etched walls. Etching of proton-exchanged lithium niobate can prevent the LiF deposition to a large extent because of the greatly reduced lithium concentration in lithium niobate. We performed different inductively coupled plasma etching processes using SF 6 or CHF 3 / Ar on proton-exchanged lithium niobate. Negligible underetching and nearly vertically etched walls on proton-exchanged lithium niobate samples were obtained by CHF 3 / Ar gas at chamber pressure of 6 mTorr and 130 V dc bias.
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Key takeaways
AI
Plasma etching of proton-exchanged lithium niobate yields an etching rate of approximately 5.7 µm/h.
CHF3/Ar at 6 mTorr achieves nearly vertical etched walls with negligible underetching.
Proton exchange reduces LiF redeposition, improving etch rates and profiles for lithium niobate.
Etching selectivity of proton-exchanged lithium niobate to chromium mask is 32:1 under optimal conditions.
First photonic crystal waveguide structures were successfully fabricated with an etching depth of 1.5 µm.

Figures (7)
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“SCCM denotes standard cubic centimer per minute. TABLE I. Dry etching parameters, etching rate, and average selectivity.
Fic. 1. Optical microscope images of the etched surface of PE-LN in dif- ferent gases. The straight stripe was not etched because of Cr mask. (a) Etched with CF, (1). (b) Etched with SF, (2).
Fic. 2. PE-LN surface etched by SF, gas. On each side of the stripe, the under-etching rates are 3.5 and 4.0 wm/h, respectively.
Fic. 4. PE-LN surface etched by CHF;/Ar gas. The width of PE-LN stripe is almost the same as that of Cr, which indicates the reduced under-etching effect.
Fic. 3. SEM picture of end face of PE-LN etched by SF, gas. Asymmetric etching on two sides of the ridge structure is shown.
Fic. 5. SEM picture of end face of PE-LN etched by CHF;/Ar gas; a nearly vertical etched wall is shown. IV. CONCLUSION
Fic. 6. SEM micrograph of a PE-LN photonic crystal waveguide. Interpore distance of the periodic pattern is 500 nm. Etching parameters are CHF;/Ar etching gas, 1500 W ICP power, 130 V dc bias, 6 mTorr chamber pressure, and no substrate cooling.
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References (10)
W. Sohler, Thin Solid Films 175, 191 ͑1989͒.
J. G. Scott, A. J. Boyland, S. Mailas, C. Grivas, O. Vagner, S. Lagoutte, and W. Eason, Appl. Surf. Sci. 230, 138 ͑2004͒.
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D. M. Manos and D. L. Flamm, Plasma Etching: An Introduction ͑Aca- demic, New York, 1989͒, p. 476.
H. Nagata, N. Mitsugi, K. Shima, M. Tamai, and E. M. Haga, J. Cryst. Growth 187, 573 ͑1998͒.
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V. Fedorov, Y. Korkishko, A. Alkaev, and E. Maslennikov, Proceedings of the 11th European Conference on Integrated Optics ͑ECIO'03͒, Prague, 2003, Vol. 1, p. 385.
V. Foglietti, E. Cianci, D. Pezzetta, C. Sibilia, M. Marangoni, R. Osellame, and R. Ramponi, Microelectron. Eng. 67-68, 742 ͑2003͒.
A. P. Milenin, C. Jamois, R. B. Wehrspohn, and M. Reiche, Microelec- tron. Eng. 77, 139 ͑2005͒. 11 www.webelements.com
FAQs
AI
What etching rate was obtained for proton-exchanged lithium niobate with SF6?
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The study achieved an etching rate of approximately 1.5 µm/h for proton-exchanged lithium niobate with SF6, significantly higher than pure lithium niobate.
How does proton exchange influence etching rates of lithium niobate?
add
Proton exchange allows for up to 85% substitution of Li ions, resulting in an etching rate ratio of approximately 3 between proton-exchanged LN and pure LN.
What etching process yielded nearly vertical walls in proton-exchanged LN?
add
Using inductively coupled plasma-reactive ion etching with CHF3/Ar gas at 6 mTorr yielded nearly vertical walls with an angle of 82°.
What is the selectivity ratio of PE-LN to the Cr mask during etching?
add
The selectivity of proton-exchanged lithium niobate to the chromium mask was found to be approximately 46:1 using SF6.
What were the outcomes of microscopy analyses post-etching of PE-LN?
add
Scanning electron microscopy revealed cracks on CF4-etched PE-LN and smooth surfaces on SF6-etched PE-LN, indicating differences in etching processes.

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</reference>

<statements>
1. Reducing the lithium concentration at the surface via proton exchange (PE) markedly suppresses LiF formation during F‑based plasma etching, which increases etch rate and makes it easier to obtain vertical sidewalls and clean profiles. PE‑assisted dry etching has been used to form deep ridges in LN with better morphology than in congruent LN, precisely because the lower Li content reduces the amount of involatile LiF available to redeposit. Surface H₂‑plasma treatments that substitute protons and relax surface stress have also been shown to improve hard‑mask quality and long‑etch fidelity, indirectly mitigating plasma‑induced defects and redeposition issues during extended ICP runs.
</statements>

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