Isotropic plasma-thermal atomic layer etching of aluminum nitride using SF6 plasma and Al(CH3)3

Wang, Haozhe; Hossain, Azmain; Catherall, David S.; Minnich, Austin J.

doi:10.1116/6.0002476

Journal of Vacuum Science &Amp; Technology A

2023

DOI: 10.1116/6.0002476

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Isotropic plasma-thermal atomic layer etching of aluminum nitride using SF6 plasma and Al(CH3)3

Haozhe Wang

Azmain Hossain

David S. Catherall

et al.

Abstract: We report the isotropic plasma atomic layer etching (ALE) of aluminum nitride using sequential exposures of SF6 plasma and trimethylaluminum [Al(CH3)3]. ALE was observed at temperatures greater than 200 °C, with a maximum etch rate of 1.9 Å/cycle observed at 300 °C as measured using ex situ ellipsometry. After ALE, the etched surface was found to contain a lower concentration of oxygen compared to the original surface and exhibited a ∼35% decrease in surface roughness. These findings have relevance for applica… Show more

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Cited by 3 publications

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Isotropic atomic layer etching of GaN using SF6 plasma and Al(CH3)3

Chittock,

Shu,

Elliott

et al. 2023

Journal of Applied Physics

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GaN is an enabling material for light emitting diodes, advanced radio frequency, and power semiconductor devices. However, fabrication of GaN devices often relies on harsh etch processes, which can leave an etch damage layer, limiting final device performance. In this work, an isotropic atomic layer etching (ALE) process involving SF6 plasma and trimethylaluminium [Al(CH3)3] is presented for the controlled etching of GaN, which reduces oxygen and carbon contamination while smoothing the surface. The ALE chemistry was first examined with density functional theory. A comparison between proposed thermal and plasma-driven reactions is made by implementing Natarajan–Elliott analysis, highlighting that the plasma process is a good candidate for GaN ALE. Saturation was experimentally confirmed for both ALE half-cycles at 150 and 300 °C, with etch rates of 0.31 ± 0.01 and 0.40 ± 0.02 nm/cycle, respectively. Analysis of the films post-ALE shows that the RMS roughness of the films decreases from 2.6 ± 0.1 to 1.9 ± 0.1 nm after 25 nm of etching at 300 °C, in agreement with a previously developed curvature-dependent smoothing model. Taken together, this ALE process enables accurate GaN thickness tuning, surface cleaning, and surface smoothing, allowing for further development of GaN devices.

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Isotropic atomic layer etching of GaN using SF6 plasma and Al(CH3)3

Chittock,

Shu,

Elliott

et al. 2023

Journal of Applied Physics

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Quasiatomic layer etching of silicon nitride enhanced by low temperature

Shanks,

Ahmed,

Femi-Oyetoro

et al. 2023

Journal of Vacuum Science &Amp; Technology A

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Plasma atomic layer etching is a dry etching process using a dose step to modify a material’s surface chemistry and an etch step to remove the modified surface layer. This method of etching has certain advantages over reactive ion etch due to its self-limiting etch process for highly controllable etch depth and reduced surface roughness. In this paper, we expand upon an anisotropic, plasma atomic layer etch recipe used to etch thin films of silicon nitride, which uses an H2 plasma to modify the surface layer of the material and an SF6 etch step to remove the modified surface. Several modifications are made to the recipe, including a reduction in the pressure during the SF6 step from 500 to 20 mT, to allow compatibility with modern inductively coupled plasma-reactive ion etch systems. We then explore this recipe at low wafer temperature and find a reduction of spontaneous isotropic SF6 etching. This results in an enhancement in the self-limiting aspect of the etch process, an improvement of the etched sidewall homogeneity, and a decrease in the etched surface roughness, which has the potential to be useful for reducing optical loss in silicon nitride waveguides and other nanoscale devices made in silicon nitride.

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Isotropic plasma-thermal atomic layer etching of superconducting titanium nitride films using sequential exposures of molecular oxygen and SF6/H2 plasma

Hossain,

Wang,

Catherall

et al. 2023

Journal of Vacuum Science &Amp; Technology A

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Microwave loss in superconducting TiN films is attributed to two-level systems in various interfaces arising in part from oxidation and microfabrication-induced damage. Atomic layer etching (ALE) is an emerging subtractive fabrication method which is capable of etching with angstrom-scale etch depth control and potentially less damage. However, while ALE processes for TiN have been reported, they either employ HF vapor, incurring practical complications, or the etch rate lacks the desired control. Furthermore, the superconducting characteristics of the etched films have not been characterized. Here, we report an isotropic plasma-thermal TiN ALE process consisting of sequential exposures to molecular oxygen and an SF6/H2 plasma. For certain ratios of SF6:H2 flow rates, we observe selective etching of TiO2 over TiN, enabling self-limiting etching within a cycle. Etch rates were measured to vary from 1.1 Å/cycle at 150°C to 3.2 Å/cycle at 350°C using ex situ ellipsometry. We demonstrate that the superconducting critical temperature of the etched film does not decrease beyond that expected from the decrease in film thickness, highlighting the low-damage nature of the process. These findings have relevance for applications of TiN in microwave kinetic inductance detectors and superconducting qubits.

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Isotropic plasma-thermal atomic layer etching of aluminum nitride using SF6 plasma and Al(CH3)3

Cited by 3 publications

References 55 publications

Isotropic atomic layer etching of GaN using SF6 plasma and Al(CH3)3

Isotropic atomic layer etching of GaN using SF6 plasma and Al(CH3)3

Quasiatomic layer etching of silicon nitride enhanced by low temperature

Isotropic plasma-thermal atomic layer etching of superconducting titanium nitride films using sequential exposures of molecular oxygen and SF6/H2 plasma

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