Search

On-chip photonic devices based on SiO 2 are of interest for applications such as microresonator gyroscopes and microwave sources. Although SiO 2 microdisk resonators have achieved quality factors exceeding one billion, this value remains an order of magnitude less than the intrinsic limit due to surface roughness scattering. Atomic layer etching (ALE) has potential to mitigate this scattering because of its ability to smooth surfaces to sub-nanometer length scales. While isotropic ALE processes for SiO 2 have been reported, they are not generally compatible with commercial reactors, and the effect on surface roughness has not been studied. Here, we report an ALE process for SiO 2 using sequential exposures of Al(CH3)3 (trimethylaluminum) and Ar/H2/SF6 plasma. We find that each process step is self-limiting, and that the overall process exhibits perfect synergy, with neither isolated half-cycle resulting in etching. We observe etch rates up to 0.58 Å per cycle for thermally grown SiO 2 and higher rates for ALD, plasma enhanced chemical vapor deposition, and sputtered SiO 2 up to 2.38 Å per cycle. Furthermore, we observe a decrease in surface roughness by 62% on a roughened film. The residual concentration of Al and F is around 1%–2%, which can be further decreased by O2 plasma treatment. This process could find applications in smoothing of SiO 2 optical devices and thereby enabling device quality factors to approach limits set by intrinsic dissipation. [ABSTRACT FROM AUTHOR]

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 SF 6 /H 2 plasma. For certain ratios of SF 6 :H 2 flow rates, we observe selective etching of TiO 2 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. [ABSTRACT FROM AUTHOR]

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 applications of AlN in nonlinear photonics and wide bandgap semiconductor devices. [ABSTRACT FROM AUTHOR]