Atomic layer etching of SiO_2 using sequential exposures of Al(CH_3)_3 and H_2/SF_6 plasma
arxiv(2024)
摘要
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(CH_3)_3
(trimethylaluminum, TMA) and Ar/H_2/SF_6 plasma. We find that each process
step is self-limiting, and that the overall process exhibits a synergy of 100
We observe etch rates up to 0.58 Å per cycle for thermally-grown SiO_2
and higher rates for ALD, PECVD, and sputtered SiO_2 up to 2.38 Å per
cycle. Furthermore, we observe a decrease in surface roughness by 62
roughened film. The residual concentration of Al and F is around 1-2
can be further decreased by O_2 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.
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