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1. Fluorocarbon based atomic layer etching of Si 3 N 4 and etching selectivity of SiO 2 over Si 3 N 4

   https://doi.org/10.1116/1.4954961  

   Li, Chen ; Metzler, Dominik ; Lai, Chiukin Steven ; Hudson, Eric A. ; Oehrlein, Gottlieb S. ( July 2016 , Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films)
2. Scaling of atomic layer etching of SiO 2 in fluorocarbon plasmas: Transient etching and surface roughness

   https://doi.org/10.1116/6.0000941  

   Wang, Xifeng ; Wang, Mingmei ; Biolsi, Peter ; Kushner, Mark J. ( May 2021 , Journal of Vacuum Science & Technology A)
3. Threshold Ion Energies and Cleaning of Etch Residues During Inductively Coupled Etching of NiO/Ga 2 O 3 in BCl 3

   https://doi.org/10.1149/2162-8777/ac9ff3  

   Chiang, Chao-Ching ; Xia, Xinyi ; Li, Jian-Sian ; Ren, Fan ; Pearton, S. J. ( November 2022 , ECS Journal of Solid State Science and Technology)

   BCl 3 is an attractive plasma etchant for oxides because it is a Lewis acid used to scavenge native oxides on many semiconductors due to the strong B–O bonding. We investigated BCl 3 -based dry etching of the NiO/Ga 2 O 3 heterojunction system. BCl 3 /Ar Inductively Coupled Plasmas produced maximum etch rates for NiO up to 300 Å.min −1 and 800 Å.min −1 for β -Ga 2 O 3 under moderate plasma power conditions suitable for low damage pattern transfer. The selectivity for NiO: Ga 2 O 3 was <1 under all conditions. The ion energy threshold for initiation of etching of NiO was between 35–60 eV, depending on the condition and the etch mechanism was ion-driven, as determined by the linear dependence of etch rate on the square root of ion energy incident on the surface. By sharp contrast, the etching of Ga 2 O 3 had a stronger chemical component, without a well-defined ion energy threshold. The as-etched NiO and Ga 2 O 3 surfaces show chlorine residues, which can be removed on both materials by the standard 1NH 4 OH: 10H 2 O or 1HCl: 10H 2 O rinses used for native oxide removal. According to the location of the Cl 2p 3/2 peak, the Cl is ionically bonded. 

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4. Bromine Etching of Patterned YBa 2 Cu 3 O 6+x Nanoscale Thin Films for High-Temperature Superconducting Devices

   https://doi.org/10.1021/acsanm.1c03098  

   Vinay, Miranda L. ; LeFebvre, Jay C. ; Cai, Han ; Forman, Joseph ; Cybart, Shane ( December 2021 , ACS Applied Nano Materials)
5. Voltage waveform tailoring for high aspect ratio plasma etching of SiO 2 using Ar/CF 4 /O 2 mixtures: Consequences of ion and electron distributions on etch profiles

   https://doi.org/10.1116/6.0002290  

   Krüger, Florian ; Lee, Hyunjae ; Nam, Sang Ki ; Kushner, Mark J. ( January 2023 , Journal of Vacuum Science & Technology A)

   The quality of high aspect ratio (HAR) features etched into dielectrics for microelectronics fabrication using halogen containing low temperature plasmas strongly depends on the energy and angular distribution of the incident ions (IEAD) onto the wafer, as well as potentially that of the electrons (EEAD). Positive ions, accelerated to high energies by the sheath electric field, have narrow angular spreads and can penetrate deeply into HAR features. Electrons typically arrive at the wafer with nearly thermal energy and isotropic angular distributions and so do not directly penetrate deeply into features. These differences can lead to positive charging of the insides of the features that can slow etching rates and produce geometric defects such as twisting. In this work, we computationally investigated the plasma etching of HAR features into SiO 2 using tailored voltage waveforms in a geometrically asymmetric capacitively coupled plasma sustained in an Ar/CF 4 /O 2 mixture at 40 mTorr. The tailored waveform consisted of a sinusoidal wave and its higher harmonics with a fundamental frequency of 1 MHz. We found that some degree of control of the IEADs and EEADs is possible by adjusting the phase of higher harmonics φ through the resulting generation of electrical asymmetry and electric field reversal. However, the IEADs and EEADs cannot easily be separately controlled. The control of IEADs and EEADs is inherently linked. The highest quality feature was obtained with a phase angle φ = 0° as this value generated the largest (most negative) DC self-bias and largest electric field reversal for accelerating electrons into the feature. That said, the consequences of voltage waveform tailoring (VWT) on etched features are dominated by the change in the IEADs. Although VWT does produce EEADs with higher energy and narrower angular spread, the effect of these electrons on the feature compared to thermal electrons is not large. This smaller impact of VWT produced EEADs is attributed to thermal electrons being accelerated into the feature by electric fields produced by the positive in-feature charging. 

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