Isotropic Atomic Layer Etching of ZnO Using Acetylacetone and O₂ Plasma

Abstract

Atomic layer etching (ALE) provides Ångström-level control over material removal and holds potential for addressing the challenges in nanomanufacturing faced by conventional etching techniques. Recent research has led to the development of two main classes of ALE: ion-driven plasma processes yielding anisotropic (or directional) etch profiles and thermally driven processes for isotropic material removal. In this work, we extend the possibilities to obtain isotropic etching by introducing a plasma-based ALE process for ZnO which is radical-driven and utilizes acetylacetone (Hacac) and O2 plasma as reactants. In situ spectroscopic ellipsometry measurements indicate self-limiting half-reactions with etch rates ranging from 0.5 to 1.3 Å/cycle at temperatures between 100 and 250 °C. The ALE process was demonstrated on planar and three-dimensional substrates consisting of a regular array of semiconductor nanowires (NWs) conformally covered using atomic layer deposition of ZnO. Transmission electron microscopy studies conducted on the ZnO-covered NWs before and after ALE proved the isotropic nature and the damage-free characteristics of the process. In situ infrared spectroscopy measurements were used to elucidate the self-limiting nature of the ALE half-reactions and the reaction mechanism. During the Hacac etching reaction that is assumed to produce Zn(acac)2, carbonaceous species adsorbed on the ZnO surface are suggested as the cause of the self-limiting behavior. The subsequent O2 plasma step resets the surface for the next ALE cycle. High etch selectivities (∼80:1) over SiO2 and HfO2 were demonstrated. Preliminary results indicate that the etching process can be extended to other oxides such as Al2O3.

Self-Limiting Temperature Window for Thermal Atomic Layer Etching of HfO2 and ZrO2 Based on the Atomic-Scale Mechanism

“…6 Thermal ALE relies on temperature and thermochemically favourable reactions to remove surface species. 10 While there have been many examples of thermal ALE of a range of materials, including: HfO 2 , 4,9,11,12 ZrO 2 , 4,12 SiO 2 , 13 , Al 2 O 3 , 12,[14][15][16][17][18] AlN, 19 AlF 3 , 20 TiO 2 , 21 TiN, 22,23 W, 24,25 WO 3 , 25 ZnO 26 and GaN 27 and for other ALE techniques including Ar neutral beam ZrO 2 , 28 plasma ALE SiO 2 , 29,30 ZnO, 31 GaN 32,33 and ALE of Si 3 N 4 34 using infrared annealing, the details of the mechanism of the ALE process still require significant work to understand. The first step in ALE is the formation of a reactive but non-volatile layer on the initial film, which is followed by a material removal step to take off only the modified layer as indicated schematically in Figure 1.…”

Microphase segregation and selective chain scission of poly(2‐methyl‐2‐oxazoline)‐block‐polystyrene

“…In order to meet the miniaturization demands of the microelectronics industry, there has been a longstanding interest in developing techniques that push the physical limits of patterning. Top‐down approaches, such as photolithography and imprint lithography, have primarily enabled access to sub‐10 nm feature sizes in the past decades by leveraging advances in engineering and processing . However, bottom‐up approaches have gained attention because sub‐10 nm feature sizes may be more readily generated routinely.…”

Insight into the removal and reapplication of small inhibitor molecules during area-selective atomic layer deposition of SiO2

“…Hacac has been reported to be a suitable reactant for ALE of Al 2 O 3 at 250°C. 36 In our process, repeated Hacac and H 2 plasma exposures were found to etch the Al 2 O 3 slightly (with 0.0036 ± 0.0002 nm/cycle, see Fig. S2 in the supplementary material 46 ), most likely through the formation of Al(acac) 3 .…”