Atomic Layer Etching of Al 2 O 3 Using F Radical and Al Precursors: Surface Reaction and Reaction Mechanism Study

In order to overcome the miniaturization of semiconductor devices, devices with a three-dimensional (3D) structure, such as FinFET and 3D vertical NAND devices, were introduced. The manufacturing of 3D devices requires both anisotropic etching in the vertical direction and isotropic etching in the horizontal direction. Therefore, a new technology with atomic-level precision is required for isotropic etching, which is dependent on wet etching. It is the thermal atomic layer etching (ALE) process that meets these requirements. Since the first report in 2016, the thermal ALE processes by alternating exposures to HF vapor and a metal precursor have been reported for various thin films. However, HF has issues with safety and corrosion. Recently, ALE processes using F radicals produced by inductively coupled plasma (ICP) of SF 6 or NF 3 have been reported [1,2]. However, the study on the reaction mechanism of F radicals is lacking. In this study, the surface reaction was studied for the modification and removal steps by NF 3 remote plasma and Al precursors. We used quartz crystal microbalance (QCM) to measure the mass change during the ALE process and X-ray photoelectron spectroscopy (XPS) to analyze the composition of the modified layer. The mechanism of ALE using F radical was different from that using HF, due to the absence of H atoms. Density functional theory (DFT) simulation shows that amorphous carbon or fluorocarbon layer can be formed during the ALE by F radicals. Al precursor with fewer organic ligands was beneficial to suppress the formation of a carbon-containing surface layer. Acknowledgments This research was supported by the MOTIE (Ministry of Trade, Industry & Energy (project number 20012588) and KSRC (Korea Semiconductor Research Consortium) support program for the development of the future semiconductor device. References [1] N. Chittock et al., Appl. Phys. Lett. (2020) [2] J. Kim et al., J. Vac. Sci. Technol. A (2022)