(Invited) Characterization of Isotropic Thermal ALE of Oxide Films in Nanometer-Size Structures

Isotropic atomic layer etching (ALE) is increasingly becoming an option and even a necessity for modern chip manufacturing. Especially for application such as 3D-NAND memory, the ability to perform isotropic etches will be a critical addition to the established suite of reactive ion etching. In this work, we have characterized the reaction of aluminum oxide (Al2O3) via the vapor-based DMAC ligand exchange mechanism in nanometer-size structures in which the oxide is buried below a silicon nitride mask. In the oxide, we measured vertical and horizontal etch rates and found that the etch showed some residual anisotropy even though all elements of the etch itself (flow, no plasma) were none-directional. We applied a simple Monte-Carlo simulation to show that anisotropy is caused by a delay in the onset of the horizontal etch beneath the mask and by molecular scattering effects in the vapor phase above the nano-structures. We are contrasting these results with experimental findings in structures without an anisotropy of the etch.