Unlocking the synergy of ALD and ALE: tailoring crystallinity and etch rates in ZnO thin films at the atomic scale

Abstract

Atomic layer processes offer atomic-scale control over thin-film properties, essential for continued semiconductor scaling. While bottom-up approaches using atomic layer deposition (ALD) are well established, top-down methods via atomic layer etching (ALE) have recently gained attention. However, most ALE studies have focused on reaction mechanisms, with limited understanding of the resulting thin-film properties. To address this, we investigated ZnO thin films fabricated by ALD alone and by ALD followed by ALE etch-back, focusing on thickness-dependent crystallographic changes. Etching was conducted using acetylacetone (Hacac) and O<inf>2</inf> plasma. X-ray diffraction (XRD) revealed that the secondary (103) plane emerged at a lower thickness in ALD + ALE ZnO than in ALD-only films. Comparative analysis of the (002) and (103) peaks indicated preferential etching of the (002) plane during ALE. These experimental findings were supported by density functional theory (DFT) simulations and analysis of crystallographic polarity. This study provides new insight into the anisotropic etching behavior of ZnO and demonstrates how ALE alters crystallographic orientations, offering guidance for atomic-scale control of oxide thin films.