A dry-wet quasi-ALE approach for transition metals: tungsten as a model system

Abstract

A dry-wet Quasi-ALE (Q-ALE) process is demonstrated for tungsten, combining self-limiting O2 plasma oxidation with timed wet-chemical oxide removal in 1 M HCl solution at room temperature (RT). Inductively coupled plasma mass spectroscopy (ICP-MS) and electrochemical measurements were used to study oxide dissolution kinetics. Quantification revealed an initially high etch rate of the surface that gradually decreased and stabilized to a low background value. This evolution is attributed to the rapid dissolution of the plasma-generated bulk WO3, followed by the slower removal of the interfacial suboxide layer. Subsequently, the process reached a steady-state regime characterized by trace residual oxide coverage and a background etch driven by simultaneous reoxidation and metal dissolution. Although the background contribution is low, the removal step is halted before its onset to ensure controlled and selective material removal. These results were complemented by post operando X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and conductive atomic force microscopy (C-AFM) measurements. An etch rate of 8 Å/cycle was achieved and validated on both blanket and patterned films deposited by physical vapor deposition (PVD) and atomic layer deposition (ALD) using industrial-scale equipment. This demonstrates the lab-to-fab scalability of the process, thereby enabling angstrom-level precision for advanced semiconductor manufacturing.