Mechanism of Thermal Atomic Layer Etch of W Metal Using Sequential Oxidation and Chlorination: A First-Principles Study

Abstract

Thermal atomic layer etch (ALE) of W metal can be achieved by sequential self-limiting oxidation and chlorination reactions at elevated temperatures. In this paper, we analyze the reaction mechanisms of W ALE using the first-principles simulation. We show that oxidizing agents such as O 2 , O 3 , and N 2 O can be used to produce a WO x surface layer in the first step of an ALE process with ozone being the most reactive. While the oxidation pulse on clean W is very exergonic, our study suggests that runaway oxidation of W is not thermodynamically favorable. In the second ALE pulse, WCl 6 and Cl 2 remove the oxidized surface W atoms by the formation of volatile tungsten oxychloride (W x O y Cl z ) species. In this pulse, each adsorbed WCl 6 molecule was found to remove one surface W atom with a moderate energy cost. Our calculations further show that the desorption of the additional etch products is endothermic by up to 4.7 eV. Our findings are consistent with the high temperatures needed to produce ALE in experiments. In total, our quantum chemical calculations have identified the lowest energy pathways for ALE of tungsten metal along with the most likely etch products, and these findings may help guide the development of improved etch reagents.

Thermal Atomic Layer Etching of Aluminum Oxide (Al2O3) Using Sequential Exposures of Niobium Pentafluoride (NbF5) and Carbon Tetrachloride (CCl4): A Combined Experimental and Density Functional Theory Study of the Etch Mechanism

“…In ALEt, the conversion step can form an oxide, fluoride, − or another type of reactive surface that differs from the actual etch target. In the etch step, ligands from the coreactant molecules can undergo surface reactions such as ligand-exchange transmetalation, ,, fluorination, or chlorination , to form species that may leave the surface.…”

In silico design of a thermal atomic layer etch process of cobalt

“…We have previously used density functional theory (DFT) based quantum chemical simulations to validate experimental findings such as etch rates and compute thermodynamic properties to estimate the reaction energy requirements of individual ALE steps and understand the underlying etch mechanisms of ALE processes for, e.g., Al 2 O 3 , 50 metallic W, 51 HfO 2 , and ZrO 2 . 52 Compared to experiments, computational studies offer a relatively inexpensive way to investigate a broad range of thermal ALE processes.…”