Simultaneous Co-localized TiO2 Etching and W Atomic Layer Deposition Using WF6 as a Dual-Functional Reactant

Thin film deposition and etching are two of the most widely used chemical processes in semiconductor manufacturing, and they are commonly carried out in distinct processing steps. In this work, we investigate low-temperature (250 °C) surface reactions that occur when a TiO₂ surface undergoes chemical vapor etching, while at the same time, a layer of W metal is deposited at the location where the TiO₂ was etched. The W deposition is performed using SiH₄/WF₆ exposures in an atomic layer deposition (ALD) sequence, where the WF₆ provides a dual function as a precursor for W ALD and a reactant for TiO₂ etching. Exposing TiO₂ to WF₆ leads to the formation of a mixed TiWO_xF_y surface layer that can be volatilized (i.e., etched) by further WF₆ exposure. However, exposing the TiWO_xF_y to SiH₄ promotes surface reduction so that subsequent WF₆ exposure promotes W deposition. Introducing a controlled partial pressure of SiH₄ in a SiH₄/WF₆ ALD sequence allows etching of TiO₂ to continue but also promotes simultaneous W ALD so that the deposition and etch reactions “compete” for available WF₆. Notably, the resulting W layer is formed at the location originally occupied by TiO₂, thereby demonstrating “etch-replacement deposition.” In this case, the etch reactants are able to diffuse through the deposited W layer allowing more than 15 nm of TiO₂ etching and 20 nm of W deposition. The results presented here provide insights into the interactions between deposition and etching reaction mechanisms, creating new opportunities for integrated atomic layer processing.