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 TiWOxFy surface layer that can be volatilized (i.e., etched) by further WF6 exposure. However, exposing the TiWOxFy 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.