Controlled Air Gap Formation between W and TiO₂ Films via Sub‐Surface TiO₂ Atomic Layer Etching

Thin film deposition and etching are typically considered as distinct processes. Recent findings show that when SiH 4 and WF 6 are used to deposit W by atomic layer deposition (ALD) at 250 °C onto TiO 2 , the process produces a W film while simultaneously, the TiO 2 layer under the W is removed by spontaneous chemical vapor etching (CVE). Here, TiO 2 CVE using WF 6 or MoF 6 , and atomic layer etching (ALE) using WF 6 /BCl 3 under conditions where the TiO 2 layer is pre‐coated with a W layer up to 20 nm thick is investigated. Etch reactants diffuse through the W layer and produce volatile etch products. When the W‐coated TiO 2 consists of a lined array, the TiO 2 is etched vertically and laterally, producing a self‐supporting W film and a vacant air gap. Additional W ALD cycles produce a W film on the TiO 2 surface beneath the first W layer, and additional ALE cycles remove more TiO 2 , producing a second air gap. However, Al 2 O 3 ALD, SiOC‐H molecular layer deposition, and PEDOT chemical vapor deposition processes do not deposit films on the underlying TiO 2 . These results offer insight into transport mechanisms of volatile etching and deposition precursors through ALD W and mechanisms enabling air‐gap formation.