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 and WF are used to deposit W by atomic layer deposition (ALD) at 250 °C onto TiO, the process produces a W film while simultaneously, the TiO layer under the W is removed by spontaneous chemical vapor etching (CVE). Here, TiO CVE using WF or MoF, and atomic layer etching (ALE) using WF/BCl under conditions where the TiO 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 consists of a lined array, the TiO 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 surface beneath the first W layer, and additional ALE cycles remove more TiO, producing a second air gap. However, AlO ALD, SiOC-H molecular layer deposition, and PEDOT chemical vapor deposition processes do not deposit films on the underlying TiO. These results offer insight into transport mechanisms of volatile etching and deposition precursors through ALD W and mechanisms enabling air-gap formation.