Area selective atomic layer deposition of SnO₂ as an etch resist in fluorine based processes

Here, we propose SnO2 as a reactive ion etching (RIE) mask in fluorine-based etching processes. Tin forms nonvolatile compounds with fluorine at the process temperatures enabling tin to function as an etch mask. We investigate atomic layer deposition (ALD) of SnO2 on silicon thermal oxide, silicon native oxide, H-terminated Si(001), and polystyrene surfaces using tetrakis(dimethylamino) tin(IV) and H2O at 170 °C to understand film nucleation patterns. Pinhole free films of approximately 1 nm thick SnO2 form on silicon thermal oxide and silicon native oxide and resist etching with SF6 under conditions that etch 0.3 μm into silicon. Nucleation delays were observed on H-terminated Si(001) producing continuous films with pinhole defects. Etch proof-of-concept is studied by UV crosslinking polystyrene, dissolving away non-crosslinked polystyrene to expose native oxide, and depositing 20–100 ALD cycles of SnO2. Well-defined grid patterns are transferred 1.2 μm into Si(001) with SF6 RIE when 50 ALD cycles of SnO2 are grown, which is approximately 4 nm thick.