Enhancing selectivity in area-selective atomic layer deposition of Al2O3 on Cu using N2 co-flow†

To achieve fully self-aligned via schemes aimed at addressing edge placement errors, we propose a simple and effective method of enhancing Al₂O₃ selectivity during area-selective atomic layer deposition (ALD) on a short-chain self-assembled monolayer, dodecylphosphonic acid (DDPA). The introduction of N₂ co-flow during the trimethylaluminum (TMA) injection step significantly enhanced selectivity by reducing the probability of TMA–DDPA interactions, due to decreased residence time and dilution of reactive TMA species. This approach yielded selectivity comparable to that obtained using longer-chain octadecylphosphonic acid without N₂ co-flow. The N₂ co-flow-induced selectivity enhancement and its practical applicability were demonstrated through transmission electron microscopy studies of Al₂O₃ deposition on SiO₂ and Cu surfaces after DDPA coating, both with and without N₂ co-flow. Studies on the Al₂O₃ deposition rate showed that N₂ co-flow effectively delayed Al₂O₃ nucleation by suppressing the degradation of the blocking capability of DDPA. Additional ALD half-cycle experiments (involving only TMA-N₂ injection and N₂ purging steps), water contact angle measurements, and X-ray photoelectron spectroscopy analyses confirmed that DDPA degradation caused by TMA exposure was effectively suppressed by high N₂ co-flow.