Copper Oxidation Improves Dodecanethiol Blocking Ability in Area‐Selective Atomic Layer Deposition

Abstract In recent years, area‐selective atomic layer deposition (AS‐ALD) has attracted increasing interest for its applications in back‐end interconnect processes, and selective deposition of Al₂O₃ is of particular interest because Al₂O₃ can serve as an etch hard mask. However, Al₂O₃ is one of the most difficult ALD systems to block. In this work, a strategy is presented to enhance the blocking ability of dodecanethiol (DDT) self‐assembled monolayers (SAMs) against Al₂O₃ ALD. It is shown that by conducting DDT deposition on a slightly oxidized Cu surface, which is mainly composed of Cu₂O, rather than on a freshly acid‐etched Cu surface, which mainly consists of metallic Cu, the quality of the DDT SAM can be improved. It is further shown that the DDT SAMs formed on Cu₂O‐covered Cu substrates are about 3–4 times more effective in blocking Al₂O₃ than that on acid‐etched Cu surfaces when ALD is performed under subsaturation condition. However, as the Cu oxidation process continues, CuO is formed and the blocking ability of DDT degrades. Finally, selective Al₂O₃ deposition on DDT‐treated Cu/low‐k patterns using the combined strategy of Cu oxidation and subsaturation conditions achieves selectivity of 0.99 after 4 nm of Al₂O₃ ALD.