Area-Selective Atomic Layer Deposition Assisted by Self-Assembled Monolayers: A Comparison of Cu, Co, W, and Ru

Abstract

Area-selective atomic layer deposition (AS-ALD) is a promising “bottom-up” alternative to current nanopatterning techniques. Self-assembled monolayers (SAM) have been successfully employed as deactivating agents to achieve AS-ALD. In this work, the formation of octadecylphosphonic acid (ODPA) SAMs is studied on four technologically important metal substrates: Cu, Co, W, and Ru. The SAM quality is shown to be dependent on temperature, solvent, and the nature of the substrate. The blocking ability of the ODPA-treated substrates is evaluated using ZnO and Al2O3 model ALD processes. Spectroscopic analyses reveal that ODPA-assisted ALD blocking can be achieved to varying degrees of success on each metal. ODPA-protected W showed >90% selectivity after 32 nm ZnO and 8 nm Al2O3 ALD, exhibiting the best blocking overall. For all substrates, ZnO ALD proved consistently easier to block than Al2O3, indicating the importance of precursor chemistry. Additionally, we show that the self-correcting process previously reported for Cu using an acetic acid etchant can be extended to Co. This process improves selective deposition of Al2O3 on patterned Co/SiO2 with feature sizes as small as 25 nm. Additional studies reveal that feature size and density affect the apparent selectivity in SAM-based AS-ALD, highlighting the importance of such considerations in future process developments.