Role of Precursor Miscibility in Area-Selective Atomic Layer Deposition

Area-selective atomic layer deposition (AS-ALD) is of increasing importance in nanostructure fabrication, and precursor selection is critical to realizing a successful process. This work explores the role of the precursor in achieving AS-ALD of Al₂O₃ on a dielectric (SiO₂) in the presence of a metal (Cu/CuO_x). Four different precursors-dimethylaluminum isopropoxide (DMAI), trimethylaluminum (TMA), triethylaluminum (TEA), and triisobutylaluminum (TIBA)-are tested against a benzenethiol (BT) inhibitor. BT forms monolayers on Cu, whereas on CuO_x it forms a thick crystalline multilayer composed of 1D-coordination polymers of Cu-thiolate (CuBT). This work observes that DMAI provides exceptional selectivity: 22 nm of Al₂O₃ can be deposited on patterned substrates with 99.9% selectivity, and in the case of thick CuBT can achieve excellent pattern transfer on nanoscale patterns with well-defined material interfaces. In contrast, none of the alkylaluminum precursors show significant selectivity, a result attributed to their miscibility in the CuBT multilayer leading to its degradation. This work proposes that the miscibility of the alkylaluminum precursors depends on ligand length and structure. The results show that the ligand-dependent miscibility and subsequent degradation of CuBT impact the location of Al₂O₃ nucleation. This study highlights new considerations for AS-ALD process design to achieve high selectivity.