Role of Precursor Choice on Area-Selective Atomic Layer Deposition

• Published in: Chemistry of materials 2021-06, Vol.33 (11), p.3926-3935
• Main Authors: Oh, Il-Kwon, Sandoval, Tania E, Liu, Tzu-Ling, Richey, Nathaniel E, Bent, Stacey F
• Format: Article
• Language: English
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/acs.chemmater.0c04718

Area-selective atomic layer deposition (AS-ALD) is a highly sought-after strategy for the fabrication of next-generation electronics. This work reveals how key precursor design parameters strongly influence the efficacy of AS-ALD by comparing a series of precursors possessing the same metal center but different ligands. When the number of methyl and chloride groups in Al­(CH3) x Cl3–x (x = 0, 2, and 3) and the chain length of alkyl ligands in AlC y H2y+1 (y = 1 and 2) are changed, the effect of precursor chemistry (reactivity and molecular size) on the selectivity is elucidated. The results show that optimized parameters for the Al2O3 ALD processes on a self-assembled monolayer (SAM)-terminated substrate, which serves as the nongrowth surface, differ significantly from those on a Si substrate. Chlorine-containing precursors need a much longer purging time on the SAMs because of a stronger Lewis acidity compared to that of alkyl precursors. With reoptimized conditions, the ALD of Al2O3 using the Al­(C2H5)3 precursor is blocked most effectively by SAM inhibitors, whereas the widely employed Al­(CH3)3 precursor is blocked least effectively among the precursors tested. Finally, we show that a selectivity exceeding 0.98 is achieved for up to 75 ALD cycles with Al­(C2H5)3, for which 6 nm of Al2O3 film grows selectively on SiO2-covered Si. Quantum chemical calculations show significant differences in the energetics of dimer formation across the Al precursors, with only ∼1% of AlCl3 and Al­(CH3)2Cl precursors but 99% of the alkyl precursors, Al­(CH3)3 and Al­(C2H5)3, existing as monomers at 200 °C. We propose that a combination of precursor reactivity and effective molecular size affects the blocking of the different precursors, explaining why Al­(C2H5)3, with weaker Lewis acidity and relatively large size, exhibits the best blocking results.