Role of Precursor Choice on Area-Selective Atomic Layer Deposition

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 AlCyH2y+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. Chlorinecontaining 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 similar to 1% of AlCl3 and Al(CH3)(2)Cl precursors but 99% of the alkyl precursors, Al(CH3)(3) and Al(C2H5)(3), existing as monomers at 200 degrees 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.