The vapor-phase reaction of dodecanethiol (DDT) with copper oxide surfaces and the molecular level composition and structure of the resulting films were examined. Atomic force microscopy, cross-sectional transmission electron microscopy, and electron energy loss/electron dispersive spectroscopy reveal that, instead of forming self-assembled monolayers, DDT etches CuO surfaces to create ∼8 nm thick Cu-thiolate multilayers. These layers are composed of surprisingly well-ordered crystallites, oriented either parallel or perpendicular to the substrate surface. Pre-etching of the CuO to expose the underlaying copper metal is shown to prevent the formation of multilayers and instead allow for the formation of the expected monolayers. Water contact angle and Fourier transform infrared spectroscopy are further shown to be ineffective at distinguishing the multilayer and monolayer thiol films. Interestingly, the multilayer films are unstable in air, ripening into particles 20 μm wide and several hundred nanometers tall over the course of a week. Air exposure also leads to the slow oxidation of the sulfur and copper within the films at a rate similar to what has been seen before for DDT monolayers. As a result, the multilayers show no significant improvement over monolayers in the prevention of oxidation.

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.

Monolayer and multilayer dodecanethiols (DDT) can be assembled onto a copper surface from the vapor phase depending on the initial oxidation state of the copper. The ability of the copper-bound dodecanethiolates to block atomic layer deposition (ALD) and the resulting behavior at the interfaces of Cu/SiO2 patterns during area-selective ALD (AS-ALD) are compared between mono- and multilayers. We show that multilayer DDT is ∼7 times more effective at blocking ZnO ALD from diethylzinc and water than is monolayer DDT. Conversely, monolayer DDT exhibits better performance than does multilayer DDT in blocking of Al2O3 ALD from trimethylaluminum and water. Investigation into interfacial effects at the interface between Cu and SiO2 on Cu/SiO2 patterns reveals both a gap at the SiO2 edges and a pitch size-dependent nucleation delay of ZnO ALD on SiO2 regions of multilayer DDT-coated patterns. In contrast, no impact on ZnO ALD is observed on the SiO2 regions of monolayer DDT-coated patterns. We also show that these interfacial effects depend on the ALD chemistry. Whereas an Al2O3 film grows on the TaN diffusion barrier of a DDT-treated Cu/SiO2 pattern, the ZnO film does not. These results indicate that the structure of the DDT layer and the ALD precursor chemistry both play an important role in achieving AS-ALD.

Area-selective atomic layer deposition (AS-ALD) is attracting increasing interest, but the process usually requires substrate materials with substantially different chemical properties. We introduce a process that expands the application to more general material systems by demonstrating AS-ALD on patterns with chemically similar materials. The substrate materials investigated are Al2O3, HfO2, TiO2, Ta2O5, and SiO2. By taking advantage of differential reactivity of octadecylphosphonic acid (ODPA) self-assembled monolayers (SAMs) on the various dielectric surfaces, we use the SAMs as ALD inhibitors to achieve selective ALD of both ZnO and Al2O3. With SiO2 as the growth surface, the best blocking performance against ZnO and Al2O3 ALD is achieved on ODPA-protected Al2O3 and HfO2 substrates which reach selectivities above 0.9 after 14 nm ZnO and 2.5 nm Al2O3 growth, respectively, on control Si wafers. Selectivity between different metal oxides is also explored, including HfO2/Al2O3 patterns. With the optimization of solvent and ODPA SAM deposition time, selectivity above 0.9 can be achieved for at least 4 nm ZnO ALD on a HfO2 growth surface, while preventing growth on an Al2O3 nongrowth surface. This study introduces a strategy for achieving more general selectivity and opens up the possibility for new applications in next generation electronic devices.

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