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 Al 2 O 3 model ALD processes. Spectroscopic analyses reveal that ODPA-assisted ALD blocking can be achieved to varying degrees of success on each metal. ODPAprotected W showed >90% selectivity after 32 nm ZnO and 8 nm Al 2 O 3 ALD, exhibiting the best blocking overall. For all substrates, ZnO ALD proved consistently easier to block than Al 2 O 3 , 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 Al 2 O 3 on patterned Co/SiO 2 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.

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.

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.

Metal-assisted chemical etching (MacEtch) is an emerging anisotropic chemical etching technique that has been used to fabricate high aspect ratio semiconductor micro-and nanostructures. Despite its advantages in unparalleled anisotropy, simplicity, versatility, and damage-free nature, the adaptation of MacEtch for silicon (Si)-based electronic device fabrication process is hindered by the use of a gold (Au)-based metal catalyst, as Au is a detrimental deep-level impurity in Si. In this report, for the first time, we demonstrate CMOS-compatible titanium nitride (TiN)-based MacEtch of Si by establishing a true vapor-phase (VP) MacEtch approach in order to overcome TiN-MacEtch-specific challenges. Whereas inverse-MacEtch is observed using conventional liquid phase MacEtch because of the limited mass transport from the strong adhesion between TiN and Si, the true VP etch leads to forward MacEtch and produces Si nanowire arrays by engraving the TiN mesh pattern in Si. The etch rate as a function of etch temperature, solution concentration, TiN dimension, and thickness is systematically characterized to uncover the underlying nature of MacEtching using this new catalyst. VP MacEtch represents a significant step toward scalability of this disruptive technology because of the high controllability of gas phase reaction dynamics. TiN-MacEtch may also have direct implications in embedded TiN-based plasmonic semiconductor structures for photonic applications.

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