Bottom-up nanofabrication by area-selective atomic layer deposition (ALD) is currently gaining momentum in semiconductor processing, because of the increasing need for eliminating the edge placement errors of top-down processing. Moreover, area-selective ALD offers new opportunities in many other areas such as the synthesis of catalysts with atomic-level control. This Perspective provides an overview of the current developments in the field of area-selective ALD, discusses the challenge of achieving a high selectivity, and provides a vision for how area-selective ALD processes can be improved. A general cause for the loss of selectivity during deposition is that the character of surfaces on which no deposition should take place changes when it is exposed to the ALD chemistry. A solution is to implement correction steps during ALD involving for example surface functionalization or selective etching. This leads to the development of advanced ALD cycles by combining conventional two-step ALD cycles with correction steps in multistep cycle and/or supercycle recipes.

Area-selective atomic layer deposition (ALD) is rapidly gaining interest because of its potential application in self-aligned fabrication schemes for next-generation nanoelectronics. Here, we introduce an approach for area-selective ALD that relies on the use of chemoselective inhibitor molecules in a three-step (ABC-type) ALD cycle. A process for area-selective ALD of SiO2 was developed comprising acetylacetone inhibitor (step A), bis(diethylamino)silane precursor (step B), and O2 plasma reactant (step C) pulses. Our results show that this process allows for selective deposition of SiO2 on GeO2, SiNx, SiO2, and WO3, in the presence of Al2O3, TiO2, and HfO2 surfaces. In situ Fourier transform infrared spectroscopy experiments and density functional theory calculations underline that the selectivity of the approach stems from the chemoselective adsorption of the inhibitor. The selectivity between different oxide starting surfaces and the compatibility with plasma-assisted or ozone-based ALD are distinct features of this approach. Furthermore, the approach offers the opportunity of tuning the substrate-selectivity by proper selection of inhibitor molecules.

Area-selective atomic layer deposition (ALD) is currently attracting significant interest as a solution to the current challenges in alignment that limit the development of sub-5 nm technology nodes in nanoelectronics. Development of area-selective ALD processes with high selectivity requires understanding of the mechanisms involved in the loss of selectivity. In this work, the use of acetylacetone (Hacac) inhibitor molecules in ABC-type cycles for area-selective ALD of SiO 2 is investigated as a model system to gain insights into precursor blocking. In situ infrared spectroscopy measurements show that at saturation, Hacac adsorbs in a mixture of chelate and monodentate bonding configurations. Hacac adsorbates in monodentate configuration were found to desorb as a result of purging or to be displaced by bis(diethylamino)silane (BDEAS) precursor dosing and therefore significantly contribute to the loss of selectivity during area-selective ALD. Density functional theory (DFT) calculations reveal that the observed displacement reactions originate from attractive interactions between BDEAS precursor molecules and Hacac adsorbates in monodentate configuration. Moreover, the DFT calculations show that the strength of this interaction is dependent on the chemical structure of the precursor molecule. The obtained insights indicate that careful selection of both inhibitor and precursor molecules is required to improve the selectivity of area-selective ALD.

Despite the rapid increase in the number of newly developed processes, area-selective atomic layer deposition (ALD) of nitrides is largely unexplored. ALD of nitrides at low temperature is typically achieved by employing a plasma as the coreactant, which is not compatible with most approaches to area-selective ALD. In this work, a plasma-assisted ALD process for area-selective deposition of TiN was developed, which involves dosing of inhibitor molecules at the start of every ALD cycle. Aromatic molecules were identified as suitable inhibitor molecules for metal/dielectric selectivity because of their strong and selective adsorption on transition metal surfaces. A four-step (i.e., ABCDtype) ALD cycle was developed, which comprises aniline inhibitor (step A) and tetrakis(dimethylamino)titanium precursor (step B) dosing steps, followed by an Ar−H 2 plasma exposure (step C), during which a substrate bias is applied in the second half of the plasma exposure (step D). This process was demonstrated to allow for ∼6 nm of selective TiN deposition on SiO 2 and Al 2 O 3 areas of a nanoscale pattern with Co and Ru non-growth areas. The TiN deposited using this ABCD-type process is of high quality in terms of resistivity (230 ± 30 μΩ cm) and impurity levels. This developed strategy for area-selective ALD of TiN can likely be extended to area-selective ALD of other nitrides.

With downscaling of device dimensions, two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) such as WS2 are being considered as promising materials for future applications in nanoelectronics. However, at these nanoscale regimes, incorporating TMD layers in the device architecture with precise control of critical features is challenging using current top-down processing techniques. In this contribution, we pioneer the combination of two key avenues in atomic-scale processing: area-selective atomic layer deposition (AS-ALD) and growth of 2D materials, and demonstrate bottom-up processing of 2D WS2 nanolayers. Area-selective deposition of WS2 nanolayers is enabled using an ABC-type plasma-enhanced ALD process involving acetylacetone (Hacac) as inhibitor (A), bis­(tert-butylimido)-bis­(dimethylamido)-tungsten as precursor (B), and H2S plasma as the co-reactant (C) at a low deposition temperature of 250 °C. The developed AS-ALD process results in the immediate growth of WS2 on SiO2 while effectively blocking growth on Al2O3 as confirmed by in situ spectroscopic ellipsometry and ex situ X-ray photoelectron spectroscopy measurements. As a proof of concept, the AS-ALD process is demonstrated on patterned Al2O3/SiO2 surfaces. The AS-ALD WS2 films exhibited sharp Raman (E 2g 1 and A 1g) peaks on SiO2, a fingerprint of crystalline WS2 layers, upon annealing at temperatures within the thermal budget of semiconductor back-end-of-line processing (≤450 °C). Our AS-ALD process also allows selective growth on various TMDs and transition metal oxides while blocking growth on HfO2 and TiO2. It is expected that this work will lay the foundation for area-selective ALD of other 2D materials.