Atomic layer deposition (ALD) is a thin film deposition technique with excellent uniformity and conformality at nanoscale due to its unique surface self-saturated reactions of precursors and counter reactants. However, the isotropic growth of ALD is one of the bottlenecks to enable the seamless gap-filling in high aspect ratio structures, such as holes and trenches because the opening of structures is closed off at a certain thickness, resulting in formation of a void. In this work, we introduce an area-selective ALD (AS-ALD) process to realize seamless deposition in 3D nanostructures by using a gradient adsorption of a Ti source precursor inhibitor namely TiCp*(OMe)₃. The TiCp*(OMe)₃ inhibitor can block the growth of TiO2 ALD (using Tetrakis(dimethylamido)titanium-TDMAT precursor) up to 900 cycles (ca. 50 nm) with a high selectivity of ca. 91.3 %. For the gradient AS-ALD, the density of inhibitor adsorption inside 3D structures is controlled by exposure of the TiCp*(OMe)₃ inhibitor, and the deposition of TiO₂ is inhibited in the following TiO₂ ALD depending on the surface concentration of the inhibitor. The results show the ability to control the growth of TiO₂ ALD in the hole pattern (aspect ratio =16). The gap can be filled up from bottom to determined position inside hole without any seams in the centerline. Theoretical calculations by Density functional theory (DFT), Monte Carlo (MC) simulation show high consistency with the experimental results. The concept of gradient AS-ALD could be extended to other ALD materials system for better and simplified process in many various applications.

Titanium oxide (TiO₂) area-selective deposition (ASD) has been studied for applications such as hard masks for tone inversion, dielectric layers, solar cells, and photocatalysis due to the etch resistance, high dielectric constant, and high refractive index of TiO₂. While these studies¹ have successfully demonstrated several nanometers of selective deposition using various passivation, activation, and defect mitigation techniques, there is still work needed to understand selectivity loss mechanisms in order to further expand selectivity windows to reach commercial requirements. Herein we evaluate selectivity loss mechanisms of TiO₂ deposited on trimethyl-silane passivated SiO₂ substrates from TiCl₄/H₂O.

Dimethylamino-trimethylsilane (DMA-TMS) passivates SiO₂ substrates with a 300 s exposure at 250 °C while Si, TiO₂, TiN, and Ru surfaces remain unaffected.² This DMA-TMS passivated SiO₂ limits TiO₂ surface coverage to ~5% after 100 cycles (3.8 nm on the growth surface) at 150 °C, as characterized by scanning electron microscopy (SEM) and Rutherford backscattering spectrometry (RBS) (Fig. 1).

Nuclei on the non-growth surface were analyzed with SEM and atomic force microscopy (AFM) to gain insight on nucleation mechanism, adsorption kinetics, and possible impact of diffusion (Fig. 2). Particle size distributions (PSDs) reveal a high concentration of small nuclei even for high cycle numbers. This indicates new nuclei generation on the non-growth surface during deposition. Kinetic modeling³ was employed to fit experimental data according to this information using an estimated site generation rate of 4.6x10^-5 sites cm^-2 cycle^-1 and a 30-cycle nucleation delay. Modeling results correspond to a thickness of ≈4 nm TiO₂ while maintaining 90% selectivity (t_S = 0.9 = 4.02 nm).* Furthermore, we compare PSDs at low (150 °C) and high (300 °C) deposition temperatures to evaluate changes in species diffusivity and loss of effectiveness in the passivation layer. Finally, this insight is applied to develop techniques for extending TiO₂ selectivity windows, including repeated passivations and periodic etching to mitigate defects. The improved understanding on TiO₂ selectivity loss identifies effective strategies to increase selectivity to reach advanced technology nodes.

With feature dimensions of state-of-the-art semiconductor devices moving toward the 5 nm node and beyond, device fabrication based on top-down approaches is becoming ever more challenging. Recently, area-selective atomic layer deposition (ALD) has evolved as a promising method to fabricate well-defined patterns from the bottom-up with atomic-scale accuracy. Within the different approaches for area-selective ALD, the preparation of patterned substrates with material-selective organic functionalization offers a promising direction for achieving self-aligned patterns over large areas. In this study, we focus on area-selective ALD of Al₂O₃ on functionalized SiO₂ with small-molecule aminosilanes through the vapor phase. Using in situ optical surface diagnostics, we investigate the atomistic-scale mechanism that leads to the reaction of the ALD precursors with the functionalized SiO₂ surface.