Multiscale CFD modelling for conformal atomic layer deposition in high aspect ratio nanostructures

The high-quality and conformal thin film is of great importance to performances of functional materials and devices with high aspect ratio nanostructures. Atomic layer deposition (ALD) is known for outstanding step coverage, yet the ideal coatings in high aspect ratio nanostructures requires the process optimization. In this work, we report a computationally efficient multiscale computational fluid dynamics (CFD) model for an accurate study of ALD process in high aspect ratio nanostructures. The continuum model of precursor mass transfer and surface micro-kinetics in the high aspect ratio nanostructure is coupled to the reactor scale CFD model. The dynamic distribution of the precursor in the high aspect ratio nanostructure is captured and the competition of the surface deposition with the precursor transfer has been analyzed. The complete ALD process parameters including pulse, pressure-holding and purging are studied. Increasing the gas flow rate correspondingly reduces the gas phase reaction, ensures the conformability, and shortens the process time. Pressure-holding leads to a better film conformality for the diffusion-limited ALD process, especially for precursors of low reactivity. The experiment of ALD coating in nanopores with an aspect ratio up to 100:1 agrees well with our simulation results, indicating the validity of the multiscale model. Multiscale modelling provides a manner to quantitatively study the comprehensive effects of full-scale parameters for better conformity and process efficiency.