Computational fluid dynamics modeling of spatial atomic layer deposition on microgroove substrates

Abstract

Abstract Spatial atomic layer deposition (ALD) is a promising high-throughput technique capable of producing ultrathin films on large substrates. Compared to flat wafers, deposition on substrates with microstructures has a wider range of applications such as photovoltaic cells, electronics, flexible displays, etc. However, spatial ALD on microstructure substrates is a complex and strong-coupled process of fluid flow, heat and mass transfer, as well as chemical reactions. The fluid dynamics and the precursor distribution in spatial ALD are of great importance to obtain conformal growth with high throughput. In this study, a two-dimensional model coupling computational fluid dynamics with chemical kinetics is established to quantitatively explore the effect of microgroove structures on the fluid dynamics, precursor distribution and film conformality in an atmospheric spatial ALD system. Slip boundary condition is adopted to model the slip flow regime in the micro-gap between the injector and the substrate surface, and dynamic layering method is implemented to simulate an entire ALD cycle with the in-line movement of the substrate. Results show that while the flow field is very smooth with a flat substrate, vortices always exist in the micro-gap with microgroove substrates. Due to the angle differences between the flow direction and the vertical microstructure surface, the inflow and outflow of precursors and purging gas are prevented at the microgroove corners. A relatively lower moving speed of the substrate is beneficial for the saturated film growth and better film conformality. Increasing the carrier gas flow rate can effectively reduce the non-uniformity and non-conformality of the film, but the precursor utilization also decreases. Compared with the nonoptimal conditions, within a moderate range of carrier gas flow rate and substrate speed, the precursor utilization and film conformality have been improved. Focusing on the effect of the micro-scale features of the substrate, this study is a valuable step in extending spatial ALD for ultrathin films on miniature devices.