Conformality of atomic layer deposition in microchannels: impact of process parameters on the simulated thickness profile

• Published in: Physical chemistry chemical physics : PCCP 2022-04, Vol.24 (15), p.8645-866
• Main Authors: Yim, Jihong, Verkama, Emma, Velasco, Jorge A, Arts, Karsten, Puurunen, Riikka L
• Format: Article
• Language: English
• Subjects: Atomic layer epitaxy; Coefficients; Diffusion; Film growth; Free molecular flow; Gas-solid reactions; Mathematical models; Microchannels; Molecular flow; Partial pressure; Penetration depth; Process parameters; Rare gases; Simulation; Thickness; Thin films; Transition flow
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d1cp04758b

Unparalleled conformality is driving ever new applications for atomic layer deposition (ALD), a thin film growth method based on repeated self-terminating gas-solid reactions. In this work, we re-implemented a diffusion-reaction model from the literature to simulate the propagation of film growth in wide microchannels and used that model to explore trends in both the thickness profile as a function of process parameters and different diffusion regimes. In the model, partial pressure of the ALD reactant was analytically approximated. Simulations were made as a function of kinetic and process parameters such as the temperature, (lumped) sticking coefficient, molar mass of the ALD reactant, reactant's exposure time and pressure, total pressure, density of the grown material, and growth per cycle (GPC) of the ALD process. Increasing the molar mass and the GPC, for example, resulted in a decreasing penetration depth into the microchannel. The influence of the mass and size of the inert gas molecules on the thickness profile depended on the diffusion regime (free molecular flow vs. transition flow). The modelling was compared to a recent slope method to extract the sticking coefficient. The slope method gave systematically somewhat higher sticking coefficient values compared to the input sticking coefficient values; the potential reasons behind the observed differences are discussed. We simulated thickness profiles of atomic layer deposited thin films by a diffusion-reaction model in two flow regimes. The thickness profiles were affected by process parameters such as density of film, sticking coefficient, and growth per cycle.