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

Abstract

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 ALD reactant was analytically approximated. Simulations were made as function of kinetic and process parameters such as 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; potential reasons behind the observed differences are discussed.

Optical metrology of 3D thin film conformality by LHAR chip assisted method

“…The film penetration depth value, such as PD50%, can be used as such or convert it to a more universal and geometry independent value. The fundamental theory of thin film growth in high aspect ratio channels relies on diffusion and reaction kinetics based physical models [3,4] and It has a strong correlation to the aspect ratio. Since the aspect ratio can be determined from variable geometries (e.g., holes or trenches or complex shape features), it has been proposed by Cremers et al [8] to use a hole equivalent aspect ratio to overcome the empirical form of published data.…”

“…Present cross-sectional 3D thin film conformality characterization practice is laborious, and the lead time to results is long. Alternative, significantly improved approach has been demonstrated by using Lateral High Aspect Ratio (LHAR) test structures as substrates [2][3][4]. The LHAR method enables to use conventional planar optical metrology tools such as linescan reflectometry or ellipsometry to measure thin film conformality in high aspect ratio structures.…”

Simulation of conformality of ALD growth inside lateral channels: comparison between a diffusion–reaction model and a ballistic transport–reaction model

“…This work was presented as a talk at the AVS 23rd International Conference on Atomic Layer Deposition (ALD 2023) in Bellevue, Washington, Jul 23–26, 2023. Earlier versions of this work have been presented as a talk at the ALD 2021 conference (online) by Yim et al 46 and as a poster at the ALD 2022 conference, Belgium, by Velasco et al 47 We acknowledge the computational resources provided by the Aalto Science-IT project.…”