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

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.

Saturation profile based conformality analysis for atomic layer deposition: aluminum oxide in lateral high-aspect-ratio channels.

Atomic layer deposition (ALD) raises global interest through its unparalleled conformality. This work describes new microscopic lateral high-aspect-ratio (LHAR) test structures for conformality analysis of ALD. The LHAR structures are made of silicon and consist of rectangular channels supported by pillars. Extreme aspect ratios even beyond 10 000 : 1 enable investigations where the adsorption front does not penetrate to the end of the channel, thus exposing the saturation profile for detailed analysis. We use the archetypical trimethylaluminum (TMA)-water ALD process to grow alumina as a test vehicle to demonstrate the applicability, repeatability and reproducibility of the saturation profile measurement and to provide a benchmark for future saturation profile studies. Through varying the TMA reaction and purge times, we obtained new information on the surface chemistry characteristics and the chemisorption kinetics of this widely studied ALD process. New saturation profile related classifications and terminology are proposed.