ALD Growth Per Cycle Conformality Calculator
Nanofabrication & Thin Film Engineering: Model self-limiting Atomic Layer Deposition (ALD), Langmuir precursor chemisorption saturation, and step coverage inside deep trenches.
ALD Chemistry & Cycle Parameters
Film Thickness, Conformality & Deposition Time
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Atomic Layer Deposition (ALD) Surface Kinetics
ALD is the cornerstone thin-film deposition technique for sub-7nm FinFET/GAAFET gate dielectrics (high-k HfO2), 3D NAND capacitor liners, and barrier metals.
1. Langmuir Self-Limiting Chemisorption
The surface fraction $\theta$ covered during precursor exposure is described by Langmuir adsorption kinetics:
θ(t) = 1 - exp( -S₀ · Φ_dose / N_sites )
where $\Phi_{dose} = \int P dt$ is the precursor exposure in Langmuirs ($1\text{ L} = 10^{-6}\text{ Torr}\cdot\text{s}$).
Frequently Asked Questions
Why does Atomic Layer Deposition (ALD) provide near 100% conformality in 3D structures?
Unlike CVD or PVD, ALD relies on sequential, self-limiting surface chemisorption reactions. Once every accessible surface ligand is bonded to precursor molecules, reaction halts completely, preventing preferential build-up on line-of-sight top surfaces and allowing precursors to permeate into high-aspect-ratio trenches.
Why does precursor exposure requirement scale with the square of the aspect ratio (AR²)?
Inside deep, narrow trenches (where mean free path $\lambda > W$), gas molecules travel via Knudsen diffusion, colliding with sidewalls millions of times before reaching the bottom. The Gordon-Ball-Gheorghiu model proves that the saturation exposure dose required to achieve 100% bottom coverage scales as $\text{Dose}_{min} \propto AR^2$.
What is the "ALD Temperature Window"?
The ALD window is the substrate temperature range within which growth per cycle (GPC) remains strictly constant. Below this window, precursor condensation or incomplete activation occurs; above it, precursor thermal decomposition (CVD-like parasitic growth) or precursor desorption degrades thickness control.