Modeling growth kinetics of thin films made by atomic layer deposition in lateral high-aspect-ratio structures

Abstract

The conformality of thin films grown by atomic layer deposition (ALD) is studied using all-silicon test structures with long narrow lateral channels. A diffusion model, developed in this work, is used for studying the propagation of ALD growth in narrow channels. The diffusion model takes into account the gas transportation at low pressures, the dynamic Langmuir adsorption model for the film growth and the effect of channel narrowing due to film growth. The film growth is calculated by solving the diffusion equation with surface reactions. An efficient analytic approximate solution of the diffusion equation is developed for fitting the model to the measured thickness profile. The fitting gives the equilibrium constant of adsorption and the sticking coefficient. This model and Gordon's plug flow model are compared. The simulations predict the experimental measurement results quite well for Al 2 O 3 and TiO 2 ALD processes.

Nickel Supported on Mesoporous Zirconium Oxide by Atomic Layer Deposition: Initial Fixed-Bed Reactor Study

“…Atomic layer deposition (ALD) is a thin film growth method that allows the preparation of uniform inorganic material layers on arbitrarily complex three-dimensional structures. The three-dimensional uniformity, also termed "conformality," is a consequence of the systematic use of repeated, selfterminating (saturating, irreversible), separated gas-solid reactions of at least two compatible compounds [1][2][3][4][5][6]. While the principles of ALD were formulated already in the 1960s and 1970s, independently twice [7][8][9][10][11][12][13][14], it was in the 1990s that ALD was promoted as a tool for nanotechnology [15] and during the 2000s that ALD has enabled the continuation of Moore's law of transistor miniaturisation [16].…”

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

“…1,[29][30][31] For an ideal ALD process, the penetration depth of a coating is known to scale with the square root of the reactant dose, where the dose equals partial pressure of reactant multiplied by exposure time. 29,[32][33][34] The reactivity of the compounds, often described by a (lumped) sticking coefficient c A (A stands for Reactant A), further influences the speed at which uniform thickness is attained. 1,31,35,36 Non-ideal reactions, such as unwanted CVD through decomposition of one of the reactants or through the mixing of reactant pulses, or non-saturation of the reactions, would compromise the conformality.…”

“…In turn, Schwille et al 30,41 fabricated centrosymmetric LHAR cavities resembling structures used in microelectromechanical systems (MEMS) processing; here, the limiting gap height was 4.5 mm. Recently, building upon the process of Gao et al, 40 improved microscopic rectangular LHAR channels have been developed and used, but not yet described in detail; 33,36,[42][43][44] describing them is among the goals of this work. LHAR structures have been employed to study the conformality of an emerging small minority of the more than 700 published ALD processes; 45 Al 2 O 3 from Me 3 Al (TMA) and H 2 O; 30,31,33,36,40,46 3 and O 2 /Ar plasma.…”

“…Recently, building upon the process of Gao et al, 40 improved microscopic rectangular LHAR channels have been developed and used, but not yet described in detail; 33,36,[42][43][44] describing them is among the goals of this work. LHAR structures have been employed to study the conformality of an emerging small minority of the more than 700 published ALD processes; 45 Al 2 O 3 from Me 3 Al (TMA) and H 2 O; 30,31,33,36,40,46 3 and O 2 /Ar plasma. 44,48 Common to LHAR approaches has typically been to measure the saturation profile of the ALD process and to extract kinetic information of the film growth through modelling.…”

“…1 Often, a model is assuming either reversible or irreversible single-site Langmuir adsorption (A + * " A*) to describe an ALD reaction step, and the (lumped) sticking coefficient for the reaction is extracted from fitting a model to the saturation profile. 30,31,33,36 For example, Dendooven et al 31 extracted the sticking coefficient of TMA on Al 2 O 3 and studied its effect on step coverage with LHAR features. They also combined LHAR studies with a Monte Carlo algorithm to study the conformality of Al 2 O 3 and AlN by PEALD.…”