Understanding the Growth Mechanisms of Multilayered Systems in Atomic Layer Deposition Process

• Published in: Chemistry of materials Vol. 30; no. 6; pp. 1971 - 1979
• Main Authors: Wiegand, Christoph W, Faust, René, Meinhardt, Alexander, Blick, Robert H, Zierold, Robert, Nielsch, Kornelius
• Format: Journal Article
• Language: English
• Published: American Chemical Society 27-03-2018
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/acs.chemmater.7b05128

In atomic layer deposition (ALD), the initial growth is of particular interest because it defines the nucleation behavior and determines the minimum number of cycles to achieve a closed layer. The growth rate is quantified by the growth per cycle (GPC). Due to nucleation inhibition or enhancement, the initial GPC for ALD processes of a given material system onto a specific substrate may differ from its (steady-state) literature value because the GPC is mostly noted as an average value of at least a few hundred cycles. However, the knowledge of the growth behavior within the first few cycles is of particular importance in context of super cycles and nanolaminates. Individual ALD cycles of the host material (e.g., TiO2) are replaced by those for the deposition of another compound (e.g., Al2O3) to infiltrate the host material with a dopant. For a precise dosage/doping and tailor-made synthesis, knowledge of the individual GPC is crucial. Herein, precise quartz crystal microbalance (QCM) studies were used to investigate the initial growth of TiO2 onto Al2O3 (deposited by ALD) (1) and vice versa the initial growth of Al2O3 onto TiO2 (2). In case 1, an enhanced initial GPC of the TiO2 deposition was observed that was close to the equilibrium value of Al2O3 deposition. In the second case, the initial GPC of Al2O3 was found to be close to the equilibrium value of TiO2 deposition. The growth process itself can be simply modeled by a superposition of parallel growth onto itself and onto the foreign species. We attribute our observations to an ALD process intrinsic inhibition of the TiO2 growth.