Dynamic parameter estimation of atomic layer deposition kinetics applied to in situ quartz crystal microbalance diagnostics (original) (raw)
Related papers
Review of Scientific Instruments, 2002
A chemical reactor was constructed for growing thin films using atomic layer deposition ͑ALD͒ techniques. This reactor utilizes a viscous flow of inert carrier gas to transport the reactants to the sample substrates and to sweep the unused reactants and reaction products out of the reaction zone. A gas pulse switching method is employed for introducing the reactants. An in situ quartz crystal microbalance ͑QCM͒ in the reaction zone is used for monitoring the ALD film growth. By modifying a commercially available QCM housing and using polished QCM sensors, quantitative thickness measurements of the thin films grown by ALD are obtained in real time. The QCM is employed to characterize the performance of the viscous flow reactor during Al 2 O 3 ALD.
Kinetic Monte Carlo Study of the Atomic Layer Deposition of Zinc Oxide
The Journal of Physical Chemistry C, 2018
Atomic layer deposition (ALD) has emerged as an important technique for thin film deposition in the last two decades. Zinc oxide thin films, usually grown via DEZ/H 2 Oprocess, have seen much interest both in application and in theoretical research. The surface processes related to the growth of the thin film are not entirely understood and the conceptual picture of the ALD process has been contradicted by recent experiments where ligands from the zinc pulse persist on the surface even after extended water pulse exposures. In this work, we investigate the overall growth of the zinc oxide thin films grown via DEZ/H 2 O-process by modelling the surface chemistry using first principles kinetic Monte Carlo for the first time. The kinetic Monte Carlo allows us to implement density functional theory calculations conducted on zinc oxide (100) surface into a kinetic model and extract data directly comparable to experimental measurements. The temperature dependent growth profile obtained from our model is in good qualitative agreement with the experimental data. The onset of thin film growth is offset from the experimentally data due to the underestimation of the reaction barriers within density functional theory. The growth per cycle of the deposited film is overestimated by 18% in the kinetic model. Mass-gain during an ALD cycle is in qualitative agreement with experimental quartz-crystal microbalance data. The main mass-gain within an ALD cycle is obtained during the DEZ pulse and mass-change during the water pulse negligible. The cause of low film growth at low temperatures is due to the high reaction barriers for ethyl-elimination during the water pulse. This kinetic barrier results in low film growth as no new DEZ can adsorb to the ethyl-saturated surface. At elevated temperatures ethyl-elimination becomes accessible, resulting in the ideal layer-by-layer growth of the film. However, a large fraction of ethyl-ligands persist on the surface after each ALD cycle even at high temperatures. This results in ethyl-ligands being encapsulated into the film lattice. This is likely due to an incomplete set of reaction pathways and it
Journal of Electronic Materials, 2017
ZnO thin films are interesting for applications in several technological fields, including optoelectronics and renewable energies. Nanodevice applications require controlled synthesis of ZnO structures at nanometer scale, which can be achieved via atomic layer deposition (ALD). However, the mechanisms governing the initial stages of ALD had not been addressed until very recently. Investigations into the initial nucleation and growth as well as the atomic structure of the heterointerface are crucial to optimize the ALD process and understand the structure-property relationships for ZnO. We have used a complementary suite of in situ synchrotron x-ray techniques to investigate both the structural and chemical evolution during ZnO growth by ALD on two different substrates, i.e., SiO 2 and Al 2 O 3 , which led us to formulate an atomistic model of the incipient growth of ZnO. The model relies on the formation of nanoscale islands of different size and aspect ratio and consequent disorder induced in the Zn neighbors' distribution. However, endorsement of our model requires testing and discussion of possible alternative models which could account for the experimental results. In this work, we review, test, and rule out several alternative models; the results confirm our view of the atomistic mechanisms at play, which influence the overall microstructure and resulting properties of the final thin film.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2018
This paper describes the use of a high-stability quartz-crystal microbalance (QCM) to measure the mass of a gas absorbed on and in the metal electrode on the quartz oscillator, when the gas pressure is low and the gas can be considered as rigidly attached to the metal, so the viscosity effects are negligible. This provides an absolute measure of the total mass of gas uptake as a function of time, which can be used to model the kinetic processes involved. The technique can measure diffusion parameters of gases in metals close to room temperature at gas pressures much below one atmosphere, as relevant to surface processes such as atomic layer deposition and model studies of heterogeneous catalysis, whereas traditional diffusion measurements require temperatures over 400 °C at gas pressures of at least a few Torr. A strong aspect of the method is the ability to combine the “bulk” measurement of absorbed mass by a QCM with a surface-sensitive technique such as Auger electron spectroscop...
Nanomaterials, 2020
ZnO is a remarkable material with many applications in electronics and catalysis. Atomic layer deposition (ALD) of ZnO on flat substrates is an industrially applied and well-known process. Various studies describe the growth of ZnO layers on flat substrates. However, the growth characteristics and reaction mechanisms of atomic layer deposition of ZnO on mesoporous powders have not been well studied. This study investigates the ZnO ALD process based on diethylzinc (DEZn) and water with silica powder as substrate. In-situ thermogravimetric analysis gives direct access to the growth rates and reaction mechanisms of this process. Ex-situ analytics, e.g., N2 sorption analysis, XRD, XRF, HRTEM, and STEM-EDX mapping, confirm deposition of homogenous and thin films of ZnO on SiO2. In summary, this study offers new insights into the fundamentals of an ALD process on high surface area powders.
Kinetic measurements during transient film growth on zinc
Quimica Nova, 2009
The electrochemical behaviour of zinc has been extensively studied in alkaline and acid media, but only a few studies have been reported in neutral solutions, particularly in deaerated media. Zinc passivation in neutral medium and the effect of the ClO4- ion on the nucleation and growth of the passive layer is studied in this paper by a transient technique at different electrolyte concentrations and applied potentials. ZnO growth rate was shown to decrease with increasing electrolyte concentration. Moreover, passive layer growth occurred followed by pitting nucleation and growth. Film growth and pit nucleation are explained by means of the Macdonald and Engell-Stolica models.
Analytical Chemistry, 2009
We have studied the deposition of Zn metal onto a polished gold-coated quartz crystal with in situ tappingmode atomic force microscopy (AFM), while simultaneously recording chronoamperometric and acoustic impedance quartz crystal microbalance (QCM) measurements. We are able to demonstrate good correlation between the three techniques. Modeling of the chronoamperometric data recorded for the initial nucleation process of the same experiment suggests that nucleation initially occurred via a progressive mechanism. Crystallites of different sizes were clearly visible from the AFM images throughout the whole deposition time monitored, suggesting that sustained nucleation also occurs via a progressive mechanism.
Reactor scale simulation of an atomic layer deposition process
Chemical Engineering Research and Design, 2015
To simulate an atomic layer deposition (ALD) process in a reactor scale, three-dimensional deposition of Al 2 O 3 from trimethylaluminum and ozone inside a viscous flow reactor is investigated. The chemistry mechanism used includes both gas-phase and surface reactions. The simulations are performed for a fixed operating pressure of 10 torr (1330 Pa) and two substrate temperatures at 250 • C and 300 • C. The Navier-Stokes, energy, and species transport equations are discretized through the finite volume method to simulate transient, laminar and multi-component reacting flows. It is found that the larger surface reaction rate constant, and the greater concentrations of gaseous reactants at the substrate result in higher deposition rates on the substrate at 300 • C. At a fixed substrate temperature, the deposition rate distributions are the same among all the cycles that indicate a constant growth rate at each cycle. As a result, Al 2 O 3 growth rates of 3.78 angstrom/cycle and 4.52 angstrom/cycle are obtained for the substrate temperatures of 250 • C and 300 • C, respectively.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1998
This article describes a high-resolution quartz crystal microbalance (QCM) with a reproducibility of 0.2 Hz at 6 MHz, provided the frequency is always measured at the same temperature of the microbalance to within 0.1 °C. This enables the microbalance to measure a change in mass equivalent to about 0.1 monolayer of oxygen atoms. Due to its high mass sensitivity, the QCM can be used for absolute measurements of the stoichiometry of ultrathin oxide films. An absolute measure of the stoichiometry of ultrathin metal oxides is difficult to obtain by other means. In this technique, one measures the frequency shift after the deposition of about one monolayer of the metal film onto the gold electrode of the quartz crystal, in ultrahigh vacuum. The deposited film is then oxidized to completion in a low pressure of oxygen gas, and the frequency shift measured again, at the same temperature as before. The ratio of the frequency shifts and the atomic masses gives the oxide stoichiometry. Follow...