Concordant element of the oxidation kinetics—Interpretation of ellipsometric measurements on Zr

Alekszej Romanenko,Emil Agócs,Zoltán Hózer,Peter Petrik,Miklós Serényi

doi:10.1016/j.apsusc.2021.151543

Alekszej Romanenko, Emil Agócs + Show 3 more

Open Access

https://doi.org/10.1016/j.apsusc.2021.151543

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Abstract

In this study we report on the growth of ZrO2 films upon the gradual thermal annealing of Zr in the temperature range of 500–700 K. The thickness of the oxide was monitored by in-situ spectroscopic ellipsometry with temporal and thickness resolutions of a few seconds and a few nanometers, respectively. A remarkable feature of the process was that the growth of the oxide can be terminated immediately when decreasing the temperature by a few K. This suggests that, in addition to the driving force, a built-in control adjusts the final thickness determined only by the temperature in sync with the formation and growth of dense oxide films. The derived phenomenological model includes the concept of a ‘depletion layer’ known from semiconductor physics. The validity of the model and the pressure dependence of oxidation is discussed.

Highlights

The first of oxide growth models originate from Wagner’s assumption that metal oxidation takes place by diffusion of charged particles and is valid for thick film growth (x > 1 μm) at high temperatures [1]
The choice was settled on a onelayer model, which was used with an effective medium approximation (EMA) model for the surface layer, whereas the substrate was described by Lorentz oscillators
A simple phenomenological model was developed that attempts to relate the parameters of the transport properties of the atomic oxygen to the results of kinetics measured by ellipsometry in a thickness range that has not yet been studied in detail

Summary

Introduction

The first of oxide growth models originate from Wagner’s assumption that metal oxidation takes place by diffusion of charged particles and is valid for thick film growth (x > 1 μm) at high temperatures [1]. By raising a linear diffusion equation, which incorporates the electric field across semiconducting passive oxides, Wagner found that the film growth is parabolic [2]. Cabrera and Mott developed another approach where an electric field (Mott potential) controls the diffusion of ionic point defects necessary for oxidation [3]. They suggested in 1949 that thin film growth was directly dependent on the migration of interstitial cations where the rate limiting step is cation injection at the metal/film interface. There have been numerous studies conducted on Zr [6,7,8] In many cases, these resulted in the determination of material parameters, such as the diffusion coefficient [9,10,11]

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