In situ oxidation studies of Cu thin films: Growth kinetics and oxide phase evolution

Yeliz Unutulmazsoy,Mirco Chiodi,Lars P H Jeurgens,Claudia Cancellieri,Sebastian Siol,Luchan Lin

doi:10.1063/1.5131516

Yeliz Unutulmazsoy, Mirco Chiodi + Show 4 more

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https://doi.org/10.1063/1.5131516

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Abstract

A comprehensive understanding of the oxidation of Cu thin films in the low-temperature regime is of fundamental interest and particularly relevant for applications in the fields of micro- and nanoelectronics, sensors, catalysis, and solar cells. The current study reports on the oxidation kinetics of PVD grown Cu thin films (20–150 nm thick) and the oxide phase evolution from Cu2O to CuO upon thermal oxidation in the temperature range of 100–450 °C. XRD investigations in the laboratory and at the synchrotron show that the oxide phase formation critically depends on the oxidation conditions such as temperature and oxygen partial pressure. The real-time synchrotron XRD measurements reveal that the formation of the CuO phase only starts after complete oxidation of the Cu films to Cu2O films. In situ resistance measurements were performed to follow the oxide growth rate of Cu2O on Cu films in the temperature range of 100–300 °C in air and in 10 mbar pO2. It is found that the oxidation kinetics of Cu films to Cu2O films follows the linear rate law, which is attributed to surface reaction controlled oxidation. The oxygen dissociation rate at the gas–solid interface is the rate-limiting process. A dramatic decrease in the linear oxidation rate is observed at low oxygen partial pressures. The fundamental differences between the oxidation rate-limiting processes of Cu as compared to other transition metal films are discussed.

Highlights

Cu is one of the most commonly used metals for interconnections in micro- and nanoelectronic devices, sensing components, and power electronics owing to its high electrical and thermal conductivity
The native oxide on the metal surface can be elaborately removed by alternating cycles of ionsputtering and subsequent high-temperature annealing under ultrahigh vacuum (UHV) conditions prior to in situ oxidation
The oxidation kinetics of Cu thin films in the temperature range of 100–300 °C for film thicknesses between 20 and 150 nm was investigated and found to follow a linear rate law, which indicates that the oxidation process is surface reaction controlled

Summary

Introduction

Cu is one of the most commonly used metals for interconnections in micro- and nanoelectronic devices, sensing components, and power electronics owing to its high electrical and thermal conductivity. The few reported studies on the low-temperature oxidation kinetics of Cu thin films generally have been performed at a single temperature (or narrow temperature range) and/or at a single (or undefined) oxygen partial pressure ( pO2) (see Table I). The initial oxidation rate on bare metal surfaces is extremely fast due to the electric-field assisted diffusion of the ions through the oxide film under influence of the so-called Mott field. the initial stages oxidation studies on bare metal surface are typically performed at

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