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

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 Cu 2 O 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 Cu 2 O films. In situ resistance measurements were performed to follow the oxide growth rate of Cu 2 O on Cu films in the temperature range of 100-300°C in air and in 10 mbar pO 2 . It is found that the oxidation kinetics of Cu films to Cu 2 O 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.

The Oxidation of Copper in Air at Temperatures up to 100 °C

“…Low-temperature oxidation of Cu to Cu 2 O was reported to follow linear law [13,14] or logarithmic law [18]. Oxidation of Cu 2 O to CuO was reported to follow parabolic [13] or logarithmic [17] rate law.…”

“…However, linear growth of the oxide layer has also been reported. Unutulmazsoy et al [13] studied the oxidation of Cu thin films in the temperature range of 100-450 • C and found that the formation of the CuO phase only starts after complete oxidation of Cu to Cu 2 O. The oxidation kinetics of Cu to Cu 2 O followed the linear rate law, which refers to surface reaction controlled oxidation, in the temperature range of 100-300 • C, whereas the oxidation kinetics of Cu 2 O to CuO seemed to be controlled by a parabolic rate law.…”

“…Copper oxides have potential applications in solar cells, semiconductors, gas sensors, catalysts, etc. Many researchers have studied the oxidation behavior of bulk copper metal [5][6][7][8] and copper thin films [9][10][11][12][13][14] at elevated temperatures in air. The main outcome of these studies indicated that copper oxidation products, Cu 2 O (cuprous oxide) and CuO (cupric oxide), are formed on the surface of copper at various temperatures and exposure times, and the growth of these oxide layers follows most frequently the parabolic law, indicating that the growth rate decreases with time and some maximum thickness range is expected.…”

Strain depth profiles in thin films extracted from in-plane X-ray diffraction

“…The as-deposited Cu thin films [face-centered cubic (f.c.c. ), Fm3m, a Cu = 3.615 Å ] have a pronounced {111} fiber texture (Unutulmazsoy et al, 2020). Accordingly, the 111, 200, 220 and 331 reflections were measured at specific tilt angles (depending on the texture).…”

Study of Interfaces in Hf/Fe System Using Magneto‐Optical Kerr Effect and Soft X‐Ray Absorption Spectroscopy

“…Studies in the literature show that the thickness of surface oxide layer in metallic films is 2-3 nm. [26,27] As the thickness of the top Hf layer is 4.3 nm, it follows that the 1-2 nm thick Hf layer interfaced with Fe would still be metallic. All the interface roughnesses are in the range of 0.3-0.5 nm.…”