Abstract. Recently, copper oxide thin film has been studied because of its low cost, sensitivity to ambient condition and easiness to produce oxide thin film. It is one of the p-type semiconductor oxides materials that are suitable to be used as gas sensing material. In order to improve the sensitivity and to optimize the properties of copper oxide thin film, it is essential to study the physical structure of copper oxide. In current studies, copper oxide thin film has been deposited by RF magnetron sputtering at different substrate bias voltages and oxygen flow rates. The results reveal that the deposition rate decreased when the oxygen flow rate above 4 sccm. SEM image reveal that nanostructure copper oxide was also obtained when the oxygen flow rate was above 4 sccm. On the other hand, no significant effect on the substrate bias voltage toward the sputter deposition rate was observed.
Magnetron sputtering plasma for the deposition of copper oxide thin film has been investigated using optical emission spectroscopy and Langmuir probe. The intensity of the light emission from atoms and radicals in the plasma were measured using optical emission spectroscopy (OES). Then, Langmuir probe was employed to estimate the plasma density, electron temperature and ion flux. In present studies, reactive copper sputtering plasmas were produced at different oxygen flow rate of 0, 4, 8 and 16 sccm. The size of copper target was 3 inches. The dissipation rf power, Ar flow rate and working pressure were fixed at 400 W, 50 sccm and 22.5 mTorr, respectively. Since the substrate bias plays an important role to the thin film formation, the substrate bias voltages of 0, -40, -60 and -100 V were studied. Based on OES results, oxygen emission increased drastically when the oxygen flow rate above 8 sccm. On the other hand, copper and argon emission decreased gradually. In addition, Langmuir probe results showed a different ion flux when substrate bias voltage was applied. Based on these plasma diagnostic results, it has been concluded that the optimized parameter to produce copper oxide thin film are between -40 to -60 V of substrate bias voltage and between 8 to 12 sccm of oxygen flow rate.
Cupric Oxide (CuO) is one of the p-type metal oxide semiconductors that are suitable for use in gas sensing device. The copper oxide thin film was prepared on silicon wafer by sputtering of pure copper target at difference deposition time of 5 min, 10 min and 15 min using RF magnetron sputtering technique. Argon flow rate, oxygen flow rate, RF power and working pressure were fixed at 50 sccm, 8 sccm, 400 W and 22.5 mTorr, respectively. The influence of the deposition time towards the surface morphology, topography and thickness has been investigated. SEM and AFM analysis showed that the grain size of the films increases with the increase of deposition time. However, the surface structure of the films remains the same. In addition, it is noticed that when the deposition time increased, the surface of the films becomes rougher. The deposition rate was approximately 29 nm/min, and it was evaluated from the film thickness deposited at several times.
There are several techniques to deposit the metal oxide thin film such as electron beam evaporator, pulse laser deposition and reactive magnetron sputtering deposition. In this experiment, magnetron sputtering deposition techniques will be used to produce a copper oxide thin film due to its simplicity and repeatability performance. Recently, copper oxide thin film has been studied because of its low cost material, sensitivity to ambient condition and easiness to produce oxide thin film. It is one of the p-type semiconductor oxides materials that are suitable to be used as a gas sensing material. In order to increase the sensitivity and to optimize the properties of copper oxide thin film, it is essential to study on the plasma properties during the deposition of copper oxide. In current studies, Langmuir probe was used to investigate the effect of substrate bias towards the fabrication of copper oxide thin film at rf dissipation power of 400 W. The oxygen flow rate was fixed at 8sccm. The Langmuir probe tip was focus at roughly 2 cm above the substrate holder. The ion and electron current were collected from the plasma environment. Then the electron temperature, electron density, ion density, ion flux, Debye length and plasma potential at various substrate biases were evaluated from the current-voltage curve. The electron temperature at various oxygen flow rates was almost unchanged. The effect of substrate bias toward the electron temperature was also almost unseen, except that the electron temperature at-40 V bias voltage was slightly lower than others. In addition, the ion flux at the same plasma condition shows that the ion flux was higher at-40 V substrate bias voltage. The results suggest that the ion bombardment effect toward the deposited copper oxide thin film would be higher at low oxygen flow rate. Thus it will create a rough surface morphology or nanostructured copper oxide thin film. This is a potential ways to improve the sensitivity of copper oxide gas sensor.
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