Nitrogen flow rate effects on copper nitride thin film growth by reactive DC magnetron sputtering for photodetection

Copper nitride thin films have been expected to be used in photodetection applications [1].
In this work, copper nitride films were deposited on glass substrates using reactive DC
magnetron sputtering process with constant voltage of 350 V at room temperature. The high
purity of copper target was used and the ratio of gas flow rate, N₂/(N₂+Ar), was varied from
0 to 0.86. After deposition, the four-point probe measurement was used for the sheet resistance
characterization. The structural properties of the films were investigated using X-ray
diffractometer and Raman spectrometer. The sheet resistance increased from about 10-1 ohm/sq
to 106 ohm/sq when the N₂/(N₂+Ar) ratio increased from 0 to 0.86. For all gas flow rate ratios,
Raman peak positions were lower than that of Cu₃N at 635 cm-1 and seemed to increase from
614 cm-1 to 620 cm-1 as increasing N₂/(N₂+Ar) ratio. The lower value of the peak position
(< 635 cm-1) was possibly due to the deviation from the stoichiometry of the Cu₃N on the film’s
surface [2]. For the N₂/(N₂+Ar) ratio of 0, X-ray diffraction (XRD) pattern confirmed
the deposited film was Cu film. For the N₂/(N₂+Ar) ratios of 0.67 and 0.86, the XRD spectra
can be fitted with the diffraction patterns of Cu₃N. According to the Raman and XRD
measurements, the stoichiometry of bottom part of the deposited films may be close to Cu₃N
than that of the top part. From all results, the deposited films changed from copper films to
copper nitride films when the N₂/(N₂+Ar) ratio increased. Finally, the electrical properties of
Cu₃N thin films from this process can be a potential candidate for future photodetection devices.