Figure 1. X-ray diffraction pattern of Cu₃N films deposited at different RF Power and the working pressure of 3.5 Pa (left) and 5.0 Pa (right).

The stoichiometry of Cu₃N is studied in the films deposited on silicon by using FTIR and Raman techniques. These two techniques give information on the vibrational state of the molecular bonds that are found in the films. Both techniques are considered as complementary. As shown the Figure 2 and Figure 3, the FTIR and Raman peaks reveal the formation of Cu₃N. The Figure 2 shows the FTIR spectra of the films as function of the RF power values, where a band around the wavenumber of 650 cm^-1 was observed, being the typical peak of the stretching vibrations attributed to Cu-N bonds. The peaks at 5.0 Pa are wider than the ones obtained at 3.5 Pa and closer to 650 cm^-1; while the band of the samples deposited at 150 and 200 W is quite far from the ≈ 650 cm^-1, revealing the change in their structure. On the other hand, the Figure 3 depicts the Raman spectra where the typical bands of Cu₃N thin films, found at the wavelength of ≈ 634cm^-1 [19], are the characteristic ones of Cu-N bonds [20] . A slight shift to lower wavenumbers is observed when the RF power increases, attributed to deviation from the stoichiometric level more evident at high RF powers where the Cu₃N structure is Cu-rich [21]. Whereas, the sample deposited at 200 W and 5.0 Pa presents a Raman spectrum completely different, which can be attributed to the appearance of CO₂ and/or CO absorption bands [22].