## 3 Results and Discussion  
Figure 3 shows the X-ray diffraction patterns of the sputtered and electroplated Cu thin films. All samples had the preferred orientation of Cu (111) plane, and the reduction of Cu (111) peak was more noticeable in the sputtered Cu thin films after the two-step plasma treatment. Almost no copper oxide or copper nitride peaks were observed in the XRD (X-ray diffraction) analysis due to the extremely thin oxide or nitride formation on the top surface of Cu thin films. Cu grain size was estimated using the Scherrer equation (grain size = K\(\lambda\)/\(\beta\)cos\(\theta\) where K is a shape facto, \(\lambda\) is the X-ray wavelength, \(\beta\) is the line broadening at half the maximum intensity, and \(\theta\) is the Bragg angle. ), and the sputtered Cu thin film showed slightly larger grain size than the electroplated Cu thin film, and the grain size increased about 10 nm after the two-step plasma treatment. This agreed with the TEM (transmission electron microscopy) results shown in Figure 4. The SEM images in Figure 4a showed a larger grain in the sputtered Cu thin film, and the diffraction patterns in Figure 4b showed small grains in random orientation since the diffraction resulted in circles instead of set of sharp dots. Both Cu thin films showed (111) planes, but the electroplated Cu thin film exhibited more defects such as dislocations and stacking faults than the sputtered Cu thin films as shown in Figure 4c. Further studies on the chemical states of copper, oxygen, and nitrogen were undertaken using the XPS (X-ray photoelectron spectroscopy) analysis shown in Figure 5. For the as-deposited sample, the Cu2p peak of the sputtered Cu and electroplated Cu in Figure 5a occurred at 932.18 eV and 932.28.7 eV, respectively. The peak at 932.2 eV may be linked to a pure metallic copper (Cu\({}^{0}\)) or the Cu\({}^{1+}\) chemical state of Cu\({}_{2}\)O [18; 19; 20], but it is most likely related to Cu\({}_{2}\)O because the O1s peak at \(-\)530.2 eV in Figure 5b indicates Cu\({}_{2}\)O state. After the two-step plasma treatment, it was found that the Cu\({}_{2}\)O peak at 932.2 eV had almost disappeared, and the CuO peak appeared at 934.08 eV in Figure 5a. In addition, the Cu2p binding energy of the sputtered Cu moved toward a slightly higher binding energy at around 932.58 eV than the electroplated Cu. In Figure 5b the O1s peak at \(-\)530.2 eV had also  
Figure 3: XRD analysis of sputtered and electroplated Cu thin films. disappeared, and the only strong OH-related peak at 531.2 eV appeared. The N1s peak observed at 397.38 eV in Figure 5c, and the Cu2p peak at 932.58 eV in Figure 5a, which is a higher binding energy than the chemical state of Cu\({}^{0}\) and the Cu\({}^{1+}\) of Cu\({}_{2}\)O, led to the formation of Cu\({}_{4}\)N at the surface. The qualitative analysis of nitride formation using Cu2p XPS survey data is summarized in Table 2. It is clearly showed that the sputtered Cu showed little more Cu\({}_{4}\)N formation than the electroplated Cu. This seems to be because the electroplated Cu thin film may have more copper oxide on the surface than the sputtered Cu thin film initially due to the electroplating process characteristics and has a high surface roughness (Rq) due to small grains. In Figure 6, the measured surface roughness by AFM confirmed that the sputtered Cu had a much lower roughness value than the electroplated Cu, as expected from the TEM results. After the two-step plasma treatment, the surface roughness decreased in both the sputtered and electroplated Cu surfaces. The XPS analysis strongly implies that the two-step plasma treatment sufficiently removed copper oxide on Cu surface and formed copper nitride to prevent further oxidation. Figure 4: TEM analysis of plasma treated Cu thin films: (**a**) cross-sectional images, (**b**) diffraction pattern indexing, (**c**) lattice indexing. Figure 5: XPS analysis: (**a**) Cu2p, (**b**) O1s, (**c**) N1s.