## 3 Results and Discussion  
Figure 1 shows the thickness of the TiN thin film measured as a function of source power, which was adjusted from 50 W to 175 W. Thickness was found to increase linearly  
with increased source power primarily because a greater sputtering power corresponded with stronger field strength among electrons. Consequently, the number of sputtered particles increased owing to the increased avalanche multiplication effect [17]. Accordingly, a faster sputtering rate corresponded with a greater thickness of TiN thin film that can be obtained with an increased source power under the same sputtering time. The thickness of TiN thin film measured as a function of source power was fitted by the function  
\[\text{Y}=A_{1}\times X+A_{2} \tag{1}\]  
where \(A_{1}\) is the deposition rate (\(A_{1}\) = 0.548 nm/W), \(X\) is the source power, and \(A_{2}\) is a small offset (\(A_{2}\) = 5.6 nm). The inset in Figure 1 shows the cross-sectional SEM image of TiN thin film on the Si/SiO\({}_{2}<\)100\(>\) substrate. Figure 2 shows the surface morphology of the as-deposited TiN thin films on the Si/SiO\({}_{2}<\)100\(>\) substrate as characterized by SEM. The TiN thin film deposited at a low source power of 50 W had relatively small dense particles with small void spacing and a smooth and uniform surface, as shown in Figure 2a. With increased source power, the grain size moderately expanded and the grain boundaries increased. This tendency became more obvious at higher source power (150 and 175 W), as displayed in Figure 2e,f. The inset images of Figure 2 show the cross-sectional morphology of TiN film at various source power and confirmed that the thickness of TiN film significantly increased with enhanced source power. The surface morphology of TiN thin film, in each case, was analyzed by SEM measurement for the corresponding sample. XRD study revealed the effect of source power on film crystallinity (Figure 3a). At a low source power of 50 W, only two peaks appeared at 43.6\({}^{\circ}\) and 51.2\({}^{\circ}\) of 20, corresponding to TiN and Ti2N, respectively. With increasing the source power, the peak intensity of Ti2N decreased while the TiN peaks became dominant. Above 100 W of source power, well-developed TiN peaks appeared at 36.8\({}^{\circ}\), 42.7\({}^{\circ}\), 62.1\({}^{\circ}\), and 74.3\({}^{\circ}\), corresponding to (111), (200), (220), and (311) orientation of TiN phase, respectively. A high source power formed a thick film with enhanced diffusion of nitrogen, resulting in predominant TiN phases [18]. However, the TiN peak position shift toward the lower diffraction angles at higher source power suggests the deficiency of the Ti component [19]. Figure 1: Variation in thickness of TiN thin film on the Si/SiO\({}_{2}<\)100\(>\) substrate with various source power. AFM analysis directly provided the surface roughness of TiN thin film from the three-dimensional AFM image, as shown in the inset of Figure 3b. The surface roughness (RMS roughness, \(\rm{R_{q}}\)) of TiN thin film strongly depended on the source power. At a lower source power (50 W), the film was very smooth and the \(\rm{R_{q}}\) value was low (\(\sim\)0.4 nm). \(\rm{R_{q}}\) continuously increased with enhanced source power, reaching 1.3 nm at 175 W of source power, as indicated in Figure 3b. A higher sputtering power and higher energy of incident ions or atoms caused clusters or grains to more easily aggregate and grow. Consequently, within a certain range of sputtering power, particle size was proportional to the sputtering power, which primarily explained the increase in \(\rm{R_{q}}\) with increased the source power [17]. Moreover, the surface mounds gradually grew and the roughening phenomenon intensified with increased thickness of TiN thin film at a higher source power [20]. Figure 3b also shows the resistivity of TiN thin film as a function of source power. With enhanced source power from 50 W to 100 W, resistivity drastically decreased from 171 m\(\Omega\)\(\cdot\)cm to 14 m\(\Omega\)\(\cdot\)cm.