## 4 Conclusions  
The surface and mechanical properties of a TiN thin film deposited as the substrate temperature process variable of the DC magnetron sputtering system were studied using different techniques including both destructive and non-destructive methods. The TiN thin film showed a 48% relaxation of the residual stress from about 5.9 GPa at ambient  
\begin{table}
\begin{tabular}{c c c c c} \hline  & **LSAW Velocity** & **Residual Stress** & **Nanoscratch Test** & **RMS Roughness** \\  & **(m/s)** & **(Gpa)** & **(mN)** & **(nm)** \\ \hline Ambient temperature & 4952 & 5.938 & 108.03 & 0.685 \\ \hline
100 \({}^{\circ}\)C & 5096 & 5.024 & 109.05 & 0.938 \\ \hline
200 \({}^{\circ}\)C & 5165 & 3.818 & 111.02 & 1.078 \\ \hline
300 \({}^{\circ}\)C & 5200 & 2.138 & 118.05 & 1.248 \\ \hline \end{tabular}
\end{table}
Table 4: Overall results of the TiN thin film measurement experiment.  
Figure 5: Measurement of V(z) curve using scanning acoustic microscopy of TiN thin film deposited as a variable of substrate temperature: (**a**) measured V(z) curve; (**b**) change in the surface acoustic wave velocity corresponding with the substrate temperature variable.  
temperature to about 2.138 GPa at 300 \({}^{\circ}\)C; this was attributed to the reduction in the defects and the relaxation of the lattice strain in the thin film caused by the effect of the heat applied to the substrate.  
The adhesion properties were approximately 108.03, 109.05, 111.02, and 118.05 mN at ambient temperature, 100, 200, and 300 \({}^{\circ}\)C, respectively. The adhesion of the TiN thin film was improved as the substrate temperature increased.  
The changes in the surface wave velocity of the LSAW observed using the ultrasonic microscope of the TiN thin film were approximately 4952, 5096, 5165, and 5200 m/s at ambient temperature, 100, 200, and 300 \({}^{\circ}\)C, respectively. The surface wave velocity of the TiN thin film deposited at 300 \({}^{\circ}\)C was about 5% higher than that of the TiN thin film deposited at ambient temperature. The presented data suggest that the adhesion properties of the TiN thin film tended to increase with a decrease in the residual stress; the velocity of the LSAW also tended to increase. The residual stress and velocity of the surface acoustic wave are inversely proportional, and the change in the critical load value and the velocity of the surface acoustic wave are proportional.  
These results can be applied to the evaluation of the residual stress and adhesion properties of thin films using the V(z) technique using an ultrasonic microscope.  
Conceptualization, D.K. and Y.S.K.; methodology, D.K.; validation, D.K., Y.S.K., J.N.K. and I.K.P.; formal analysis, D.K. and Y.S.K.; investigation, D.K.; data curation, D.K.; writing--original draft preparation, D.K.; writing--review and editing, D.K., Y.S.K., J.N.K. and I.K.P.; visualization, D.K. and Y.S.K.; supervision, I.K.P.; project administration, D.K.; funding acquisition, I.K.P. All authors have read and agreed to the published version of the manuscript.  
This study was supported by the Research Program funded by the Seoul Tech (Seoul National University of Science and Technology), grant number 2021-1168.  
Not applicable.  
The authors declare no conflict of interest.