## 3 Results and Discussion
### Characteristics of SiN\({}_{\mathrm{x}}\) Thin Films
In the narrow pattern, the temperature condition of 250 \({}^{\circ}\)C yielded side and bottom coverages of 73% and 80%. As the deposition temperature increased to 500 \({}^{\circ}\)C, improved film conformality was obtained with side and bottom coverages of 81% and 87%. The wet etch rate (WER) test was performed to investigate SiN\({}_{\rm x}\) etching properties. A diluted HF solution (1:100) was used. The LPCVD of Si\({}_{3}\)N\({}_{4}\) film at 730 \({}^{\circ}\)C was referenced for the WER test. As shown in Table 1, the wet etch rate decreased with increasing deposition temperature. In the above-mentioned Figure 2, as the deposition temperature increases, the film density also improved due to the increase of the refractive index [28; 29]. It is understandable that the wet etch rate decreases with increasing deposition temperature, considering the fact that the film density is inversely proportional to WER [17]. The physical properties of the SiN\({}_{\rm x}\) film based on the CSN-2 precursor have been studied. Thin films with good step coverage and excellent etching properties were obtained at 500 \({}^{\circ}\)C. In order to improve the progress made through the previously described two-step process (CSN-2/purge/N\({}_{2}\) plasma/purge), an H\({}_{2}\) plasma step was added between the CSN-2 and N\({}_{2}\) plasma step to improve the characteristics of the thin film used as a gate spacer. In logic devices, the actual gate spacer process proceeds at temperatures below 400 \({}^{\circ}\)C to prevent implant out-diffusion and unwanted metal oxidation in the high-k metal gate (HKMG). Thus, we performed a comparative study between the two-step and three-step processes at 350 \({}^{\circ}\)C. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Temp.** (\({}^{\circ}\)C) & **250** & **350** & **500** \\ \hline Wet Etch Rate (Å/min) & 57 & 43 & 35 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Wet etch rate of the RPALD SiN\({}_{\rm x}\) film as a function of deposition temperature. Figure 6: Transmission electron microscopy (TEM) images for step coverage of the RPALD SiN\({}_{\rm x}\) film as a function of deposition temperature in a wide pattern at **(a)** 250 \({}^{\circ}\)C, **(b)** 350 \({}^{\circ}\)C, and **(c)** 500 \({}^{\circ}\)C and in a narrow pattern at **(d)** 250 \({}^{\circ}\)C, **(e)** 350 \({}^{\circ}\)C, and **(f)** 500 \({}^{\circ}\)C.  
N\({}_{2}\) plasma not only removes the ligand of the precursor, but also facilitates the chemisorption of the silicon precursor. However, the N radicals have an exceptionally short life time compared to H radicals or O radicals. Due to this short lifetime, recombination loss occurs and the ligand is not completely removed from the precursor, such that the step coverage and quality of the thin film deteriorates. By introducing the H\({}_{2}\) plasma before the N\({}_{2}\) plasma, efficient ligand removal from the surface can be achieved by H radicals with a long lifetime. The SiN\({}_{x}\) films with an excellent step coverage and wet etch rate were obtained [21; 22; 23; 24]. As shown in Figure 7a, as the H\({}_{2}\) plasma exposure time increases in the three-step process, the deposition rate decreases because the influence of the H\({}_{2}\) plasma forms an NH\({}_{2}\) or SiH group, which make reactions with the precursor difficult. In contrast, the deposition rate improved by fixing the H\({}_{2}\) plasma and increasing the N\({}_{2}\) plasma time as seen in Figure 7b. This is because the N\({}_{2}\) plasma regenerates the reaction sites on the surface where the -H or -NH\({}_{2}\) group is terminal and forms an undercoordinated surface. Therefore, the precursor easily reacts with the surface [16]. As shown in Figure 8, TEM images show step coverage with various H\({}_{2}\) plasma exposure times. Compared with the case of As-dep films, the step coverage improves with increasing H\({}_{2}\) plasma exposure time. In general, we can observe that the step coverage is greatly improved at the bottom/top compared to the side/top.