Morphology observation of the deposited films after hydrogen reduction. 52

hydrogen reduction

Figure 5.17 provides the planar views SEM images for the deposited films at various plating time with 0.6 M NaNO2(aq) after hydrogen reduction at 200℃ for 2 hr.

In comparison to the composite films in Figure 5.2 at identical plating time, planar views of the composite films after H2 reduction revealed surface holes. The formation of surface holes was likely from the reduction of ruthenium oxide in the composite films. As the as-deposited films underwent a reduction reaction by H2, the ruthenium oxide in the deposited films became metallic ruthenium. This reaction led to volume shrinkage of the deposited films. In addition, the formation of surface holes probably suggested roughness in the films would become larger than that of the as-deposited films. On the other hand, as the plating time increased, the number of surface holes in the deposit per unit area was increased as well. This result is attributed to more ruthenium oxide reduction. Because thickness for the composite films increased with the plating time, more ruthenium oxide was reduced at the same unit area. Therefore, the number of the surface holes in reduced films increased with the plating time.

Similarly, the same results were observed in Figure 5.18 and Figure 5.19.

Figure 5.17 Planar views for the deposited films at various plating time with 0.6 M NaNO_2(aq) after H₂ reduction at 200℃ for 2 hr; (a) 30, (b) 60, (c) 120, (d) 240, and (e) 480 min, respectively.

(a)

(b)

(c)

(d)

(e)

Figure 5.18 Planar views for the deposited films at various plating time with 0.06 M NaNO2(aq) after H2 reduction at 200℃ for 2 hr; (a) 30, (b) 60, (c) 120, (d) 240, and (e) 480 min, respectively.

(a)

(b)

(c)

(d)

(e)

Figure 5.19 The planar views of deposited films at various plating time with 0.03 M NaNO2(aq) after H2 reduction at 200℃ for 2 hr; (a) 30, (b) 60, (c) 120, (d) 240, and (e) 480 min, respectively.

(a)

(b)

(c)

(d)

(e)

5.2.2 Phase and crystallinity characterization for the deposited

films after hydrogen reduction

Figure 5.20 displays the XRD analysis for the as-deposited films with various concentrations of NaNO2(aq) for 480 min plating time followed by H2 reduction at 200

℃ for 2 hr. In Figure 5.20, some diffraction peaks were observed, and they were assigned to ruthenium metal at 38^ (100), 42^ (002), 44^ (101), respectively. On the other hand, no diffraction peaks for the ruthenium oxide were observed after hydrogen reduction. This result suggested that RuO2 and Ru composite films were successfully reduced to ruthenium metal films by hydrogen. However, the widths for the diffraction peaks in Figure 5.20 were broad after hydrogen reduction. Therefore, we suspect that the films were crystallized with poor crystallinity by H₂ reduction at 200℃. That is to say, the amorphous as-deposited films were reduced to crystalline ruthenium metal films after hydrogen treatment.

20 30 40 50 60 70

Figure 5.20 XRD patterns for the as-deposited films with various concentrations NaNO2(aq) for 480 min plating time and followed by H2 reduction at 200℃ for 2 hr versus the standard pattern; (a) 0.03, (b) 0.06, and (c) 0.6 M, respectively.

5.2.3 Characterization of the oxidation states for the deposited

films after hydrogen reduction

Figure 5.21 demonstrates the XPS spectra of Ru 3p3/2 line for the deposited film with 0.06 M NaNO2(aq) at 120 and 480 min plating time followed by H2 reduction for 2 hr at 200℃. The binding energies of the deposited films in Figure 5.21 were 462.2 and 462.7 eV, respectively. In comparison to the results in Figure 5.8, the binding energies in Figure 5.21 shifted to lower energy, which suggested that the primary oxidation states of ruthenium decreased after hydrogen reduction. This result indicates that the composite films have been reduced to ruthenium metal films. In addition, this finding agreed well with the results of XRD in Figure 5.20 mentioned above.

Figure 5.22 presents the XPS spectra of oxygen 1s line for the deposited films described in Figure 5.21. The binding energies were 532 and 532.1 eV, respectively.

Compared with the results in Figure 5.9, Figure 5.22 revealed absence of small shoulder at higher binding energy, from 535 to 540 eV. This result suggested that the ruthenium oxide in the composite films was successfully reduced to metallic ruthenium by hydrogen. In addition, the signal of oxygen in Figure 5.22 indicated that water was adsorbed on surface of the films.

475 470 465 460

(a) 120 and (b) 480 min, respectively.

540 535 530 525

Figure 5.22 XPS spectra for the O 1s line from the deposited films with 0.06 M NaNO_2(aq) at various plating time followed by H₂ reduction at 200℃ for 2 hr; (a) 120 and (b) 480 min, respectively.

5.2.4 Raman spectroscopy characterization for the deposited

films after hydrogen reduction

Raman spectra for the composite films with 0.6 M NaNO_2(aq) at various plating time followed by hydrogen reduction are shown in Figure 5.23. In comparison to the results of Figure 5.14, no stretching modes of RuO₂ and broad peaks were observed.

This result indicated that ruthenium oxides in the composite films were completely reduced to ruthenium metal by hydrogen. On the other hand, no broad peak at 500 cm^–1 suggested that strain caused by lattice mismatch was decreased considerably.

That ruthenium oxide was reduced to ruthenium, which would lead to the volume reduction, produced more defects in the deposited films so that the strain was decreased.

Figure 5.24 and Figure 5.25 exhibit Raman spectra for the composite films at various plating time with 0.06 and 0.03 M NaNO_2(aq) followed by hydrogen reduction.

Similarly, the results mentioned in Figure 5.23 were observed in Figure 5.24 and Figure 5.25 as well.

200 400 600 800 1000 various plating times after H2 reduction; (a) Cu substrate as a blank, (b) 30, (c) 60, (d) 120, (e) 240, and (f) 480 min, respectively.

200 400 600 800 1000 120, (e) 240, and (f) 480 min, respectively.

200 400 600 800 1000

Wavelength

(

cm^-1

)

(a) Cu blank (b) 30 (c) 60

Intensity

(d) 120 (e) 240 (f) 480

Figure 5.25 Raman spectra for the composite films with 0.03 M NaNO2(aq) at various plating times after H2 reduction; (a) Cu substrate as a blank, (b) 30, (c) 60, (d) 120, (e) 240, and (f) 480 min, respectively.

5.3 Characterization of composite RuO

2

and Ru films after argon annealing

5.3.1 Morphology observation of the deposited films after argon

annealing

Figure 5.26 displays the planar views of SEM images for the composite films at 30, 120, and 480 min plating time with 0.06 M NaNO2(aq) followed by Ar annealing for 2 hr at 400℃. In Figure 5.26, the composite films remained smooth with small particles after Ar annealing. In comparison to the results in Figure 5.3, the particles in the composite films in Figure 5.26 became larger after argon annealing. The behavior resulted from diffusion of materials at elevated temperature. The components for the deposited films, RuO₂ and Ru, were likely to aggregate at 400℃. Therefore, the particle sizes for the composite films in Figure 5.26 were increased compared with that in Figure 5.3.

Figure 5.26 Planar views for the deposited films at various plating time with 0.06 M NaNO2(aq) followed by Ar annealing at 400℃ for 2 hr; (a) 30, (b) 120, and (c) 480 min, respectively.

(a) (c)

(b)

5.3.2 Phase and crystallinity characterization for the deposited

films after argon annealing

Figure 5.27 provides the as-deposited films with different concentrations of NaNO2(aq) for 480 min plating time followed by argon annealing at 400℃ for 2 hr.

Because the XRD analysis in Figure 5.13 suggested that the as-deposited films were amorphous, the as-deposited films underwent argon annealing to crystallize the amorphous films. Annealing was performed under Ar atmosphere because ruthenium was easily oxidized by oxygen under elevated temperature [19]. In Figure 5.27, in addition to the diffraction peaks from substrate, both diffraction peaks of ruthenium oxide and that of ruthenium were observed. This result indicated that the as-deposited amorphous films became crystalline composite films. In addition, this finding is compatible with the result of XPS in Table 5.2.

20 30 40 50 60 70

Figure 5.27 XRD patterns for the as-deposited films with various concentrations NaNO2(aq) for 480 min plating time followed by Ar annealing at 400℃ for 2 hr versus the standard pattern; (a) 0.03, (b) 0.06, and (c) 0.6 M, respectively.

Chapter 6 Conclusions

We summarize the significant finding in following points;

1. A novel electroless plating recipe was developed to deposit composite RuO2

and Ru composite films. Its formulation included K₂RuCl₅·xH₂O, NaNO₂, NaOH, and NaClO.

2. Different adding steps, three concentrations of NaNO₂, and various plating time were selected during the deposition process. In addition, a two-stage electroless reaction step is presented with clear explanation.

3. Stability for the plating solutions was confirmed by UV-Vis absorption spectra with narrow maximum wavelength distribution. Lifetime for the plating baths with different concentrations of NaNO2(aq) at 40 ℃ was determined from 36–160 hr. In contrast, at room temperature the lifetime was 132–209 hr. Besides, the results of XPS for the deposited films with various plating time suggest that the components during the entire plating process remain the same.

4. From a variety of qualitative characterization, the as-deposited film was identified as an amorphous RuO2 and Ru composite film. Its thickness ranged from 35–300 nm, and the uniformity from 120 min plating time was between 2.05–6.70%.

5. Combining results of plating solution lifetime and that of roughness for the as-deposited films, the desirable concentration for the NaNO2 was 0.06 M.

6. A crystalline Ru film was demonstrated by a H₂ annealing on the composite film at 200℃ for 2 hr.

7. A crystalline RuO₂ and Ru composite film was obtained via carrying out the an Ar annealing at 400℃ for 2 hr on the composite film.

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