**5. Annealing process effect on indium particles' catalyst**

The indium-coated silicon substrate annealed in the conventional furnace during 45 min at 600°C shows elongated and inhomogeneous islands of micrometric sizes (**Figure 3**). The chosen work temperature is well above the indium melting temperature (157°C), offering sufficient kinetic energy to metallic atoms to form regular particles. The observed morphology could be attributed to the presence of indium oxide. X-ray diffraction (XRD) analysis was performed to confirm these observations.

### **Figure 3.**

*(a) SEM image of indium-coated silicon substrate annealed under conventional process. Inset: Cross-sectional SEM view of the as-deposited indium-coated silicon substrate.*

In **Figure 4**, we compare the XRD spectra of the as-deposited indium layer and the annealed sample. The XRD patterns of the as-deposited sample show only the presence of the planes of the tetragonal crystal structure of indium. However, after annealing, the XRD spectrum shows the disappearance of indium peaks except two peaks. These peaks are replaced by peaks attributed to indium oxide planes with the presence of very intense (222) indium oxide peak. Indium oxide can explain the obtained indium particles morphology. This phenomenon is attributed to the high melting temperature (1900°C) of indium oxide compared to the chosen annealing temperature.

So, in order to ameliorate the indium particles properties, a hydrogen plasma treatment was performed in a PECVD reactor at a substrate temperature of 400°C during 10 min, with two different flow rates of 60 and 100 sccm. XRD analysis shows the persistence of indium oxide presence after 60 sccm H2 treatment, indicating that this flow rate is not sufficient to eliminate all In2O3. When increasing hydrogen flow, In2O3 peaks have been disappeared and replaced by indium peaks (**Figure 5**). This result is confirmed by the SEM image of the obtained structures (**Figure 6**). It is noticed that the indium particles become more homogeneous and regular in size and form. Quasi-spherical particles with average size of 440 nm (**Figure 6(c)**) are obtained.

H2 plasma treatment leads to the indium oxide elimination as depicted by Eq. (2) and the indium loss through evaporation leading to particles properties enhancement (density, size, and shape). Moreover, XRD results highlight the fact that the H2 plasma flow rate (100 sccm) was sufficient to eliminate all indium oxide.

$$2\,\mathrm{3H}\_{2} + \mathrm{In}\_{2}\mathrm{O}\_{3} \to 2\,\mathrm{In} + \mathrm{3H}\_{2}\mathrm{O} \tag{2}$$

#### **5.1 Discussion**

In this section, we have noted the indium oxide formation during the conventional annealing that is attributed to the oxygen presence. This observation is explained by the low vacuum pressure in the furnace (10−2 mbar) where the heating is mainly provided by thermal conduction. In order to eliminate the oxygen and

**Figure 4.** *XRD spectra of as-deposited indium layer and annealed sample.*

*Investigation of Indium Oxide Effect on Indium Particles Properties Used as Silicon Nanowires… DOI: http://dx.doi.org/10.5772/intechopen.93648*

#### **Figure 5.**

*XRD spectra of annealed layers and treated by H2 treatment with flow rates of 60 and 100 sccm.*

#### **Figure 6.**

*(a-b) SEM images of indium particles obtained after conventional annealing followed by H2 treatment with flow rate of 100 sccm (c) the corresponding histogram indicating the size distribution.*

form pure indium particles, samples must be annealed in ultra-vacuum atmosphere; however, the thermal conduction will be very slow. In this case, the annealing will occur for long durations consuming thereby much energy.

**Figure 7.**

*(a) SEM image of indium particles obtained after RTA annealing; A: 300°C, B: 350°C, C: 400°C, and D: 450°C and (b) the corresponding histogram indicating the size distribution.*

*Investigation of Indium Oxide Effect on Indium Particles Properties Used as Silicon Nanowires… DOI: http://dx.doi.org/10.5772/intechopen.93648*

**Figure 8.** *XRD patterns of the sample annealed at 450°C.*

In order to overcome this problem, RTA annealing based on radiation heating by infrared short waves (400–1400 nm) is used. The heating duration could be decreased, thanks to high silicon absorption in this wavelength range.

Indium-coated substrates were annealed at different temperatures (300, 350, 400, and 450°C) during 5 min. It is noticed in **Figure 7(a)** that for the temperatures 300 and 350°C, the surface morphologies are quite similar. The substrates are covered with inhomogeneous particles in size and shape, with a high surface density. An improvement in the particles shape is obtained at 400°C. At the temperature of 450°C, quasi-spherical and homogeneous particles are obtained. The structures elaborated at 450°C show an average size of 422 nm (**Figure 7(b)**). This amelioration is attributed to the indium oxide absence as confirmed by XRD (**Figure 8**).
