Magnetron sputtering technique for analyzing the influence ...

3.1

Check now

X-Ray diffraction analysis (XRD)

The X-ray diffraction patterns of the films deposited on SiO2/Si substrates, at different RF powers are shown in Fig. 1. In Fig. 1(a) and (b) labels show low sputtering powers of 100 W and 200 W, respectively, there was no peak in their XRD pattern and the deposited films indicate non-crystalline feature. As the sputtering power increases to 300 leading to 400 W, new diffraction peaks at 2θ&#;=&#;30.9° and 2θ&#;=&#;61.6° corresponding to (001) and (430) reflection planes of orthorhombic aluminum silicone oxide structure (JCPDS card No. 002&#; and 002&#;) observed in the XRD pattern of the deposited films, as shown in Fig. 1, label (a) and (b). Furthermore, in Fig. 1 label (c) shows the peak at 2θ&#;=&#;80.01° also attributed to X-ray photons diffracted from aluminum silicone oxide structure (JCPDS card No. 002&#;). The appearance of these diffraction peaks at higher sputtering powers may be attributed to surface diffusion of Al sputtered atoms on the substrate. It seems that higher RF power enhanced mobility energy of Al sputtered atoms on the surface of the substrate to diffuse in the substrate during growth stage and formed a new phase of aluminum silicone oxide. In other word, higher sputtering power induced high incident ion energy, resulting in high surface mobility and mean diffusion path of sputtered atoms [26]. In addition, X-ray diffraction pattern, Fig. 1 label (d) exhibits a weak diffraction peak around 38.3° belongs to the (111) reflection planes of aluminum structure (JCPDS card No. 004&#;). Moreover, a peak of X-ray photons diffracted (111) planes of Si substrate lattice structure can be seen a 2θ&#;=&#;69.6°. Increasing the intensity of diffraction peaks by increasing the RF power confirms a better crystallinity of the samples at higher RF powers. By increasing the sputtering power, the sputtering yield becomes high and the sputtered particles are ejected with higher energy and the growth of a more crystallized phase [26]. It seems that the peak at 2θ&#;=&#;61.6° is the preferred crystalline orientation in higher RF power and is so strong in 300 W.

X-ray diffraction pattern of the Al thin films deposited on SiO2/Si substrate at different RF powers of shown in label (a) 100 W, (b) 200 W, (c) 300 W and (d) 400

Full size image

3.2

Surface morphological analysis

3.2.1

Surface roughness

The surface roughness was analyzed using atomic force microscopy (AFM) in contact mode for all samples. Figure 2 illustrates the three-dimensional-AFM micrographs of the Al films deposited at different sputtering powers. The root mean squared (RMS) roughness of surface is the main parameters for the characterization of the surface structure [27, 28].

$${\text{RMS = }}\sqrt {\frac{{\mathop \sum \nolimits_{{{\text{n}} = 1}}^{{\text{N}}} \left( {{\text{Z}}_{{\text{n}}} - {\overline{\text{Z}}}} \right)^{2} }}{{{\text{N}} - 1}}}$$

where \(\overline{\mathrm{Z}}\) is the average height and N is the number of data points. The roughness of the films deposited at different RF powers is plotted in Fig. 3. The RMS roughness of the as-deposited film initially rose to 16.95 nm when the sputtering power was raised to 200 W, as shown in Fig. 3. Thereafter, it decreased to 12.16 nm when the deposition increased to 300 W. This behavior may be explained in the following way: (i) At a low RF power of 200 W, the atoms or ions have low energy and tended to &#;stay&#; at the site of its arrival, thus creating a much rougher surface [26, 29]; (ii) At a high RF power of 300 W, the kinetic energy of the incoming atoms, particles or ions, increases that enhances the lateral diffusion of the ions or particles, and then the surface roughness decreases. Moreover, it was discovered that as the RF power was increased to 400 W, the roughness increased. This may be attributed to the fact that the higher power improved the energy of the incoming ionized species and decreased the rearrangement time of the atoms on the substrate before arrival of next atoms [29, 30], which thereby resulted in higher surface roughness [26].

3D AFM images of Al films deposited on SiO2/Si substrate at various sputtering powers: a 100 W, b 200 W, c 300 W and d 400 W

Full size image

The RMS roughness of Al thin films deposited on SiO2/Si substrate as a function of sputtered RF power

Full size image

If you want to learn more, please visit our website Acetron.

At high RF power, the argon gas and the deposition particles inside the sputtering chamber acquire very kinetic high energy, which may lead to: (i) high deposition rate, growth and recrystallization leading to large grain sizes, (ii) excess collisions between target atoms and ions reducing the mean-free-path of the target atoms and therefore lowering sputtering yield and hence less crystallization and film growth [31, 32]. The results presented in sample 2 and 4 can well be attributed to the first reason.

Although the RMS values are highly influenced by the RF power, our result shows that there exists no direct correlation between the increase in RF power and RMS values. The finest and well-defined grained microstructure was observed at the power of 300 W and the highest RMS roughness values are obtained on the surface of films sputtered at a power of 400 W. According to our study, the RF power of 300 W is the optimum condition for deposition of Al thin film.

3.2.2

Scanning electron microscopy analysis (SEM)

Figure 4 illustrates the SEM micrographs of the deposited films showing, at lower RF powers, the deposited films are composed of small, homogenous and well-defined grains. In addition, interconnected porous structures between the grains were observed. The presence of these porous structures is attributed to the high roughness values. The SEM images indicate that with an increase of RF power led to the growth of larger grains. In fact, with increasing sputtering RF power, the deposition particles did not have enough time to latterly diffuse on the substrate, and accumulated together to form larger grains [26]. This result is in good agreement with the results of AFM analysis.

SEM images of the Al thin films deposited on SiO2/Si substrate at different RF Powers: a 100 W, b 200 W, c 300 W and d 400 W

Full size image

3.2.3

FT-IR characterization

The Fourier-transformed infrared spectroscopy (FT-IR) is an analytical technique which is used to investigate the chemical structure and molecular bonding of the materials. The infrared spectra of the produced samples in the range of 500&#; cm&#;1 are depicted in Fig. 5. In the lower frequency region, the minor absorption peak (low intensity) appearing at around 619 cm&#;1 can be assigned to a coupled Al-O and Si-O (out-of-plane) bond [33, 34]. Furthermore, the absorption peak which is located at around 655 cm&#;1 is arising from in-plane Al-O vibration rather than Al&#;O&#;Si vibration [35]. According to the literatures [34, 36], the presence of weak absorption peaks at about 669 cm&#;1 and 684 cm&#;1 is related to the vibrations modes of Si&#;O band. Moreover, the absorption band at 694 cm&#;1 is corresponding to symmetrical bending vibrations of Si&#;O whereas vibration band at 792 cm&#;1 can be attributed to symmetrical stretching vibrations of Si&#;O [37]. Furthermore, the characteristic vibration at 937 cm&#;1 can be assigned to O-Si-O bond [38]. Besides, the absorption band at about 943 cm&#;1 can be associated with stretching mode of Si-OH [39]. The infrared absorption band at  cm&#;1 is attributed to the tetrahedral stretching vibration of silicon-apical oxygen (Si-O) [40]. Moreover, the absorption bands at about  cm&#;1 and  cm&#;1 can be related to the antisymmetric stretching vibrations mode of Si-O-Si of silica and O-H deformation, respectively [41]. Furthermore, the bands in the range of &#; cm&#;1 are assigned to the Si-O-Si stretching bands of low &#;crystallinity&#; phases, mainly amorphous silica [38]. In addition, in the higher frequency region, the absorption bands at approximately  cm&#;1,  cm&#;1 and  cm&#;1 are attributed to the OH stretching modes of Al (OH) Si [42] and (Al Al) O-OH [43] Si-OH groups, respectively. The observation of OH stretching modes in all the samples may be due to the presence of silicate in the substrate. Furthermore, the FTIR results show that the varying RF power affect the chemical structure of the deposited films [44].

FTIR spectra of the Al thin films deposited on SiO2/Si substrate at different RF powers: (a) 100 W, (b) 200 W, (c) 300 W and (d) 400 W

Full size image

The intensity of an absorption band in FTIR spectra depends on the number of the specific bonds present [45].

Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula SiO2, most commonly found in nature as quartz and in various living organisms. In many parts of the world, Silicon Dioxide (Fused Quartz)(SiO2) Sputtering Targets (Size:1&#;&#; ,Thickness:0.125&#;&#; , Purity: 99.995%) is the major constituent of sand. Notable examples of silicon dioxide include fused quartz, fumed silica, silica gel, and aerogels. Silicon dioxide is used in structural materials, microelectronics (as an electrical insulator), and as components in the food and pharmaceutical industries.

Silicon dioxide is a widely used thin film material. Silicon dioxide (Fused Quartz) sputtering targets has many excellent properties such as anti-resistance, hardness, corrosion resistance, dielectric, optical transparency etc. There are many fields that silicon dioxide is used. In microelectronic field, silicon dioxide is widely used as the most common dielectric. As silicon dioxide (Fused Quartz) sputtering targets has adjustable forbidden band width, it can be served as light absorption layer of the thin film of amorphous silicon solar cells to improve light absorption efficiency. Silicon dioxide also can be used as the gate dielectric layer of MOS and CMOS devices or the thin film transistor. In optical field, silicon dioxide is utilized for passive or active optical devices, which not only have excellent light-admitting quality but also have other basic functions, such as electro-optic modulation and optical amplification. Therefore, silicon dioxide can be used as waveguide film, AR coating and antireflection film. In the packaging industry, silicon dioxide film is used as a barrier layer of polymer packaging materials. Most of modern packaging materials cannot offer a sufficient barrier against permeation of gases, which will lead to a reduced self-life of food and drink. Just because of this, a silicon dioxide film deposited on the surface of polymer packaging becomes popular and indispensable. Besides, silicon dioxide film also can be used as a corrosion protective layer of metals. Because of the universal application of silicon oxide films in various fields, preparation of silica with high quality is always an important content of scientific research. Preparation methods of silica change with its different purposes and requirements .At present, there are a lot of preparation methods of silica, mainly including physical vapor deposition (PVD), chemical vapor deposition (CVD), sol-gel method, oxidation method etc. Among them, physical vapor deposition (PVD) includes evaporating deposition, sputtering deposition and ion plating; chemical vapor deposition (CVD) mainly includes traditional chemical vapor deposition and plasma enhanced chemical vapor deposition (PECVD). In addition, atmospheric pressure plasma deposition technology is also a common coating technology, because it does not need to vacuum, suitable for mass deposition.

Original Source

Want more information on sio2 sputtering? Feel free to contact us.