Generation of Charged Ti Nanoparticles and Their Deposition Behavior with a Substrate Bias during RF Magnetron Sputtering

Abstract

This study is based on the film growth by non-classical crystallization, where charged nanoparticles (NPs) are the building block of film deposition. Extensive studies about the generation of charged NPs and their contribution to film deposition have been made in the chemical vapor deposition (CVD) process. However, only a few studies have been made in the physical vapor deposition (PVD) process. Here, the possibility for Ti films to grow by charged Ti NPs was studied during radio frequency (RF) sputtering using Ti target. After the generation of charged Ti NPs was confirmed, their influence on the film quality was investigated. Charged Ti NPs were captured on amorphous carbon membranes with the electric bias of −70 V, 0 V, +5 V, +15 V and +30 V and examined by transmission electron microscopy (TEM). The number density of the Ti NPs decreased with increasing positive bias, which showed that some of Ti NPs were positively charged and repelled by the positively biased TEM membrane. Ti films were deposited on Si substrates with the bias of −70 V, 0 V and +30 V and analyzed by TEM, field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and X-ray reflectivity (XRR). The film deposited at −70 V had the highest thickness of 180 nm, calculated density of 4.974 g/cm3 and crystallinity, whereas the film deposited at +30 V had the lowest thickness of 92 nm, calculated density of 3.499 g/cm3 and crystallinity. This was attributed to the attraction of positively charged Ti NPs to the substrate at −70 V and to the landing of only small-sized neutral Ti NPs on the substrate at +30 V. These results indicate that the control of charged NPs is necessary to obtain a high quality thin film at room temperature.

Effect of Pressure on the Film Deposition during RF Magnetron Sputtering Considering Charged Nanoparticles

“…At the same time, they will be repelled by the substrate with the bias of +50 V, decreasing the number density of Ti NPs captured on the TEM membrane (Figure 3c,f). In agreement with these results, Kwon et al reported that the positively charged Ti NPs were generated during Ti RF sputtering [32]. The strong dependence of the number density of Ti NPs on the electrical bias in Figure 3 indicates not only that some of the Ti NPs are electrically charged but also that they were formed in the gas phase instead of being nucleated on the TEM membrane.…”

“…One possible way to determine which of the small neutral NPs and atoms is a dominant flux for film deposition would be studying the crystallinity of the film deposited under the positive bias. A similar study was conducted by Kwon et al [32]. The results will be shown later.…”

“…Jeon et al [26] reported that porous films with a rough surface morphology were obtained under the condition in which neutral NPs were generated, whereas dense films with a smooth morphology were obtained under the condition in which charged NPs were generated during the thermal evaporation of copper. This aspect was also studied by Kwon et al [32], who reported that neutral NPs produce not only films of poor crystallinity but also films of low density. To determine whether neutral atoms or neutral NPs are the main flux, the crystallinity of films, which can be analyzed by XRD, should be examined.…”

“…Recently, the generation of negatively charged NPs and their contribution to film growth were studied during DC sputtering of Ag [31]. Only one paper was published on the generation of positively charged NPs and their contribution to film growth during RF sputtering of Ti [32]. Thus, a more systematic study is needed concerning how the generation of charged NPs is affected by processing parameters such as pressure in the sputtering process.…”

Improvement of Substrates Properties by Incorporating Titanium Nanoparticles Deposited by DC Diode Sputtering Approach

“…However, an electric bias in these techniques would be used toward the anode, which can overlap within the plasma or require complicated and costly requirements. So the DC sputtering technique can be considered a simple and low cost to obtain metal's and alloy's thin films [24]. In the physical vapor deposition (DC sputtering process), an electron is accelerated from the cathode toward the argon atom and collide with it to produce the argon ion, this ion has a positive charge, so it will attract toward the cathode to eject an atom from the target toward the substrate.…”