## 3 Plasma Sources
### Radio Frequency Plasma Source  
RF plasma sources are more dominant in applications using physical bombardment types of reactions. Many of the RF plasmas reviewed operated in strip format, cleaning one strip at a time, and were found to utilize frequencies in the RF range of the electromagnetic spectrum, generally at 13.56 MHz [3]. Two main types of couplings in which RF fields can be applied to the plasma were reviewed, namely capacitive and inductive coupling, as will be described below. Capacitively coupled plasma (CCP) systems generate plasma by applying radio frequency (RF) power between two parallel electrodes [31]. One electrode is connected to the RF generator while the opposing electrode is grounded, creating an oscillating electric field that sustains the plasma discharge in the inter-electrode region [7]. Typical CCP configurations feature electrode gaps of 1-10 cm and operate at RF power levels between 0.5 and 2 kW, with the exact parameters depending on specific application requirements. The plasma density is around \(1\times 10^{15}\) to \(1\times 10^{16}\) m\({}^{-3}\)[7]. In contrast with capacitively coupled plasmas, inductively coupled plasma (ICP) systems generate plasma through an electromagnetic field created by an RF-powered coil positioned outside the plasma chamber, typically separated by a dielectric window. The \begin{table}
\begin{tabular}{c c c} \hline
**Parameter** & **References** & **Parametric Score** \\ \hline Energy Distribution and & When compared with other plasma sources, such as radiofrequency (RF) or microwave plasmas, direct current (DC) plasmas typically exhibit less uniform energy distribution and lower plasma uniformity. DC plasmas rely on a continuous electric field, which can lead to localized heating and an uneven energy distribution. By pulsing the DC power, the plasma operates in short, controlled bursts, which reduces localized heating and allows for better management of energy distribution across the plasma volume. However, pulsed DC plasmas still generally fall short of the uniformity achieved by RF or microwave plasmas, which benefit from higher-frequency oscillations and more efficient energy coupling [14; 19; 24]. & 4/10 \\ \hline Plasma Stability & DC plasmas are generally less stable compared with other plasma systems, such as MW plasmas. This is especially true when the system is working at higher power levels. Stability issues arise due to the formation of arcs or thermal instabilities, which can occur when the plasma transitions from a glow discharge to an arc discharge. It is also important to note that the stability of DC plasmas is highly dependent on the current-voltage characteristics and the gas composition [26]. & 4/10 \\ \hline Plasma Energy Density & Due to the intermittent nature of the discharge and the dielectric barrier, which limits the power that can be delivered to the plasma, DBD systems have lower energy density than other plasma systems, such as RF plasmas [18; 27; 28; 29]. & 6/10 \\ \hline Electron Temperature & DC plasma systems achieve moderate electron temperature levels in the range of 1-5 eV. In higher-powered cleaning systems, this can go up to 10 eV [30]. & 6/10 \\ \hline \end{tabular}
\end{table} 
Table 3: Grading of parameters for direct current plasma source. primary RF source (often 13.56 MHz) drives the coil, inducing a time-varying magnetic field that ionizes the gas and sustains a high-density plasma. Many ICP systems employ a secondary RF bias source connected to the substrate holder, allowing independent control of ion energy while maintaining high plasma density. This dual-source configuration enables the precise tuning of both plasma density (typically 1016-1018 m\({}^{-3}\)) and ion bombardment energy, making ICP systems superior to single-source CCP devices for applications requiring high-density, low-pressure plasmas with independent control of ion flux and energy [7; 31].