## 3 Plasma Sources
### Direct Current and Pulsed Direct Current Plasma Source  
Direct current (DC) plasma sources represent the simplest and most fundamental type of plasma generation system. These sources operate by applying a continuous voltage potential between two electrodes in a low-pressure gas environment. This creates a stable glow discharge through electron avalanche ionization. Their straightforward design, consisting essentially of a power supply, anode, and cathode, makes them particularly advantageous for basic plasma studies and industrial applications where process simplicity is prioritized over precise control. However, DC plasmas are typically limited to conductive or semi-conductive target materials, as dielectric surfaces cause charge accumulation that terminates the discharge. Therefore, the setup would consist of two electrodes having an opposite polarity being installed in the plasma chamber in contact with the gas. A high voltage is applied across the electrodes to ionize the gas [6].  
In a pulsed direct-current plasma source system, the energy transfer can be managed by controlling the duty cycle. Pulsed direct current (DC) plasma sources offer superior control over energy transfer through precise modulation of the duty cycle. Through the use of pulsed systems, higher charged densities can be achieved with less lead frame damage being caused [6; 25]. Table 3 shows the grading parameter scores achieved for DC plasmas sources.  
\begin{table}
\begin{tabular}{c c c} \hline
**Parameter** & **Scores** & **Score Explanation** \\ \hline \multirow{6}{*}{Plasma Energy Density (Focus on Achievable Ion/Radical Density Necessary for Processing)} & High Scores (8–10) & Sources capable of generating high-density plasmas (e.g., \(>\)10\({}^{11}\)–10\({}^{12}\) cm\({}^{-3}\) ions/radicals) efficiently, leading to faster cleaning rates. \\ \cline{2-3}  & Moderate Scores (4–7) & Sources that produce moderate plasma densities, suitable for cleaning but potentially slower or less intense than high-density sources. \\ \cline{2-3}  & Low Scores (0–3) & Sources typically characterized by lower plasma densities, which may limit processing speed or the intensity of plasma–surface interactions. \\ \hline \multirow{6}{*}{Electron Temperature (Effective Range for Generating Reactive Species)} & High Scores (8–10) & Sources that typically operate with electron temperatures (e.g., 2–10 eV) highly effective for generating the desired reactive species (radicals, ions) through electron impact dissociation and ionization of process gases, without excessive ion energies that could cause damage. \\ \cline{2-3}  & Moderate Scores (4–7) & Sources achieving electron temperatures that are effective but might be in a range less optimal for certain gas chemistries or require more power to achieve desired radical densities. \\ \cline{2-3}  & Low Scores (0–3) & Sources where electron temperatures are typically too low for the efficient generation of key reactive species for common cleaning gases, or conversely, too high, leading to undesirable ionization states or excessive heating/damage if not well-controlled. \\ \hline \end{tabular}
\end{table}
Table 2: _Cont._