Fundamentals of Pulsed Plasmas for Materials Processing
Pulsed plasmas offer the use of much higher power (during each pulse) compared to continuously operated plasmas, and additional new parameters appear such as pulse duty cycle. Pulsed processing may help meeting the demands of increasingly sophisticated materials processes, including thin film deposition, plasma etching, plasma cleaning of surfaces, and plasma immersion ion implantation. The high kinetic energy of ions allows processes to occur far from thermodynamic equilibrium. Pulsed plasmas are driven by external pulsed power sources, and one has to consider the power source and the plasma as a coupled system. The dynamic plasma impedance is a key quantity from an electrical engineering point of view. From a plasma physics point of view, one needs to consider the dynamics of plasma species, their density and energy distribution, ionization and recombination reactions, and, most importantly, the development of transient sheaths. Dimensionless scaling parameters are a useful tool putting the variety of plasma parameters in relation to characteristic quantities. This is illustrated by several examples of pulsed processes relevant to thin film deposition. The emerging technology of pulsed sputtering is discussed in detail including the possibility to achieve the mode of self-sustained self-sputtering during each pulse.