Fundamentals of pulsed plasmas for materials processing

Abstract

Fundamentals of Pulsed Plasmas for Materials Processing André AndersLawrence Berkeley National Laboratory, University of California, 1 Cyclotron Road, Berkeley, California 94720-8223 AbstractPulsed 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.3

Characterization of pulsed dc magnetron sputtering plasmas

“…These accelerated electrons are most likely the reason for the observed spike in the electron temperature. Further development of the sheath involves a rearrangement of the ion density, which occurs on a timescale that is approximately five times the inverse ion plasma frequency [35], about a microsecond in the present case. Experiments show that the stabilization of the plasma in the vicinity of the substrate takes much longer by comparison.…”

“…The sheath formation proceeds in a few steps [35]. Since the plasma density does not go to zero at the end of the 'reverse time', there is a residual rarified plasma present at the beginning of the 'on-time'.…”

High power impulse magnetron sputtering discharge

“…This can be achieved since the plasma is relatively weakly ionized and more charge carriers are generated as needed. 70 The constant k depends on the target material, gas pressure, gas type, magnetic field shape, and the geometry of the discharge. As the discharge is sustained by secondary electron emission from the cathode by ion bombardment, the discharge current at the target consists of electron current I e and ion current I i or…”

Surface modification of biomaterials using plasma immersion ion implantation and deposition

“…Thus, the plasma can be considered as a collection of electrons, single-or multi-charged positive or negative ions accompanied by neutral atoms, excited particles, electromagnetic radiation, molecules and some molecular fragments. In plasma, the densities of excited particles, ions and electrons as well as the intensity of the electromagnetic radiation far exceed those that are found in more mundane situations encountered elsewhere [33].…”