@article {1834,
	title = {Spatial distribution of average charge state and deposition rate in high power impulse magnetron sputtering of copper},
	journal = {Journal of Physics D},
	volume = {41},
	year = {2008},
	pages = {135210-1-6},
	abstract = {<p>The spatial distribution of copper ions and atoms in high power impulse magnetron sputtering (HIPIMS) discharges was determined by (i) measuring the ion current to electrostatic probes and (ii) measuring the film thickness by profilometry. A set of electrostatic and collection probes were placed at different angular positions and distances from the target surface. The angular distribution of the deposition rate and the average charge state of the copper species (including ions and neutrals) were deduced. The discharge showed a distinct transition to a high current mode dominated by copper self-sputtering when the applied voltage exceeded the threshold of 535 V. For a lower voltage, the deposition rate was very low and the average charge state was found to be less than 0.4. For higher voltage (and average power), the absolute deposition rates were much higher, but they were smaller than the corresponding direct current (DC) rates if normalized to the same average power. At the high voltage level, the spatial distribution of the average charge state showed some similarities with the distribution of the magnetic field, suggesting that the generation and motion of copper ions is affected by magnetized electrons. At higher voltage, the average charge state increases with the distance from the target and locally may exceed unity, indicating the presence of significant amounts of doubly charged copper ions.</p>},
	author = {David Horwat and Andr{\'e} Anders}
}
@conference {1731,
	title = {Physics of High Power Impulse Magnetron Sputtering},
	booktitle = {ISSP2007: The 9th International Symposium on Sputtering \& Plasma Processes},
	year = {2007},
	abstract = {<p>High power impulse magnetron sputtering is characterized by discharge pulses whose target power density exceeds conventional sputtering power densities by two orders of magnitude or more; the goal is to provide a large flux of ionized sputtered material. The processes of pulse evolution are briefly reviewed, including secondary electron emission, self-sputtering, and rarefaction. Using a pulse power supply capable of providing constant voltage for target peak power densities up to 5 kW/cm<sup>2</sup>, the evolution of the current-voltage characteristics was investigated for copper and titanium. It is shown that the characteristic cannot be reduced to value pairs. Rather, a strong but reproducible development exists. The details depend on the argon pressure and applied voltage. Each target material exhibits a distinct and sharp transition to a high current regime that appears to be dominated by metal plasma. Despite the higher sputter yields for copper, the transition to the high current regime occurs much earlier and stronger for titanium, which may be attributed to a higher secondary electron yield and hence a higher density of electrons confined in the magnetron structure. At high currents, the closed-drift Hall current generates a magnetic field that weakens plasma confinement, thereby enabling large ion currents to reach a biased substrate.</p>},
	author = {Andr{\'e} Anders and Joakim Andersson and David Horwat and Arutiun P. Ehiasarian}
}
