Ionized Flux Fraction Research Articles

Are the argon metastables important in high power impulse magnetron sputtering discharges?

We use an ionization region model to explore the ionization processes in the high power impulse magnetron sputtering (HiPIMS) discharge in argon with a titanium target. In conventional dc magnetron sputtering (dcMS), stepwise ionization can be an important route for ionization of the argon gas. However, in the HiPIMS discharge stepwise ionization is found to be negligible during the breakdown phase of the HiPIMS pulse and becomes significant (but never dominating) only later in the pulse. For the sputtered species, Penning ionization can be a significant ionization mechanism in the dcMS discharges, while in the HiPIMS discharge Penning ionization is always negligible as compared to electron impact ionization. The main reasons for these differences are a higher plasma density in the HiPIMS discharge, and a higher electron temperature. Furthermore, we explore the ionization fraction and the ionized flux fraction of the sputtered vapor and compare with recent experimental work.

Ionization of sputtered Ti, Al, and C coupled with plasma characterization in HiPIMS

The ionization of sputtered Ti, Al, and C has been investigated in non-reactive high-power impulse magnetron sputtering discharges using Ar as a process gas. Two complementary techniques, time-resolved Langmuir probe diagnostics and a recently developed gridless ion meter, have for the first time been used to estimate absolute values of the ionized fractions of the sputtered material. To cover a range of commonly used discharge conditions we have carried out measurements for different process gas pressures, discharge current densities, and pulse lengths. It is found that by increasing the current density from 0.5 to 2.0 A cm−2 there is a general increase of independently of target material and position in time with maximum plasma densities of about 1 × 1018–5 × 1018 m−3 above the target race track. Also the ionized flux fraction, measured by ion meter, is increased when increasing the current density and reaches a maximum value of 78% in the Al discharge. By using the recorded and values to calculate the ionization probability of the sputtered material, and benchmark these results using the ion meter, we also show that Langmuir probe diagnostics is a useful tool to estimate trends and changes in the degree of ionization for different process conditions.

Investigation of ionized metal flux in enhanced high power impulse magnetron sputtering discharges

The metal ionized flux fraction and production of double charged metal ions Me2+ of different materials (Al, Cu, Fe, Ti) by High Power Impulse Magnetron Sputtering (HiPIMS) operated with and without a pre-ionization assistance is compared in the paper. The Electron Cyclotron Wave Resonance (ECWR) discharge was employed as the pre-ionization agent providing a seed of charge in the idle time of HiPIMS pulses. A modified grid-free biased quartz crystal microbalance was used to estimate the metal ionized flux fraction ξ. The energy-resolved mass spectrometry served as a complementary method to distinguish particular ion contributions to the total ionized flux onto the substrate. The ratio between densities of doubly Me2+ and singly Me+ charged metal ions was determined. It is shown that ECWR assistance enhances Me2+ production with respect of absorbed rf-power. The ECWR discharge also increases the metal ionized flux fraction of about 30% especially in the region of lower pressures. Further, the suppression of the gas rarefaction effect due to enhanced secondary electron emission of Me2+ was observed.

Ionization mechanism in the high power impulse magnetron sputtering (HiPIMS) discharge

The ionization mechanism and the temporal behavior of the plasma parameters in a high power impulse magnetron sputtering (HiPIMS) discharge are investigated using a time dependent global (volume averaged) model. The metal ion fraction and the ionized flux fraction are shown to be very high, the sputtered metal is almost fully ionized. During the pulse on period electron impact ionization is the most effective process in creating metal ions while charge exchange becomes the dominant process in creating metal ions after the pulse is off.