Revisiting particle dynamics in HiPIMS discharges. I. General effects

Abstract

A detailed experimental study of high power impulse magnetron sputtering processes is performed by time-resolved imaging of the ground state sputtered particles. New details related to the behavior of both neutral and singly ionized atoms are shown, as a result of separate treatment of the plasma-on and plasma-off time phases. In Paper I, the ion/neutral density redistribution in the ionization zone during sputtering is analyzed; the role of main discharge parameters, such as pulse repetition rate, pulse energy, etc., is discussed systematically. The time-resolved evolution of the ground state levels population for both sputtered neutrals and ions is also considered. In addition, propagation of the sputtered particles is analyzed using 2D density gradient diagrams calculated based on the measured particle density distributions. The results of this work are compared, when possible, to the data obtained previously [Britun et al., J. Appl. Phys. 117, 163302 (2015)].

Plasma wave after HIPIMS pulse: time-resolved diagnostic of HIPIMS copper plasma using a homemade Langmuir probe

“…However, apart from the first peak, which occurs within the time T on , further density peak(s) are sometimes observed after the end of T on . A second peak attributed to ion 3,9,10) and electron currents/densities 3,4,6,11,12) after T on was reported by previous studies.…”

“…n i increases to around 4 × 10 18 m −3 , and n e reaches 1 × 10 18 m −3 . Previous research found that two peaks of n i 3,10) and n e 3,4,6,11,12) were observed, with densities of 10 18 m −3 . One of the peaks appeared within T on and another peak appeared after the end of T on .…”

“…Metastable atoms coexist with ions in the HIPIMS plasma, and their amounts can be comparable. 10,22) So, there is no doubt about the supply of sufficient metastable atoms for ionisation. On the other hand, ion bursts related to spokes induce electron jets.…”

“…Furthermore, the lifetime of hot electrons after T on is long. 30) Therefore, long-lasting metastable atoms and energetic electrons ionise to generate the second density peak. In addition, the velocity of the second peak is estimated from the delay time and the probe position.…”

Delayed Discharge Bridging Two Sputtering Modes from Modulated Pulsed Power Magnetron Sputtering (MPPMS) to Deep Oscillation Magnetron Sputtering (DOMS)

“…These techniques, which have dramatically increased the ionization degree of plasma, have attracted attention collectively as a new method, i.e., ionized physical vapor deposition (I-PVD) [11,15]. In recent years, both of these techniques have achieved an improvement in film deposition rate by introducing multi-pulsing as a deep oscillation magnetron sputtering (DOMS) [16][17][18][19][20][21][22][23][24] technique with a large number of pulses in MPPMS and as a multi-pulse HiPIMS (m-HiPIMS) [25][26][27][28][29][30][31] technique with multiple bipolar pulses in HiPIMS. Improvements in the film deposition rate through the introduction of multiple pulses are brought about due to the long-duration pulse sputtering per cycle in the former and due to the reduction of the rearward attraction for sputtered particle ions to the target in the latter.…”