Dynamics of reactive high-power impulse magnetron sputtering discharge studied by time- and space-resolved optical emission spectroscopy and fast imaging

Abstract

Time- and space-resolved optical emission spectroscopy and fast imaging were used for the investigation of the plasma dynamics of high-power impulse magnetron sputtering discharges. 200 μs pulses with a 50 Hz repetition frequency were applied to a Cr target in Ar, N2, and N2/Ar mixtures and in a pressure range from 0.7 to 2.66 Pa. The power density peaked at 2.2–6 kW cm−2. Evidence of dominating self-sputtering was found for all investigated conditions. Up to four different discharge phases within each pulse were identified: (i) the ignition phase, (ii) the high-current metal-dominated phase, (iii) the transient phase, and (iv) the low-current gas-dominated phase. The emission of working gas excited by fast electrons penetrating the space in-between the electrodes during the ignition phase spread far outwards from the target at a speed of 24 km s−1 in 1.3 Pa of Ar and at 7.5 km s−1 in 1.3 Pa of N2. The dense metal plasma created next to the target propagated in the reactor at a speed ranging from 0.7 to 3.5 km s−1, depending on the working gas composition and the pressure. In fact, it increased with higher N2 concentration and lower pressure. The form of the propagating plasma wave changed from a hemispherical shape in Ar, to a droplike shape extending far from the target in N2. An important N2 emission rise in the latter case was detected during the transition at the end of the metal-dominated phase.

An ionization region model for high-power impulse magnetron sputtering discharges

“…The left panel (a) shows the flux terms involved in the particle balance for argon atoms (equation (4) density. This is consistent with Langmuir probe measurements in our discharge [5,22], and with optical emissions in another HiPIMS device [23] that demonstrate a significant amount of fast electrons during discharge ignition.…”

“…We will therefore use this F PWR and explore the time development during a HiPIMS pulse in section 3.1, and test the sensitivity to the assumption of the extent in the z direction of the IR in section 3.2. [18,21,23] that show rapid changes in this time scale. For times shorter than about 10-15 µs, the IRM assumption of a constant size of the IR is therefore not valid, and we can only make some qualitative observations.…”

“…Kadlec [26] has used a Monte Carlo method to simulate the neutral particle flow during a HiPIMS pulse showing a strong rarefaction, heating of the background gas, and the formation of a shock wave. [39] These shock waves have been demonstrated experimentally by Hala et al [23]. These are clearly important processes for the operation of a HiPIMS discharge but are beyond the scope of this work.…”

“…Hala et al [23] used fast imaging techniques in a HiPIMS discharge similar to ours (unbalanced, with a 100 mm diameter chromium target) and demonstrated that, after a highly variable ignition phase of 10-20 µs, strong light emission is established from a relatively steady region extending 2-3 cm from the target. The surrounding bulk plasma filled with plasma on a longer time scale, but the light intensity stays an order of magnitude lower, indicating a much lower ionization rate here.…”

Study of magnetic iron nitride thin films deposited by high power impulse magnetron sputtering

“…Moreover, due to high metal ionization this technique has a better scope for controlling film properties deposited via reactive sputtering. As such HiPIMS has been frequently utilized for the deposition of metal nitrides such as Al-N, [6] Cr-N, [7][8][9] Ti-N, [10] Nb-N, [11] etc. and metal oxide thin films such as TiO 2 , [12,13] Al 2 O 3 , [14,15] ZnO, [16] ZrO 2 , [17] and Fe 2 O 3 .…”