Cross-field ion transport during high power impulse magnetron sputtering

Abstract

In this study, the effect on thin film growth due to an anomalous electron transport, found in high power impulse magnetron sputtering (HiPIMS) has been investigated for the case of a planar circular magnetron. An important consequence of this type of transport is that it affects the way ions are being transported in the plasma. It was found that a significant fraction of ions are transported radially outwards in the vicinity of the cathode, across the magnetic field lines, leading to increased deposition rates directly at the side of the cathode (perpendicular to the target surface). Furthermore, this mass transport parallel to the target surface leads to that the fraction of sputtered material reaching a substrate placed directly in front of the target is substantially lower in HiPIMS compared to conventional direct current magnetron sputtering (dcMS). This would help to explain the lower deposition rates generally observed for HiPIMS compared to dcMS. Moreover, time-averaged mass spectrometry measurements of the energy distribution of the cross-field transported ions were carried out. The measured distributions show a direction-dependent high-energy tail, in agreement with predictions of the anomalous transport mechanism.

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

“…The reason for this choice is that this particular magnetron sputtering discharge has been extensively studied [5][6][7][17][18][19][20][21][22]. It is driven by a Sinex I HiPIMS power supply from Chemfilt Ionsputtering, delivering 100 µs long discharge pulses at a repetition frequency of 50 Hz, with a peak current of 100 A, and a peak voltage of −800 V which decreases monotonically during the pulse (see figure 1(b)).…”

An introduction to thin film processing using high-power impulse magnetron sputtering

“…7 From ionenergy measurements in HiPIMS discharges, it has been found that the average ion energy in the bulk plasma during the discharge pulse is around 20 eV without the use of any substrate bias. 7,49 As it turns out, ion energies in the range of 20-30 eV have been shown to have a densifying effect on thin films, 50 which is a very fortunate result and will be explored further in Section III C dealing with thin film growth. In Fig.…”

“…70,71 It results in an increase of ions being transported parallel to the target surface and lost to the walls instead of arriving at the substrate position, and thus reducing the deposition rate. 49 Ongoing work on plasma modeling of HiPIMS discharges, where one can arbitrarily turn on and off mechanisms believed to affect the deposition rate, will most likely shed more light on the subject. 72 Last, it should be pointed out that there are many situations where the quality of the coating is far more important than the deposition rate and one should, as always, be careful when making these comparisons based on only one or a few properties.…”

“…7). 12 In HiPIMS discharges, part of the ions moves along off-normal, with respect to the target, directions 49 (see Section II D). This anomalous ion transport results in differences in the flux, the energy, and the composition of the deposited and bombarding species as functions of the deposition angle.…”

Argon metastables in HiPIMS: time-resolved tunable diode-laser diagnostics

“…One of the main advantages with this technique is the dramatic increase of the ionization degree of the metallic vapor, where it has been shown that the HiPIMS plasma generates large quantities of highly energetic ions [2] with, in some cases, a directed flux of charged species [3]. The mechanisms involved in how these energetic particles are transported and how they interact with the neutral gas background as well as the bulk plasma are not fully understood, but it is clear that they have a dramatic effect on thin film growth, such as densification and improved adhesion as well as improved film quality [4,5].…”