On the film density using high power impulse magnetron sputtering

Abstract

On the film density using high power impulse magnetron sputtering, 2010, SURFACE and COATINGS TECHNOLOGY, (205) AbstractThe influence on thin film density using high power impulse magnetron sputtering (HiPIMS) has been investigated for eight different target materials (Al, Ti, Cr, Cu, Zr, Ag, Ta, and Pt).The density values as well as deposition rates have been compared to results obtained from thin films grown by direct current magnetron sputtering (DCMS) under the same experimental conditions. Overall, it was found that the HiPIMS deposited coatings were approximately 5-15 % denser compared to the DCMS deposited coatings. This could be attributed to the increased metal ion bombardment commonly seen in HiPIMS discharges, which also was verified using a global plasma model to assess the degree of ionization of 2 sputtered metal. One key feature is that the momentum transfer between the growing film and the incoming metal ions is very efficient due to the equal mass of film and bombarding species, leading to a less pronounced columnar microstructure. As expected the deposition rates were found to be lower for HiPIMS compared to DCMS. For several materials this decrease is not as pronounced as previously reported in the literature, which is shown in the case of Ta, Pt, and Ag with rate HiPIMS /rate DCMS ~ 70-85 %, while still achieving denser coatings.

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

“…In a recent report by Samuelsson et al, 8 it was found that the rates are typically in the range of 30-80% compared to DCMS depending on target material. In Fig.…”

“…for this behavior is mainly related to the fact that the ionization potential is material dependent and for metals used in magnetron sputtering commonly found in the range E IP 5 5.99 eV (Al) to E IP 5 11.26 eV (C), meaning that Al is more easily ionized than C. In plasma discharge modeling by both Hopwood 39 and Samuelsson et al, 8 these trends are clearly shown and in Fig. 2, one such example is illustrated for HiPIMS using a 100 ls discharge pulse of À880 V and 30 A peak current (corresponding to a peak current density of about 1.5 A cm À2 ).…”

“…This means that the ion flux fraction is larger than the degree of ionized metal and therefore it is not uncommon to find that although the degree of ionization only reaches about 50%, the ionized flux fraction at the substrate can be more than 90%. 8 The HiPIMS plasma has also shown the presence of multiply charged ions for various target materials, 7,[41][42][43][44] which is rarely found in other types of magnetron discharges but often found in cathodic arc discharges. 45 One implication of having this type of ions is that they enable sustained self-sputtering, 6 meaning that they will sputter enough material for continued ionization and release enough secondary electrons to keep the plasma burning assuming that enough sputtered metal ions can be attracted back to the target.…”

“…The discharge current peaks at about 30 A at ;50 ls into the pulse (the peak current density is about 1.5 A cm À2 ). A 100 ls square voltage pulsed of À880 V was used in the modeling (from Samuelsson et al 8 with permission from Elsevier). deposition takes place during the pulse-off time because of the time needed for sputtered material to reach the substrate.…”

“…In Fig. 4, reported deposition rates are given for various target materials based on the data from Helmersson et al 62 and Samuelsson et al 8 The most common explanation to the reduction in deposition rate stems from a work by Christie, 63 where back-attraction of metal ions to the target followed by selfsputtering causes a reduction in the amount of sputtered particles reaching the substrate. Controlling and optimizing the potential profile in the cathode region will, therefore, greatly affect the number of metal ions incident on the target surface, 64 which so far has not been fully explored.…”