Experimental verification of deposition rate increase, with maintained high ionized flux fraction, by shortening the HiPIMS pulse

Abstract

High power impulse magnetron sputtering (HiPIMS) is an ionized physical vapor deposition technique, providing a high flux of metal ions to the substrate. However, one of the disadvantages for industrial use of this technique is a reduced deposition rate compared to direct current magnetron sputtering (dcMS) at equal average power. This is mainly due to a high target back-attraction probability of the metal ions with typical values in the range 70%–90% during the pulse. In order to reduce this effect, we focused on the contribution of ion fluxes available immediately after each HiPIMS pulse; a time also known as afterglow. Without a negative potential on the target at this stage of the HiPIMS process, the back-attracting electric field disappears allowing remaining ions to escape the magnetic trap and travel toward the substrate. To quantify the proposed mechanism, we studied the effect of HiPIMS pulse duration on the outward flux of film-forming species in titanium discharges, which are known to exhibit more than 50% reduction in deposition rate compared to dcMS. By shortening the HiPIMS pulse length, it was found that the contribution to the outward flux of film-forming species from the afterglow increases significantly. For example, HiPIMS discharges at a constant peak current density of about 1.10 A cm−2 showed a 45% increase of the deposition rate, by shortening the pulse duration from 200 to 50 μs. Ionized flux fraction measurements, using a gridless quartz crystal micro-balance-based ion meter, showed that this increase of the deposition rate could be achieved without compromising the ionized flux fraction, which remained approximately constant. The key to the achieved optimization of HiPIMS discharges lies in maintaining a high peak discharge current also for short pulse lengths to ensure sufficient ionization of the sputtered species.

Time-resolved ion energy distribution functions during a HiPIMS discharge with cathode voltage reversal

“…Beyond the control of the IEDF to tailor ion energy, one of the longest running drawbacks to HiPIMS is reduced deposition rates compared to dcMS, primarily due to return of ionized material in the sheath to the target [8]. There has already been an effort to mitigate this through lowering the main pulse duration even without a kick pulse [9]. In the course of investigating the shape of the IEDF, integrations of the IEDF were likewise produced in order to determine relative total ion flux.…”

“…Crucial to the adoption of high-power impulse magnetron sputtering (HiPIMS) as both a research and production deposition technique is the improvement in deposition rate [1][2][3], relative to direct current magnetron sputtering (dcMS) [4]. Previous efforts have included alterations to magnet pack design [5][6][7], and shortening of the negative pulse length [8,9]. Substantial effort was made to experimentally demonstrate the ability of HiPIMS to generate increased ion fraction [10] through manipulation of the negative pulse alone [11,12], typically at pressures below 1.33 Pa.…”

Biased quartz crystal microbalance method for studies of CVD surface chemistry induced by plasma electrons

“…The electrical connection is based on the same principle as has been used in the case of the so-called gridless ion meter. 11,13 The ground connection of the QCM oscillator was connected to the top electrode of the crystal through a 220 nF capacitor, which allows for the QCM high frequency single-ended signal to pass through and be measured while at the same time blocking the DC biasing voltage applied to the top electrode of the crystal from entering the QCM oscillator. Moreover, a 100 nF capacitor was connected in between bottom QCM electrode and the signal input of the QCM oscillator, in order to shield the QCM high frequency signal from any external interference.…”

On how to measure the probabilities of target atom ionization and target ion back-attraction in high-power impulse magnetron sputtering

“…13,14 We use the version of the IRM that includes the consideration of an afterglow, which is important to account for, since the contribution to the deposition rate of the afterglow can be a significant portion of the total deposition rate, 9 which has been verified experimentally. 34 Furthermore, we introduce the explicit treatment of two separate Ar metastable levels ( 3 P 2 at 11.548 eV and 3 P 0 at 11.723 eV). These changes include an update of the corresponding forward and backward electron impact excitation cross sections to and from the metastable levels and a new ionization cross section from these metastable levels.…”