Time evolution of ion fluxes incident at the substrate plane during reactive high-power impulse magnetron sputtering of groups IVb and VIb transition metals in Ar/N2

Abstract

Reactive transition-metal (TM) nitride film growth employing bias-synchronized high power impulse magnetron sputtering (HiPIMS) requires a detailed knowledge of the time evolution of metal-and gas-ion fluxes incident at the substrate plane in order to precisely tune momentum transfer and, hence, provide the recoil density and energy necessary to eliminate film porosity at low deposition temperatures without introducing significant film stress. Here, we use energy-and time-dependent mass spectrometry to analyze the evolution of metal-and gas-ion fluxes at the substrate plane during reactive HiPIMS sputtering of Groups IVb and VIb TM targets in Ar/N2 atmospheres. The time-and energy-integrated metal/gas ion ratio + / + incident at the substrate is significantly lower for Group IVb TMs (ranging from 0.2 for Ti to 0.9 for Hf), due to high N2 reactivity which results in severely reduced target sputtering rates and, hence, decreased rarefaction. In contrast, for less reactive Group VIb metals, sputtering rates are similar to those in pure Ar as a result of significant gas heating and high + / + ratios, ranging from 2.3 for Cr to 98.1 for W. In both sets of experiments, the peak target current density is maintained constant at 1 A/cm 2. Within each TM group, + / + scales with increasing metal-ion mass. For the Group-VIb elements, sputtered-atom Sigmund-Thompson energy distributions are preserved long after the HiPIMS pulse, in contradistinction to Group-IVb TMs for which the energy distributions collapse into narrow thermalized peaks. For all TMs, the N + flux dominates that of N2 + ions, as the

Growth of dense, hard yet low-stress Ti0.40Al0.27W0.33N nanocomposite films with rotating substrate and no external substrate heating

“…A pulsed substrate bias V s = -500 V is applied synchronously with 110-μs-HiPIMS pulses, based upon time-and energy-resolved mass spectroscopy analyses performed at the substrate position, which revealed the time-and energy-integrated W + /(Ar + + N 2 + ) ion ratio during W-HiPIMS pulse as high as ~100. 15 The bias offset is set at 20 μs, which corresponds to the transit time for most energetic W + ions at the shortest target-substrate separation. The bias pulse length is set at the maximum available value of 200 μs to ensure energetic W + bombardment even at the longest target-substrate distance.…”

“…W + irradiation is selected based on previous ion mass spectrometry studies performed at the substrate position, which showed severe Ar rarefaction during HiPIMS pulses, while sputtering in Ar/N 2 gas mixtures to such extent that the time-and energy-integrated metal/gas ion ratio during W-HiPIMS pulse was ~100. [14][15] Such conditions imply large flexibility in the choice of bias pulse offset and pulse length as both Ar + and N 2 + ion fluxes are essentially eliminated during the time period of several hundred μs following the ignition of the HiPIMS pulse. This allows efficient W + irradiation of the growing film surface, while minimizing Ar + incorporation, even when the substrate-target separation is continuously changing during substrate rotation, by using relatively long bias pulses.…”

Engineered ion-bombardment as a tool in thin film deposition

“…Hecimovic et al [63] investigated in detail the origin of the IEDF in HiPIMS and found that the high energy tail can be fitted with a Maxwell distribution, which indicates that the sputtered ions are also thermalized, though this will depend a lot on the pressure and the distance between the target and the substrate [62]. It is also common to see a distinct energy shoulder between the thermal ion population and the high energy tail [64,67,102,[104][105][106][107] and this was argued by Maszl et al [103] to be due to the presence of self-organizing ionization zones called spokes [108][109][110][111], which results to a potential hump that can accelerate ions [103,112]. An example of the IEDF of Ti + ions in a HiPIMS discharge is shown in Fig.…”

Multifunctional transition metal diboride thin films grown by magnetron sputtering with metal-ion irradiation

“…An additional feature of HiPIMS discharges is a time separation between metal-and gas-ion fluxes incident at the substrate due to the rarefaction of working gas in front of the target [84,88]. This effect can be utilized during the film growth to independently control the momentum and energy of incident ionized species through the application of substrate bias pulses (metal-ion-synchronized HiPIMS) [88][89][90]. This approach has been employed in papers II and III of this thesis.…”