Connection between target poisoning and current waveforms in reactive high-power impulse magnetron sputtering of chromium

Global models of high-power impulse magnetron sputtering (HiPIMS) plasmas in the literature predict a unique connection between target current waveform and oxidation state of the target (metallic versus poisoned): in the metallic mode, the current waveform reaches a plateau due to metal atom recycling, in the poisoned mode a triangular current waveform is predicted driven by plasma gas recycling. This hypothesis of such a unique connection is tested by measuring the surface chemical composition of chromium magnetron targets directly during reactive high-power impulse magnetron sputtering (r-HiPIMS) by spatially resolved x-ray photoelectron spectroscopy (XPS). The sputtering setup was connected to the ultra-high vacuum XPS spectrometer so that the targets could be transferred between the two chambers without breaking the vacuum. The O2/Ar feed gas ratio, the input power and the pulse frequency of the HiPIMS plasmas were varied. The racetrack oxidation state was measured for different plasma parameters and correlated to the target current waveform shape. It was found that a shift of the target operation from the poisoned mode at low powers to the metallic mode at high powers when operating the discharge at 20 Hz pulse frequency occurs. The transition between these modes was directly correlated with analysis of the Cr2p core level peak on the complete target area. A unique correlation between the metallic and poisoned state of the target and the plateau and triangular current waveform was identified for very low powers and very high powers. In the intermediate power range, such a unique connection is absent. It is argued that the presence of already a small fraction of metal on the target may induce a plateau current waveform despite a significant oxidation of the target. This implies a finite contribution of metal sputtering during the pulse that dominates the recycling and leads to a plateau current waveform. Consequently, the shape of current waveforms cannot easily be connected to target poisoning, but a more detailed modeling of the recycling mechanisms is required.

[1]  J. Benedikt,et al.  Influence of spokes on the ionized metal flux fraction in chromium high power impulse magnetron sputtering , 2018 .

[2]  J. Gudmundsson,et al.  A unified treatment of self-sputtering, process gas recycling, and runaway for high power impulse sputtering magnetrons , 2017 .

[3]  S. Konstantinidis,et al.  The Target Material Influence on the Current Pulse during High Power Pulsed Magnetron Sputtering , 2017, Front. Phys..

[4]  A. Anders.  Tutorial: Reactive high power impulse magnetron sputtering (R-HiPIMS) , 2017 .

[5]  J. Gudmundsson,et al.  A study of the oxygen dynamics in a reactive Ar/O2 high power impulse magnetron sputtering discharge using an ionization region model , 2017 .

[6]  A. Keudell,et al.  Composite targets in HiPIMS plasmas: Correlation of in-vacuum XPS characterization and optical plasma diagnostics , 2017 .

[7]  D. Mckenzie,et al.  Evolution of target condition in reactive HiPIMS as a function of duty cycle: An opportunity for refractive index grading , 2017 .

[8]  T. Kubart,et al.  Evolution of sputtering target surface composition in reactive high power impulse magnetron sputtering , 2017 .

[9]  C. Maszl,et al.  Influence of nitrogen admixture to argon on the ion energy distribution in reactive high power pulsed magnetron sputtering of chromium , 2017 .

[10]  A. Keudell,et al.  Electric potential screening on metal targets submitted to reactive sputtering , 2017 .

[11]  K. Strijckmans,et al.  Perspective: Is there a hysteresis during reactive High Power Impulse Magnetron Sputtering (R-HiPIMS)? , 2017 .

[12]  J. Gudmundsson,et al.  An ionization region model of the reactive Ar/O2 high power impulse magnetron sputtering discharge , 2016 .

[13]  Gunnar A. Niklasson,et al.  Low-temperature synthesis of thermochromic vanadium dioxide thin films by reactive high power impulse magnetron sputtering , 2016 .

[14]  A. von Keudell,et al.  Revising secondary electron yields of ion-sputtered metal oxides , 2016 .

[15]  J. Vlček,et al.  A parametric model for reactive high-power impulse magnetron sputtering of films , 2016 .

[16]  A. Keudell,et al.  Elementary surface processes during reactive magnetron sputtering of chromium , 2015 .

[17]  A. von Keudell,et al.  Note: Ion-induced secondary electron emission from oxidized metal surfaces measured in a particle beam reactor. , 2015, The Review of scientific instruments.

[18]  F. Pan,et al.  Discharge current modes of high power impulse magnetron sputtering , 2015 .

[19]  K. Strijckmans,et al.  Corrigendum to Modeling reactive magnetron sputtering: Fixing the parameter set Surf. Coat. Technol. 206(17) (2012) 3666–3675 , 2015 .

[20]  U. Helmersson,et al.  Process stabilization by peak current regulation in reactive high-power impulse magnetron sputtering of hafnium nitride , 2015, 1509.07002.

[21]  D. Mckenzie,et al.  The role of pulse length in target poisoning during reactive HiPIMS: application to amorphous HfO2 , 2015 .

[22]  K. Strijckmans,et al.  A time-dependent model for reactive sputter deposition , 2014 .

[23]  T. Kubart,et al.  Understanding the discharge current behavior in reactive high power impulse magnetron sputtering of oxides , 2013 .

[24]  S. Ólafsson,et al.  Current–voltage–time characteristics of the reactive Ar/O2 high power impulse magnetron sputtering discharge , 2012 .

[25]  K. Strijckmans,et al.  Modeling reactive magnetron sputtering: Fixing the parameter set , 2012 .

[26]  U. Helmersson,et al.  High power impulse magnetron sputtering discharge , 2012 .

[27]  S. Ólafsson,et al.  Current-voltage-time characteristics of the reactive Ar/N2 high power impulse magnetron sputtering discharge , 2011 .

[28]  Andrea R. Gerson,et al.  Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Sc, Ti, V, Cu and Zn , 2010 .

[29]  S. Konstantinidis,et al.  High power pulsed magnetron sputtering: A review on scientific and engineering state of the art , 2010 .

[30]  E. Wallin,et al.  Transition between the discharge regimes of high power impulse magnetron sputtering and conventional direct current magnetron sputtering , 2009 .

[31]  D. Depla,et al.  Determination of the effective electron emission yields of compound materials , 2008 .

[32]  J. Andersson,et al.  High power impulse magnetron sputtering : Current-voltage-time characteristics indicate the onset of sustained self-sputtering , 2007 .

[33]  D. Depla,et al.  Towards a more complete model for reactive magnetron sputtering , 2007 .

[34]  Johan Haemers,et al.  Understanding the discharge voltage behavior during reactive sputtering of oxides , 2007 .

[35]  D. R. Penn,et al.  Calculations of electron inelastic mean free paths. III. Data for 15 inorganic compounds over the 50–2000 eV range , 1991 .

[36]  Brian R. Strohmeier,et al.  An ESCA method for determining the oxide thickness on aluminum alloys , 1990 .