Self-Sputtering of an Inverted Cylindrical Magnetron for Ion Beam ...

Oral Session60 mA for the cylinder case even when the dischargecurrent exceeded 90 A.7260483624120Discharge current, AdischargeFC ion beam current, mAion beam200 300 400 500 600 700 800Time, μsFig. 4. Pulse shapes of discharge current and beam current.Ar, p = 8 ⋅ 10 –5 torr. U a = 30 kVFigure 5 presents the radial distribution of the ionbeam current density as measured with a movableFaraday cup. Unlike to the planar magnetron case, thering discharge structure is not visible in the cylindricalmagnetron.Ion beam current density, mA/cm 21.61.41.21.00.80.60.40.20.00 2 4 6 8 10 12Distance from center, cmFig. 5. Radial distribution of the ion beam current density.p = 8 ⋅ 10 –5 torr. I d = 90 AThe next two figures, Figs. 6 and 7, present the resultsof experiments investigating the development ofthe ion beam’s charge state composition during thedischarge pulse. The results show for the cylindricalmagnetron case that it is possible to reach conditionswhen metal ions dominate over the gaseous ions.However, the situation is not as clear cut as it waswith the planar magnetron.The gas ions were displaced and replaced later inthe pulse when considering the inverted cylindricalmagnetron compared to the planar magnetron casethen for the flat magnetron case. Additionally, theratio of metal to gas ions is remains smaller for thecylindrical magnetron. This may well be associatedwith the directionality of the sputtering process where484032241610 kV, total beam current 25 mA20 kV, total beam current 55 mA30 kV, total beam current 60 mA80sputtered atoms are preferentially emitted normal tothe target surface, generally obeying a cosine-like angulardistribution.Fig. 6. Time-of-flight (TOF) ion beam spectrum. Ar,p = 8 ⋅ 10 –5 torr, I d = 90 A, U a = 30 kV, measured 250 µsafter discharge ignitionIon fractions, normalized1.00.80.60.40.20.01.00.80.60.4TOF FC current, normilizedC + N 2 + Cu 2+ Ar + Cu +2 3 4 5 6 7Time, μsDischargeCu +0.2Ar +20Ar 2+ Cu 2+0.000 50 100 150 200 250 300 350 400Time, μs100Fig. 7. Temporal development of metal and gaseous ionbeam fractions corresponding to the discharge current pulseshape. Ar, p = 8 ⋅ 10 –5 torr, I d = 90 A, U a = 30 kV4. ConclusionsThe results obtained with an inverted cylindrical magnetrondischarge follow the general trends previouslyseen with a planar magnetron operating in selfsputteringmode. The cylindrical magnetron featuresself-sputtering and can serve as the feedstock plasmafor an ion source. In both cases, metal ions can beextracted. However, the inverted cylindrical magnetrondischarge delivers lower ion extraction current,and the discharge and ion current exhibits greaternoise (fluctuations) and instabilities. There is a need tooperate at much higher discharge currents due to thegreater cathode area, this, however, is limited by theincreasing likelihood for a glow to arc transition. Inthe present configuration it was shown that the pulsedmagnetic field can be used to trigger the dischargepulses. However, such field may not be optimized forion source operation.806040Discharge current, A15

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