Maximizing the Potential of Rotatable Magnetron Sputter Sources for Web Coating Applications V.Bellido-Gonzalez, Dermot Monaghan, Robert Brown, Alex Azzopardi, Gencoa, Liverpool UK
Structure of presentation Anode importance in planar and rotatable magnetrons and effect on substrate heating Magnetic options for rotatable magnetrons for web coating and heat load effects Case study: electrical and optical properties of reactive and non-reactive AZO layers formed with different rotatable magnetic geometries and varying substrate temperatures Conclusions NREL
A magnetron sputtering plasma Confinement between a negatively biased target and closed magnetic field produces a dense plasma. High densities of ions are generated within the confined plasma, and these ions are subsequently attracted to negative target, producing sputtering at high rates. + + - Resulting erosion of the sputter target Negatively biased target -V High density plasma by exb field
Anode s in magnetron plasma s A plasma is effectively an electric circuit with the target a negatively biased cathode and the chamber or separate mean providing the anode for the circuit return. Anodes are commonly earthed, although a positive charge is also possible. Whilst the plasma confinement in the near target area is governed by the magnetic field, the plasma spread away from the target is primarily an anode interaction effect.
Electrons will spiral around field lines until enough energy is lost to escape the magnetic trap.
If an anode intersects a magnetic field line it will collect the electrons, so they are lost to the plasma and do not add to substrate heating
Comparison of the plasma expansion with an anode that intersects with the magnetic field and one moved just 1mm to avoid a magnetic interaction
Whilst for a planar magnetron discharge and anode can be used to confine the plasma, typically for rotatable magnetron no anode is close-by
Rotatables great for target life and target use but not good for substrate heat load No reaction product on the surface cleans itself
Absence of anode can be seen in a plasma spread away from the target area DC AC
Heat load on substrates from magnetron sputtering plasmas There are several factors that contribute to the overall heat load on a substrate: Positive ions from the plasma. Electrons (primary and secondary) from the plasma. Thermal energy input due to the heat of condensation of the atoms. The thermal energy from the coating flux is comprised of the standard enthalphy (heat of condensation) of the given material plus the kinetic energy of the atoms. That leaves the heating effect from the plasma electrons and ions. For a DC based magnetron discharge this can be as high as 75% of the heat load and 95% for an RF magnetron based plasma [1]. Since the enthalphy is unavoidable during coating, the major means of reducing heat on the substrate is via the plasma control.
Heat load on substrates contributions dominated by primary and secondary electrons and argon ions plasma heating rather than atomic M.Andritschky et al, Vacuum/volume 44, pages 809 to 813, 1993, 0042-207X
Heat load on substrates from different DC & AC plasma and with different anode arrangements
Magnetic design and anode position will affect the substrate heating for rotatable magnetrons in the same way as planar magnetrons The above is the conventional magnetic arrangement for rotatables used by all manufacturers.
AC power mode and electron movement - + AC provides excellent arc suppression perfect for reactive oxides and TCO s But increases the plasma at the substrate definitely not perfect for temperature of web! e -
Industry standard magnetics with AC power mode and electron movement AC current leaks 70 mm 120 mm 100 mm
Lower impedance linked magnetics as a solution for better plasma control away from the target area - + e - e -
Plasma to substrate interaction by assymetric magnetics and tilting New Gencoa patent
Magnetic field Gencoa DLIM bars no AC leakage DLIM stands for Double Low AC current channelled Impedance Magnetics NREL 70 mm 120 mm 100 mm
Plasma control by Double Low Impedance Magnetics - DLIM Adjustment of angle relative to substrate position DC AC
Comparison of substrate temperature in-front of a double AC rotatable magnetron DLIM has a 20 C lower temperature for same conditions 160 Temperature on probes across (every 25 mm) 150 Temperature (indicator) 140 130 120 110 100 0 2 4 6 8 10 12 probe position T across DLIM T across BOC
For single magnetrons or for DC discharges anodes needs to be different to the AC pair case, hence a magnetically linked auxiliary anode is used
DC discharges the angle of the magnetic pack relative to the magnetic anode can be adjusted to drive the plasma away from the substrate The anode has a combined magnetic trapping with electron acceleration due to either a positive bias or as the floating earth return for the power supply.
Supplementary magnetic anodes for rotatable cathodes with DC & DC pulsed power More stable environment to avoid process drifts The introduction of an optional magnetically guided hidden auxiliary anode and gas bar offers the following benefits: lower plasma heating of the substrate x3 power possible for web coating reduced substrate movement influence on the plasma impedance lower discharge voltages lower impedance lower TCO resistivity less drift of plasma impedance and instability for non-conducting layers more consistent uniformity gas injected uniformly and protects hidden anode surface
Gencoa have developed a wide range of magnet bar options for rotatable magnetrons in order to control the plasma better Gencoa Rotatable Magnet Bar Products LS Low strength RF Radio frequency SSF Standard Strength Focused PP-RT Unbalanced ion assist processes HSS700 HSS850 HSS1000 High strength options TCO Transparent conduction oxide films LH/Web Single cathode with lower heating of substrate DLIM For better dual cathode AC discharges DLIM-DC-TCO Single anode shared between 2 cathodes for TCO Applications Low strength for higher voltage sputtering Strength optimized for RF power modes with active anode Standard field strength of 550 Gauss over the target with balanced field design Single and multi-cathode unbalanced magnetic designs for high levels of ion assistance for deco and hard coatings High Strength Single for thicker targets or lower discharge voltages range of 700, 850 & 1000 Gauss versions available Single cathode magnetics with active anode for reduced resistivity TCO layers for DC and DC pulsed operation (patented) Single cathode magnetics with active anode for reduced heat loads during vacuum web coating for DC and DC pulsed operation allows up to 3 x the power level compared to conventional magnetics (patented) Double cathode Low Impedance Magnetics for high rate reactive deposition of oxides with lower substrate heating and plasma interference (patented) Double cathode low TCO resistivity magnetics for DC powered double magnetrons with an additional active anode (patented) Component parts supplied Magnet pack Active magnetically guided anode
CASE STUDY use of DLIM magnetics to compare AZO layers from ceramic targets with AZO layers deposited reactively
Ceramic AZO on rotatable Good Concept, but! Moderately expensive ceramic targets and bonding Micro-arcing leads to variable & non-optimum product quality adds power modes and material costs Long target burn in before stable film properties can be > 24hrs Possible plasma damage of growing film - increasing resistivity, Limitation of composition and crystal structure good and bad Some areas to improve Hard arc count Hard arc count during pulsed-dc sputtering of ceramic AZO (ENI DCG + Sparc-le V) 600 500 400 300 200 100 * SCI Sputtering Components Inc 0 3 4 5 6 7 8 9 10 11 12 13 Power (kw)
Variation of AZO properties for DLIM dual rotatable cathode with pulsed DC power Variation of sheet resistance and resistivity with O2
Variation of AZO properties for DLIM dual rotatable cathode with pulsed DC power Variation of sheet resistance and resistivity with T Ts vs. Sheet resitance (ceramic AZO, 10 kw p-dc 100kHz, 2us, 500nm) DLIM 30 Sheet resistance (Ohm/sq) 26 22 18 14 10 9.2e-4 8.4e-4 7e-4 0 50 100 150 200 250 Ts (deg. C)
Controlled reactive sputtering will yield lower costs in production than ceramic AZO Price will be 70-50% current ceramic based costs * Szyszka et al
Reactive gas controllers common in other optical coating sectors
ZnAl dual rotatable + O 2 - TRIPLE RAMP CONDITIONING Reactive Sputtering Hysteresis Signals, % 100 90 80 70 60 50 40 30 20 10 0 0 50 100 150 200 250 Time, s SetPoint (%) Sensor (%) Actuator (%)
Plasma Emission for ZnAl + O 2 during control Reactive Sputtering Control Plasma Emission 40000 35000 Plasma Emission, counts 30000 25000 20000 15000 10000 5000 ZnAl + O2 in control 0 250-5000 350 450 550 650 750 850 Wavelength, nm
Different sensor control modes possible for reactive AZO O 2 gas Penning-PEM Lambda Target V Process- PEM
Reactive dual rotatable AZO deposition process window Process control using plasma monitoring ZnAl + O 2 reactive control dual rotatable 100 100 90 MFC feedback, sccm 80 70 60 50 40 30 20 Gas Feedback (SCCM) O2 PEM value % O2 PEM setpoint % 80 60 40 20 O2 PEM and target V Sensors (%) 10 Target V % 0 0 0 100 200 300 400 500 Time, s
DLIM magnetics dual magnetron AC power current / voltage characteristics 475 mm long Zn:Al target no O 2, 0-8kW AC power I, A 10 8 6 2mTorr 5mTorr 10mTorr Expon. (10mTorr) Expon. (5mTorr) Poly. (2mTorr) 4 2 0 450 500 550 600 650 700 750 800 850 U, V
Comparison of deposition rates for reactive and ceramic and DLIM/BOC magnetics Mean thickness across the deposition zone 500 450 400 Thickness (nm) for 2.5 min deposition at 5.3 kw AC BOC reactive (RT) DLIM reactive (RT) DLIM ceramic (RT) DLIM ceramic (150 deg C) deposited thickness 350 300 250 200 150 100 50 0 Deposition conditions
Comparison of electrical properties for ceramic and DLIM for optimized layers without substrate heating resistivity, Ohm-cm 1.00E+00 1.00E-01 1.00E-02 1.00E-03 Resisitivity DLIM (reactive and ceramic AZO) at room temperature (static coating every 25 mm under double magnetron cathodes) 0 2 4 6 8 10 12 resistivity AZO DLIM (RT) resistivity reactive DLIM 1.00E-04 Sample position
Comparison of reactive AZO in-front of a double AC rotatable magnetron Comparing the 2 different magnetic designs Resisitivity BOC & DLIM at room temperature (every 25 mm) 1.00E+00 0 2 4 6 8 10 12 resistivity, Ohm-cm 1.00E-01 1.00E-02 1.00E-03 resistivity BOC resistivity DLIM 1.00E-04 Sample position
Comparison f ceramic AZO in-front of a double AC rotatable magnetron Comparing 2 different substrate temperatures Resisitivity DLIM ceramic AZO target at RT and 150 deg C (samples every 25 mm) resistivity, Ohm-cm 1.00E+00 1.00E-01 1.00E-02 1.00E-03 0 2 4 6 8 10 12 resistivity AZO DLIM (RT) resistivity AZO DLIM (150 deg C) 1.00E-04 Sample position
TCO film properties and rates also depend on target rotation speed R07# NO TARGET ROTATION Resistivity map for static deposition across 2 targets 3000 1.00E+00 Thickness, nm 2500 2000 1500 1000 500 0 0 2 4 6 8 10 12 sample (every 25 mm) ZnAl: 152 mm diam x 475 mm L AC-MF: 5.3 kw (Huettinger) Ar press.: 3E-03 mbar 1.00E-01 1.00E-02 Log scale 1.00E-03 1.00E-04 Ohm-cm thickness resistivity target rotation speed: 0 rpm Substrate static T/S: 95 mm Temp: Room Temp. Dep. time: 10 mins Higher resistivity on areas of high negative Oxygen ion bombardment
Reactive AZO properties under same conditions but with target rotation R08# as R07 with Target Rotation 3000 1.00E+00 Thickness, nm 2500 2000 1500 1000 500 1.00E-01 1.00E-02 Log scale 1.00E-03 Ohm-cm thickness resistivity 0 0 2 4 6 8 10 12 sample (every 25 mm) ZnAl: 152 mm diam x 475 mm L AC-MF: 5.3 kw (Huettinger) Ar press.: 3E-03 mbar 1.00E-04 target rotation speed: 5 rpm Substrate static T/S: 95 mm Temp: Room Temp. Dep. Time: 10 mins
AZ+O 2 film properties at Room Temperature and 150ºC with similar properties R09 (at RT) and R17(at 150 deg C) 3000 1.00E+00 2500 1.00E-01 Thickness, nm 2000 1500 1000 1.00E-02 Log scale Ohm-cm t (at 150ºC) t (at RT) r (at 150ºC) r (at RT) 1.00E-03 500 0 1.00E-04 0 2 4 6 8 10 12 sample (every 25 mm)
Room temperature films have better optical density Optical Density at 550nm & Resistivity for R09 (at RT) and R17(at 150 deg C) 0.2 1.00E-02 0.18 Optical Density at 550nm 0.16 0.14 0.12 0.1 0.08 0.06 0.04 1.00E-03 Log scale 1.00E-04 Ohm-cm od (at 150ºC) od (at RT) r (at 150ºC) r (at RT) 0.02 0 1.00E-05 0 2 4 6 8 10 12 sample (every 25 mm)
With reactive processes transmission can tuned over a wide range and tuned with electrical properties for different applications Coating thickness for both is 1.8µm 3Ω/sq
AZ+O 2 transmittance in the visible spectrum good low temp transparency 120 T(%) R09 (at RT) and R17 (at 150ºC) 100 T(%) R09 T(%) R17 Transmission 80 60 40 20 Coating thickness ~ 2.4 µm 0 325 525 725 925 wavelength, nm
Room temp transparency for ceramic and reactive films both 20 Ωsq films
Conclusions Acknowledgements Alternative magnetic designs have been developed to control the plasma electrons in rotatable based sputtering arrangements in order to limit the heating of web based substrates. The use of magnetic guiding of the electrons away from the substrate will limit heating. For AC rotatable pairs the DLIM design is optimum and for DC power the use of an auxiliary magnetic anodes with or without a positive biasing. Reactive AZO deposited from dual rotatable magnetrons can be readily tuned over a wide range and all have much lower internal stress than the ceramic approach. Reactive AZO deposited with DLIM and MF power show equally good or better properties at without substrate heating when compared to elevated temperatures allowing high quality deposition onto temperature sensitive substrates. Special thanks to Heraeus for providing AZO and Zn:Al targets.