Maximizing the Potential of Rotatable Magnetron ... Maximizing the Potential of Rotatable Magnetron

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  • Maximizing the Potential of Rotatable Magnetron Sputter Sources for Web Coating Applications V.Bellido-Gonzalez, Dermot Monaghan, Robert Brown, Alex Azzopardi, Gencoa, Liverpool UK

  • • 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

    Structure of presentation

  • A magnetron sputtering plasma

    + + -

    N eg

    at iv

    el y

    bi as

    ed ta

    rg et

    -V

    High density plasma by exb field

    Resulting erosion of the sputter target

    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.

  • 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

  • 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 from magnetron sputtering plasmas

  • 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

    e-

    - +

    • 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!

  • Industry standard magnetics with AC power mode and electron movement

    70 mm

    100 mm 120 mm

    AC current “leaks”

  • 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

  • NREL

    Magnetic field – Gencoa DLIM bars – no AC leakage DLIM stands for Double Low

    Impedance Magnetics

    70 mm

    100 mm

    120 mm

    AC current “channelled”

  • Plasma control by Double Low Impedance Magnetics - DLIM

    Adjustment of angle relative to substrate position

    DC

    AC

  • 100

    110

    120

    130

    140

    150

    160

    0 2 4 6 8 10 12

    Te m

    pe ra

    tu re

    (i nd

    ic at

    or )

    probe position

    Temperature on probes across (every 25 mm)

    T across DLIM T across BOC

    Comparison of substrate temperature in-front of a double AC rotatable magnetron

    DLIM has a 20̊C lower temperature for same conditions

  • 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 Rotatable Magnet Bar

    Products Applications Component parts

    supplied LS

    Low strength Low strength for higher voltage sputtering

    RF Radio frequency

    Strength optimized for RF power modes with active anode

    SSF Standard Strength

    Focused

    Standard field strength of 550 Gauss over the target with balanced field design

    PP-RT Unbalanced ion

    assist processes

    Single and multi-cathode unbalanced magnetic designs for high levels of ion assistance for deco and hard coatings

    HSS700 HSS850

    HSS1000 High strength options

    High Strength Single for thicker targets or lower discharge voltages – range of 700, 850 & 1000 Gauss versions available

    TCO Transparent

    conduction oxide films

    Single cathode magnetics with active anode for reduced resistivity TCO layers for DC and DC pulsed operation (patented)

    LH/Web Single cathode with

    lower heating of substrate

    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)

    DLIM For better dual

    cathode AC discharges

    Double cathode Low Impedance Magnetics for high rate reactive deposition of oxides with lower substrate heating and plasma interference (patented)

    DLIM-DC-TCO Single anode shared between 2 cathodes

    for TCO

    Double cathode low TCO resistivity magnetics for DC powered double magnetrons with an additional active anode (patented)

    Gencoa have developed a wide range of magnet bar options for rotatable

    magnetrons in order to control the plasma better

    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!

    Some areas to improve • 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

    * SCI – Sputtering Components Inc

    Hard arc count during pulsed-DC sputtering of ceramic AZO (ENI DCG + Sparc-le V)

    0

    100

    200

    300

    400

    500

    600

    3 4 5 6 7 8 9 10 11 12 13 Power (kW)

    H ar

    d ar

    c co

    un t

  • Variation of AZO properties for DLIM dual ro