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

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