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

+ + -

Neg

ativ

ely

bias

ed ta

rget

-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

Tem

pera

ture

(ind

icat

or)

probe position

Temperature on probes across (every 25 mm)

T across DLIMT 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 13Power (kW)

Har

d ar

c co

unt

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

10

14

18

22

26

30

0 50 100 150 200 250

Ts (deg. C)

Shee

t res

ista

nce

(Ohm

/sq)

8.4e-4 9.2e-4

7e-4

* Szyszka et al

Controlled reactive sputtering will yield lower costs in production than ceramic AZO

Price will be 70-50% current ceramic based costs

Reactive gas controllers ‘common’ in other optical coating sectors

Reactive Sputtering Hysteresis

ZnAl dual rotatable + O2 - TRIPLE RAMP CONDITIONING

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250Time, s

Sign

als,

% SetPoint (%)Sensor (%)Actuator (%)

Reactive Sputtering Control Plasma Emission

Plasma Emission for ZnAl + O 2 during control

-5000

0

5000

10000

15000

20000

25000

30000

35000

40000

250 350 450 550 650 750 850

Wavelength, nm

Pla

sma

Em

issi

on, c

ount

s

ZnAl + O2 in control

Different sensor control modes possible for reactive AZO

Penning-PEM

Target V

Lambda

Process-PEM

O2 gas

Reactive dual rotatable AZO deposition process window

ZnAl + O2 reactive control dual rotatable

0

10

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500Time, s

MFC

feed

back

, scc

m

0

20

40

60

80

100

O2 P

EM a

nd ta

rget

V

Sens

ors

(%)

Gas Feedback (SCCM)O2 PEM value %O2 PEM setpoint %Target V %

Process control using plasma monitoring

DLIM magnetics dual magnetron AC power current / voltage characteristics

475 mm long Zn:Al target no O2, 0-8kW AC power

0

2

4

6

8

10

450 500 550 600 650 700 750 800 850

U, V

I, A

2mTorr5mTorr10mTorrExpon. (10mTorr)Expon. (5mTorr)Poly. (2mTorr)

0

50

100

150

200

250

300

350

400

450

500

Deposition conditions

depo

site

d th

ickn

ess

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)

Comparison of deposition rates for reactive and ceramic and DLIM/BOC magnetics Mean thickness across the deposition zone

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+000 2 4 6 8 10 12

resi

stiv

ity, O

hm-c

m

Sample position

Resisitivity DLIM (reactive and ceramic AZO) at room temperature (static coating every 25 mm under double

magnetron cathodes)

resistivity AZO DLIM(RT)resistivity reactive DLIM

Comparison of electrical properties for ceramic and DLIM for optimized layers

without substrate heating

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+000 2 4 6 8 10 12

resi

stiv

ity, O

hm-c

m

Sample position

Resisitivity BOC & DLIM at room temperature (every 25 mm)

resistivity BOCresistivity DLIM

Comparison of reactive AZO in-front of a double AC rotatable magnetron Comparing the 2 different magnetic designs

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+000 2 4 6 8 10 12

resi

stiv

ity, O

hm-c

m

Sample position

Resisitivity DLIM ceramic AZO target at RT and 150 deg C (samples every 25 mm)

resistivity AZO DLIM (RT)

resistivity AZO DLIM (150deg C)

Comparison f ceramic AZO in-front of a double AC rotatable magnetron Comparing 2 different substrate temperatures

TCO film properties and rates also depend on target rotation speed

R07# NO TARGET ROTATION

0

500

1000

1500

2000

2500

3000

0 2 4 6 8 10 12sample (every 25 mm)

Thic

knes

s, n

m

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

Ohm

-cm

thicknessresistivity

target rotation speed: 0 rpm Substrate static T/S: 95 mm Temp: Room Temp. Dep. time: 10 mins

ZnAl: 152 mm diam x 475 mm L

AC-MF: 5.3 kW (Huettinger)

Ar press.: 3E-03 mbar

Higher resistivity on areas of high negative Oxygen ion bombardment

Log scale

Resistivity map for static deposition across 2 targets

Reactive AZO properties under same conditions but with target rotation

R08# as R07 with Target Rotation

0

500

1000

1500

2000

2500

3000

0 2 4 6 8 10 12sample (every 25 mm)

Thic

knes

s, n

m

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

Ohm

-cm

thicknessresistivity

target rotation speed: 5 rpm Substrate static T/S: 95 mm Temp: Room Temp. Dep. Time: 10 mins

ZnAl: 152 mm diam x 475 mm L

AC-MF: 5.3 kW (Huettinger)

Ar press.: 3E-03 mbar

Log scale

AZ+O2 film properties at Room Temperature and 150ºC with similar properties

R09 (at RT) and R17(at 150 deg C)

0

500

1000

1500

2000

2500

3000

0 2 4 6 8 10 12sample (every 25 mm)

Thic

knes

s, n

m

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

Ohm

-cm t (at 150ºC)

t (at RT)r (at 150ºC)r (at RT)

Log scale

Room temperature films have better optical density

Optical Density at 550nm & Resistivity for R09 (at RT) and R17(at 150 deg C)

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0 2 4 6 8 10 12sample (every 25 mm)

Opt

ical

Den

sity

at 5

50nm

1.00E-05

1.00E-04

1.00E-03

1.00E-02

Ohm

-cm od (at 150ºC)

od (at RT)r (at 150ºC)r (at RT)

Log scale

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

0

20

40

60

80

100

120

325 525 725 925

Tran

smis

sion

wavelength, nm

T(%) R09 (at RT) and R17 (at 150ºC)

T(%) R09 T(%) R17

AZ+O2 transmittance in the visible spectrum good low temp transparency

Coating thickness ~ 2.4 µm

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.