Comparison of reactive and ceramic AZO and. ITO from dual rotatable
magnetrons. V.Bellido-Gonzalez, Dermot Monaghan, Robert. Brown, Alex
Azzopardi ...
Comparison of reactive and ceramic AZO and ITO from dual rotatable magnetrons
V.Bellido-Gonzalez, Dermot Monaghan, Robert Brown, Alex Azzopardi, Gencoa, Liverpool UK
Structure of presentation
• Overview of basic magnetic designs for rotatable magnetrons for DC and AC sputtering • Anode importance in rotatable magnetrons and effect on substrate heating and plasma interaction • Magnetic options for rotatable magnetrons with positive guiding of plasma electrons • Case study: electrical and optical properties of reactive and non-reactive AZO layers formed with different rotatable magnetic geometries • Case study: electrical and optical properties of reactive ITO layers formed with different rotatable magnetic geometries • Conclusions
NREL
Whilst for a planar magnetron discharge and anode can be used to confine the plasma, typically for rotatable magnetron no anode is close-by
Accurate positioning of the magnetic field to ensure erosion to the end of the target
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
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.
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
Effect of active magnetically guided anode on the sputter target voltage for a GRS75 – 75mm OD dual DC powered arrangement & Al target material
Magnetic design for a double magnetron used in industry currently
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 – potentially damaging some layer structures and substrates!
Industry standard magnetics with AC power mode and electron movement AC current “leaks”
70 mm 100 mm 120 mm
Lower impedance ‘linked’ magnetics as a solution for better plasma control away from the target area
-
AC current “leaks”
+
70 mm 100 mm 120 mm
e-
e-
Plasma to substrate interaction by assymetric magnetics and tilting Gencoa patent
Magnetic field – Gencoa DLIM bars – no AC leakage DLIM stands for Double Low Impedance Magnetics AC current “channelled”
NREL
70 mm 100 mm 120 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 20̊C lower temperature for same conditions
Temperature on probes across (every 25 mm) 160 T across DLIM T across BOC
Temperature (Deg C)
150 140 130 120
110 100 0
2
4 6 probe position
8
10
12
CASE STUDY use of DLIM and standard 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 Hard arc count during pulsed-DC sputtering of ceramic AZO (ENI DCG + Sparc-le V)
Hard arc count
600 500 400 300
* SCI – Sputtering Components Inc
200 100 0 3
4
5
6
7
8
9
Power (kW)
10
11
12
13
Ceramic AZO layer properties – variation of properties with process parameters Problematic but presents an opportunity to improve
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
Sheet resistance (Ohm/sq)
30 26 22
8.4e-4
18
9.2e-4 7e-4
14 10 0
50
100
150
Ts (deg. C)
200
250
Controlled reactive sputtering is x 3 the rate in production than ceramic AZO
Price will be < 50% current ceramic based costs * Szyszka et al
Different sensor control modes possible for reactive AZO via feedback controller
Penning-PEM O2 gas
Lambda
Target V
ProcessPEM
Basic process parameters for all depositions
ZnAl: 152 mm diam x 475 mm L AC-MF: 5.3 kW (Huettinger) Ar press.: 3E-03 mbar
target rotation speed: 5 rpm Substrate static T/S: 95 mm Temp: Room Temp. Dep. Time: 10 mins
Comparison of deposition rates for reactive and ceramic and DLIM/BOC magnetics Under conditions for optimum layer properties
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)
500 450
400 deposited thickness
350 300 250 200 150 100 50 0 Deposition conditions
Comparison of electrical properties for ceramic AZO, standard (BOC) & DLIM without substrate heating and AC power
Comparison of 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) 1.00E+00 0
2
4
6
8
resistivity, Ohm-cm
resistivity AZO DLIM (RT)
1.00E-01 resistivity AZO DLIM (150 deg C)
1.00E-02
1.00E-03
1.00E-04 Sample position
10
12
Comparison of electrical properties for ceramic and DLIM for optimized layers without substrate heating and with AC power Resisitivity DLIM (reactive and ceramic AZO) at room temperature (static coating every 25 mm under double magnetron cathodes) 1.00E+00
resistivity, Ohm-cm
0
2
4
6
8
10
1.00E-01
1.00E-02
1.00E-03 resistivity AZO DLIM (RT)
1.00E-04
resistivity reactive DLIM
Sample position
12
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
resistivity BOC resistivity DLIM
1.00E-02
1.00E-03
1.00E-04 Sample position
AZ+O2 film properties at Room Temperature and 150ºC with similar properties
R09 (at RT) and R17(at 150 deg C) 3000
1.00E+00
2500 2000 1500
1.00E-02 Log scale
1000 1.00E-03 500 0
1.00E-04 0
2
4
6
8
sample (every 25 mm)
10
12
Ohm-cm
Thickness, nm
1.00E-01 t (at 150ºC) t (at RT) r (at 150ºC) r (at RT)
Room temperature films have better optical density with DLIM magnetics
Optical Density at 550nm & Resistivity for R09 (at RT) and R17(at 150 deg C) 0.2
1.00E-02
0.16 0.14
1.00E-03
0.12
Log scale
0.1 0.08 1.00E-04
0.06 0.04 0.02 0
1.00E-05 0
2
4
6
8
sample (every 25 mm)
10
12
Ohm-cm
Optical Density at 550nm
0.18
od (at 150ºC) od (at RT) r (at 150ºC) r (at RT)
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+O2 transmittance in the visible spectrum good low temp transparency
T(%) R09 (at RT) and R17 (at 150ºC) 120 T(%) R09
Transmission
100
T(%) R17
80
Coating thickness ~ 2.4 µm
60 40 20 0 325
525
725 wavelength, nm
925
For ITO & other sputtered TCO’s low damage on hot surfaces provide best quality Crystal structure and doping is critical for all TCO’s
Resistivity change with target voltage and substrate temp. (see reference 2)
Resistivity (x 10-4 Ohm.cm)
11 10 9 8 7 6 5 4 3 2 1 0
-400 V
-250 V
-110 V
0
100
200
300
Substrate Temperature C
400
500
Jumbo Glass, TCO film property tuning using ‘Speedflo’ reactive sputtering controller with a dual rotatable magnetron
160
90
140
80
120
70 60
100
50
Optimised
80
Development
40
60
30 Sheet resistance Transmission
40
20
20
10
0
0 38
40
42
44
46
O2 Set-point (%)
48
50
52
Transmission (%)
Sheet resistance (ohms)
InSn+O2 using Speedflo control for reactive production of ITO
Reactive ITO comparison of conventional magnetic design and DLIM with AC power mode
1.20E-03
1.00E-03
Resistivity Ohm/cm
8.00E-04
6.00E-04 DLIM RESISTIVITY BOC RESITIVITY 4.00E-04
2.00E-04
0.00E+00 0
1
2
3
4
5
6
7
Sample position every 25mm
8
9
10
11
Reactive ITO comparison of conventional magnetic design and DLIM with AC power mode at 150̊ C
1.00E-02
0
1
2
3
4
5
6
7
8
9
10
Resistivity Ohm/cm
DLIM RESISTIVITY BOC RESISTIVITY
1.00E-03
1.00E-04
11
Reactive ITO with DLIM, AC power mode and varying substrate temperature
9.00E-04
Resistivity, Ohm.cm
8.00E-04
7.00E-04
6.00E-04
5.00E-04
4.00E-04
3.00E-04 0
1
2
3
4
5
6
7
8
9
10
DLIM resistivity 80 degrees C
DLIM resistivity 120 degrees C
DLIM resistivity 150 degrees C
DLIM resistivity 180 degrees C
11
Parameters for ITO Ceramic Tests
• For ITO from ceramic targets several process parameters affect the electrical conductivity of the ITO film: • Standard strength magnetics – 520 Gauss over target surface, average target voltage 370 Volts • Deposition power 2.5kW per target – 2 targets – total 5 kW • Target to substrate separation 10cm & 15cm • Deposition time 30 sec – static substrates • Average ITO film thickness 130-140nm • Ar & O2 gas flow – introduced at central and / or outer gas bars • Central magnetically guided anode varied from earthed, floating and +15 V. • Angle of the magnetic to the anode varied from 0, 30, 60 & 90̊ • Substrate temperature – RT 20̊C, 180̊ C.
Ceramic ITO with DLIM – TCO (active anode, DC power mode and room temperature substrate (no heating)
Resistivity Ω.cm
1.0E-02
1.0E-03
DC DC Pulsed 1.0E-04
Ceramic ITO rotatable, Active Anode +15V, Room Temp. Substrate, no O2 gas
Ceramic ITO with DLIM – TCO (active anode +15v, 0, floating, DC power and room temperature substrate (no heating)
Ceramic ITO rotatable, Active Anode +15V & 0V, Room Temp. Substrate, no O2 gas, pure DC target power
Resistivity Ω.cm
1.0E-02
1.0E-03
Anode Floating Anode Grounded Anode +15V 1.0E-04
Ceramic ITO with DLIM – TCO (active anode +15v, varying DC modes and room temperature substrate (no heating)
Ceramic ITO rotatable, Active Anode +15V, Room Temp. Substrate, no O2 gas, Pulsed DC Power Variation
Resistivity Ω.cm
1.0E-02
1.0E-03
50kHz pulsed DC 100 kHz pulsed DC Pure DC Power 1.0E-04
Ceramic ITO with DLIM – TCO (active anode +15v, DC power modes and varying gas mixtures (no heating)
Ceramic ITO rotatable, Active Anode +15V, Room Temp. Substrate, no O2 gas, Pulsed DC Power Variation
Resistivity Ω.cm
1.0E-02
1.0E-03
zero O2 added, 50 kHz pulse 2.5% O2 added 1.0E-04
2% O2 added Pure DC Power 2% O2 added, 100 kHz pulsing
Ceramic ITO with DLIM – TCO (active anode +15v & FL, DC 50kHz pulse and varying gas modes (no heating)
Ceramic ITO rotatable, Active Anode, Room Temp. Substrate, Variable Gas Pulsing, Pulsed DC 50kHz
Resistivity Ω.cm
1.0E-02
1.0E-03
10 sccm constant gas, anode+15V 2.5 - 10 sccm pulsed gas profile, anode +15V 1.0E-04
1.25 - 5 sccm gas pulsing, anode +15V 1.25 - 5 sccm gas pulsing, anode floating
Ceramic ITO with DLIM – TCO (active anode +15v & 0v, DC 50kHz pulse and varying magnetics tilt angle (no heating)
Ceramic ITO rotatable, Active Anode Variation, Room Temp. Substrate, Variable Tilt Angle, Pulsed DC 50kHz, 2-3% O2 constant flow
Resistivity Ω.cm
1.0E-02
1.0E-03
Zero mag bar tilt, anode earthed zero mag bar tilt, anode +15V 1.0E-04
30 deg mag bar tilt, anode earthed
Conclusions ITO Ceramic so far
• For ITO from ceramic targets several process parameters affect the electrical conductivity of the ITO film: • Average resistivities of 5 x 10-3 to 4.6 x 10-4 Ω.cm can be achieved on room temperature substrates depending upon process parameters • Power mode – 50kHz DC optimum compared to pure DC or 100kHz • Gas Injection position – more tests needed for conclusions • Anode Bias - +15V best but earthed also good • O2 gas flow – optimum needed for transparency and electrical properties – gas pulsing can reduce resistivity peaks • DLIM produces lower substrate heating • DLIM TCO magnetics (with anode) lowers resistivity • Under optimum conditions high resistivity peaks can be eliminated • More tests are needed to achieve close to the best parameters and explore all possibilities
Conclusions AZO Acknowledgements • For AC rotatable pairs the DLIM linked magnetic design improves the electrical properties of an AZO based TCO for both ceramic and reactive processing routes. • 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 and energy savings. • Reactive ITO is optimised with DLIM magnetics and elevated substrate temperatures with a plasma interaction effect varying with temperature. • Reactive ITO displays low resistivity with AC power • Special thanks to Heraeus for providing AZO and Zn:Al targets and to the Indium Corporation of America for the In:Sn target.
