Post on 14-Feb-2021
Cracker valve and plasma control process for reactive sputtering with Selenium & Sulphur
Dr. Iván Fernández-Martínez, Ambiörn Wennberg
Fernando Briones
Raquel Gonzalez, Pedro Melgar
Victor Bellido-González, Dermot Monaghan, Benoit Daniel, Joseph Brindley , Gencoa Ltd, UK
Other activities include on-site process implementation, training and tuning
GENCOA current products cover 3 sputtering related areas
Reactive gas controller & endpoint detector
Linear ion sources
planar & rotatable Magnetron Sputter
Cathodes and Magnetic Systems
• Introduction to reactive sputtering • Existing CIGS processing routes and one system concept • Feedback control and cracker design •Reactive sputtering of sulphur and selenium based layers with Cu, In & Zn target materials • Conclusions
NREL
Structure of presentation
Reactive Sputtering is highly unstable, but advanced control makes widespread
production process in many sectors
Reactive gas input
To pumps
Layer creation
Sp
utter T
arg
et
Process Sensors
Process controller
Objective is to bring established high volume flexible process
to delivery of calcogens for CIGS layers
Key technology requirement in order to implement this is the delivery of the solid Se & S species to the reactive process environment at high speed - in the vapor phase - main topic of this presentation.
The attraction of the reactive sputtering route has been recognised and
several companies have sought success
Mo
CIG(S,Se)
CdS or ZnS
ITO , AZO Solyndra, Miasole, Daystar have all pursued and implemented the reactive sputtering method, but due to technical and commercial challenges all have failed.
Older more established technologies of evaporation and sputtering with a 2nd stage selenization and sulphurization have won out – FOR NOW!
But it is accepted that the existing technologies cannot approach the
theoretical maximum efficiencies of 30%
In order to achieve the higher efficiencies total flexibility to readily change layer compositions and layer combinations with a reliable process is required.
A pure sputter based approach can achieve this so long as the current challenges of the Se and S delivery are overcome. I ‘believe’ that the biggest technical challenge that faced Solyndra, Daystar and possibly Miasole, was lack of good control of the Se and S gas combined with lack of a fast feedback and precise dosing method.
Cracker zone - Up to 850°C Homogeneous gas delivery Corrosion resistant parts
Evaporation zone – RT to 550°C Temperature control ±0.1°C Corrosion resistant parts Large capacity deposit
Hermetic fast actuating valve
• Fluxes from 20 msec • Flux rate up to 15 Hz • complete flux shut-off
Principle of the gas delivery units – pulsed cracker valve – patent pending
Operation principle: pulsed mode
0 1 2 3 4 5 6 7 8 90
20
40
60
80
100
120
Se
flu
x (
A/s
ec
)
Pulsing frequency (Hz)
20ms
40ms
100ms
Aperture time
Time OFF
Flux ON
Time ON
Flux OFF
Test setup – 2 x planar magnetrons 0.5m long with MF power
Effusion cell cracker for reactive gas injection
Response of the valve and target condition with varying pulse widths
Time OFF
Flux ON
Time ON
Flux OFF
100ms : 1Hz
400ms : 1Hz
Valve actuator
Target voltage response
Video of plasma appearance with Se pulse gas input
Plasma optical emission spectrum with pure copper (inlaid graph) & with Cu
combined with Sulphur (main graph)
Cu I
510.5 nm
515.3 nm
521.8 nm
200 400 600 800 10000
2x104
4x104
6x104
Inte
nsity (
a.u
.)
Wavelength (nm)
500 520 540
6x103
1x104
2x104
Inte
nsity (
a.u
.)Wavelength (nm)
Having a fast and stable Se & S delivery system completes the cycle required for
total control of the process
SENSOR INPUTS
ACTUATOR OUTPUT
REACTIVE GAS INJECTION
Hysteresis ramps: P.E.M.
0 500 1000 1500 20000
2
4
6
8
10
Va
lve
fre
qu
en
cy (
Hz)
Time (s)
0
20
40
60
80
100S
en
so
r (%
)
Fully poisoned
‘Metal’
Sulphur flow (valve duty cycle)
Transition regime
λ Sensor (CCD)= 510.8nm (Cu)
Hysteresis ramps: P.E.M. & target voltage, displays classic reactive sputtering
behaviour which indicates needs feedback control
0
20
40
60
80
100
Se
nso
r (%
)
500 1000 1500 2000 25000
2
4
6
8
10
Va
lve
fre
qu
en
cy (
Hz)
Time (s)
Fully poisoned
Sulphur flow
(valve duty cycle)
Sensor (CCD)= 510.8nm (Cu)
570
600
630
660
690
Ta
rge
t p
ote
ntia
l (V
)
0 500 1000 1500 20000
2
4
6
8
10
Va
lve
fre
qu
en
cy (
Hz)
Time (s)
Sulphur flow
(valve duty cycle)
0
20
40
60
80
100
SetPoint (%)
Sensor (%)
Sensor
(%)
720 740 760 780 800 820 840
0
20
40
60
Actu
ato
r (%
)
Time(s)
Actuator (%)
Example of Selenium flow adjustment via feedback control of the pulsed
cracker valve by plasma emission sensing of Se
Active feedback control – changing set-points and controlling compositions at
different levels to demonstrate control
20
40
60
80
SetPoint (%)
Sensor (%)
Sensor
(%)
300 400 500 600 700 800
0
20
40
Actu
ato
r (%
)
Time(s)
Actuator (%)
80% 60% 40% 80%
SetPoint
Cu rich S poor
Cu poor S rich
-15 -10 -5 0 5 10 150
100
200
300
400
500
600
700
800
Position (cm)
Cu+S
Th
ickn
ess (
nm
)
-15 -10 -5 0 5 10 150
25
50
75
100
S
Cu
C
om
po
sitio
n (
at
%)
Position (cm)
Thickness and composition distribution for a Copper Sulphide
combination of materials
Example of reactively sputtered CuInGaSe2 structure - No serious
layer or cell development to be performed
300 350 400 450 500
Inte
nsity (
a.u
.)
Wavelength (nm)
Zn
Cu
In
Zn In Cu
Plasma emission spectrums for In, Cu & Zn in the presence of Sulphur
In / S
10
20
30
40
50
60
70
80
90
100
Se
nso
r (%
)
500 1000 1500
0
2
4
6
8
Va
lve
fre
qu
en
cy (
Hz)
Time (s)
550
600
650
700
750
800
Ta
rge
t p
ote
ntia
l (V
)
λ Sensor (CCD) = 451.7nm (In) Target potential
Hysteresis ramps: P.E.M. & target voltage for the Indium & Sulphur system
In
Indium target (In) + Sulphur (S) – target displays classical
transition mode appearance
In2S3 deposition
In2S3 In2S3:V 20 40 60
0
200
400
Co
un
ts (
a.u
.)
2
(103)
(203)
(206)
(318) (103)
Tetragonal -In2S3 on glass at 250ºC
20
40
60
80
Se
nso
r (%
)
λ Sensor (CCD) = 307.4nm (Zn)
Target potential
Zn / S
400 800 1200
0
3
6
Va
lve
fre
qu
en
cy (
Hz)
Time (s)
600
640
680
Ta
rge
t p
ote
ntia
l (V
)
Hysteresis ramps: P.E.M. & target voltage for the Zinc & Sulphur system
The control process is good and rotatable magnetrons are better for
cleanliness and productivity
• A rotating target is self-cleaning so is an easier process to control compared to planar type targets
• Rotating targets offer higher rates and longer lifetimes
• CuGa, CuIn, CuInGa, In, Zn rotatable targets are readily available
• A fast feedback process for reactive sputtering of several layers in a CIGS cell has been shown
• CuInGa, Zn, In elements can be combined with both S and Se with a high degree of control and in varying combinations
• This technology makes the highly developed graded structures possible that will be required to improve cell efficiency
• The 2nd stage selenization / sulphurization can be removed
• A single stage purely sputtered cell is readily achievable with non-reactive and reactive sputtering
General Conclusions
References attributed to Niki et al, Prog. Photovolt. Res. Appl. 2010 18 453-466
Employment opportunities exist at Gencoa for people with good
scientific backgrounds or with plasma knowledge.
Victor Bellido-González
Dermot Monaghan
Benoit Daniel
Joseph Brindley
Fernando Briones
Ambiörn Wennberg
Ivan Fernandez
Thank you for listening and acknowledgments
Raquel Gonzalez, Pedro Melgar