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Combined PECVD Process Sensors
in Thin Film Silicon-Based
Solar Cell Manufacturing
Onno Gabriel1, Lutz Eichhorn2, Bernd Stannowski1,
Michael Klick2, Rutger Schlatmann1
1 PVcomB, Helmholtz-Zentrum Berlin, Germany2 Plasmetrex GmbH, Berlin, Germany
13th European Advanced Process Control and Manufacturing Conference
Hilton Dresden Hotel, Germany - April 15-17, 2013
Competence Centre Thin-Film- and Nanotechnology
for Photovoltaics Berlin
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 20132
PV Market Growth
� > 5% PV contribution to electricity in Germany.
� c-Si technology „made in China“ @ 14-15 % module efficiency is
dominating.
� Competitiveness for large PV systems in southern Europe is reached.
30 GWp
= 215 Mio m2
(Source: EPIA)
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 20133
PV Manufactoring Costs
� Manufactoring costs are driven towards 0.5 $/Wp
� Due to lower efficiency of thin film PV modules (10-14% vs. 14-
15%) even lower cost are required („BOS penalty)
Source: Ch. Breyer et al.
EUPVSEC 2011
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 20134
Plasma Processes in Photovoltaic Industry
Material Functional Thin Films Deposition techniques
Front contact TCOs: ZnO, SnO2, ITO Sputtering, CVD
Absorber material a-Si:H, µc-Si:H,
p- und n-doped layers
low-pressure PECVD
Contact layers Al, Ag Sputtering, Evaporation
Interface layers TCOs, a-SiC:H, a-SiO:H low pressure PECVD
Passivation layers Si:N low pressure PECVD, ETP
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 20135
Thin Film Silicon Solar Cells
Sputter Line A600 V7 Leybold Optics
PECVD clusterAKT1600 Applied Materials
glass
TCO
a-Si:H
(top cell)
µc-Si:H
bottom cell)
ZnO:Al
Al
encapsulation
foil
glass
3 m
m3
mm
3 µ
mSun light
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 20136
Si BaselineSi Baseline
CIGS BaselineCIGS Baseline
Mo sputtering
back contact
P1 laser scribe
Cu/In /Ga
sputtering
Cleaning
Se evaporation
RTP
Chemical Bath
Deposition CdS/KCN
P3 scribing
ZnO: i-ZnO
sputtering front contact
Glass cleaning
P2 scribing
Cleaning
Etching
Encapsulation
TCO coated glass
PVcomB: Two Reference Lines for 30 x 30 cm2 Modules
Cleaning
P1 laser scribe
P2 laser scribing
P3 laser scribing
Glass substrates
ZnO/Ag sputtering
back contact
ZnO:Al sputtering
front contact
Silicon PECVD
Sputter Line A600 V7 Leybold Optics
PECVD clusterAKT1600 Applied Materials
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 20137
PECVD Tool AKT1600A (Applied Materials)
AKT 1600A
cluster tool
ChA
ChBLoad
lock
ChD
� Three chamber PECVD cluster tool,
� Substrate size 30 x 30 cm²,
� fully automatic processing of up to 6
substrates per load.
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 20138
Customized PECVD Chamber Window
Connector NEED Sensor View port OES
Outside
Side view
Inside
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 20139
In situ Diagnostics at AKT Process Chambers
� Optical Emission Spectroscopy (OES)
� Non-linear Extended Electron Dynamics (NEED)
� Mass Spectrometer / Residual Gas Analyzer (RGA)
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 201310
Optical Emission Spectroscopy (OES)
200 300 400 500 600 700 8000
100
200
300
400
500
600
700
800
µc-Si:H BCi deposition
a-Si:H BCn deposition
Si
Si
Si
SiH
Hβ
Inte
nsity (
a.u
.)
Wavelength (nm)
H2 fulcher
Hα
400 500 600 700 800 900 10000
500
1000
1500
2000
F
F
F
N2
N2
Process start
Process end
F
N2
N2
NF
N2
Inte
nsity (
a.u
.)
Wavelength (nm)
NF3 plasma clean
Species Transition Wavelength
Si 3s23p2 – s23p4s 288.3 nm
SiH X2Π – A2Δ 409 – 422 nm
Hα n=3 – n=2 656.3 nm
Hβ n=4 – n=2 486.1 nm
H2 2s3Σ+g – 3p3Π−
u 570 – 640 nm
F 2s22p4(3P)3s -
2s22p4(3P)3p
703.7 nm
F 2s22p4(3P)3s -
2s22p4(3P)3p
624.0 nm
Ar 3s23p4(3P)4s -
3s23p4(3P)4p
496.5 nm
Deposition
Chamber Clean� Relative densities of
electronically excited atoms and
small molecules (radicals).
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 201311
Mass Spectrometry / Residual Gas Analysis (RGA)
µc-Si-i
a-Si-H BCn
SiHx
47SiF
Hx
67SiHF2?44CO244SiCH6?
48SiHF?49SiH2F?
16O
14N
19F
20HF
18H2O
21?
89?
Si2Hx
85SiF3
Si2Hx
SiF3
44CO2
48SiHF49SiH2F16O
14N
18H2O34PH3
19F20HF
47SiF
SiHx
Hx
89?
� Relative densities of stable
atoms and molecules after
ionization/dissociation in the
QMS.
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 201312
Nonlinear Extended Electron Dynamics (NEED)
Source: Plasmetrex GmbH
RF discharge: Equivalent circuit
-0.05
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
0.04
0.05
0 36.87 73.74 110.61 147.48
Time (ns)
Current @ sensor (a.u.)
Voltage @ generator (a.u.)
NEED raw data
Pump
νeff - collision rate
ωgen - generator frequency
ωe - electron/plasma frequency
ne - electron density
Plasma resistivity = νeff ωgen
ωe (ne)2
(basically the collision rate
over electron density)
Resonance frequency of the total system depending on the bulk inductance Lp , the sheath capacitances
Cs and the inductance of the electrode system/chamber LC. (all directly depending on electron density, chamber design and
gap between electrode and substrate)
1
2
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 201313
Data Management and Analysis
NEED
OES OES
spectra
Logfiles, Recipes
Mass
spectra
ChARGA
ChB
NEED
data
Sun
Workstation
Input
folder
PVcomB Data Server:
Scripts
MySQL
data base
Web
Server
Desktops,
Laptops
Desktops,
Laptops
LL
ChD
AMAT
cluster tool
Other Processes
+ Cell/Module
Analytics
AKT Process Data Base (03/2013):
� 101,000 AKT process steps
� 28 Mill. AKT parameters
� 2.5 Mill. OES spectra
� 1 Mill. mass spectra (RGA)
� 6 Mill. NEED data points
Desktops,
Laptops
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 201314
�What process parameters
influence the quality of deposited
thin films and, thus, the solar cell
performance?
�Methods for PECVD process
monitoring?
Process parameters
Thin film growth process
Solar cell performance
Plasma properties
✓
✓
?
?
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 201315
Substrate / Surface / Plasma
Temperatures
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 201316
Glass substrate
Substrate / Surface / Plasma Temperatures
Electrode / Susceptor
(Temperature stabilized)
Heat
transfer
Plasma
1 µm
3 mm
4-5 cm
Higher plasma gas temperature result in a
higher surface temperature Tsur depending
on the thickness of glass substrates [1].
[1] S. Nunomura, M. Kondo and H. Akatsuka, Plasma Sources Science and Technology 15 (2006) 783-789
Thin film
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 201317
Process Monitoring: µc-Si:H Absorber Layers
RF power (W)
H2 gas flow (sccm)
Tsub (°C)
controlled by PECVD recipe
automatic AKT control loop
(three different PECVD runs)
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 201318
Impact of Process Parameters on OES Signals
OES: Hα line (a.u.)
� higher SiH4 conc.
→ higher ne density,
→ more excitaWon, more
emitted light.
� OES oscillations correlated
with Tsub → changes in gas
density due to temperature
oscillations.
� Ratio between emission lines
constant.
H2 gas flow (sccm)
Tsub (°C)
OES: Hα / Hβ (a.u.)
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 201319
Impact of Process Parameters on NEED Signals
H2 gas flow (sccm)
Tsub (°C)
NEED: Plasma Resistivity (a.u.)
NEED: Resonance Frequ. (MHz
νeff ωgen
ωe2 ~
νeff
ne
� same trend: higher SiH4 conc.
→ higher ne density,
→ changes in gas density due
to temperature oscillations.
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 201320
Impact of Substrate Temperature on NEED Data
� NEED data measured during the
deposition of 25 different a-Si:H i-layers.
� Substrate temperature Tsub varied
between 190 and 220°C
� The plasma resistivity follows the
expected trend, i.e. ~1/Tkin:
plasma resistivity ~
collision rate νeff ~ gas density n
gas density n ~ pV/(kBTkin)
→ plasma resisWvity ~ 1/Tkin
y = 3672.2x-1.081
10.0
10.5
11.0
11.5
12.0
12.5
13.0
13.5
170 180 190 200 210 220 230 240
NE
ED
: Pla
sma
Re
sist
ivit
y
Tsub (°C)
y = -0.0006x2 + 0.2684x - 24.167
4
5
6
7
170 180 190 200 210 220 230 240
NE
ED
: Re
son
an
ce F
req
ue
ncy
(M
Hz)
Tsub (°C)
νeff ωgen
ωe(ne)2
High pressure / low RF power
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 201321
Chamber Cleaning & Conditioning
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 201322
NF3/Ar Chamber Clean
NF3 gas flow (sccm)
Ar gas flow (sccm)
Pressure (Torr)
RF power (W)
AKT logfiles
Ar (470 nm)
Hα (656 nm)
F (703 nm)
Hβ (486nm)
Optical
Emission
Spectroscopy
H2 (m = 2)
SiH2 (m=30)
SiF3 (m=85)
HF (m =20)
F (m=19)
NF3 (m=71)
Mass
Spectrometry
Ar/NF3 plasma clean (500s) Ar purge
2 31
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 201323
Ar/NF3 Chamber Clean
NEED: Resonance frequency (MHz)
NEED: Plasma resistivity (×10)
Pressure (Torr) Etch end points
(assumption):
- susceptor
- electrode
- entire chamber
2
3
1
Hα @ 656 nm (thick)
Hβ @ 486 nm (thin)
Ar @ 696 nm
F @ 703 nm
2 31
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 201324
Reproducibility Over Many Processes
� Chamber clean (NF3/Ar plasma) after p-layer deposition, data of 9 runs:P
lasm
a r
esi
stiv
ity
Re
son
an
cefr
eq
ue
ncy
(MH
z)C
ha
mb
er
pre
ssu
re(T
orr
)
(Black curve: different chamber history, 1st run of the day)
Pressure (Torr)
NEED: Plasma Resistivity (a.u.)
NEED: Resonance Frequ. (MHz
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 201325
Run-to-Run Stability
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 201326
Example I: TCi Layer Deposition @ 190°C / 220°CT s
ub (°
C)°
NE
ED
: P
lasm
a
resi
stiv
ity
NE
ED
: R
eso
na
nce
fre
qu
en
cy (
MH
z)
Tsub = 190°C
Tsub = 220°C
pib i layer
νeff ωgen
ωe (ne)2
n~ 1/Tkin~
Reproducibility: i Layer Depositions
� NEED parameters during i-layer deposition of 10 single junctions
in one single day:
14.0
14.2
14.4
14.6
14.8
15.0
15.2
15.4
Pla
sma
resi
stiv
ity
Deposition start
Deposition end
4.5
4.6
4.7
4.8
4.9
5.0
5.1
Re
son
ance
fre
qu
en
cy (
MH
z)
Deposition start
Deposition end
� Clear trend over the day –
temperature effect?
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 201328
Long Term Stability
NE
ED
: P
lasm
a
resi
stiv
ity
NE
ED
: R
eso
na
nce
fre
qu
en
cy (
MH
z)
Chamber A
Susceptor
Crash �
NEED data in Jan/Feb 2012 averaged during TCi layer deposition:
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 201329
Long Term Stability
NE
ED
: P
lasm
a
resi
stiv
ity
NE
ED
: R
eso
na
nce
fre
qu
en
cy (
MH
z)Susceptor
defectA
KT:
Tsu
b(°
C)
Susceptor
exchange
new temperature control loop
new susceptor grounding Source: Plasmetrex GmbH
Combined PECVD Process Sensors in Thin Film Silicon-Based Solar Cell Manufacturing European APCM 201330
Summary
� PECVD Process monitoring established and evaluated at PVcomB in a reference
line for silicon-based thin film solar cell manufacturing.
� NEED, OES and MS result in complementary data giving insights into the
deposition process.
� NEED is proven to be a reliable in-line monitoring tool.
Thank you for your attention!
This work was supported by the Federal Ministry of Education (BMBF) and the state
government of Berlin (SENBWF) in the framework of the program “Spitzenforschung
und Innovation in den Neuen Ländern” (grant no. 03IS2151) and by the BMBF and the
Federal Ministry for Environment, Nature Conservation and Nuclear Safety (BMU) in
the framework of the program “Innovationsallianz Fotovoltaik” (grant no. 0325317C).
PVcomB Research Network
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