reliable double printing of ag contacts for c-si applied ...€¦ · 3 applied materials / external...
TRANSCRIPT
Applied Materials / External Use
Reliable double printing of Ag contacts for c-Si cell manufacturingM. Galiazzo
Apr,14th 2010 - Secondmetal Workshop Konstanz
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Applied Materials / External Use
Outline
1. Double Printing principle2. Experimental results of DP
wafers processed at Baccini lab and Helios production
3. Experimental results of DP in production
Solar cell manufacturing
Cell characterization and metrology
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Applied Materials / External Use
Double Printing vs. Single Printing
Al-BSF
Si bulk
P diffusion
SiN
Front Ag
SP and DP cell design
100-110um
15-20um 25-35um
70-80um
Target: reduce finger width and increase finger thickness Standard up-front process flow Compatible with existing production lines (3 + 1 printers)
Isc ↑ ↑, Rs==, FF==, eta ↑ ↑
B.Raabe et al, 20°EUPVSEC Barcelona 2005
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Applied Materials / External Use
DP Simulation
Screen design optimizationmodel inputs– Finger width/thickness, nr
– Emitter Rsheet
– Paste conductivity– Contact resistance
Output eff, FF, Isc Model predicts 0.27/0.3 abs eff
increase from SP with110um/15um to DP with80um/25um depending on finger nr
Finger width ↓↓, thickness↑↑, more fingers required to keepsame FF and eff
Eta vs. Finger nr / Finger width
15.80%
15.90%
16.00%
16.10%
16.20%
16.30%
16.40%
16.50%
15 25 25 25 25
110 90 80 70 60Finger thickness (um)
Finger width (um)E
ta (%
)
69 fingers
78 fingers
87 fingers
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Applied Materials / External Use
DP test 1
Test 90 cells/lot
3 busbars
SP 69 finger, 80um stdmesh screen opening, paste A
DP 65 finger, 80um+80um Esatto Technology ® qualifiedscreen, paste A+A
0.12 abs eff increase -9% paste for DP Model exp 0.115 abs eff
increase for DP
width (um)
thickness (um) aspect ratio
weight (mg) Pmpp (W) Umpp (V) Impp (A) Uoc (V) Isc (A)
Rs (mOhm)
Rsh (Ohm) FF (%) eta
SP paste A 109,1 27,7 0,25 212,0 3,896 0,519 7,505 0,619 8,003 0,0025 122,6609 78,69 16,01DP paste A+A 95,7 38,5 0,40 193,0 3,925 0,518 7,575 0,620 8,075 0,0027 114,5429 78,44 16,13difference -13,4 10,8 0,15 -19,0 -0,3 0,12
SP vs. DP design 1
16.01%
16.13%109.1
95.7
27.7
38.5
15.94%
15.96%
15.98%
16.00%
16.02%
16.04%
16.06%
16.08%
16.10%
16.12%
16.14%
SP paste A DP paste A+A
eta
0.0
20.0
40.0
60.0
80.0
100.0
120.0
Wid
th, t
hick
ness
(um
)
etawidth
thicknessLinear (eta)
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Applied Materials / External Use
DP test 2 – Optimized screen design
3 busbars screen design 65Ohm/sq emitter
Group 1: SP 69 fingers, 80um stdmesh screen, paste A
Group 2: DP 69 fingers, 60um+50um Esatto Technology qualified screen, paste B+B
Group 3: DP 69 fingers, 60um+60um Esatto Technology qualified screen, paste A+A
80um
60um
50um
60um
60um
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3)
80um
60um
50um
60um
60um
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80um
60um
50um
60um
60um
4 5
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2)
3)
156mm multi wafers - Helios
Texturing - Helios
POCl diffusion - Helios
PSG etch - Helios
SiN ARC - Helios
Front side DP – BCS lab
Back side print - Helios
Firing - Helios
Laser isolation - Helios
Testing – Fraunhofer ISE
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Applied Materials / External Use
DP test 2 – Contact resistance
TLM contact resistance analysis performed on 2 cells of each group
Low difference in ρc values between groups(due to different finger widths)
Group 1 shows lowest contact resistance RC
Group 1 shows lowest specific contact resistance ρc
+ / - %Rsh [ ΩΩΩΩ/sq] 67,7446 0,1219 0,2ρρρρc [ ΩΩΩΩcm 2] 0,0023 0,0002 8,5
Rc [ ΩΩΩΩ] 0,4885 0,0336 6,9Rc w [ ΩΩΩΩcm] 0,4885 0,0343 7,0
8597124 TLM sample 1
+ / - %Rsh [ ΩΩΩΩ/sq] 65,6175 0,2324 0,4ρρρρc [ ΩΩΩΩcm 2] 0,0030 0,0005 15,4
Rc [ ΩΩΩΩ] 0,8339 0,1051 12,6Rc w [ ΩΩΩΩcm] 0,8339 0,1064 12,8
8597124 TLM sample 2
+ / - %Rsh [ ΩΩΩΩ/sq] 62,4937 0,1314 0,2ρρρρc [ ΩΩΩΩcm 2] 0,0013 0,0003 21,1
Rc [ ΩΩΩΩ] 0,2902 0,0459 15,8Rc w [ ΩΩΩΩcm] 0,2902 0,0463 16,0
8597046 TLM sample 1
+ / - %Rsh [ ΩΩΩΩ/sq] 63,4412 0,1434 0,2ρρρρc [ ΩΩΩΩcm 2] 0,0028 0,0003 9,8
Rc [ ΩΩΩΩ] 0,6521 0,0535 8,2Rc w [ ΩΩΩΩcm] 0,6521 0,0545 8,4
8597046 TLM sample 2
+ / - %Rsh [ ΩΩΩΩ/sq] 66,5400 0,1744 0,3ρρρρc [ ΩΩΩΩcm 2] 0,0025 0,0004 16,2
Rc [ ΩΩΩΩ] 0,6957 0,0714 10,3Rc w [ ΩΩΩΩcm] 0,6957 0,0725 10,4
8618630 TLM sample 1
+ / - %Rsh [ ΩΩΩΩ/sq] 63,5825 0,1871 0,3ρρρρc [ ΩΩΩΩcm 2] 0,0030 0,0006 18,5
Rc [ ΩΩΩΩ] 0,7852 0,0804 10,2Rc w [ ΩΩΩΩcm] 0,7852 0,0816 10,4
8618630 TLM sample 2
Group1
ρc= 2 ± 0.8 mΩcm²
Group2
ρc= 2.6 ± 0.3 mΩcm²
Group3
ρc= 2.8 ± 0.3 mΩcm2
80um
60um
50um
60um
60um
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80um
60um
50um
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60um
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80um
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Applied Materials / External Use
DP test 2 – CoRRescan map
Group 3:
Medium quality of contact/emitter
Homogeneous potential drop
Very high local potential drop (corner)
Average potential: 6.2 mV
Maximum potential: 152.3 mV
Group 1 (:
High quality of contact/emitter
Homogeneous and low potential drop
Average potential drop: 4 mV
Maximum potential drop: 44.4 mV
Group 2:
Medium/low quality of contact/emitter
Rather Inhomogeneous potential map
High local potential drops
Average potential drop: 7.1 mV
Maximum potential drop: 50.3 mV
80um
60um
50um
60um
60um
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80um
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50um
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60um
50um
60um
60um
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Applied Materials / External Use
DP Test 2 - R s-PL Measurements
Group 3:
More Inhomogeneous apperance than 2
Firing belt visible
No clear side effects visible
Edge effects visible
Group 1:
Rather homogeneous
Some finger interruptions
Edge effects visible
Group 2:
Inhomogenous appearance
Firing belt visible
Right side of wafers higher resistance
Edge effects visible
80um
60um
50um
60um
60um
4 5
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1)
2)
3)
80um
60um
50um
60um
60um
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80um
60um
50um
60um
60um
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Applied Materials / External Use
Group1
Group2 Group3
DP test 2 – Finger morphologyWaferGroup Width Thickness Aspect Weight
(um) (um) Ratio (g)1 91,8 21,6 0,24 0,1852 76,3 23 0,30 0,173 74,7 26,9 0,36 0,16
Final Dried Print
80um
60um
50um
60um
60um
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80um
60um
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Group 2: -8% paste consumptionGroup 3: -14% paste consumption
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Applied Materials / External Use
DP test 2 – Electrical data
16,1
16,2
16,3
16,4
16,5
16,6
16,7
16,8
16,9
2 3
1 single printing 2 double printing A 3 double printing B
η in
%
Cell group1
77,6
77,8
78,0
78,2
78,4
78,6
78,8
2 3
1 single printing 2 double printing A 3 double printing B
FF
in %
Cell group1
33,4
33,6
33,8
34,0
34,2
34,4
34,6
34,8
35,0
2 3
1 single printing 2 double printing A 3 double printing B
J SC in
mA
/cm
2
Cell group1
0,50
0,55
0,60
0,65
0,70
0,75
0,80
0,85
0,90
2 3
1 single printing 2 double printing A 3 double printing B
RS in
Ωcm
2
Cell group1
80um
60um
50um
60um
60um
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60um
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80um
60um
50um
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1)
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3)
Jsc +0.4/0.5mA/cm2 - reduced shadingFF -0.2/-0.5% - reduced RsVoc +1.5/3mV – reduced contact area and J 0
Measured @ Fraunhofer ISE
Cell group
Voc Jsc Eta FFSserLfDfI
EC[mV] [mA/cm²] [%] [%] [Ω*cm²]
1 614.3 33.95 16.34 78.34 0.632 617.6 34.34 16.57 78.14 0.723 615.8 34.53 16.56 77.88 0.76
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Applied Materials / External Use
DP test 2 – Results
…starting from an aggressive finger geometry for single printing baseline(92um x 22um, aspect ratio 0.26)
…achieved an aspect ratio in DP of 0.3-0.36 Group 2: 0.23% eff increase with -8% paste Group 3: 0.22% eff increase with -14% paste Other customer demos at BCS lab show eff increase betwee n 0.2%
and 0.35%
Developments Demonstrated aspect ratio in DP of 0.5 (35um x 70um)
Create cells with this finger geometry for improved eff gain
From the LAB to the FAB…
13
Applied Materials / External Use
DP production – 12” screen
12”, 90um + 90um Esatto Technology qualified screens 125mm, mono wafers Commercial paste for SP
20k prints (1 day)
Avg 0.2-0.25% eff increase for DP Optimized print process
Production monitor 12"
60,070,080,090,0
100,0110,0120,0130,0140,0
0 5000 10000 15000 20000
Production
Fin
ger
wid
th (
um)
17,5
17,6
17,7
17,8
17,9
18
18,1
18,2
Effi
cien
cy (%
)
double print widthefficiency
DP avg eff17.91%
SP avg eff17.7%
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Applied Materials / External Use
DP production – 15” screen
15”, 90um + 90um Esatto Technology qualified screens 125mm mono wafers Commercial paste for SP (not optimized) Production monitor 105k cells (4 continuative days) Check for screen deformation/wear leading to misalignment Screen change when avg finger width for DP exceeds 125um or mechanical
breakage Optimized print process
Production monitor DP 15"
60,0
70,0
80,0
90,0
100,0
110,0
120,0
130,0
140,0
0 20000 40000 60000 80000 100000
Wafer production
Fin
ger w
idth
(u
m)
17,5
17,6
17,7
17,8
17,9
18
18,1
Effi
cien
cy (
%)
double print width
efficiency
30000 >90000
52000 48000print1
print2
DP avg eff
SP avg eff
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Applied Materials / External Use
Conclusion / Next steps
Demonstrated 0.23% abs eff increase for DP with significant paste saving using Esatto Technology qualified consumables (starting froman aggressive SP baseline)
Consistent agreement between simulation and experimental data Further optimization leads to >0.3% abs eff increase (already
achieved with customer demos) LAB results already transfered successfully to the production floor Achieved high screen stability under optimized printing conditions Available inline process monitoring and closed loop operation
Paste optimization, expecially for high conductivity layer Demonstrate benefit of DP at module level Testing fine line DP cells (35um x 60-70um) Demonstrate DP over Selective Emitter with Esatto Technology
16
Applied Materials / External Use
Thanks for your attention!
Dec ‘09 March ‘10