Session II Galliazo 3rd Metallization Workshop

Paste B via plug
Thermo Gravimetric Analysis (TGA) to detect solid content, paste drying behavior Paste A (continuous line) solid content = 86.9%
Paste B (dotted) solid content = 87.4%
Critical Zones In Via-filling Print
1. High conductivity over the corner: adequate thickness 2. Low via hole resistance 3. No shunting on the front side: backside paste must cover the corner 4. No front side paste infiltration: hole completely capped 5. High lateral conductivity: sufficient paste deposition
Via plug
6
Applied Materials External Use
MWT Paste Analysis: TGA
Paste A via fill Weight [%]
Deriv. Weight [%/°C] Temperature [°C]
Applied Materials External Use
– MWT pastes rheological properties – paste comparison – Printing behavior
• Filling vs. vacuum setting
– Hole conductivity vs. paste filling
Alignment for MWT cells Preliminary cell results
Reduction of cell-module efficiency losses in module interconnection
– Less resistance, less fill factor losses
Improved module aesthetics
PERC MWT cell – 17.3% on mc-Si STD MWT cell – 16.8% on mc-Si
columns Print direction rows
Print begin
Print end
Print and Vacuum 1-1.5s
Non uniform filling behavior Longer vacuum time for first rows
12 Applied Materials External Use
time[s]
G'
G''
time [s]
G'
G''
Sinusoidal stress applied to the sample to simulate printing behavior Paste A: G’ (elastic modulus) rapidly drops under applied stress and G’’ (viscous modulus) is bigger than G’ during printing Paste B: smaller decrease in G’ than Paste A, more viscous behavior during printing Paste B recovers immediately after printing (no relevant variation in G’ modulus)
Reliable, Production-Ready Metallization Process For MWT Solar Cells
Marco Galiazzo, Diego Tonini, Alessandro Voltan, Claudia Bottosso, Giorgio Cellere
Rotational rheometer AR2000ex
ห้องสมุดไป่ตู้
Shear rate [1/s]
Usual shear thinning behavior: viscosity decreases as a function of shear rate. At 10 s-1, Paste A 40 Pa*s – Paste B 200 Pa*s
10 Applied Materials External Use
Equipment For MWT Metallization
Special nest design for each MWT pattern Suitable also for standard process Precise wafer placement to avoid paste stains No paper on the nests 3 different vacuums circuits
MWT Process: Vacuum Start At Print End
columns
rows Measurement of via filling
Print end
Print begin
Print 1-1.5s
Vacuum 0.1-0.5s
Uniform filling behavior, same vacuum time for all rows No impact on tool cycle time
Neidert et al. 24th EUPVSEC, 2009, pp. 1424-1429
5 Applied Materials External Use
Hole Metallization: Via Fill Vs. Via Plug
Depending on cell design via fill vs. via plug is required BCS is investigating these approaches at lab scale:
– Wafer holding vacuum – Low level suction vacuum – High level suction vacuum
11
Applied Materials External Use
MWT Process: Vacuum Start At Print Begin
Tipically higher solid content leads to higher viscosity
7
MWT Pastes: SEM Analysis
Paste A: flat flakes would flow more easily through smaller vias Paste B: smaller particles distribution results in higher viscosity and helps to make stronger bonds in paste structure
Charleroi, 3rd Metallization Workshop October 25, 2011
Applied Materials External Use Applied Materials External Applied Materials External
Outline
MWT cell structure MWT process flow Metallization of MWT cells
Less shading (0.3% abs eff gain + reduced paste consumption, up to 30%)
– Metal fraction: conventional 3BB cell ~7%, MWT ~4.5% – Higher short-circuit current density Jsc 1-1.5mA/cm2 – Higher Voc recombination current is reduced by lower metallized area
print
1000
pre-print
6.453 20.86 98.75
post-print
pre-print
post-print
100 120.5
100
106.422
34.828
56.484
70.656
84.703
151.86
203.2
134.704
168.969
186.047
220.34
48.719
via fill via plug
flake particles
irregularly shaped particles
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Applied Materials External Use
MWT Pastes: Viscosity
Higher solid content, compact structure Viscosity [Pa*s] Paste A via fill Paste B via plug
3 Applied Materials External Use
Process Flow
Additional/modified process steps
– Laser drilling – Via metallization – Laser contact isolation