The document summarizes research on fabricating through-silicon vias (TSVs) using copper electroplating in an electrolyte mixed with supercritical carbon dioxide. It describes the TSV fabrication process, the experimental setup using supercritical CO2, and the results of testing different fabrication parameters. The best hermeticity was found at 2500 psi pressure, the lowest electrical resistance at 1100 psi and 3 A/dm2 current density, and the fastest electroplating time of 3 hours was at 2000 psi and 7 A/dm2. Supercritical CO2 electroplating offers benefits over traditional methods by providing complete filling of structures using a simple setup without additives in less time.

1. FABRICATION OF
THROUGH-SILICON-VIA
(TSV) BY COPPER
ELECTROPLATED IN AN
ELECTROLYTE MIXED
WITH SUPERCRITICAL
CARBON DIOXIDE
AUTHORS
H.C. Chuang , J. Sánchez , A.H. Liao , C.C. Shen , and C.C.
Huang

2. Contents
• Introduction
• Fabrication
• Process for TSV Chip
• Sc-O2 Electroplating
• Result and Discussion
• Conclusion

3. Introduction
• The industry standard for PCB interconnection
relies on cables in the 2D planes, in order to
make it lighter devices with more functionality
with keeping Moore’s Law, fabrication and
packaging technology need to evolved. Many
researcher’s doing enhancement to develop new ways
to improve IC’s.
• One method develop 3D IC’s , the core technology
behind it TSVs.
• TSVs fabrication rely on traditional
electroplating.
• Supercritical CO2 electroplating
• Yoshida et al. first proposed the use of

4. Fabrication TSV chip
fabrication
4” single SI wafer with thickness 525 µm.
Si chips clean heating at 110°C for 20 minutes wash with
acetone , isopropyl alcohol and DI water.
A layer of PR spin coated 25 µm and etching ~70 µm for TSV are
pattern by UV lithography.
The TSV hole etched aspect ratio 1:7.5 after etching cut into
2x2 cm chip and placed into oxidation furnace to deposit at
SIO2 insulation layer on sidewall of TSVs holes.
TI adhesion layer and CU seed layer deposited on back side of
SI chip after placed in a convention oven to dry PR for 1 hour
at 85°C.
As the final preparation step, the chip is soaked in agitated
neutral degreasant, then activating acid and finally rinsed
with DI water. When all this is finished, the sc-CO2-enabled
electroplating can be performed to fill the TSV holes in
“bottoms-up” manner.

5. Fabrication Process For TSV
Chip

6. Sc-CO2
Electroplatin
g
1. CO2 Tank
2. Heat Exchange Unit
3. High Pressure Pump
4. Air Compressor
5. Chamber Encased With Circulating Hot
Water Tubing
6. Electroplating Bath
7. Power Supply
8. Pressure And Temperature Control Unit
9. Water Pumps
10. Hot Water Tank
11. Cold Water Tank
12. Pressure Valves

7. Component Quantity (g/L)
CuSO4 200
H2SO4 50
Cl 0.0385
Parameter Quantity
Pressure 1100, 1500, 2000, 2500 [psi]
Current density 3, 5, 7 [A/dm2 ]
Temperature 50°C
CO2 concentration 47 % (vol.)
Components of electrolyte used in
this study
Fabrication parameters used for this study

8. Result
and
Discussio
n
for hermeticity by means of a helium
leaking detector to check for any cracks
on the TSV structure. Only when it is
stablished that there are no cracks or
defects found, will the TSV chip be
subjected to the other tests. To test for
the electrical properties, a four-point
setup was used to measure the electrical
resistance by analyzing the input current
relationship with the voltage readings;
such a setup is shown in figure . It was
determined that the structures can
withstand 10 A without burnout. 10 A was
chosen due to equipment restrictions, but
it is a high value for industrial

9. Experimental Setup For Four-point
Resistance Test

10. For our purposes, a very important parameter is the current
density, which is the input current (0 ~ 10 A) divided by
the surface area of the TSV chip (0.04 dm2 ). The
relationship between current density and voltage for some
selected values is shown in figure.
Relationship Between Current Density And
Voltage

11. A higher current density means faster
filling of the structures, but also faster
electrolysis of water, implying there will
be more H+ ions as bubbles forming around
the cathode which also might be able to
enter the micro-size holes, creating voids
in the metal filling. At the highest
current density for this study (7 A/dm2 ),
it only required 3 hours to completely fill
the TSV structure, although few voids might
Cross-sectional View Of
Fabricated TSV Structure
With Voids

12. Relationship Between Current Density
And
Electroplating Time

13. Conclusion
In this study, micro-size through-silicon vias were filled by copper
electroplating in an electrolyte mixed with supercritical carbon dioxide, in
other words, sc-CO2-enabled electrolyte.
Different parameters for supercritical pressure and electroplating current
density were tested and compared amongst each other and also compared with
the traditional electroplating methods. Tests were performed to assess the
hermeticity and electrical properties of the fabricated structures.
The best hermeticity was found at 2500 psi, the lowest electrical resistance
(.002 Ω) was found at supercritical pressure of 1100 psi and current density
of 3 A/dm2. If we take into account the similarity in physical properties
between the sc-CO2 bubbles and the medium, the quickest electroplating time
of 3 hours was achieved at 2000 psi with the highest current density of 7
A/dm2 .
Such results clearly proved congruent with our ideology that supercritical
pressure and current density greatly affect the fabricated structures.
Finally, sc-CO2-enabled electroplating can overcome any issues of
complicated electroplating setups, complicated chemical mixtures and
extended fabrication time because it only needs a simple DC power supply
setup, needs no additives to achieve complete filling of structures and it
is faster than traditional methods. .

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YOU!