Microscale Device Fabrication: Electrochemical Deposition EMD of Metals

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Microscale Device FabricationElectrochemical
Deposition (EMD) of Metals

• By
• Mahmoud Hayat
• and
• Cerise McLaren

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The Project
The goal of the project is to deposit copper
onto a pattern that is put on a silicon wafer.
The copper deposit on the pattern creates a
circuit on the silicon wafer. Copper is being
used instead of a previously more commonly used
silver because it has a greater conductivity and
less resistivity than silver. The silicon wafer
will be used as a printed circuit board (PCB)
that are found in a variety of different
mechanical equipment, such as computers and cell
phones.
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Day One In the Lab

• This is a photograph of our work station. This
  is a setup of the electrochemical deposition of
  copper wires. In this experiment copper is
  transferred from a positively charged wire to a
  negatively charged wire in a solution made of
  H2SO4, HCL, CuSO4 and H2O. The negatively charged
  wire becomes thicker with copper and the
  positively charged wire becomes thinner.

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Day TwoIME Manufacturing LabPhotolithography

The Process

• Clean silicon wafer with acetone, methanol and DI
  water. Blow dry with nitrogen gas.
• Soft bake wafer at 90o C for two minutes.
• Place wafer on spinner turn on vacuum to prevent
  wafer from moving. Add 24 drops photo resist in
  center of wafer and start the spinner.
• Hard bake wafer at 120o C for ten minutes.

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• Place wafer under a mask that has a pattern where
  copper will be deposited onto the aluminum plated
  silicon wafer. Expose wafer to ultraviolet light
  for 30 seconds. Immerse wafer in developing
  solution for three to four minutes. Clean wafer
  with DI water and blow dry with nitrogen gas.
• Soft bake wafer for two minutes and check the
  pattern on the wafer under a microscope.
• The wafer is now ready for electrochemical
  deposition.

The wafers after the photolithography process.
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Equipment in the IME Manufacturing Lab
Acetone, methanol and DI water used to clean the
wafers
The lab equipment
Ovens and masking machine
Spin coater
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Day Three Deposition of Copper
alligator clips
solution
power source
mixer
After creating an image on the silicon wafer the
electrochemical deposition of copper can begin.
The first step is to make the solution. After
mixing the solution the beaker is to be placed on
the mixer that uses a magnet stir bar to stir
liquids. The surface area of the exposed spots on
the silicon wafer are measured and put into an
equation to calculate the amps needed to deposit
copper onto the wafer. A piece of copper wire or
sheet of copper is placed in the beaker with the
positive alligator clip, held in place and
allowed to sit in the solution. The silicon wafer
is placed in the beaker with the negative
alligator clip, held in place with the image side
facing the piece of copper and allowed to sit in
the solution about two or three centimeters from
the piece of copper. The mixer is turned on at a
medium speed and the power source is turned on to
the amps that were calculated from the surface
area. The process usually takes about twenty five
minutes.
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Day Three Results and Conclusions
Results The expected result of the
electrochemical deposition experiment was that
copper would be deposited on the exposed pattern
on the silicon wafer. The two wafers that were
used in the experiments were not deposited with
copper or had very small trace amounts of
copper. Conclusion The possible reasons that the
exposed areas on the wafer did not become
deposited with copper are the following 1) The
aluminum plating on the silicon wafer was very
thin. Because of this, the current travelling
form the power source was not strong enough
because the thin aluminum was not thick enough to
allow a strong current. 2) The silicon wafers
may have been defected in the process of
photolithography, such as being scratched or
touched with invasive chemicals.
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The Grand Conclusion What we learned and what we
could have done better

• This project taught us
• how to mix chemicals properly and safely
• how to deposit copper onto other metals
• the process of photolithography
• how silicon wafers are made and what they are
  used for
• how to calculate amps needed for a specific
  surface area
• how to work as a team

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Electromechanical Deposition of Copper The Fun
Stuff
These are pieces of aluminum and brass that were
deposited with copper
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Acknowledgements Partial support for this work
was provided by the Intel Faculty Fellowship and
the National Science Foundations Course,
Curriculum and Laboratory Improvement Program
under grant DUE-0127175