an insiders guide to The Art of Spin Coating

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an insiders guide toThe Art of Spin Coating

• Dr. Occhiogrosso,
• Apra Mattoo, Arielle Galambos, Mitchell Fourman
• July 1, 2003

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Say Hi to Si

• A diamond cutter is used to cut Si wafers. DO NOT
  touch the Si wafer with your hands. Use tweezers
  to handle wafer.
• Place diamond cutter on the very edge of the Si
  wafer and press down firmly. The Si wafer should
  cleave easily.
• Si wafer can cleave either as triangles or
  squares depending on the arrangement of atoms in
  the Si crystal lattice structure. Try and use (1
  0 0) wafers because they cleave as squares and
  are very easy to cutyou will most likely not
  find them. . .

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The Need to Clean

• Cleaning Si wafers is a multi-step process
  determined by the type of Si surface needed
• New packages of Si wafers are pre-treated to be
  slightly hydrophobic. What does this mean?
• However, for the purposes of spin-coating you
  either want a very hydrophilic surface or a very
  hydrophobic surface. You have to create such a
  surface through your cleaning technique.

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HYDROPHILIC Si

• Fill a beaker with 511 H2O H202NH4OH and
  place on hot plate for 15mins at 80oC to remove
  any organic contamination.
• Rinse wafers in deionized water
• 101 H20HF for 30 seconds to remove metallic
  contaminants as a result of step 1 by etching
  silicon dioxide
• Mix H2SO4H20H202 (piranha) in a 113 ratio in
  a glass beaker.Place beaker onto hot plate for 2
  hours slightly below boiling. You must be present
  while your Si wafers are boiling. You cannot go
  out to lunch while your Si wafers on boiling. You
  can read Harry Potter as you wait. This step
  removes any alkali ions, metal hydroxides and
  trace heavy metals to create new clean oxide
  layer.

• Remove Si wafers and rinse thoroughly with
• de-ionized water for 5 min.

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HYDROPHOBIC Si

• Mix Ammonium Flouride Solution
• Mix 100g of NH4F with 125mL of H20. Its most
  likely already made. Ask for assistance if you
  have to make it.
• Mix NH4FHF in a 61 ratio and immerse wafer for
  3-4 min. .
• Rinse wafer with de-ionized water.
• Dry wafer with N2 gas.
• NOTE HF will burn your bones. More precisely it
  melts your bones and gives you cancer. Actually
  you will die before you get cancer from the
  severity of the burnsso its not a known
  carcinogen, but its still pretty darn toxic.
  REU/GRAD STUDENTS must assist you w/ HF

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Spin Coating Polymer Solutions onto Si Wafers

• Make your polymer solution. Follow handout
  protocol for polybutadiene.
• Using tweezers, place your cleaned, cut Si wafer
  onto the center of the bench-top spinner that is
  under the hood.
• Pipette your polymer solution apply drop-wise
  to Si wafer.
• Spin your sample immediately for about 30 seconds
  at 2500rpms.
• Our spinner is not this nice and is often broken.
  Ask a grad student to show you how to clean the
  spinner.

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OOOO Pretty Colors!

• As you spin you will quickly notice a color
  change occurring on you Si wafer. The variety in
  color is dependant on your polymer and the
  density of your solution and unique to each
  polymer.
• The colors are due to the fact that different
  thickness of polymer film diffract different
  wavelengths of light. In spinning, the polymers
  thickness changes as it disperses evenly across
  the Si wafer. The general rule is the darker your
  color, the thicker your film.
• A dark blue film will have a thickness of about
  1000A. A colorless film will be less than 500A.

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Any Questions?

• No questions? Fine, then finish answering the
  questions on the 3-page worksheet you received.
  REUs are to please assist.