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Lithography[edit | edit source]

Ultra Violet Lithography (UVL)[edit | edit source]

Masks for UVL[edit | edit source]

Various types of masks are in use for UVL:

  • Chrome-on glass maks for structures down to micron-resolution
  • Acetate masks for structures with minimum dimensions of tens of microns

Resists for UVL[edit | edit source]

Negative UVL resists[edit | edit source]

Positive UVL resists[edit | edit source]

Electron Beam Lithography (EBL)[edit | edit source]

Electron beam lithography offers linewidths down to the few nm range, much smaller than what can bea achieved by optical lithography. One drawback is that the pattern writing is a serial process and hence very time consuming for larger structures.

Resources on the net

What determines the EBL resolution[edit | edit source]

  • Beam diameter
  • Resist sensitivity
  • development method
  • Proximity effect
  • Resist thickness

Electron beam resists[edit | edit source]

Negative E-beam resists[edit | edit source]

negative e-beam resists will remain in the irradiated areas after development.

  • Electron beam induced deposition
  • PMMA
  • SU-8

Positive E-beam resists[edit | edit source]

Positive e-beam resists will be removed in the electron irradiation areas upon development. PMMA Typical PMMA process

  • 300nm PMMA think film made by spinning 950k PMMA 5% in anisole at 5000rpm for 30sec (avoid bubbles in the resist when placing it on the wafer, use about 3ml for a 4" wafer).
  • drying 180C Hot plate for 2 min or oven bake for at least 2h at 180 C. Oven takes longer than hot plate as convection heat trasnfer is slower than contact transfer.
  • Electrob beam lithography. Dosage depends on pattern density and acceleration voltage.
  • Developing in MIBK:IPA (1:3) for 60s and rinse in IPA for 30s.
  • Post bake to improve etch resistance. 30 min at 110C
  • 5 mBar Oxygen plasma in faraday cage for 20 sec to remove residual resist.
  • For instance metal evaporation to form metal structures, followed by liftoff 5 min in hot remover s-1165 and acetone in several fresh baths to remove liftoff fragments.
    • ZEP

Resist Coatings[edit | edit source]

  • Spinning
  • Electrochemical coating
  • Spray coating (Spray coaters are made by eg. EVG)
  • Drop casting
  • Self assembled monolayers

References[edit | edit source]

See also notes on editing this book about how to add references Microtechnology/About#How to Contribute.