< Microtechnology

Lithography

Ultra Violet Lithography (UVL)

Masks for UVL

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

Negative UVL resists

Positive UVL resists


Electron Beam Lithography (EBL)

Electron beam lithography offers linewidths downton 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

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

Electron beam resists

Negative E-beam resists

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

  • Electron beam induced deposition
  • PMMA
  • SU-8

Positive E-beam resists

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

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

References

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

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