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
- SPIE Handbook of Microlithography, Micromachining and Microfabrication has an online chapter on EBL
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
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.
Resist Coatings[edit | edit source]
- 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.