Microtechnology/Lithography

=Lithography=


 * SPIE Handbook
 * Intro to lithography

=Ultra Violet Lithography (UVL)=
 * Photolithography
 * Photoresist

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

Negative UVL resists

 * PMMA
 * SU-8

Positive UVL resists
=Electron Beam Lithography (EBL)= 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

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

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.