UV Negative Resist Formulation

    Polyvinyl cinnamate early 1960's

    Cyclized polyisoprene polymers
                sensitizers
                        quinones (polyvinyl)
                        azido compounds (polyvinyl & polyisoprene)
                        nitro compounds (polyvinyl)
    Solvents/Developers
                acetic acid } polyvinyl
                notrobenzene } polyvinyl
                Furfural } polyvinyl
                Xylene } polyisoprene
                Benzene } polyisoprene
    Disadvantages
                linewidth
                swelling and shrinks

UV Positive Resist Formulation

    Common phenol formaldehyde novolac

    Sensitizer
                napthoquinone diazide
    Solvents/Developers
                ethylene glycol monomethyl
                with dilvents butyl acetate, xylene
    Advantages
                broader optical range
                easier to remove

X-Ray Lithography

    X-Ray lithography (XRL) consists of proximity printing of a mask onto a wafer.

    Advantages
                1) resolution and process simplicity (linewidth<1 mm)
                2) no need for multilevel resist systems used in e-b lithography
                3) XRL parallel writing process, e-beam is a serial; XRL higher throughput

Ion-Beam Lithography

Potential Applications - Scanning ion microscopy, X-Ray and optical mask repair, secondary ion mass spectrometry with submicron resolution, ion beam lithography, maskless implantation doping of semiconductors.
Source - liquid metal source (Ga, In, Au) doping, beam diameter ~ 0.1 m m, Current density 0.5 A/cm²

Scanning Ion Microscopy

    Very similar to a semiconductor.
    Advantage
                Secondary electrons
                Sputtered neutral
                Secondary ions
                Photons

Multilevel Resists

    The purpose of multilevel resists are to develop high resolution straight-walls, suitable for metal lift-off.
 
The Lift-Off Process
 
 

The above process requires the metal film to be thinner than the photoresist.  This requirement limits the metal linewidth.  Thinner linewidths normally require thinner photoresist layers.  Multilevel and special single resist solve this level-off problem.

Single-layer lift-off - this technique involves tolune or chlorobenzene soaks.  These soaks harden the resist near the surface and produce straight walls.

Planarizing layer acts as a portable conformal mask.

    Advantages
                Sensitivity
                Linewidth control
                Height-to-width aspect ratio
                Proximity effects
                Focus Tolerance
                Resist Image Profile

Applys to optical, E-beam, X-ray, Ion-beam Lithography.