Although several materials can be modified by a heated tip, the choice of resist material plays a crucial role for the NanoFrazor technology.

Polyphthalaldehyde (PPA)

We recommend using polyphthalaldehyde as a standard resist due to its remarkable properties and its wide acceptance in the community. PPA is a so-called self-amplified unzip polymer which instantaneously decomposes into its volatile monomers upon an external trigger like a heat pulse. The unzipping is an endothermic reaction confining the spread of heat in the resist, enabling high-resolution patterning. The decomposition products evaporate immediately without re-deposition on the substrate. Patterned PPA does not need wet chemical development and due to its high glass-transition temperature, it can directly be used as an etch mask with high mechanical stability.

SwissLitho has a strong expertise with transfer layers for pattern transfer using PPA. Furthermore, within the framework of the Eurostars project: PPA-Litho we are actively researching novel PPA variants for specific applications.

Evaporated PPA Monomer

PPA Specifications

  • High spin coating applicability: Very flat, smooth and thin films possible
  • Positive-tone resist, “exposed” areas are removed
  • No wet chemical development necessary
  • Also demonstrated for laser, e-beam or x-ray lithography
  • High mechanical stability, high glass transition temperature
  • Efficient NanoFrazor patterning: Self-amplified decomposition reaction/unzipping of the polymer chain
  • High resolution possible: Endothermic decomposition reaction confines spread of heat
  • Immediate evaporation of volatile decomposition products at room temperature
  • No measurable re-deposition on the substrate
  • Suitable as mask for various pattern transfer methods
Linear PPA

PPA Key Features

Film preparationSpin coating
SolventsAnisole (standard), Cyclohexanone
Soft bake90 °C for 3 min
Decomposition temperature~ 140 °C
Glass transition temperature> 120 °C
Film thickness range5 - 200 nm
Roughness Rq< 0.3 nm
Lateral resolution (half-pitch demonstrated)8 nm
Vertical resolution (step size, demonstrated)1 nm
Minimum heating time per pixel (demonstrated)1 µs
Etch selectivity to Si5:1 (> 10:1 was demonstrated)
Cyclic Phthalaldehyde

Resist Alternatives

There is a wide range of other materials that can be used as thermosensitive resists for the NanoFrazor lithography process. Below is a selection of materials that have been successfully patterned with the NanoFrazor. All of them have some advantages and disadvantages. Please contact us for more information.

PPC (Polypropylene carbonate)
Molecular glasses
Diels-Alder polymers (maleimide/furan-based)
Supramolecular Polymer Glasses
Sterol-based QSR-5 (negative tone resist)