There are many materials that can be modified by a heated probe tip. But for the NanoFrazor technology, the choice of resist material plays a crucial role.

Polyphthalaldehyde (PPA)

We recommend to use 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.

PPA Key Features

  • 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

PPA Specifications

Film preparation Spin coating
Solvents Anisole (standard), Cyclohexanone
Soft bake 90 °C for 3 min
Decomposition temperature ~ 140 °C
Glass transition temperature > 120 °C
Film thickness range 5 - 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 rate (RIE with CHF3) 5 nm/min (15 nm/min SiO2)

Thermosensitive Resists-1
Thermosensitive Resists-2