Polyimide

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Polyimides (PI) are a class of chemicals which contains the imide group, where a nitrogen is connected to two carbonyl groups via a single sigma bond O=C-NR-C=O, widely used in microfabrication fabrication. They are used as photoresist (photopatternable), substrate, sacrificial layer, planarization material and structural material. Polyimides have excellent chemical and radiation resistance and low water absorbance, are good dielectrics and are thermally stable up to approx. 350°C, and some are bio compatible. Polyimides have good mechanical properties, films have low stress and some are vacuum compatible (i.e. Kapton, Vespel). There are some machinable polyimides, like Vespel (also good dielectric) that is often used in UHV. Polyimides are fabricated in a wide variety of chemical derivatives to enhance a particular property. In microfabrication polyimide can be spun (available in different viscosities) and cured, patterned, used as a substrate (films come in different thicknesses, and sizes, with and without adhesive).

Equipment

Polyimides are spun and cured at LNF. LNF stocks PI in two viscosities from HD Microsystems PI: 2610 (1 µm - 2.5 µm) and 2611 (3 µm - 9 µm). They are available from the LNF Store in 100g brown bottles.

Deposition Equipment

• Spun in Spinner CEE Apogee ROBIN (full wafers) and Solvent Bench 94 (pieces)
• Cured in YES PB8-2B-CP Vacuum Oven

Etching Equipment

• Dry etch in Plasmatherm 790

Characterization Equipment

Polyimide can be charaterized in the following instruments:

• Thickness in NanoSpec 6100 Refractometer or Reflectometer KLA Filmetrics F54
• Optical constants and thickness in the Woollam M-2000 Ellipsometer
• Roughness in the Bruker ICON AFM

Applications

At LNF polyimides are used as:

• Substrate material for flexible electronics, sensors, probes, etc.
• Planarization material
• Dielectrics
• Sacrificial layer
• Kapton® tape, a polyimide developped by DuPont™, is widely used in plasma based processes as masking material

Technical Data

• Technical data for PI 2600 series

References

• NASA Review of Polyimide Used in the Manufacturing of Microsystems