Negative poly(hydroxystyrene-co-MMA) photoresist
As an alternative to the polyhydroxystyrene negative resist, a CAR negative resist based on the copolymer poly(hydroxystyrene- co -MMA) was designed which can also be developed under aqueous-
Coloured negative photoresists
Allresist now also offers colored negative resists with the designation SX AR-N 8500. The difference to FUJIFILM resists is that only dyes and no pigments are dissolved in the resists. This allows to achieve a high resolution and high edge sharpness.
CAR 44 on copper
If negative photoresist CAR 44 (AR-N 4400) is directly used on copper or copper-containing substrates, the following points must be observed.
Dose-dependent structure size with negative resists
The desired structure size also largely depends on the exposure dose used. In the case of overexposure, structures begin to widen which is particularly pronounced during laser exposure.
Generation of undercut structures with negative resists
With laser direct exposure, a slight undercut of the structures can be generated: The upper part of the layer is more strongly irradiated due to the absorption of the resist and consequently more intensely crosslinked.
Sensitive negative resist for 405 nm laser direct exposure
Negative resist AR-N 4400-10 can be structured with laser direct exposure at an exposure wavelength of 405 nm. Different arrays are shown in the figure.
Water-based resists
Layers are after exposure treated with H2O2 and developed with water. Allresist has developed similar negative resists within the framework of a research project.
NIR-laser structurable photoresists
By adding suitable dyes to negative-working CAR resists, even a patterning beyond the usual wavelength range is possible if pulsed lasers with sufficiently high intensity are used for exposure.
Sensitive negative PMMA resist (CAR)
PMMA resist are mainly used for electron beam applications or as protective coatings in aggressive wet chemical etching procedures. In principle, also a structuring of PMMA layers with deep UV exposure (220-266 nm) is possible, but the sensitivity is in this case low and long exposure times are consequently required.
Development of thick negative resist layer
If the negative resist AR-N 4400-50 is utilised, resist layers of >200 µ m can be built up in repeated coating steps (see product information of CAR 44). Decisive for the quality of the layers to be obtained is the bake procedure.