Anisolic PPA solutions can be coated onto PMMA (600k, 950k), PMMAcoMA (AR-P 617) as well as on bottom resist AR-BR 5480 (alternative to PMGI). The single layers add up in each case, and virtually no mixing takes place. It is thus possible to realize well-defined two- and three-layer systems by these means.
Figure left: schematic representation of multilayer systems with PPA and bottom resist SX AR-BR 5480/19, bottom two-layer system as described below, top three-layer system for further applications. Middle: scribed double layer on Si wafer; scan on Dektak 150. Right: schematic illustration of two-layer lift-off process with PPA as top resist (PPA/AR-BR 5480).
After coating and softbake, the upper resist layer (PPA) is scanned with a hot needle (NanoFrazor). With each contact between needle and resist, the thermolabile PPA evaporates and the desired structures are thus transferred into the layer. In the following lift-off process, at first the lower layer is removed isotropically in aqueous-alkaline solution which generates the undercut. Subsequently metal is vapour-deposited, and after the lift-off, only the metal structures remain. This process is however limited with respect to resolution due to the isotropic development. The specific properties, in particular the dissolution rate of the bottom layer, can be adapted according to customer requirements. Correspondingly, also customised resists of the AR-BR 5400 resist series are offered to interested parties for this purpose.