As an alternative to the polyimide negative resist, SX AR-N 4340/6 was developed, a highly sensitive CAR negative resist based on polyhydroxystyrene, which can be developed under aqueous-alkaline conditions. The resist layers are very well suited for the fabrication of high-temperature resistant structures, which are stable up to approximately 350°C (see figure 1).

Figure 1: SEM micrograph of a structure of SX AR-N 4340/6 with smooth surface and sharp edges, tempered at 350 °C .

There is merely a shrinkage of up to 20 % (see figure 2).

Figure 2: Shrinkage depending on temperature, measurement on Dektak 150.

The structures of the new thermostable positive resist SX AR-P 3500/8 likewise show a high resistance to high temperatures that may occur during intensive etching or implantation processes. Most commercial removers solve the resist layers easily after thermal stress up to 130 °C. In case of higher temperatures, the aqueous-alkaline remover AR 300-73 must be used. The tempered structures (above 150 °C) are inert to solvents, which allows for application in microfluidics. SX AR-N 4340/6 is suitable for other technologies as well, seeing that the resist shows high plasma etching stability and good insulating qualities besides its temperature stability.

As an alternative to the polyhydroxystyrene negative resist, a sensitive CAR negative resist based on the copolymer poly(hydroxystyrene- co -MMA) was designed which can also be developed under aqueous-alkaline conditions. The resist SX AR-N 4340/7 is stable up to temperatures of at least 250°C and thus also well suited for the generation of high-temperature stable structures. Similar to polyhydroxystyrenes, this resist is characterised by good insulating properties and a high thermal resistance. Resist layers of PSOH co MMA show only very low moisture absorption from the air.