Effect of pyrolysis on shrinkage properties of SU-8 polymer

Epoxy SU-8 has drawn a lot of attention during the last decades due to its promising mechanical and electrical properties. Extensive research regarding the mechanical properties of negative photoresists SU-8 has been carried out during the last decades. A lot of effort has been put into developing methods to properly characterize features such as effect of pyrolysis temperature and the pyrolysis time on shrinkage properties and morphology of SU-8. In this work photo patterned SU-8 were fabricated on silicon wafers by spin process for different speed steps (step (1) 250rpm and time 10sec, step (2) 450rpm and time 30sec, step (3) 0rpm and time 5sec), then Soft baked at 95°C for 4min before cooling for 10min. Exposure to ultraviolet (UV) light was necessary to obtain the shape of the mask, increase crosslinking degree in the irradiated areas and stabilizes them against the action of solvents during development step. The density of UV used was 6 mW/cm2 at 365 nm and exposure time was 5min, while the volume of SU-8 developer was 40cm3 at 10min. Samples were cut into 2cmx2cm dimensions. The pyrolysis was carried out in a closed quartz tube furnace in an inert nitrogen gas (N2) flow at 1500 standard cubic centimeters per minute (SCCM) and different parameter of temperature (350oC, 400oC, 450oC and 500oC) and time (10min and 20min). Peeling of the SU-8 occurs due to a poor adhesion of the resist to the substrate, thicker films or faster heating rates during the pyrolysis of SU-8. Increasing pyrolysis parameters (temperature and time) lead to larger vertical and horizontal shrinkage, lower sheet resistivity and roughness. The scanning electron microscope (SEM), atomic force microscopy (AFM) and profilometer were used to examine the shrinkage and roughness of SU-8, in order to gain an understanding of how it can affect the shrinkage properties and determine the optimized pyrolysis conditions.