Characterisation of residual stress in dielectric films studied by automated wafer mapping

SU-8 is a negative epoxy based photoresist, which is widely used as a structural and dielectric layer in the fabrication of MEMS devices. However this material normally develops high levels of stress during processing. This paper reports detailed quantitative data following previous work, where Parylene-C has been proposed as a possible replacement for SU-8. In particular, this paper details the characterisation of residual stress in (i) SU-8 films as a function of processing temperatures and (ii) post-processing thermal treatment of Parylene-C. This characterisation includes wafer mapping strain using rotating pointer arm test structures, and deriving the stress from independent measurements of strain and Young's modulus.