Photo-polymer wafer bonding for double layer transfer

Temporary bonding is necessary for the two-stage transfer of thin films from one substrate to another while preserving the original orientation of the film. The process developed in this study uses an SU-8 photo-polymer both as a bonding material and as a delamination material for layer transfer. SU-8 was spun onto an optically transparent handle wafer (e.g., quartz or glass) and then bonded to the layer to be transferred. The processing parameters such as pre-baking temperature and UV exposure dose affect the bonding strength. UV curing of the SU-8 through the backside of the handle wafer could be performed to obtain the ultimate bond strength at low temperatures. A laser pulse from a KrF excimer laser (lambda = 248 nm and tau = 38 ns) at a fluence of 50-150 mJ/cm(2) was used to delaminate the SU-8 bonding layer to complete the layer transfer.