Extreme Thinned-Wafer Bonding Using Low Temperature Curable Polyimide for Advanced Wafer Level Integrations

Extreme thinned wafer transfer technologies have been demonstrated by combining a selected set of temporary and permanent bonding materials. The extreme thinning was performed on the backside of a top wafer bonded on carrier wafer with the temporary glue material, subsequently followed by grinding, polishing and plasma dry etching to a final thickness of 5 μm. The properties of the temporary adhesive have been selected to be compatible with a permanent thermocompression bond of the extreme thin wafer to a final target substrate. Thus, the high thermal deformation resistance of the temporary adhesive is key. As we are dealing with extremely thin substrate, the required process uniformity and total thickness variation of each material are crucial. Hence after the spin-coating, the permanent bond polymer was planarized by a surface planer process. The performance benefit brought by this process and the final transfer steps will also be discussed.