Polyimide based Temporary Wafer Bonding Technology for High Temperature Compliant TSV Backside Processing and Thin Device Handling
Temporary wafer bonding for thin wafer processing is one of the key technologies of 3D system integration. In this context we introducethe polyimide material HD3007 which is suitable for temporary bonding of silicon wafers to carrier wafers by using a thermo compression process. Coating and bonding processes for 200 mm and 150 mm wafers with and without topography as well as two debonding concepts which are based on laser assisted and solvent assisted release processes are presented. Based on tests with temporary bonded 200 mm wafers, we found a very high compatibility of the bonded compound wafers with standard WLP process equipment and work flows suitable for backside processing of “via first” TSV wafers. Processes like silicon back grinding to a remaining thickness of 60 μm, dry etching, wet etching, CMP, PVD, spin coating of resists and polymers, lithography, electro plating and polymer curing were evaluated and are described in detail. Even at high temperatures up to 300° C and vacuum levels up to 10-4 mbar, the temporary bond layer was stable and nodelamination occurred. 60 μm thin wafers could be processed and de-bonded without any problems using both release methods. Debonding times of less than a couple minutes can be realized with laser assisted de-bonding and several minutes with a solvent based release. Compared to glues of other temporary handling systems, the proposed material offers the highest temperature budget for thin wafer backside processing as well as fast and easy debonding at room temperature.