Greener Solvents For Removing Polyimide-based Temporary Bond Adhesive Residues

Abstract:
Temporary Wafer Bonding is one of the key technologies for the fabrication of thin devices, thinned to below 100 µm thickness, as increasingly used in the growing market of advanced packaging. In order to allow downstream back end of line (BEOL) operations such as backgrinding, through-silicon via (TSV) and redistribution layer (RDL) formation or bumping, the thinned device wafer needs a rigid temporary support of a carrier wafer to guarantee mechanical stability and to avoid warping during high-temperature process steps. The bond adhesive’s requirements center on the conflict between bond stability in demanding processing environments, such as elevated process temperatures and low gas pressures on one hand, and the final residue-free removal of the adhesive after debonding on the other hand. One very prominent temporary bond adhesive is the polyimide-based HD-3007 (HD MicroSystems) which can be debonded via UV-laser debond. The cleaning of HD-3007 adhesive residues is conventionally performed using solvents containing n-methyl-2-pyrrolidone (NMP) and tetramethylammonium hydroxide (TMAH). These solvents exhibit significant toxicity to humans and environment. In this work, we examine possible socalled “green” alternatives to the above-mentioned solvents – dihydrolevoglucosenone (Cyrene), dimethyl isosorbide (DMI), 1-butyl-2-pyrrolidone (NBP), and 2-methyltetrahydrofuran (MTHF) as well as the development product Fotopur S-6104 from BASF to reduce the environmental impact and enhance the operational safety of the wafer cleaning process.