Laser direct patterning of dry etch BCB adhesive layers for low temperature permanent wafer-to-wafer bonding

The paper gives an overview of recently developed processes for Benzocyclobutene (BCB)-based patterned adhesive wafer bonding. The processes feature a post bond batch cure to support shortest cycles times of < 10 minutes per wafer bond. In order to enable such process schemes, the fabrication of patterned polymer precursor layers with sufficient remaining flow capability for thermocompression type wafer bonding applications is most important. In this work we introduce a new structuring method of non-cured CYCLOTENE" 3000 Resin for adhesive wafer bonding. The layers were spin coated, baked and subsequently patterned using a 248 nm excimer laser stepper. The equipment features a 2.5à mask projection with a resulting exposure field of 6.5 à 6.5 mm2 and allows a direct ablation patterning of polymers. By using this method, bond frame structures were patterned into up to 5 μm thick CYCLOTENE"; 3000 Resin at 200 mm silicon wafers. The wafers with the structured adhesive we re bonded at 80 °C and 0.2 MPa for 5 minutes with 200 mm glass wafers. The bonded wafer stacks were subsequently post bond batch cured to form the BCB polymer. Wafer dicing and shear tests of the bonded structures revealed excellent mechanical robustness of the BCB bond frames.