Critical adhesion energy of benzocyclobutene-bonded wafers

The dependencies of critical adhesion energy (CAE) of benzocyclobutene (BCB) bonded wafers on BCB thickness, the use of an adhesion promoter, and the materials being bonded are studied using a four-point-bending technique. The thicknesses of BCB used in the experiments ranged from 0.4 to 7.0 μm. The CAE depends linearly on BCB thickness due to the thickness-dependent contribution of plastic dissipation energy of the BCB and thickness independence of BCB yield strength. The CAE increases by approximately a factor of 2 when an AP is used for both 2.6- and 0.4-μm -thick BCB bonding layers because of chemical interactions. The CAEs measured at the interfaces between a Si wafer with plasma-enhanced chemical vapor deposited (PECVD) SiO2 and BCB and between a Si wafer with thermally grown SiO2 and BCB are approximately a factor of 3 higher than the CAE between a PG&O 1737 aluminosilicate glass wafer and BCB. The observed bond energies are about 18 and 22 J m2 at the interfaces between PECVD oxide and BCB and between thermally grown oxide and BCB, respectively. These bond energies correspond to bond densities of 12-13 and 15-16 Si-O bonds nm2.