Investigation of optical properties of benzocyclobutene wafer bonding layer used for 3D interconnects via infrared spectroscopic ellipsometry

Benzocyclobutene (BCB) used for bonding silicon wafers to enable 3D interconnect technology is characterized using spectroscopic ellipsometry (SE). SE is a non-destructive technique that has been used to characterize the thickness and dielectric properties of BCB. The infrared (IR) absorption spectrum was used to calculate the percentage of curing of BCB on 300 mm bare and bonded wafers. The percentage of curing in BCB is a key parameter that impacts the bond strength and bond quality. This study presents the potential application of IRSE for measurements on bonded wafers to characterize the chemical information, curing percentage, bond quality and thickness of the BCB bonding layer. One of the key issues in the process development and characterization of BCB bonding for 3D interconnects of 300 mm wafers is the presence of dendrites and voids between the bonded wafers. The presence of dendrites and voids was identified by using scanning acoustic microscopy (SAM) and imaged by scanning electron microscope (SEM).