Investigation of various photo-patternable adhesive materials and their processing conditions for MEMS sensor wafer bonding

In this study, various photo-patternable adhesive materials were investigated and their processing conditions are optimized in terms of bonding temperature, time and pressure. Commercially available photo-patternable adhesive materials were selected for selective wafer bonding. The selected polymer materials were SU-8 3015BX (Epoxy-based) from Microchem, TMMR N-A1000 T-3 (Epoxy-based) from TOK, THB-126N (Acrylic-based) from JSR, WPR-5100 (Phenol-based) from JSR and SINR-3570PF-20 (Siloxane-based) from Shin-Etsu Chemical. Bond strength was measured quantitatively at various bonding conditions using tensile test method. In order to investigate the influence of each process step and bonding conditions on bonding properties, thermal stability and curing behavior analysis were carried out using FT-IR (fourier-transform infrared spectroscopy) and TGA (thermo gravimetric analysis). A patterned silicon wafer was bonded to a glass wafer in order to inspect the bonding interface and any defects through the glass wafer, and diced into chips. In all materials except WPR-5100, no critical void or defect all over the bonding interface was observed, and the bonded wafers were strong enough to endure the dicing process even for WPR-5100. The cross-sectional images were obtained using SEM (scanning electron microscopy). The cavity structures for encapsulation of MEMS devices were well defined and the required bondline thickness was obtained successfully.