Critical adhesion energy at the interface between benzocyclobutene and silicon nitride layers

The effects of thermal cycling on residual stresses in both silicon nitride (SiNx) deposited on silicon wafers and benzocyclobutene (BCB) coated silicon wafers are discussed. The SiNx is deposited by plasma-enhanced chemical vapor deposition (PECVD). A model for the effect of thermal cycling on residual stresses helps explain the effects of thermal cycling on critical adhesion energy (CAE) between SiNx and BCB films in bonded wafer configuration Si SiNx BCB SiNx Si. The wafers are bonded with BCB using an established baseline process. CAE is measured using four-point bending. In thermal cycling experiments conducted between 25°C and either 350 or 400°C, the CAE at the interface between BCB and SiNx decreases. This trend in CAE agrees with our model's prediction that an increase in residual tensile stress within SiNx after thermal cycling leads to the observed decrease in CAE. This result is compared with that obtained for bonded wafer configuration Si/PECVD SiO2 /BCB/PECVD SiO2 Si, where the decrease in residual compressive stress within SiO2 induces an increase in CAE. These opposite trends in CAEs of the structures that include SiNx or SiO2 layers are caused by condensation reactions in the layers, followed by desorption of water, which makes the films more tensile.