Influencing factors in high precision fusion wafer bonding for monolithic integration

Both fusion and hybrid wafer bonding are enabling increasing integration density as well as advanced device integration strategies. In any case, wafer-to-wafer overlay accuracy is the most critical factor for successful integration in 3D stacked devices. Despite alignment of both wafers is of major impact for the post-bond overlay accuracy, initiation and control of the bond wave between both substrate wafers the essential. During contacting device wafer surfaces, wafer stress as well as bow is influencing the bond wave dynamics. Engineering the continuous wave dynamics and influencing parameters are both key for optimum post-bond overlay accuracy. Any wafer stress will result into distortion of patterns and additional misalignment term. Despite typical distortion values are well below 50nm already, further optimization of both wafer bonding as well as wafer preparation and preprocessing are key for hybrid and monolithic integration.