Electrical Performance and Reliablity of Fine-Pitch Cu Bumpless Interconnect

In this study, we demonstrated the high electrical performances of the micron-level interface obtained by the Cu bumpless interconnect. Moreover, the bumpless structure was applied to the interconnection between the actual flash memory chip and the interposer. The bumpless interconnect has been proposed to solve the thermal strain problem by the direct bonding of Cu wiring without bump-like electrodes so as to enhance the potential of interconnection density. We achieved the direct interconnection of 100,000 Cu bumpless electrodes in the diameter of 3 mum and the pitch of 10 mum by means of the surface activated bonding (SAB) method, and then estimated that the contact resistance could be as low as the range of muOmega. The increment of the contact resistance was less than 5 % with a stable interface after heated at 150 degC for 1000 hours. Moreover, a fabrication process of the Cu bumpless structure with a polyimide insulation layer was developed and then we structured a 0.1-mm-thick compact flash (CF) memory chip interconnected to a interposer chip with the same thickness through the bumpless electrodes with the dimensions of 25times25 mum ² and the pitch of 40 mum. The entire memory region was secured in the assembled flash memory chip after the formatting test of over 200 times, showing no obvious degradation after heated at 125 degC for 500 hours