New Thin Adhesive for High Density 2.5D Heterogeneous Device Integration with Cu-Cu Hybrid Bonding

Abstract

Abstract Heterogeneous integration of logic, memory, and sensor chips on interposers (2.5D) has attracted a lot of attention as a candidate for More-than-Moore technology. For the high performance 2.5D devices, high density integration of chips with narrow spacing and high density interconnections with small pitch bonding electrodes are a key technology. In the current bonding technology, solder micro-bumps (>20 μm in diameter) and non-conductive adhesives have been adopted. There may be some limitations for high density device integration with these technologies because of the protrusion of adhesives around the chips, the thermal sliding at the bonding, and the limit of solder micro-bump minimization. Hybrid bonding with a small Cu electrode (<10 μm in diameter) is a strong candidate for improving advanced device integration technology. Our goal is to develop a new adhesive which gives no protrusion, no thermal sliding, no voids, and high electrical reliability. A spin coating thin adhesive was therefore developed. The new adhesive can be cured at 200 °C. The cured adhesive film has no tackiness and has an optically flat surface. The adhesive film can be temporarily bondable to SiO2 at room temperature. After 200 °C baking, a permanent bonding can be achieved, and there is no degradation of bonding strength and no voids even after 400 °C of baking. For the applicability to the chip-on-wafer process, the adhesive film/Si wafer can be cut into chips by blade dicing without any delamination and without any apparent particles. After bonding the adhesive/Si chip to a bare Si wafer at room temperature, the thermal sliding amount after the thermal compression process (250 °C, 10 min, 1 MPa) was less than 1 μm (under the detection limit) according to optical microscopic measurements. In addition, there was no protrusion of adhesive around the chip corner from SEM. A first trial result for hybrid bonding is also reported.