Nanotwinned Copper Hybrid Bonding and Wafer-On-Wafer Integration

The bonding temperature for Cu to Cu direct/hybrid bonding is usually higher than 300 degrees C. In this study, three types of 12" wafer were fabricated: nanotwinned Cu (nt-Cu) blanket, hybrid nt-Cu/SiO2 dish shape, and hybrid nt-Cu/SiO2 pad shape respectively. The <111>-preferred orientation ratio on nt-Cu surface was analyzed to 75.1% on dish-shaped and 99.0% on pad-shaped wafers. The resistivity of nt-Cu blanket on the wafer was 2 x 10(-8) Omega.m at room temperature which is close to pure Cu. We had constructed the equation to calculate the <111>-oriented surface proportion on polished dish-shaped wafer. To get the maximum of <111>-oriented nt-Ct surface, the bottom-up plating without tilted nt- Cu grains is the solution. The root mean squared roughness value (Rq) of nt-Cu blanket and hybrid nt-Cu/SiO2 were 0.56 and 1.47 nm before bonding, respectively. The near 90 % of achieved ratio of a good bonding interface without voids had finished on wafer-to-wafer bonding. In summary, the hybrid bonding is an extraordinary interconnection technology as well as benefits future trends in advanced package. Currently, the near 90% of <111>-oriented nt-Cu surface is achieved and nt-Cu-to-nt-Cu bonding is carried out at low temperature of 250 degrees C for 1 h.