Sub-10µm Pitch Hybrid Direct Bond Interconnect Development for Die-to-Die Hybridization

Direct bond interconnect (DBI) processes enable chip to chip, low resistivity electrical connections for 2.5-D scaling of electrical circuits and heterogenous integration. This work describes SiO2/Cu DBI technology with Cu interconnect performance investigated over a range of inter-die Cu gap heights and post-bond annealing temperatures. Chemical mechanical polishing (CMP) generates wafers with a controlled Cu recess relative to the SiO2 surface, yielding die pairs with inter-die Cu gap heights ranging between 9 and 47 nm. Bonded die with different gap heights show similar per-connection resistance after annealing at 400 degrees Celsius but annealing at lower temperatures between 250 and 350 degrees Celsius results in failing or high-resistance interconnects with intermediate gaps showing lowest resistance. Cross-section scanning electron microscope (SEM) image analysis shows that the microstructure is largely independent of post-bond annealing temperature, suggesting that the temperature behavior is due to nanoscale scale interfacial effects not observable by SEM. The bond strength is affirmed by successful step-wise mechanical and chemical removal of the handle silicon layer to reveal metal from both die. This work demonstrates a 2.5-D integration method using a 3 micron Cu DBI process on a 7.5 micron pitch with electrical contacts ranging between 3.8 and 4.8 Ohms per contact plug.