Post-bond sub-500 nm alignment in 300 mm integrated face-to-face wafer-to-wafer Cu-Cu thermocompression, Si-Si fusion and oxideoxide fusion bonding

We report recent advances in tool and process hardening of a first of its kind 300 mm wafer-to-wafer (WtW) preprocessing, aligning, and bonding integrated tool. We have demonstrated sub-500 nm post-bond alignment accuracies for 300 mm WtW face-to-face (FtF) Cu-Cu thermocompression bonds, WtW FtF Si-Si fusion bonds, and WtW FtF oxideoxide fusion bonds. All process of record (POR) recipes that were developed had undetectable voids based on scanning acoustic microscope (C-SAM) measurements on representative bonded Cu, oxide, and Si blanket wafers. Optimized bonded patterned wafer splits in the Cu-Cu WtW thermocompression bonding step have shown alignment accuracies down to ~190 nm, the highest accuracy to date. Using an infrared-enabled, high speed focused ion beam (FIB) system (with XeF₂) with a CAD overlay function to assist in selective sample preparation, we have verified that the bonding interfaces at the via chain structures with 1-5 μm diameter vias show no interfacial voids. Also, there is evidence of Cu interdiffusion, as supported by transmission electron microscopy (TEM) and electron backscattering diffraction (EBSD) data.