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.