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 XeF 2 ) 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.

Abstract Focused ion beam (FIB) systems use a gallium liquid metal ion source as the source of the ions, providing a typical beam current range of 1 pA to 20-60 nA. Using a reactive gas in addition to the FIB usually enhances the etch rate from 1 to 15 times, but with the combination of xenon difluoride gas and a silicon substrate the enhancement can be over 1000 times. Such an enhancement makes the removal of large volumes of Si more practical, even with the typical upper end of FIB currents of 20-60 nA. This paper discusses the application of full-thickness silicon trenching to the process development of WtW bonding. With the increase in 3DIC, it is expected that fresh process characterization and failure analysis techniques will be required. The work presented shows the feasibility of extending FIB techniques to the process development of wafer-to-wafer bonded samples even on full-thickness wafers.

We report on recent experimental studies performed as part of a 3D integrated circuit (3DIC) production-worthy process module roadmap check for 300 mm wafer-to-wafer (WtW) copper-to-copper thermocompression bonding and face-to-face (F2F) aligning. Specifically, we demonstrate submicron alignment capabilities (3sigma alignment variability ~ 1 μm) post Cu bonding on topography M1V1-to-M2 Cu wafers with no interfacial voids observed and complete Cu interdiffusion, as supported by transmission electron microscopy (TEM) and electron back scatter diffraction (EBSD) data. Also, less than 0.1% clustered voids bonding uniformity were observed on bonded blanket Cu wafers. In addition to bonding quality characterization studies involving scanning acoustic microscopy (SAM) and confocal infra-red (IR) laser scanning microscopy, we report on the development of a prototype integrated IR, highspeed focused-ion-beam (FIB) technique with CAD overlay capabilities that enable the creation of site specific cross-sections and TEM samples to better observe bonding structures of interest.