Al-Al Direct Bonding with Sub-µm Alignment Accuracy for Millimeter Wave SiGe BiCMOS Wafer Level Packaging and Heterogeneous Integration

In this work, we demonstrate an Al-Al direct bonding process for advanced wafer-level packaging and heterogeneous integration. The wafer bonding process is performed at 300°C with an alignment accuracy of <;1 μm enabling fine-pitch wafer-to-wafer interconnections. The electrical performance of the Al-Al direct bonding is analyzed using different types of DC and RF test structures. Low resistance Al-Al bonding interconnections with mΩ-range contact resistance and insertion loss values <;0.1 dB per interconnection are realized. An interposer based WLP process flow is developed which enables high performance mm-wave SiGe BiCMOS wafer level packaging applications.