Wafer-Level 3D Unit Processes

Another approach to 3D integration is to use wafer bonding to stack die before singulation this approach is referred to as wafer-level 3D. There have been a variety of approaches to wafer-level 3D that have been demonstrated, which can be categorized by the wafer-bonding approach used oxide-to-oxide, copper-to-copper, polymer-to-polymer (or adhesive bonding), and mixtures of these approaches (such as redistribution layer bonding). Each of these four approaches will be introduced in this section, with emphasis placed on their application to 3D. The bond unit processes are described further in Section 15.4.2, and their associated CMP issues are discussed in detail in Section 15.5. 

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