3D Wafer Level Heterogeneous Integration
Authors: Wolf M Juergen , Lang Klaus-Dieter 
Published: February 2020

3D integration is worldwide considered as one of the most important key technology for microelectronics to meet the growing demands regarding more functionality with concurrent increase in performance as well as miniaturization and cost reduction. So 3D integration is of main relevance for application areas e.g. cyber physical systems, internet of things, ambient assisted living (AAL) as well as information & communication, logistics, security, automotive, health care and industrial electronics. Besides following “More Moore”, Europe is pursuing a strategy on heterogeneous integration approaches following “More than Moore”. In this context, individual and different 3D integration approaches are adapted to the specific application scenarios.
Interposers with Through Silicon Vias (TSV) are becoming a very important element for the realization of 3D System in Packages (SiPs). Main advantages of silicon interposers are the decoupling of front end/back end processing for the implementation of TSVs, redistribution layers (RDL) and the integration of active and passive devices. Besides independent manufacturing, interposers can be realized in short time-to-market time frame and in a cost effective way. TSV interposers are designed and manufactured for the different application areas which results also in different technical specifications ranging from high density TSV integration and high density RDL for digital applications to interposers for RF application as well as MEMS integration and optical interconnects.
The presentation will highlight results and technical achievements for 3D integration using TSV interposer and addresses as well the broad spectrum of topics from design, technology and reliability related to 3D systems.
Concerning technical features, interposers deal with high density wiring redistribution layers (RDL), TSVs and top/bottom side interconnect formation (bumping). This allows the electrical signal routing across the top side and to the interposer back side. Some new applications appear to require up to 4 layers RDL of less than 1μm line/space and silicon oxide/nitride dielectric layer.
Silicon interposers with TSVs provide additional features to address 3D-SiP for heterogeneous integration. These include:

Device carrier for stacked devices,

High density wiring between (stacked) components,

3D device stacking using TSVs,

Integrated passive devices

Embedding of active devices into the IP,

Functional layer integration (actors, sensors, antennas),

Modularization,

Integrated test features

For the assembly and 3D stack formation of the devices, different interconnection technologies, e.g. micro solder bumps (SnAg) and copper pillars, are used to deal especially with surface topography of the devices and warpage of the board/substrate.
Beside silicon interposer, also glass interposers are emerging elements for specific applications. Compared to silicon interposers, glass interposer currently have only limited via dimension and cannot deal with high density TSVs, e.g. <5µm diameter and 10µm pitch. For this, the supply chain is still emerging. The metallization process for silicon interposers is commonly established in wafer fabs. However, most of these facilities do not possess via-last or bumping capability.

SUMMARY

3D integration technology is one of the main drivers in packaging and system integration to meet the requirements for high functionality, highly miniaturized smart systems.
Future advanced 3D systems will result in complex 3D stacking approaches using the TSV technology. Silicon interposers with TSVs are an important element to combine different advanced devices into one miniaturized system (SiP) with high functionality and to overcome currently existing issues regarding TSV integration into active devices. One important task is the supply chain between e.g. IDMs, OSAT or packing houses.
Another crucial aspect is the balance between performance improvement and 3D manufacturing cost (TSV & packaging). So the implementation of 3D integration using TSV and interposer is very product specific. 3D integration requires, beside the technology approaches, also an overall SiP process integration approach which addresses design, technology and reliability.
Fraunhofer IZM’s center “All Silicon System Integration Dresden - ASSID” and the Fraunhofer Cluster 3D Integration (http://www.3d-integration.fraunhofer.de/en.html) are focusing on the development and prototyping of 3D systems using Cu-TSVs in active devices (via middle, via last) and silicon interposers as well.