3 D Integration : Why , What , Who , When ? SECTION 1

>> patible 3D technology (Figure 2(g-k)). Each 3D technology is briefly described below, with some academic or industrial organization names, as examples, showing the worldwide research and development activities: (a) Packaging-based 3D integration enabled by wire bonding and flip-chip bonding as shown in Figure 2(a). These include system-in-package (SiP), which is formed by stacking thinned chips with wire bonding to connect them, and package-on-package (PoP), which is formed by stacking packages such as SiPs with flip-chip bonding. These SiPs or PoPs are already commercially available products (e.g., from Amkor in the U.S. and STATS ChipPAC in Singapore). Today's new cell phones have at least one SiP or PoP. (b) Die-to-die 3D integration enabled by thinned die-to-die bonding and through-silicon-via (TSV) intercon-nections as shown in Figure 2(b). The TSVs are typically formed by laser drill (e.g., prototype eight-die memory stack by Samsung in Korea) or deep reactive-ion-etching (deep-RIE, such as a Bosch process) (e.g., University of Arkansas in the U.S. and ASET in Japan), followed by copper fill. (c) Die-to-wafer 3D integration, as shown in Figure 2(c), enabled by die-to-wafer bonding, with interchip electrical interconnections formed by post-bond via formation (e.g., Ziptronix in the U.S.) or solder (or eutectic) bonding during the die bonding process (e.g., Fraunhofer IZM in Germany). This approach uses techniques from both packaging and wafer fab, such as die pick-and-place and TSV formation, respectively. (d) Transistors formed inside the on-chip interconnect layer on a piece of recrystallized silicon film as shown in Abstract Three-dimensional (3D) integration is an emerging technology that is expected to lead to an industry paradigm shift due to its tremendous benefits. Worldwide academic and industrial research activities currently focus on technology innovations , simulation and design, and product prototypes. Anticipated applications start with memory, portable device and high-performance computers and extend to high-density multifunctional heterogeneous integration of infotech-nanotech-biotech systems.