HIGHLIGHTS

(i). Heterogeneous integration for multifunctional devices

Wafer bonding technology offers significant advantages for synthesis of heterostructures that cannot be usefully synthesized by more familiar methods such as epitaxial techniques. Materials with large misfits or different lattice structures across interfaces can be bonded without causing defect formation in the crystal adjacent to the bonded interfaces. An example of such wafer bonded Si/Ge heterostructures is shown in Fig. 1. The objective is to integrate dissimilar materials by wafer bonding technique for applications in 3 areas: (1) electrically active bonded junctions, (2) fabrication of alternative substrates for semiconductor materials with no natural lattice matched substrate, and (3) system-on-a chip (SOC) integration for multi-functionality. Material systems of interest are: Ge/Si, III-V/Si, II-VI/Si.

Fig. 1. (a) High resolution cross-sectional TEM image of the bonded Ge/Si interface. Their 4% lattice mismatch accommodated by misfit dislocations along the interface (b). (Right) How an electrically driven silicon laser might work in the future, as proposed by Canham (Nature 408 (2000) 411-412). HREM image of the bonded p-Si(100)/n-Si(100) interfaces with Si nanocrystals embedded in the oxide (far right). This structure was successfully synthesized for the first time by a combination of wafer bonding and thin film methods.