3D Integration of Inverted IndiumGalliumArsenic MSM Array to Silicon Platform by Low Temperature Chip-to-Wafer Bonding

With the continuous scaling of the pitch width following Moore's Law, the global interconnects in microprocessors and high performance application-specific integrated circuit (ASIC) face more problems than ever to fulfill the signal synchronization and energy requirement. On-chip optical interconnect is a promising solution to this problem for reduced delay time and lowered power consumption. 3D integration of active compound optoelectronic devices to silicon chip is an important approach to realize on-chip optical interconnects and thus attracts more and more interests nowadays. In this work, we investigated a low temperature approach for heterogeneous integration of III-V photodetector arrays to Si CMOS chip. The photodetectors are planar InGaAs metal-semiconductor-metal (MSM) photodetectors on semi-insulating InP substrate. The MSM arrays were flip-chip bonded to silicon wafer by low temperature metal-metal bonding based on indium-gold transient liquid phase reaction. A solid bonding was achieved with a bonding temperature of 200 ° C under compress pressure of 2 MPa. The photocurrent and the dark current were measured prior and after the 3D integration process. It was found that the dark current at bias of 2 V was reduced by 30 % while the photocurrent has increased 70 % after bonding. The total thickness of the bonding metal layers is less than 1 mu m, making it a suitable approach for applications in which vertical topology accuracy is crucial. The low bonding temperature assures the properties of III-V optoelectronic devices intact during this back end of line (BEOL) processing.