Testing And Characterization Of Silicon Wafer Direct Bonding

Silicon wafer bonding technique has been widely applied in the fabrication of silicon-on-insulator (SOI), microelectronics devices, micro-electro-mechanical-systems (MEMS) and so on, which could improve greatly the performance and reduce the cost of devices. Interfacial characterization of bonded wafers is one of the essential techniques in wafer bonding. In this paper, based on the infrared transmission (IR) theory, an inspection system for interfacial properties has been setup and applied for characterization of Si-Si bonding interface. Furthermore, interlayer thickness has been measured for comparing different bonding process. The main contents of the paper comprise:Based on the analysis and comparison of various testing methods for silicon wafer bonding and available conditions, a low-cost IR inspection system for interfacial defects such as voids and bubbles is designed and built. The software of the system is developed in the visual c++ 6.0 integrated development environment.Some image processing algorithms are studied, including the characteristics and limitations of linear filter, median filter, and the merits of SUSAN filter, and then a new infrared image filtering algorithms is proposed.The developed IR detection system is applied in Si-Si wafer direct bonding, bonded yield and the distribution of defects is rapid obtained. The bonding wave is observed during the pre-bonding process, and then the bonding process can be guided online. Field emission scanning electron microscopy (SEM) is used to test the interlayer of Si-Si direct bonded wafers, and also suggest that UV-irradiated activation could improve the silicon wafer direct bonding. Interfacial characteristics (bonded yield, voids'distribution, interlayer's thickness, bonding strength, etc.) is analyzed and compared under different pre-bonding processing conditions. The results are helpful for optimizing the bonding process.This paper provides a fast, reliable, and low-cost inspection system of interfacial defects for silicon wafer bonding; with the aid of the testing of other interfacial characteristics, it guides and optimizes the process of silicon wafer bonding.