Efficiency of H2O Diffusion Barriers at Si-Si Direct Bonding Interfaces

Direct silicon wafer bonding is an attractive way to build up stacked structures. For applications, defect free bonding is required whatever the post bonding processes, which can include thermal treatment. Direct bonding processes are usually applied with hydrophilic surfaces. Thus water trapped at bonding interfaces can induce low temperature oxidation, which is a source of gas and bonding defects. The aim of this paper is to compare the efficiency of various H2O diffusion barriers, which can be elaborated onto silicon wafers before bonding. Behaviors of thin thermal silicon oxide, thermal silicon nitride and plasma induced silicon oxynitride capping layers have been evaluated and compared to a chemical oxide layer. The efficient role of thermal oxide or oxynitride layer as a H2O diffusion barrier has been pointed out.