H2O Diffusion Barriers at Si-Si Direct Bonding Interfaces for Low Temperature Anneals

Abstract

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 using 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 efficiencies 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 standard for low temperature annealing. The efficient role of thermal oxide, nitride or oxynitride layer as a H2O diffusion barrier has been pointed out.