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Direct bonding is used to join two mirror-polished wafers without any additional material. This technique appears to be more and more used for microelectronics or microtechnologies applications such as 3D and optical integration, MEMS or heterostructure assembly. Silicon oxide (SiOx in which x is lower or equal to 2) deposition is widely used in microelectronics or microtechnologies. Thus it seems very attractive to develop tuned processes of SiOx surface preparation which would allow in many cases using the same layer (e.g. oxide layer) at the bonding interface and avoiding the development of new specific preparation process. One of the main challenges in this study is to obtain efficient bonding of deposited oxide films i.e. high bonding energy values. We will focus hereafter on the study of hydrophilic surface bonding in the low-temperature range (from room temperature to 400 ◦ C) of deposited SiOx layers. The nature of the deposited films and the effect of several surface preparations (such as chemical-mechanical polishing or plasma activation) which were applied to deposited films prior to direct bonding were investigated. Main results regarding the bonding strength are reported here.

Direct bonding is used to join two mirror-polished wafers without any additional material. This technique appears to be more and more used for microelectronics or microtechnologies applications such as 3D and optical integration, MEMS or heterostructure assembly. Silicon oxide (SiOx in which x is lower or equal to 2) deposition is widely used in microelectronics or microtechnologies. Thus it seems very attractive to develop tuned processes of SiOx surface preparation which would allow in many cases using the same layer (e.g. oxide layer) at the bonding interface and avoiding the development of new specific preparation process. One of the main challenges in this study is to obtain efficient bonding of deposited oxide films i.e. high bonding energy values. We will focus hereafter on the study of hydrophilic surface bonding in the low-temperature range (from room temperature to 400 ◦ C) of deposited SiOx layers. The nature of the deposited films and the effect of several surface preparations (such as chemical-mechanical polishing or plasma activation) which were applied to deposited films prior to direct bonding were investigated. Main results regarding the bonding strength are reported here.

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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.