Treatments of Deposited SiOx Surfaces Enabling Low Temperature Direct Bonding

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.