Mechanisms for Room-Temperature Fluorine Containing Plasma Activated Bonding

Abstract

© 2017 The Electrochemical Society. Room-temperature direct bonding is an attractive approach to combine dissimilar wafers avoiding any thermal stress by a difference of thermal expansion coefficients. In this paper, we investigate a room-temperature bonding process using fluorine containing plasma activation and propose a mechanism model to address the roles of fluorine. Details of the plasma treated surface and the bonding interface are characterized. Experimental results show that fluorinated oxide formed on the silicon surface results in a lower bonding strength at the initial bonding step before the storage. On the other hand, during storage at room temperature, fluorinated oxide asperity might be more easily softened by the interfacial water enabling a significant bonding strength enhancement. As a result, strong bonding strength of Si/Si wafer pairs, very close to the fracture energy of bulk silicon, is achieved after storage in air for 24 h, even at room temperature.