Delamination Behavior Characterization during Bond Strength Measurement

Direct bonding is a key enabler for future node 3D semiconductor devices [1]. It is crucial to have sufficient bonding strength to withstand thinning and subsequent processes. However, there is no standardized method for bonding strength measurement. The most frequently used bonding strength measurement technique is the double cantilever beam (DCB) method. However, it is known that delamination length propagates with time by water stress corrosion. Nevertheless, the reported bonding strength is not considered these phenomena. Therefore, interfacial reactions occurred by blade insertion have been deeply investigated in this study. We unveiled the influence of annealing and plasma conditions on the bonding strength measurement using the DCB method in a controlled environment. In addition, we discuss the behavior of delamination during blade insertion. Our DCB system is compatible with 300 mm wafers and the insertion of the blade is fully controlled by actuator. The blade is inserted at the bonding interface as shown in Fig.a, and the delamination length is measured from a captured IR image. Fig.b shows the results of bonding strength measurements on 300 mm bonded wafers with different annealing conditions. It can be seen that the bonding strength increases with the annealing temperature. When the annealing temperature is lower than 150℃, the delamination length is propagated by the time even when the measurement is performed in anhydrous environments. Therefore, the calculated results of bonding energy decrease due to this phenomenon. Fig.c shows the bonding energy reduction rate for each annealing temperature with time. These values are calculated based on the value immediately after insertion and after 180 seconds. The results show that water stress corrosion significantly affects the delamination length when annealed at 150℃, however, the samples annealed above 250℃ show almost no propagation of delamination length with time and the values are almost saturated. In this paper, we present the experimental results on the effects of annealing temperatures on bond strength as well as the propagation of delamination length caused by water stress corrosion. Additionally, we will discuss other factors that can affect bond strength measurements during the presentation. Figure 1