Sub 200 nm wafer-to-wafer (w2w) overlay accuracy on the entire 300 mm wafer was successfully demonstrated via wafer level Cu/SiO 2 hybrid bonding. Cu bonding pads relevant for back-side illuminated (BSI) complementary metal oxide semiconductor (CMOS) image sensor (CIS) were used for the experiment. Further, a crucial component to improve the overlay accuracy, namely the overlay model which identifies systematic alignment errors, was described.
IntroductionThe growing demand for increased functionality and higher performance in integrated circuits (ICs) requires more transistors which means the transistor and interconnect size must decrease in order to maintain the same chip size (with respect to its lateral dimensions). Because of these factors different integration schemes like three-dimensional (3D) ICs with the purpose of reducing global interconnection length become more and more relevant for increased speed and operation frequency. W2w bonding is an attractive and crucial technique for enabling 3D integration. The bonding processes of fusion bonding and metal bonding, such as metal thermocompression, eutectic, and transient liquid phase (TLP) bonding, are well established and many of them are already in mass production [1][2][3][4]. The more recent approach of hybrid wafer level bonding is an attractive technique for reliably connecting heterogeneous structures, such as connecting processor with memory, analogue IC or microelectromechanical systems (MEMS), having high-density interconnects (<10 μm pitch). Within this work the bonding process for Cu/SiO 2 hybrid structures, which is an attractive material combination for BSI CIS, was investigated [5]. Furthermore, relevant changes to improve the w2w post-bond overlay accuracy are presented, as well as the overlay model which was introduced to isolate and quantify different global misalignment root causes, such as translation, rotation and scaling.
To meet future 3D stacking requirements on wafer-to-wafer level, we successfully demonstrate oxideoxide direct bonding on 200mm with and without copper level utilizing face-to-face alignment and bonding within one process module as well as on the same chuck.
Both fusion and hybrid wafer bonding are enabling increasing integration density as well as advanced device integration strategies. In any case, wafer-to-wafer overlay accuracy is the most critical factor for successful integration in 3D stacked devices. Despite alignment of both wafers is of major impact for the post-bond overlay accuracy, initiation and control of the bond wave between both substrate wafers the essential. During contacting device wafer surfaces, wafer stress as well as bow is influencing the bond wave dynamics. Engineering the continuous wave dynamics and influencing parameters are both key for optimum post-bond overlay accuracy. Any wafer stress will result into distortion of patterns and additional misalignment term. Despite typical distortion values are well below 50nm already, further optimization of both wafer bonding as well as wafer preparation and preprocessing are key for hybrid and monolithic integration.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.