The Research Of Low Temperature Silicon Wafer Direct Bonding Method

Silicon wafer direct bonding technology has very important applications in microelectromechanical system, silicon on insulator manufacturing and 3D integration of the materials. Compared with the mediation layer bonding method and anodic bonding method, the direct bonding method avoids pollution caused by the intermediate layer and does not need the effect of external electric field. Traditional direct bonding methods need to be carried out between 800? and 1000?, but the high temperature will cause many problems such as the residual stress produced by different thermal expansion coefficient. And traditional direct bonding method needs to be done in the ultra clean laboratory environment, which means that the operating space is limited. These problems seriously hampered the development of the industrialization of the silicon wafer bonding. Therefore, looking for a method of direct bonding in conventional laboratory environment at low temperature is a big problem which needs to be settled.This paper explored a set of suitable silicon wafer direct bonding method in routine laboratory environment at low temperature by changing the parameters of bonding process and the characterization of samples after bonding. And the paper also analyzed the influence of various parameters on the boding performance and verified the bonding mechanism in several ways. Through the experiment of silicon wafer stacked, the silicon wafer stacked technology is proved to be feasible, which lays the foundation for silicon wafer direct bonding technology on the application of 3D package.The bonding of silicon wafer whose surface oxide layers are in different thickness was studied, and the results showed that the bonding rate of surface thermal oxidation silicon wafers is generally higher than that of silicon wafers under natural surface oxidation with the same bonding parameters. As for stacking the stacked silicon wafers, a good result of bonding was obtained.Bonding rate and the bonding strength of bonded wafers with different bonding parameters were studied, and the result showed that the surface bonding temperature had the greatest influence on the properties of bonding. The silicon wafers bond well and have good bonding strength when the bonding temperature reaches 200 ?. The heat treatment temperature has great influence on the bonding performance. Under the condition of same bonding rate, the silicon wafers get high bonding strength at higher temperature. Bonding pressure has a slight effect on bonding performance. With the increase of bonding pressure, the bonding rate and the bonding strength grew slowly. Pre-bonding and vacuum environment are very important for the bonding process, the bonding strength of bonded silicon wafers increased after pre-bonding in a vacuum environment.Mechanism of silicon wafer bonding was studied. The results showed that activation process has no effect on thickness of surface oxide layer and surface roughness of the silicon wafers, and the concentration of the Si-OH increased after the process of surface activation of wafers, which conform to the speculation about the bonding mechanism. The bonding the P-type and N-type silicon wafers can show the electrical performance of PN junction.