Laser Raman Spectroscopic Study On The Interfacial Stress Of Si-Glass Anodic Bonding

Anodic bonding is a technology widely used in Micro-Electro-Mechanical Systems(MEMS). The stress induced by anodic bonding often causes the break-up of structures, which can increase product cost and extend development cycle, and it has been a key issue in this field. The bonded interface has the most complex stress state, which is also the main location where structure break-up takes place. However, few studies are involved in the stress at the anodic bonded interface, especially those on the formation of interfacial structure and its influence on interfacial stress. Study on the interfacial stress is very important to the integrity of anodic bonded structures, but seldom are there some studies based on experiment about this issue. Here a study based on laser Raman spectrometer was conducted to investigate the interfacial stress in silicon-glass anodic bonding.In this study an orthogonal test of three factors and three levels was designed to investigate the effect of bonding voltage, temperature and charging time on the stress at the interface. Results show that the interfacial stress experiences increase and then decrease as the bonding voltage increases. The interfacial stress decreases as the bonding temperature increases. As the charging time increases, interfacial stress matches the tendency of decrease after increase.In order to investigate stress evolution during anodic bonding, a home-made miniaturized anodic bonding device was developed and coupled with a Raman spectrometer. It was concluded that a 80 MPa tensile stress formed in the silicon near the silicon-glass interface under the bonding condition of 400℃,-1000V and 1 atm.In addition, large-scale atomistic simulation was conducted to study the structure of silicon-glass anodic bonding interface. Simulated results combined with in situ Raman spectroscopic study revealed that the morphology of the silica at the bonded interface was most likely to be amorphous. And based on the study of different thickness of amorphous SiO2 at the bonded interface, the amorphous SiO2 thickness is at least 2 nm in the case of 90 min anodic bonding at 400℃,1atm with the DC voltage of -1000V. The silicon oxidation reaction rate is about 0.022 nm/min from 30 to 90 min.