Investigation On The Mechanism And Microstructure And Mechanical Properties Of The Anodic Bonding For The Pyrex Glass To Metals

Anodic bonding, also called field-assisted diffusion bonding, is a key technique for sealing and fabricating the MEMS (micro-electromechanical system) and the micro-instruments, bonding alkali-rich glass to metals or semiconductors. And it became increasingly important in the MEMS production. In this dissertation, the bonding technique for glass to silicon, glass to aluminium and glass to Kovar alloy are investigated. Based on the experiments, common anode process and two steps process are given, and this can be used to bonding multiple layers of wafers. The bonding mechanism and bonding parameters are analyzed. The SEM, EDS and Instron 5544 machine are applied to investigate the interfacial structure, the bonding mechanism and the tensile strength of the bonded samples.It is shown that the bonding technique mainly relied on the ions diffusion and the anode oxidize, the voltage, temperature and roughness of the surface are the important factors to influence the bonding ratio and the bonding strength. The higher the voltage and the temperature, the denser the chemical bond in the interface will be. The voltage and temperature have a complementary effect with each other. So the bonding parameters should be decided according to the requirements of the samples. There is a very obvious transitional layer in the bonding interface. The EDS results indicate that ion diffusion exists in the bonding interface and the elements distributes in the pattern of gradient.It is found in the experiments that in the bonding process of glass to silicon, it is the O^2- diffused into the silicon and react with the silicon that result the successful bonding; for the case of glass to aluminium, aluminum is motivated and drifted into the glass, at the same time the oxygen ions diffused into the bonding interface. The sodium depletion results in the diffusion of aluminum into the glass where the diffused aluminum reacts with the non-bridging oxygen. And then permanent bonding is achieved; as to glass to Kovar alloy, the Fe in the alloy was oxidized preferentially by the O^2-, the roughness and constitution of the surface of the alloy can influence the bonding process dramatically.Based on the experiment above, the bonding methods of common anode and two steps are given. Using the two methods, multiple layers can be bonded together. The common anode method can be considered two parts of the anodic bonding in parallel. In this process, the ion movements, the interfacial reaction and electrostatic field in both sides of the anode will occur at the same time. For the method of two steps, the current variation in the second step has no difference with the first step. In the bonding process, the Na⁺ can also move in the opposite direction. Compared the microstructure bonded in the first step and second step, it is almost the same with the microstructure bonded with anodic bonding method.