Experimental And Theoretical Study On Low-temperature Wafer Bonding

Bonding temperature is one of the most important indicators in wafer bonding. For many applications, high-temperature wafer bonding may generate many problems, particularly pre-structured wafers which contain temperature-sensitive structures. Thus, studies aimed at low-temperature wafer bonding are of great significance. Low-temperature wafer direct bonding with its low temperature, good bonding quality and fewer restrictions has been widely used in the fabrication of silicon-on-insulator (SOI) and Micro-Electro-Mechanical-Systems (MEMS) devices. Localized laser bonding with low entire temperature, selectivity of bonded area and easy controllability provides a simple and robust bonding method for packaging and fabrication of MEMS devices. Therefore, among current mainstream wafer bonding processes, studies have focused on the low-temperature wafer direct bonding and localized laser bonding.The main content of this paper comprise:Proposing a description of surface requirements for wafer direct bonding under low temperature. Analytical expressions of the effect of wafer bow, waviness and microroughness are deduced according to the elastic mechanics of thin plate and JKR contact theory respectively, and the results of model are compared with followed experimental data.Developing a novel pressure-free localized laser bonding process for silicon and glass. The process is realized by applying surface activation to wafers, selecting suitable laser parameters, and the bonding conditions. The impact factors, such as laser power, scanning velocity and material of base have also been studied.Simulating the temperature distribution for localized laser bonding and optimizing the process. The three dimensional temperature distribution of laser bonding with Gaussian thermal resource is modeled by using finite element method. In the model, the temperature distribution with different process parameters is simulated and the bondline width is obtained. Then the key process parameters of laser bonding including laser power, scanning velocity and initial temperature are obtained by scanning experiment. Finally, with regression analysis on the simulation results, a regression model is set up and the optimal process parameters of laser bonding are obtained. Moreover, the results can provide a theoretical basis for improving the laser bonding process.