Line bonding of wafers using transmission laser bonding technique for microsystem packaging

The transmission laser bonding (TLB) technique can not only satisfy wafer level bonding requirements but also be directly implemented into the existing semiconductor production line. Using a nanosecond pulsed Nd:YAG laser, Pyrex glass-to-silicon wafers were successfully bonded by uniformly spaced individually bonded spots. The bond strength resulting from use of the TLB technique is comparable to the strength of the bond produced by bonding techniques currently used in microsystem or micro-electro-mechanical system (MEMS) packaging. In addition to packaging, the TLB technique can also be used to conveniently assemble and encapsulate miniature devices with selective bonding areas. In this paper, the continuous line bonding produced by the TLB technique has been implemented and characterized using various sets of bonding conditions. In this paper, TLB is used to make continuous line bonding of Pyrex and silicon wafers. Continuous line bonds are typically generated by overlapping single bond spots, in which the overlapping is achieved by varying the laser scanning speed as it pastel across the wafers. This results in a wide range of laser energy density (absorbed laser fluence). The specific effects of laser energy are examined and evaluated in order to define the laser operation window which provides the optimal conditions for reliable line bonding. In addition to the bond strength evaluation, the bonded interface is analyzed by Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) to quantify the drifting or diffusion of atoms that occurs between glass and silicon wafers during the bonding process