Influences of interface oxidation on transmission laser bonding of wafers for microsystem packaging

In the fabrication of micro-devices and systems, wafer bonding offers a unique opportunity for constructing complicated three-dimensional structures. In this paper, a wafer bonding technique, called transmission laser bonding (TLB), is studied with focus on the effects of interface oxidation and contact pressure on the bonding strength. The TLB is implemented for bonding Pyrex glass-to-silicon wafers, with and without interface oxide layers, using a Q-switch pulsed Nd:YAG laser. The tensile strengths of the TLB bonded specimens are comparable to those generated by the existing major wafer bonding techniques. The advantages of TLB are also discussed with some details. The oxide thickness is measured by spectro-reflectometry while the roughness of the oxidized surfaces is quantified using Atomic Force Microscopy (AFM). The bonded interfaces are analyzed by X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES) to study the migration and diffusion of different atoms across the bonding interface and to provide the necessary information for the understanding of the bonding mechanism. A thermal penetration analysis is also provided to validate the findings of the bond strength and spectroscopic evaluations.

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