IWLPC (Wafer-Level Packaging) Conference Proceedings


Authors: Jong-Seung Park and Ampere A. Tseng
Company: Arizona State University
Date Published: 10/10/2004   Conference: IWLPC (Wafer-Level Packaging)

Abstract: In the field of microelectromechanical systems (MEMS) packaging, wafer level bonding offers a unique opportunity to combine different materials for a microassembly or an encapsulation. The conventional wafer bonding techniques require a high processing temperature and a flat surface for bonding, also conventional methods care little about local selectivity of bonding. Transmission laser bonding (TLB) not only can satisfy the requirements of wafer level bonding but also can break through the limitations of conventional wafer bonding techniques. In this paper, laser-induced wafer bonding technique for MEMS packaging applications has been investigated.

Laser bonding technique uses specific characteristics of laser to bond a transparent wafer on top of an opaque wafer. When a focused laser beam with specific wavelength is passed through a transparent wafer, highdensity laser energy is absorbed by the target opaque wafer and melts a thin surface layer, which results in a fusion joint to bond two substrates. Pulsed Nd:YAG laser with 532 nm (visible light) wavelength and 6.5 ns pulse duration is used to demonstrate glass-to-silicon wafer bonding without an intermediate layer. Laser parameters including laser fluence and focused beam diameter are experimentally determined.

The surface requirements in terms of micro-roughness and flatness are investigated by atomic force microscopy (AFM) and profilometer. The bonded interface between glass and silicon wafers is analyzed with Auger electron spectroscopy (AES) to verify the chemical composition of the bonded layer and the distribution profiles in depth. In order to characterize the laser bonding quality, laser-induced glassto-silicon bond strength is measured by tensile test under different bonding conditions of applied contact pressure, and is compared with those of conventional wafer bonding methods.

Keywords: Wafer bonding, Laser, Silicon, Glass, MEMS Packaging.

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