Transmission Laser Bonding of Glass with Silicon Wafer

As a microassembly and an encapsulation technique, wafer bonding offers a unique opportunity to combine different materials. Transmission laser bonding not only can satisfy wafer level bonding requirements, but can also be directly implemented into the existing automatic semiconductor fabrication line. In this paper, a laser-induced wafer bonding technique for micro-electro-mechanical systems (MEMS) packaging applications has been investigated using nanosecond pulsed laser. This technique uses specific characteristics of lasers to bond a transparent substrate on top of an opaque substrate. When a focused laser beam with specific wavelength is passed through a transparent wafer, high-density laser energy is absorbed by the target opaque substrate and melts a thin surface layer, which results in a fusion joint to bond two substrates. Pulsed Nd:YAG laser with visible (532 nm) light and 6.5 ns pulse duration is used to demonstrate glass-to-silicon wafer bonding. Laser parameters including laser fluence and focused beam diameter are experimentally determined. The effects of surface condition and contact pressure for the laser bonding technique are examined. The bonded interface is analyzed by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) to determine drifting or diffusion of atoms between glass and silicon wafers during the laser bonding process. The laser bond strength is measured by tensile test in order to characterize laser bonding quality.