Pressure-assisted reaction bonding between a W sheet and a Si80Ge20 alloy

Abstract

The conditions and mechanism of bonding a tungsten sheet directly onto a Si80Ge20 alloy by hot pressing have been studied. It was found that W/Si80Ge20 bonds are formed only at relatively high temperatures. The pressure and time required for bonding decrease with increasing temperature. In the initial stage, the W/Si80Ge20 reaction follows a parabolic kinetics, suggesting it is a diffusion-controlled process. The activation energy is 4.9 eV, and the parabolic rate constant is given by Kp=(4.2±0.1)×1018 exp[−(5.7±0.1)×104/T] (μm2/ min) A bonding mechanism is proposed based on scanning electron microscopic observations and chemical analyses of the interface. Selective reaction between silicon and tungsten leaves a Ge-rich layer at the W/Si80Ge20 interface, thus reducing the melting temperature. When the silicon content in the interfacial layer becomes sufficiently low, the layer melts at the hot-press temperature. Molten materials fill in voids and microcracks by the capillary effect, resulting in an intimate contact and a strong bond. A mathematical model of Si diffusion is proposed. Solving the equation by the finite-difference method, silicon composition profiles were obtained and the silicon diffusion coefficient was estimated.