Self-alignment of Silicon Chips on Wafers: a Numerical Investigation of the Effect of Spreading and Wetting

3D integration is the key to advanced microelectronic systems. Die-to-wafer assembly is a necessary step to reach full integration. Self-assembly methods are promising due to their parallel aspect, which overcomes the main difficulties of the current techniques. Especially promising are the self-assembly methods based on capillary alignment. In such a method, capillary forces are used to align the chip and evaporation of the liquid droplet eventually leads to contact and direct bonding of the chip on the fixed pad. In a preceding work, the stable and unstable displacement modes have been investigated, assuming that the fluid completely wets the surfaces of the chip and the fixed pad, and that the liquid is anchored to the all the edges. However, it appears that these assumptions are the most favorable case, which is not always reached. Poor spreading and/or occasional overflow of the liquid are the causes of poor alignment. In this work we focus on the mechanisms of spreading and overflow, and analyze the motion of the chip during the spreading. [PUBLICATION ABSTRACT]