High-Efficient Chip to Wafer Self-Alignment and Bonding Applicable to MEMS-IC Flexible Integration

In this paper, a flexible approach for chip to wafer high-accurate alignment and bonding is developed using a self-assembled monolayer (SAM). In this approach, a hydrophobic SAM, FDTS (CF₃(CF₂)₇(CH₂)₂SiCl₃), is successfully patterned by lift-off process on an oxidized silicon wafer to define the binding-sites. A certain volume of H₂O (μ/mm²) is dropped and then spread on the non-coated hydrophilic SiO₂ binding-sites for self-alignment of various microelectromechanical systems (MEMS) and IC chips by capillary force of H₂O. Our results demonstrate that reasonably high alignment speed (in milliseconds) and excellent alignment accuracy ( ≤ 1 μm) are achieved when the difference in the measured contact angle between hydrophobic FDTS and hydrophilic binding-sites is >;70°. It is also found that the hydrophilic frame at the edge of each binding-site is effective in achieving successful self-alignment, while a super fine pattern at the center of the binding-site can be used to control the bonding strength. The effects of the Au/Cr thin film pattern on self-alignment are studied and discussed in this paper to enable the application of the above approach in various MEMS-IC integration processes, especially for low-cost mass production of wireless sensor nodes.