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 H₂Oμ 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 (μ m) 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.