Communication—Fluorinated Plasma Treatments Using PTFE Substrates for Room-Temperature Silicon Wafer Direct Bonding

Abstract

We introduced polytetrafluoroethylene (PTFE) substrates and silicon wafers into oxygen plasma to form fluorinated oxide layers on the silicon surfaces, similar to sputtering processes. After a short plasma treatments (∼60 s), fluorinated oxide layers were formed and could be controlled by adjusting the size of the PTFE substrates. Two wafers were brought into contact at room temperature (∼25 • C), and the surface energy was significantly improved to ∼1.8 J/m 2 , even without employing heating. This surface energy is sufficiently high to withstand subsequent mechanical processing. No defects or nanopores were observed in the bonding interface.

Room-temperature bonding of glass chips via PTFE-assisted plasma modification for nanofluidic applications

“…However, a F signal emerged on the PTFE-assisted activated surface at 685.2 eV which was attributed to Si-F bonds. 37 Due to the sputtering effect of ions with kinetic energy and the reactivity of ROS generated in O 2 plasma, the C-F bonds of the PTFE were broken through chemical oxidation to form CO, CF x O y , and most importantly, fluorine radicals (F*), as shown in reaction (1). 28,38 The gaseous CO and CF x -O y could desorb from the PTFE surface, while neutral F* could diffuse onto the glass surface.…”

Nanofluidics: A New Arena for Materials Science

“…A strong, nanostructure‐friendly, and high‐pressure‐resistant room‐temperature (25 °C) bonding method based on a one‐step surface activation process with an O 2 /CF 4 gas mixture plasma treatment was developed. These plasma treatments are able to adjust surface groups as well as the wettability of the substrates, which is considered to facilitate bonding in mild conditions, but the bonding mechanism is still not very clear and need further elucidate. The use of the new bonding techniques thoroughly eliminates the obstacle of bonding for functional component integration in nanochannels.…”

Scalable bonding of nanofibrous polytetrafluoroethylene (PTFE) membranes on microstructures

“…This and other approaches that use chemical and plasma treatments to enhance wetting and adhesion properties of PTFE are not suitable for bonding porous hydrophobic PTFE membranes since they make the membrane wetting, rendering it unsuitable for applications discussed here. Recently, Wang and Suga [22] presented a new approach for bonding silicon substrates at room temperature in which fluorinated oxide layers were formed on silicon surfaces in a plasma chamber, and the substrates were later bonded together under pressure. Similar processes may be developed to fluorinate the substrate of interest (ceramic, metal and polymer) and bond it to an ePTFE membrane under pressure.…”