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Patterned surface modification using ambient pressure plasma processes for enhanced wafer packaging by low temperature bonding

: Eichler, M.; Mewes, H.; Thomas, M.; Klages, C.-P.; Ruddy, C.; Reinecke, H.; Reiche, M.; Gabriel, M.

Semiconductor Equipment and Materials International -SEMI-, San Jose/Calif.:
Advanced Packaging Conference 2006 : In conjunction with SEMICON Europa 2006 "Wafer Level Packaging and Beyond: From samples to volumes"; April 4, 2006; Munich, Germany
München, 2006
3 Bl.
Advanced Packaging Conference <2006, München>
SEMICON Europa <2006, München>
Fraunhofer IST ()

Wafer level packaging using silicon direct bonding is widely used for the production of Microsystems (MEMS). For most bonding processes an additional annealing step at high temperatures is required after the initial room-temperatures is required after the initial room-temperature bonding in order to increase bond strength. However, there are numerous applications, such as bonding of processed wafers for MEMS fabrication, which allow only short post-annealings at relatively low temperatures (typically < 400 °C). Therefore an activation process of bonding surfaces is desirable, resulting in high bond energies already at relatively low annealing temperatures. It has already been shown, that an exposure to dielectric barrier discharges (DBDs) as a pre-treatment for low-temperature wafer bonding yields bond energies similar or even higher than those obtained after pretreatments in low-pressure glow discharges.
This paper presents two new techniques for patterned surface modifications of wafers with atmospheric-pressure plasma processes. With these techniques the bond properties for different regions of the wafer can be controlled area-selectively in order to improve bond energies for low temperature bonding or to prohibit the sticking effect. Furthermore, surface tension can be influenced and coatings can be applied.
Compared to low-pressure plasma and wet chemical treatments, the activation with DBDs is very fast, cost efficient and environmentally friendly. The two new techniques for using DBDs to achieve an area-selective modification of surfaces are termed "Plasma Printing" (PP) and "Local Plasma Treatment" (LPT). These new methods are expected to provide new opportunities for silicon multistack systems. For these applications wafers with bonding and nonbonding areas are needed in order to realise sensors and actuators. Especially for membranes and valves the sticking effect causes major problems. One way to prevent sticking is an area-selective plasma treatment to prepare bonding and nonbonding regions.