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The device and cap wafer prior to wafer to wafer vacuum bonding.

Bonding Process

Wafer-to-wafer vacuum bonding processes

NanoGetter® can help you dramatically improve the vacuum quality of your MEMS device. The NanoGetter® material can be easily integrated into both the process and design of your micromachined device. Typically the NanoGetter® is applied to a surface in the vacuum cavity of the micromachine as illustrated below. After vacuum sealing, the NanoGetter® can absorb remaining gases that were trapped or desorb from the walls of the microcavity.

Commonly employed processes

Anodic or Electrostatic Glass to Silicode Bonding is known for generating copious amounts of oxygen during the bonding process. This oxygen will be gettered by NanoGetters®. Oxidation of these gettering materials occurs at typical anodic bond temperatures of 350ºC and 500ºC.

Glass Frit Reflow Bonding: A screen printed glass paste is re-flowed at 375º to 450ºC to seal over hermetic feedthroughs to form a vacuum seal. This process has a proven track record of working with NanoGetters® technology. Glass reflow bonding is compatible with polysilicon, LIGA and single crystal silicon MEMS.

Solder and Eutectic Bonding can be compatible with NanoGetters® if the re-flow or bond temperature is high enough. Eutectic bonds at 400ºC work well as do high temperature solder processes. NanoGetters® have worked well with Au/Sn solder sealing at 350ºC. Even though NanoGetters® work at relatively low temperatures, some very low temperature solders will not heat the MEMS wafers enough to enable passive gettering. For low temperature solders, microheating elements are required to locally raise the temperature of the NanoGetters®. With eutectic and solder bonding, it may be possible to use a blanket NanoGetter® coating on the cap wafer surface and avoid tooling costs associated with patterning NanoGetters®.

Silicon Fusion or Direct Silicon Bonding: This bonding technique requires an ultra clean silicon or silicon dioxde layer and long soaks at higher temperatures 900ºC to 1200ºC. Issues with silicide formation can be encountered with getters at these temperatures. NanoGetters® have excellent adhesion, with no peeling or particles when annealed on silicon surfaces above 900ºC.

CVD or Reactive Sealing: Various types of reactive sealing methods have been developed. Only those techniques that employ a long, narrow channel to seal off a microcavity can effectively use NanoGetters®. Care must be taken that chemical vapor deposition does not coat the NanoGetters® during the sealing operation.

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