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Handling and Contamination Control for Critical Space Applications 299

on-orbit. MEMS package contamination control requires comprehensive contamin-
ation control protocols for fabrication and assembly. The contamination effort deals
with both molecular and particulate contaminants resulted from facility environ-
ments and packaging procedures. It is important not to jump to the conclusion that
contamination is the culprit. The types of failures associated with stiction and
particulates could also be caused by design or manufacturing discrepancies such
as over or under etching. 10–12
The bulk of today’s MEMS devices are manufactured in the traditional semi-
conductor clean room facilities with air cleanliness ranges from Class 100 to Class
10,000 per FED-STD-209. Examples of damage caused by unwanted molecular and
particulate contamination suggest the deficiency of conventional facility, equip-
ment, and process at the MEMS package level. One hard-to-detect failure in MEMS
devices is particulate contamination that occurs during fabrication. The effect
produced by dust adhering to the wafer in the water process differs according to
the process. Particles also affect thermal management in photonic packages.
A typical edge-emitting communications laser diode will have an energy flux
through the facet of up to 2 million watts per square centimeter. The influence of
even slight levels of impurities or contaminating particles is disastrous for thermal
control. Therefore, the best contamination control approach is to not allow contam-
inants to generate, stay around, and finally adhere to surfaces.
Contamination-induced effects can be reduced by fabricating MEMS devices in
a better clean room facility with more stringent clean room protocols. Class 100
clean room environments with localized Class 10 work areas are optimal for post-
singulation processing. As a minimum, the device should be in a Class 100 clean
room environment from its release point until it is safely sealed in a clean, hermetic
package. Dust generated by equipment adheres directly to wafers, and thus has a
large effect. Sufficient consideration should be given to dust when selecting equip-
ment models; it is also important for device manufacturers to take steps to reduce
dust generation when setting process conditions or performing maintenance during
production. It is important to package MEMS devices in a controlled, hermetic,
particle-free environment. Every step, from die preparation to package seal, must be
performed in a Class 100 clean room environment until the device is safely sealed in
a clean hermetic package. Clean room techniques normally reserved only for wafer
fabrication must be extended to the probe, die-prep, and assembly areas.
Further contamination control improvement can be achieved by implementing
better assembly processes for MEMS devices. Certain unwanted organic compound
residues in the adhesives can lead to catastrophic optical damage (COD) of the laser
die. Outgassing occurs when materials used for die attach, bump preparation, or
packaging are included in the hermetic cavity. Improved processes keep these
materials from being included in the package, thus eliminating potential contamin-
ation sources. Because the process takes place at wafer scale, the cavity formed can
be arranged to include only the active MEMS device. With this approach, materials
known to create outgassing effects are simply excluded from the hermetic cavity.
For particulate contamination, Blanton and others at CMU have developed a
tool called contamination and reliability analysis of microelectromechanical layout

© 2006 by Taylor & Francis Group, LLC