16
COVER STORY
What can MEMS do for CMOS?
Since 2000 independent foundry Silex Microsystems has been a pure play MEMS
manufacturer. In that time they have developed an understanding of the electrical and
mechanical engineering expertise required. As the company announces its new 8”
MEMS fab they are not only ready for the next phase of the growing market but
discover that some MEMS specific processes may help with current CMOS challenges.
M
icro Electro Mechanical Systems (MEMS) different order of magnitude than for semiconductors. Silex
manufacturing requires the understanding of manufactures MEMS, complex mechanical and electric systems
mechanical and electrical engineering brought on a micro scale that are built in the form of a chip. The minute
together in devices built on a micro level. Building at such small scale makes it possible to manufacture cell phone microphones
scales has been made possible through advances in as small as a grain of rice, and to enter medical instruments into
semiconductor manufacturing. This does not mean the same the blood stream or fit a DNA lab onto a chip.
manufacturing requirements apply but that the ability to build
devices on such a tiny scale opened up new possibilities when Almost all MEMS companies founded today are fabless, which
traditional mechanical and electrical engineering concepts were means they will need a foundry partner to manufacture their
applied. It has been said that MEMS manufacturing is akin to product. The MEMS foundry scene may be a bit confusing as
applying industrial revolution engineering to a minute scale. there are a number of actors in the market that offer both
MEMS design and pure foundry manufacturing services. There is
MEMS have been seen as a potential growth extension of also a range of captive MEMS actors that offer their spare
semiconductor manufacturing ever since the market began with capacity to foundry customers. Silex was really one of the first
sensors for air bags in automobiles. Since then printer ink heads MEMS foundries to provide a solid “pure play” foundry offer.
have become the largest sector but a wide variety of products This means that Silex customers can rest assured that Silex will
now exist. Most of the players in MEMS arena have a core focus not use exposed know how to help competitors with design or
on another industry, such as semiconductor manufacturing. that manufacturing capacity will vanish as a captive player runs
MEMS is seen by some as an extension that requires similar out of excess capacity with respect to their own products.
tools with tweaking. There have not been as many companies
that focus on MEMS specifically. One company that has been Most of the steps in the MEMS manufacturing process are the
MEMS focused since they began in 2000 is independent Swedish same as those in the semiconductor industry. However, the
MEMS foundry Silex. Through their experience they have production complexity of MEMS is considerably greater since
become one of the world’s leading MEMS foundries with almost they contain three dimensional structures. Both industries use
80 customers, at least ten are large volume customers. the same manufacturing equipment, but differ in terms of
technique. Within the semiconductor industry the bulk of the
Silex Microsystems is based in Järfälla, 20 minutes north of wafer is used as a bearer, while in MEMS it is also a part of the
Stockholm by car. It is a fast growing area of commuters and product itself. MEMS has developed bonding techniques to join
business parks set in beautiful scenery with Lake Mälaren several wafers to each other as well as special etching methods
nearby. Their customers are around the world and can be found to create three dimensional structures out of the wafers.
in the medical, biotech, telecommunications and consumer
electronics industries. They also produce MEMS for the Finding the right mix
automotive and other manufacturing industries. This breadth of Manufacturing processes that are key to understanding MEMS
customers and industries is a key difference for MEMS manufacturing include wafer bonding, deep reactive ion etching
manufacturers as the volumes and types of devices are of a through the wafer, anisotropic wet etching and processing of
wafers with topography using thick resist processes. These are all
3D processing skills that are currently not occurring in CMOS
fabs. The 3D processing on perforated substrates or substrates
with large topography requires specific skills when it comes to
wafer handling and coating.
This level of manufacturing expertise requires a more demanding
capability from mechanical engineers than typical semiconductor
engineers. Realising this Silex has ensured that the mix of their
engineering staff reflects MEMS manufacturing needs. There is
an even split of MEMS and integrated circuit (IC) engineers. The
MEMS engineers bring mechanical expertise to enable devices to
Schematic cross section of through wafer interconnect and be designed and manufactured whilst the IC engineers provide
wafer level packaging of a MEMS device robust process control with effective repeatability. Both groups
www.euroasiasemiconductor.com October 2008
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