Department of ECE
Parameters about clean room
Characteristics about clean room
Contamination & Measurement
Cleaning & Materials Selection
Protocols to improve control
MEMS is the acronym of Micro Electro Mechanical
Systems. It is a highly miniaturized device or an array of
devices combining electrical and mechanical
components that is fabricated using integrated circuit
(IC) batch processing techniques and can range in size
from micrometers to millimeters.
In Europe it is called Microsystems technology (MST).
It is important for users to understand concepts
behind clean processing
Benefit from the experiences of others (standards,
Impact that a single user can have on overall process
yield can be huge!
First cleanrooms were in hospitals to prevent disease
transmission and infection in operating rooms (over 100 years
Valuable tool to prevent particulate and bio contamination
Most well known use is in semiconductor industry, but also
essential in pharmaceuticals, flat panel displays, space
program, photonics, life sciences, industrial (painting,
Essential for LCDs because of coating processes, small cell gaps
Cleanroom itself is only part of the solution
Micro-fabrication needed a very clean environment to prevent dirt or
other particles from contamination the MEMS devices .
Two pictures in clean room.
Yellow room is a special area in CLEANROOM. It is used for
photolithograhpy process. Because of the sensitivity of PR,the wafers
covered by PR must be used in yellow room. Once such
wafers(substrates) are brought outside the yellow room, most of them
might be exposed by UV.
High Efficiency Particulate Air (HEPA) Filter:
Most common type of clean room air filter
High efficiency, low pressure drop, good loading characteristics
Uses glass fibers in a paper-like medium
Are rated by their particle retention:
• A true HEPA-rated filter will retain 99.97 % of incident particles of
0.3 mm or larger.
Ultra low particulate air (ULPA) Filter:
This filters are 99.9995% efficient in removing particles 0.12 µm and
ULPA filters are used in air filtration and purification systems to
particulate levels and to stop the spread of
toxic agents and infectious diseases.
– Air is recirculated through HEPA filters with about 20 % make up.
• Vapors are entrained, so contamination potential is very high.
• Extensive gas detection and alarm systems are installed.
– Temperature is controlled to 68 - 72 °F.
– Humidity is controlled to 40 - 46 % RH.
– Room is held at positive pressure .
• Typically 0.1 in of H2O for Class 100, Class 1000, and Class 10,000
• Typically 0.3 - 0.4 in of H2O for Class 1 and Class 10
• Positive pressure constantly blows dust OUT
• (Biohazard rooms operate at negative pressure to keep bugs IN)
• Doors open inward, so room pressure closes them shut .
Positive Pressure / Airflow
Keeps contamination out of the work area
Depends on clean air input
Development of effective filtration revolutionized industry
HEPA (High Efficiency Particulate Air) and ULPA (Ultra Low
Particulate Air) Filters
All are very important!
Particulate—encompasses most contamination
Chemical—films, vapors, etc.
Biological—bacteria, viruses, etc.; for our purposes,
treat as particles
Similar concerns for rooms & equipment as for
Critical to remove contaminants that cannot be
removed by air handling
Important to follow procedures appropriate to your
What is appropriate for one industry may not be
appropriate for another
Most important thing is to develop standard
procedures and FOLLOW THEM
The efficiency of these cleaning methods depends on
the surface being cleaned
Rough or pitted surfaces are more difficult to clean
Sharp corners are difficult to clean
Why are inside surfaces of cleanrooms smooth?
Dry and wet
Dry has low (<25% ) efficiency for particles smaller than 10 microns
(about .0005 inches)
wet uses liquids which result in greater force on the particles and hence
Most facilities use DI(Distilled Water) water or isopropyl alcohol with
The choice depends on what works, cost, history, etc.
Efficiency depends of tackiness of roller, cleanliness
of tacky surface and softness of roller are also very
Choice of materials for supplies, equipment,
gowning, etc. is important
“Clean” materials can become dirty!!
Look for easy-to-clean materials
Triboelectricity can cause static problems, as can low
humidity—this exacerbates contamination problems
Biofilms!!(Biofilms form when single
microorganisms attach to a hydrated surface and
undergo a "lifestyle switch.“)
Truth: Manufacturers can achieve similar yield results
using cost effective flow hoods and isolation chambers
as with full-blown central cleanrooms
BUT: user behavior is much more critical in these
Before any work can be done in the cleanroom facility,
users must gown up in appropriate cleanroom garments.
These garments are located in a separate room at the top
of the ramp leading away from the entrance door to the
facility. Nothing should be taken into the gowning room.
All clothing and miscellaneous items (keys, cell phones,
sweaters, notebooks) that are not specifically qualified for
use inside a cleanroom must be left outside the entrance
to the facility, not in the gowning room. These items will
only contaminate the cleanroom garments which are hung
there. Please leave these extraneous items in your office
or car for the highest degree of safety. Items may be left
on the bench used for putting on shoe covers or on the
adjacent coat rack at your own risk.
Liquid Crystal Institute(LCI).
Pick up an appropriately sized coverall and put on, being
careful to avoid allowing coverall to touch floor
Put on plastic shoe covers (booties) over your shoes in
If you wear boots or other heavy contaminating shoes,
consider keeping a pair of sneakers in your office for use
in the cleanroom.
Put on hairnet, Pick up an appropriately sized head
cover and put on.
Put on safety glasses and proceed to air shower
Not wearing Safety Glasses
zippers, snaps, masks
Non-cleanroom materials in cleanroom
paper, cardboard, personnel items
Not cleaning up after you are finished
Fast motions, incorrect carrying of materials
Remember laminar flow; minimize turbulence
Minimize sources of contaminants
Avoid high particulate clothing, such as wool sweaters
Cover up! Uncovered skin can lead to more
Follow gowning procedures and restrict materials used
An educated worker is essential to proper job
performance; workers should be well versed in the
how and why of their job
Cleanroom environment is very fragile!(Easily broken or
Your actions have impact on other users
Important to follow procedures EVERY TIME
Make sure fellow workers follow procedures as well;
nothing wrong with pointing out mistakes
Be an active participant: keep an eye out for areas
that can be improved
Bring only required materials into cleanroom; if it is
not necessary to perform the task, it should not be
Personnel: only required personnel should be in the
Reduce clutter—do not store materials in clean areas
unless they have to be there!
Follow exact procedures every time
Wipe down surfaces with cleanroom wipes before and
after every usage
Remember: this can seem tedious and unnecessary,
but is essential to keeping the cleanroom maintained
at its highest levels
Contamination control is a continuous battle
User behavior has a critical impact on contamination
Proper procedures must be followed at all times
Think about your actions! Be an active participant