Presented by,

Mr.S.Sivakumar

M.Tech(DCN)

Department of ECE

Kalasalingam University.

CLEAN ROOM FACILITIES FOR MEMS DEVELOPMENT

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IntroductionCleanroom definitionsParameters about clean roomCharacteristics about clean roomContamination & MeasurementCleaning & Materials SelectionThe user!!Protocols to improve controlConclusions

Outline

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).

Definition and Fundamental Concept of MEMS

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It is important for users to understand concepts behind clean processing

Benefit from the experiences of others (standards, anecdotal information(reliable))

Impact that a single user can have on overall process yield can be huge!

Things to Remember

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Why Cleanrooms? First cleanrooms were in hospitals to prevent disease

transmission and infection in operating rooms (over 100 years ago!)

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, assembly), etc.

Essential for LCDs because of coating processes, small cell gaps

Cleanroom itself is only part of the solution

Historical Perspective

Micro-fabrication needed a very clean environment to prevent dirt or other particles from contamination the MEMS devices.

Two pictures in clean room.

   　　

Concept 1: 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.

Concept 2: Yellow room

High Efficiency Particulate Air (HEPA) Filter:

– Most common type of clean room air fi lter– High eff iciency, low pressure drop, good loading characteristics– Uses glass fibers in a paper-like medium– Are rated by their particle retention:

• A true HEPA-rated fi lter will retain 99.97 % of incident particles of 0.3 mm or larger.

Ultra low particulate air (ULPA) Filter:

This fi lters are 99.9995% eff icient in removing particles 0.12 µm and larger. ULPA fi lters are used in air fi ltration and purification systems to control airborne particulate levels and to stop the spread of toxic agents and infectious diseases.

Important parameters about clean room:

– 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 .

Characteristics of Clean Rooms  

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Positive Pressure / Airflow Keeps contamination out of the work area Depends on clean air input

Filtration Development of effective filtration revolutionized industry HEPA (High Efficiency Particulate Air) and ULPA (Ultra

Low Particulate Air) Filters Materials SelectionUser ProtocolsCleaningAll are very important!

Methods to Achieve Cleanliness

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Particulate—encompasses most contamination

Chemical—films, vapors, etc.Biological—bacteria, viruses, etc.; for our

purposes, treat as particlesSimilar concerns for rooms & equipment as

for substrates

Types of Contamination

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Critical to remove contaminants that cannot be removed by air handling

Important to follow procedures appropriate to your application

What is appropriate for one industry may not be appropriate for another

Most important thing is to develop standard procedures and FOLLOW THEM

Cleaning

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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 cleanWhy are inside surfaces of cleanrooms

smooth?

Surfaces are important

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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 better cleaning. Most facilities use DI(Distilled Water) water or isopropyl

alcohol with disinfectant. The choice depends on what works, cost, history, etc.

Vacuuming & Wet wiping

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Efficiency depends of tackiness of roller, cleanliness of tacky surface and softness of roller are also very important

Tacky rollers

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Choice of materials for supplies, equipment, gowning, etc. is important

“Clean” materials can become dirty!!Look for easy-to-clean materialsTriboelectricity 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.“)

Materials Selection

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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 areas!!!

Impact of the Cleanroom User

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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.

Gowning Procedure:

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Gowning Procedure

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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 the hallway

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

Gowning at the LCI

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Not wearing Safety GlassesImproper gowning

zippers, snaps, masksNon-cleanroom materials in cleanroom

paper, cardboard, personnel itemsNot cleaning up after you are finishedGeneral conduct

Fast motions, incorrect carrying of materialsRemember laminar flow; minimize

turbulence

Common Protocol Violations

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Minimize sources of contaminantsNo smokingNo cosmeticsAvoid high particulate clothing, such as wool

sweatersCover up! Uncovered skin can lead to more

contamination

General Cleanroom User Requirements I

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Follow gowning procedures and restrict materials used in cleanroom

An educated worker is essential to proper job performance; workers should be well versed in the how and why of their job

Protocols to Improve Contamination Control

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Cleanroom environment is very fragile!(Easily broken or damaged)Your actions have impact on other users

Important to follow procedures EVERY TIMEMake 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

You as the User

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Bring only required materials into cleanroom; if it is not necessary to perform the task, it should not be there

Personnel: only required personnel should be in the clean space

Reduce clutter—do not store materials in clean areas unless they have to be there!

Minimalism is Good

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Follow exact procedures every timeWipe down surfaces with cleanroom wipes

before and after every usageRemember: this can seem tedious and

unnecessary, but is essential to keeping the cleanroom maintained at its highest levels

Repetition is Good

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Air Flow principle for unidirectional (laminar) flow Cleanrooms

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Air flow principle in turbulent cleanrooms

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Contamination control is a continuous battleUser behavior has a critical impact on

contaminationProper procedures must be followed at all

timesThink about your actions! Be an active

participant

Conclusions

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