National nanofabrication centre

Indian Institute of Science

Bangalore

Introduction to semiconductor cleanroom

• Aim• What is cleanroom?• Why cleanroom training? • Contamination• Cleanroom protocols• Do’s and don't's

Outline

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Appreciation of cleanroom practice so that

You keep it clean

and

Do reproducible research

Aim

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What is a clean room?

• A clean room has a controlled environment– Low contamination (like dust, airborne microbes,

chemical vapours etc) – specified by the number-of-particles/ft3 at a

specified particle size• Eg: Room with < 100 particles/ft3 equal to or

larger than 0.5 micron is a class 100 clean room.

Class

maximum particles/ft³ISOequivalent≥0.1 µm ≥0.2 µm ≥0.3 µm ≥0.5 µm ≥5 µm

1 35 7 3 1 ISO 3

10 350 75 30 10 ISO 4

100 750 300 100 ISO 5

1,000 1,000 7 ISO 6

10,000 10,000 70 ISO 7

100,000 100,000 700 ISO 8

Classification of cleanrooms

Principles of the Clean EnvironmentUnidirectional - LaminarNon-unidirectional

"piston effect“- where incoming clean air "pushes" contaminated air from the room

"dilution effect“- non-parallel /non-uniform flow streams and velocities. clean air entering the room and diluting the contaminated air.

HEPA- high-efficiency particulate air filter

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Why the training?• The Clean room environment is carefully

maintained at particular standards and has equipments which are delicate and precisely calibrated

• The chemicals and gases used in the facility may be extremely hazardous

• Misuse may lead not only to destruction/malfunctioning of the device, but could also pose danger to personnel/instrument

• Molecular contaminants

• Surface contaminants

• Particulate contaminants

Contamination types

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• Out gassing• Oil vapours• Alcohols• Paints, glues, & epoxies• Aromatics; If you can smell it, suspect it as

a contaminant

Molecular contaminant sources

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• Finger prints - Oil & grease• Skin oil• Hand cream • Face cream, Wax • Polish

Sources of surface contamination

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• People (skin, scales, hair, clothing lint, etc.)

• Particle shedding materials (cardboard boxes, paper)

• Abrading actions (drilling, sawing, sanding, etc.)

• Bare wood products

Sources of particulates

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Effect of ContaminationPresence of a fibre on the mask during lithography

What you wanted What you got

Human hair on IC surface!

14/08/2013 15

High contamination source ?

• People ~75%• Ventilation ~15%• Room Structure ~5%• Equipment ~5%

Contamination Sources

You are the Primary Contaminant!

Clean room Protocols

• Rules and policies are no substitute for common sense.

• Plan ahead. Get appropriate advice.• Do not start when in doubt.• Keep good house keeping habits.• DO NOT WORK ALONE or when stressed or NOT

WELL• FOLLOW BUDDY SYSTEM, ESPECIALLY AFTER

HOURS

Violation of Rules• Depending on the gravity of violation

– You may get just a warning– You may get your booking cancelled– You may loose your registration for a short whileOrYou may loose your clean room registration all together!

REMEMBER, monitoring cameras are everywhere in the clean room!

Rules apply 24X7

Access• Download the authorization form• Fill, sign and submit it.• Read clean room protocols and safety documents.• Take the clean room test.• PASS IT, you are in!

Authority to enter does not mean authority to operate instruments

Bookings

• Be there with your sample 15 min before your booking starts

• No more than 2 bookings allowed per week• If you can’t make it to a booking, please inform

in advance (1 day before)• If you book, but do not turn up, no slots for you

for one month!• All processes have to be documented in the log

book kept near the equipment/wet bench

In the clean room

• Use appropriate personal protection equipments (PPE)– In the wet bench area– In the main clean room

Q: Why is the procedure important?

• Want the dust you generates to fall INSIDE your suit, NOT OUTSIDE.– So, the boot covers go OVER the suit, NOT UNDER

• If you put on your gloves and then use your hands to gather your hair and put it under a cap, the gloves will have oil and skin flecks on the outsides from your hair.

Protocols continued.• Visitors allowed with

permission only• Carry only things

necessary for expt• No books, pencils

allowed, ask for lint free paper for taking notes

• Use pass-through for transfer of materials – no storage allowed

Protocols continued..• Permission needs to be obtained from the concerned

authority before new material is brought into clean room

• Access to the clean room does not automatically permit the use of equipments. Specific training and authorization is needed.

• Talk to your supervisor and the concerned technologist if you need to be an authorized user.

• If equipment is found faulty, do not try to repair, inform the concerned technologist and make a note in log book

Emergency Protocol(In Response To An Alarm)

• Stop the process by pressing the emergency stop buttons of the equipments (if known)

• Immediately alert the staff concerned (phone numbers are near the door) or call BMS : “115”

• Evacuate the area by the nearest exit if ordered evacuation by the Building management system (announcement will be made)

• Evacuate if power does not restore in 2 min• Do not wait to remove the gown for evacuation• Incase of a gas leak alarm, evacuate immediately

http://sindhu.ece.iisc.ernet.in/nanofab/twikii/bin/view/Main/WebHome

Google – TWIKI iisc nnfc Entry protocol

Fire evacuation

Chemical Safety Training

• To ensure a safe environment for learning and research

• To prevent fatal Injuries and accidents HF/BHF burns

Wet benches are the only safe places for chemicals

Wet Bench Protocol• While working on wet bench, it is mandatory to

– Wear lab shoes

– Wear Aprons

– Wear safety glasses/ face shield

– Wear appropriate gloves

– Make sure exhaust is functioning

Use of gloves PVC/LATEX

– Are used protect wafers from particles generated by humans – No resistance to chemicals

NITRILLE– Thin chemical resistant gloves– Strong material : used for installation and maintenance of tools

TRIONIC (MAPA)– Thick chemical resistant gloves : used for cleaning up leaks– Nevertheless don’t put your hands in liquid chemicals!

Heavy Duty Neoprene

TRIONIC (MAPA

Chemical spill padsChemical spill pillows

Protocols• All chemicals in the fab are hazardous. Ensure

that you have read the MSDS of the chemical before use

• Never rub in your eyes or face with your hands or gloves.

• AAA principle: Always Add Acid to Water

SOMEBODY WORKING AFTER YOU IN A LAB HAS TO TRUST EVERYTHING IS CLEAN!

Strictly,• Chemicals should be used only in the fume hoods

• All chemicals in the bay need to be labeled

• Do not randomly mix chemicals since this may result in an explosion / evolution of hazardous gases

• Appropriate face masks and gloves have to be worn before starting the expt. Please note that latex gloves used for clean room entry has no chemical resistance. Wear nitrile / acid resistant glove depending on your experiment.

• Cool the chemicals before pouring them down the appropriate drain/bottle. If in doubt, ask the concerned person.

• In case of chemical spill on floor, use the appropriate chemical blanket. When the spill is on person, remove contaminated clothing and get under safety shower. Flush eyes with copious amounts of flowing water for chemical spill is in the eye.

More..• Fluoride solutions to be used only in plastic

beakers/petridishes/measuring cylinders– Fluoride etches glass!

• Other acids to be used only in glass beakers• Transferring of Chemicals allowed only with full PPE• Solutions left for cooling/later use need to be

indentified using identification chit• Please enter your process in the log book• No contact lenses please

What is an MSDS?

• What is an Material Safety Data Sheet– Tells what chemicals are in the product,– What the hazards of the chemicals are– How to protect yourself from the hazards.

• Where to get M.S.D.S– Manufacturer websites, or– Google search “MSDS + name of chemical

product” MUST READ !!

The label on the bottle also will contain some relevant information

Hazard Symbols

Disposal of Chemicals• Alkali’s and Acids can be poured down the drain

after cooling!• HF and BHF solutions to be disposed in a

single plastic bottle• Solvents in a separate bottle, separate bench

provided, should not be poured down the drain• Do not leave anything on the wet bench

uncleaned/unclaimed after use

Fluoride Solutions• Hydrofluoric acid and

Buffered HF solution– Equally hazardous– Highly dangerous due

to the internal tissue and bone damage (Decalcification) caused by contact with the colour less liquid!

Symptoms HF injury:HF 49%

• Almost immediate deep throbbing pain, burning feeling,(especially at hands and finger tips)

• Red discoloration with whitish blister, tissue under skin starts dying off, bone de-mineralises

• Systemic fluoride intoxication• Painful treatment in hospital (death possible)

Symptoms HF injury:Diluted HF solution < 20%

• Sometimes it can take upto 24 hours before symptoms appear (pain, rash)

• Might result in deeper penetration and more painful burn (especially at hands and finger tips )

• The surface symptoms are minimal or may be absent• Can cause white discolored skin, blisters seldom form• HF solution >20%<49%:• Symptoms sometimes just noticeable after a few

hours!• Treat all unlabelled, water-like solutions as HF solutions

First Aid• Wash with large amounts of water (minimum

15min)• Rub in Calcium gluconate gel (make sure your

hand is not contaminated) and cover the burn with plastic foil

• Seek medical attention• Calcium Gluconate Gel is in the First aid box at

the wet etch

Other Acids and Bases• Strong acids used:

– Sulfuric, Nitric, Hydrochloric, Phosphoric• Weak acid used

– Acetic acid• Bases used

– Potassium hydroxide, Sodium hydroxide, TMAH• The strong acids & bases are poisonous, corrosive, and will cause severe

burns to body tissue. Long term exposure will cause lung and tooth damage. The weak acids will cause eye, skin and mucous membrane irritation and burns. Some are even carcinogenic or teratogenic.

READ THE MSDS• Wash thoroughly with water (safety-shower/eye wash) for 15 min and

seek medical attention depending on the severity of the burn

Other commonly used

• Hydrogen Peroxide: Colorless. Irritation and burns to skin and eyes.

• Acetone, Isopropyl Alcohol (IPA) and Methanol:– All solvents may cause skin and eye irritation. They

are colorless & combustible, should NEVER be heated for use. Solvent vapors are toxic, use only in ventilated hoods.

Photoresists• Photoresists are organic polymers which change their chemical

structure when exposed to ultraviolet light. – Photoresists are harmful, carcinogenic and can be absorbed through

unbroken skin.– They are generally flammable and should be kept away from any source

of heat and ignition. Protective gear has to be used at all times when dealing with Photoresists

• Compressed and liquefied gases – Chemical and Physical dangers

• are caused by the properties of the gas inside and physical hazards due to the high power of a pressurized gas in a cylinder.

– Gas leakages can also displace oxygen in the fab environment and lead to unconsciousness and ultimately death.

• Do not bring any tools/ equipment from outside into the cleanroom.

• No bare clothes are allowed inside the cleanroom.

• Do not expose any facial/head hair.• Do not open the door energency exits

unnecessarily

Cleanroom Don’t’s

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• Do not open the door to the cleanroom for communication or passing of products back and forth – use the pass-through instead.

• Do not use pass-through for storage.• Do not block the air flow from the filter to

the product.• Do not congregate. No running and try to

maintain silence

Cleanroom Don’t’s

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How to Become An Authorized UserAttend NNfC

Orientation Course

Attend Weekly training

Take Cleanroom Protocol Test

Pass

User is not authorized to enter cleanroom

User is authorized to enter cleanroom

Apply for approval for specific

Equipment use

Reserve slots and use equipment

Yes

No

How to Become An Independent User

Training by equipment owners

user clears the Test

Becomes an independent user

Retraining and certification by

equipment owners

Yes

No

Apply for Training

Certification by equipment owners

Frequency of use >

once/week

NoYes

User agreement• All are expected to sign USER Agreement before becoming authorised USER• Violations of Nanofab protocol and

procedures – penalty points and restricted access and privileges

Penalty point chart

Cumulative Disciplinary action

penalty points

>30 points Loss of independent user status

for 2 weeks

>60 points 1 week suspension

>90 points 2 week suspension

>100 points Barred from access to the cleanroom.

14/08/2013 61M.N. Vijayaraghavan NNFC

Thank you