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Introduction to semiconductor cleanroom
National nanofabrication centre Indian Institute of Science Bangalore
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Outline Aim What is cleanroom? Why cleanroom training? Contamination
Cleanroom protocols Do’s and don't's
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Aim Appreciation of cleanroom practice so that You keep it clean and Do reproducible research SAFELY
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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.
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Classification of cleanrooms
maximum particles/ft³ ISO equivalent ≥0.1 µm ≥0.2 µm ≥0.3 µm ≥0.5 µm ≥5 µm 1 35 7 3 ISO 3 10 350 75 30 ISO 4 100 750 300 ISO 5 1,000 ISO 6 10,000 70 ISO 7 100,000 700 ISO 8
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Principles of the Clean Environment
Non-unidirectional Unidirectional - Laminar HEPA- high-efficiency particulate air filter This has been likened to a "piston effect" where incoming clean air "pushes" contaminated air from the room. The advantage of unidirectional flow is that airborne particles are carried out of the room in minimum time and the shortest path, thereby giving them less chance to start any trouble. Laminar flow cleanrooms have generally parallel streamlines and approximately uniform velocity throughout. They "clean" the air by transporting particles in the direction of the airflow out of the cleanroom. Non-unidirectional rooms have non-parallel flow streams and non-uniform velocities. These rooms operate on the principle of the "dilution effect," with clean air entering the room and diluting the contaminated air. This mechanism is similar to placing a garden hose into a bucket of muddy water and stirring the water while letting the excess drain out over the top. Eventually the clean water entering the bucket will dilute and displace the dirty water. Non-un directional: The air flow system is the same as the common air-conditioning system except it uses a HEPA filter and more air changes to reduce the contamination level. This type of clean room is generally employed to maintain Class 1,000 to 10,000, but when it is supplemented by local laminar flow work stations, it can provide a high degree of contamination control for critical operations. The construction cost is economical. "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.
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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
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Contamination types • Molecular contaminants • Surface contaminants • Particulate contaminants Contamination during process
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Molecular contaminant sources
Out gassing Oil vapours Alcohols Paints, glues, & epoxies Aromatics; If you can smell it, suspect it as a contaminant
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Sources of surface contamination
Finger prints - Oil & grease Skin oil Hand cream Face cream, Wax Polish
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Sources of particulates
People (skin, scales, hair, clothing lint, etc.) Particle shedding materials (cardboard boxes, paper) Abrading actions (drilling, sawing, sanding, etc.) Bare wood products
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What you wanted What you got
Effect of Contamination Presence of a fibre on the mask during lithography What you wanted What you got
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Human hair on IC surface!
14/08/2013
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High contamination source ?
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Contamination Sources
People ~75% Ventilation ~15% Room Structure ~5% Equipment ~5%
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You are the Primary Contaminant!
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Clean room Protocols Rules and policies are no substitute for common sense. Please note that strict action will be taken against those violating the rules 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. Cleanroom hours: 6 am to 12 midnight, all 7 days of a week Please contact any of the management representatives if you have suggestions or feedback
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Cleanroom protocols Please wash your hands and face with lots of water before coming into the clean room If you ate something just before coming into the cleanroom, drink water and rinse your mouth thoroughly If you smoke, drink water before coming into the cleanroom Do not come in with torn and/or dirty socks
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Cleanroom entry Allowed: Clean, dry clothes are mandatory.
Half/full sleeved shirts (shirts should cover from arms to waist) and full length pants (covering from waist to ankles) are required. Churidhars and Salwars are allowed. Clean socks or stockings are mandatory. Note: Please make sure that long or medium length hair is tied back. Contact lenses are strictly prohibited
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Cleanroom Entry: Not allowed
Clothes which are dusty, dirty or wet Sleeveless clothes, shorts or short-pants Tank tops, halter tops and sphagetti strap tops Sarees, skirts and gowns Clothes which shred fiber like fur, mohair etc Deodrants, perfumes and cosmetics including hand cream Heavy jewellery and decorative accessories including flowers People suffering from cough, cold or respiratory diseases People with pacemakers
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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
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Bookings Be there with your sample 15 min before your booking starts, 30 minutes before a litho slot 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
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In the clean room Use appropriate personal protection equipments (PPE)
In the wet bench area In the main clean room
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Gowning procedure for NNFC
gowning.wmv
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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.
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Cleanroom entry 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
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Equipment usage Two type of users: Dependent/ Independent
Dependent authorised users: Only day time access / process done by facility technologist Independent users: Anytime access, after proper training Talk to your supervisor and the concerned technologist if you need to be an independent user. If equipment is found faulty, do not try to repair, inform the concerned technologist and make a note in log book Only chemicals in the cleanroom chemical list allowed
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Restricted materials Sulfur
Fast diffusing and toxic metals like Fe, Cu, Cd, Mn, Zn, Sb, Se, As and Hg and their alloys PDMS (PV lab)
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New Materials Entry Permission needs to be obtained from the concerned authority before new material is brought into clean room (procedure in twiki) Send detailed mail to Dr. Savitha containing the following details Prior process Post process MSDS of the material Why the cleanroom need to be used
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Cleanroom Don’t’s Do not bring any tools/ equipment from outside into the cleanroom. No using cellphones during processes even if connected to hands-free. Do not expose any facial/head hair. Do not open the door emergency exits unnecessarily
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Cleanroom Don’t’s Do not open the door to the cleanroom for communication or passing of products back and forth – use the pass-through instead. Do not congregate. No running and try to maintain silence
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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 while Or You may loose your clean room registration all together! REMEMBER, monitoring cameras are everywhere in the clean room! Rules apply 24X7
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Emergency Response 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
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Alarm Response Common Alarms: Fire and Smoke Gas alarms
In the cleanroom corridor, outside Films room Inform BMS at 115 and wait for instructions If asked to evacuate, do it by the nearest exit Gas alarms Specific to equipments, mainly LPCVD, Diffusion furnace and PECVD Alert nearby users and evacuate immediately through emergency exit Inform BMS by calling 115 from the cleanroom outside corridor phones
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http://sindhu. ece. iisc. ernet
Entry protocol Fire evacuation Google – TWIKI iisc nnfc
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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
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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
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Use of gloves PVC NITRILLE TRIONIC (MAPA)
Chemie Opleiding Use of gloves PVC 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! The choice of gloves is dependent of the kind and the duration of the work that has to be executed with them and the kind of chemicals that have to be manipulated. Certain tests are done to check the resistance to chemicals and the strength of the material. Before use the gloves should be checked to see if there are any holes in them. The reuse of gloves should be avoided. Only the thick Trionic (Mapa) gloves can be reused, but make sure they are not contaminated. Other gloves should be thrown away inside out immediately after use so that the contamination stays at the inside. Dienst Contaminatie Controle
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F-telon gloves (Teflon incorporated)
TRIONIC (MAPA Chemical spill pillows Chemical spill pads
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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!
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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
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Hazard Symbols
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Strictly, Chemicals should be used only in the fume hoods
All chemicals in the bay need to be labeled Solutions left for cooling/later use need to be indentified using identification chit Do not randomly mix chemicals since this may result in an explosion / evolution of hazardous gases Appropriate face masks/ goggles 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.
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Use of glassware Fluoride solutions to be used only in plastic beakers/petridishes/measuring cylinders Fluoride etches glass! Other acids to be used only in glass beakers Exchange of glassware between benches strictly not allowed Glassware is labeled and belongs to particular benches Transferring of Chemicals allowed only with full PPE Please enter your process in the log book No contact lenses please
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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 Si wafer/glass pieces to be discarded in the designated bin at the wet etch
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Chemical spill On person On the floor
Remove contaminated clothing and get under safety shower Seek medical attention Inform BMS On the floor Small Dilute with water and put spill blankets, discard spill blankets in the plastic dustbin Big Come out and close the door to the wet etch Inform BMS immediately Take precautions not to breathe in the fumes
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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!
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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)
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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
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First Aid Wash with large amounts of water (minimum 5min)
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
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Other Acids and Bases Strong acids used: Sulfuric, Nitric, Hydrochloric, Phosphoric Weak acid used Acetic acid Bases used Potassium 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. First aid: Wash thoroughly with water (safety-shower/eye wash) for 15 min and seek medical attention depending on the severity of the burn
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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.
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Photoresists Photoresists are organic polymers which change their chemical structure when exposed to ultraviolet light. 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
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Penalty points at the wet benches (nx times for second violation)
Using without booking slots: 15 points Not wearing proper PPE (gloves/ goggles): 15 points Exchanging glassware: 15 points Leaving solutions without identification chit: 15 points Leaving bench unclean: 30 points Using BHF/HF/ Vaporizer carelessly: 100 points (immediate suspension of cleanroom access)
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How to Become An Authorized User
Attend NNfC Orientation Course Attend Weekly training Take Cleanroom Protocol Test No Pass User is not authorized to enter cleanroom Yes User is authorized to enter cleanroom Apply for approval for specific Equipment use using FOM software Reserve slots and use equipment
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How to Become An Independent User
Apply for Training Training by equipment owners Certification by equipment owners user clears the Test No Yes Becomes an independent user Frequency of use > once/week Yes No Retraining and certification by equipment owners
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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
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Penalty point chart (representative)
Cumulative Disciplinary action penalty points >30 points One week suspension on wet bench >45 points One week suspension full cleanroom >60 points week suspension, no cleanroom access >100 points Barred from access to the cleanroom.
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Call BMS immediately at 115
Minor Spill Criteria Not in immediate danger of an explosion, fire or a health issue Not spreading further (is only on small area (<2x2 ft) and is not HF Dangerous only by direct contact Can be managed by existing PPE Chemical spill On person Remove clothing and get under safety shower Inform BMS immediately at 115 On bench/ floor Dilute with water and absorb the spill using chemical spill blankets/ pillows Dispose the spill blankets in the plastic dustbin Try not to breathe the fumes Evacuate and put red tape across the door preventing user entry Call BMS immediately at 115 Minor spill Major spill
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Wash with large amounts of water (min 5 min)
HF exposure Wash with large amounts of water (min 5 min) Apply calcium gluconate gel using uncontaminated gloves Call BMS immediately at 115 Continue applying Calcium gluconate gel till your get to the doctor
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M.N. Vijayaraghavan NNFC
14/08/2013 M.N. Vijayaraghavan NNFC
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Cleanroom Corridor Dry Etch Room Entry Cleanroom inner corridor
E-Litho 1 F Litho 2 Wet Etch room C Films Gowning Diffusion 5 target sputter tool CPD GaN Reactor Sintering and Annealing Oxidation and Doping LPCVD PECVD ALD DRIE Sputtering Units EVG Aligner Laser Writer RIE- F RIE-Cl Old Wet bench New Wet E-Beam evaporator Cleanroom Corridor EVG Bonder Bench Oven SU8 Developer Chiller Old CMOS EP Bench WB4 WB3 Tube Cleaning WB1 WB2 WB5 Safety Shower In line Char N2 Emergency Rescue and EHS Officer N1 Control room Laundry Air shower Equipment Development MJB3 Mask aligner Microscope Tempress Dry/Wet Oxidation Dektak Four point probe FTP Ellipsometer G Litho 3 control Raith E-Line Raith Pioneer Ar ion milling Multi target sputter and PLD tool First Aid box EYE WASH Savitha P, NNFC
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Thank you
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