Introduction to semiconductor
cleanroom
National nanofabrication centre
Indian Institute of Science
Bangalore
Outline
•
•
•
•
•
•
Aim
What is cleanroom?
Why cleanroom training?
Contamination
Cleanroom protocols
Do’s and don't's
2
Aim
Appreciation of cleanroom practice so that
You keep it clean
and
Do reproducible research
3
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.
Classification of cleanrooms
maximum particles/ft³
ISO
equivale
nt
Class
≥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
750
300
100
ISO 5
100
1,000
1,000
7
ISO 6
10,000
10,000
70
ISO 7
100,000
100,000
700
ISO 8
Principles of the Clean Environment
Non-unidirectional
Unidirectional - Laminar
HEPA- highefficiency
particulate air
filter
"dilution effect“- non-parallel /nonuniform flow streams and velocities.
clean air entering the room and
diluting the contaminated air.
"piston effect“- where incoming clean
air "pushes" contaminated air from
the room
6
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
Contamination types
• Molecular contaminants
• Surface contaminants
• Particulate contaminants
8
Molecular contaminant sources
•
•
•
•
•
Out gassing
Oil vapours
Alcohols
Paints, glues, & epoxies
Aromatics; If you can smell it, suspect it as
a contaminant
9
Sources of surface contamination
•
•
•
•
•
Finger prints - Oil & grease
Skin oil
Hand cream
Face cream, Wax
Polish
10
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
11
Effect of Contamination
Presence 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 ?
Contamination Sources
•
•
•
•
People ~75%
Ventilation ~15%
Room Structure ~5%
Equipment ~5%
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.
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, 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
In the clean room
• Use appropriate personal protection
equipments (PPE)
– In the wet bench area
– In the main clean room
Gowning procedure for NNFC
gowning.wmv
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.
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
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
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)
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
Cleanroom Don’t’s
• 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 emergency exits
unnecessarily
33
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
34
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
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
Alarm Response
• Common Alarms: Fire and Smoke
– 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
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
– 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!
F-telon gloves (Teflon incorporated)
Chemical spill pads
TRIONIC (MAPA
Chemical 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!
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
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.
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
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
• On person
Chemical spill
– 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
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 demineralises
• 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
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
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
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.
– 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
Penalty points at the wet benches
• 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)
How to Become An
Authorized User
Attend
Weekly
training
Attend NNfC
Orientation
Course
Take Cleanroom
Protocol Test
Pa
ss
No
Yes
User is authorized
to enter cleanroom
Apply for approval
for specific
Equipment use
Reserve slots and
use equipment
User is not authorized
to enter cleanroom
How to Become An
Independent User
Apply for
Training
Training by
equipment owners
Certification by
equipment owners
No
user
clear
s the
Test
Yes
Becomes an
independent user
Y
es
Freque
ncy of
use >
once/w
eek
No
Retraining and
certification by
equipment owners
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
Community service: Cleanup
work in the bays
>45 points
Cleanup and training other users/
one week suspension
>60 points
2 week suspension, no
cleanroom access
>100 points
Barred from access to the
cleanroom.
14/08/2013
M.N. Vijayaraghavan NNFC
62
Entry
MJB3
Mask
aligner
EVG
Bonder
Safety
Shower
WB1 WB2
WB5
In line Char
E-Beam evaporator
FTP
WB4
Wet Etch room
EP Bench
Micro
scope
Old
CMOS
bench
New Wet Old Wet
bench
bench
N2
Emergency
Rescue
and EHS
Officer
C
l
e
a
n
r
o
o
m
N1
Control
room
C Films
WB3
E-Litho 1
Laser
Writer
Four point
probe
Sputtering Units
C
l
e
a
n
r
o
o
m
EVG
Aligner
Laundry
Dektak
Ellipsometer
Air
shower
Gowning
First Aid box
Oven
EYE WASH
Dry Cleanroom
Etch
Room
Cleanroom
inner
corridor
inner
corridor
C
o
r
r
i
d
o
r
C
o
r
r
i
d
o
r
F Litho 2
New Wet
Bench
SU8
Developer
Oven
Diffusion
DRIE
RIE- F
Sintering and
Annealing
G Litho 3
RIE-Cl
Raith ELine
Chiller
control
Raith
Pioneer
ALD
PECVD
5 target
sputter
tool
Oxidation and
Doping
LPCVD
Ar ion
milling
GaN
Reactor
Equipment Development
Multi
target
sputter
and PLD
tool
Tempress
Dry/Wet
Oxidation
CPD
Savitha P, NNFC
63
Thank you