IA_Safety Issues for MicroFabrication

Semiconductor Manufacturing Technology

Safety Issues


Safety Issues

Definitions of Safety Terms

Hazardous: Any chemical or substance that has adverse effects on the health or safety of people.

Toxic: Any chemical or substance that seriously damages biological tissue. Examples are phosphine and arsine.

Flammable: Any liquid or gas that is capable of igniting into fire.

Pyrophoric: Any material that ignites spontaneously in air below 55°C (130°F). An example is silane.

Examples of Hazards in Semiconductor Manufacturing

• Process chemicals

• Highly flammable gases

• Pyrophoric gases

• Corrosive gases

• Toxic or caustic liquids

• High voltages

• Solvents

• Mechanical hazards

• High temperatures• Radiation

– UV– Laser– X-ray

• Freezing temperatures

Hazard Warning Sign

Figure A.1

333322

Red

White

YellowBlue

Health Hazard0 Normal, no hazard1 Slight hazard2 Hazardous3 Extremely hazardous4 Deadly

Fire Hazard0 Nonflammable1 Above 200ºF2 Below 200ºF3 Below 100ºF4 Below 73ºF

Reactivity0 Stable, nonreactive1 Unstable if heated2 Violently reactive3 May detonate with

heat or shock4 May detonate

Specific HazardOXY OxidizerACI AcidALK AlkaliCOR CorrosiveW Use no water

Radiation hazard

Definitions of Exposure Limits(Refer to p. 602 for details)

• TLV-TWA: Threshold limit values – time weighted average.

• TLV-STEL: Threshold limit values – short term exposure limit.

• IDLH: Immediately dangerous to life and health.

• PEL: Permissible exposure limit.

How Chemicals Enter the Body

1. Contact with skin or eyes.

• Wear safety glasses and no contact lens.

• Use goggles to protect normal eyewear.

• Wear the appropriate glove type for the job. Chemicals absorbed through the pores of the skin can enter the body and cause damage to vital organs.

• Use full face shield when pouring or mixing chemicals.


2. Ingestion (swallowing).

• Certain toxic chemicals can be fatal when even a minute amount in ingested.

• Never bring food or drink into areas where chemicals are being used. It is good practice to wash hands with soap and water when leaving the workplace.


3. Inhalation.• Breathing toxic gases may result in burns or

damage to lung tissue and can pass into the bloodstream, damaging other organs.

• The workplace must be well-ventilated. If unusual odors are detected, notify someone in charge and leave the area. Sound an alarm if appropriate.

Common Information in MSDS

• Chemical name

• Date prepared

• PEL & TLV

• Health effects

• Physical/Chemical characteristics

• Fire/Explosion data

• Reactivity hazard data

• Health hazard dta

Common Terms Used in an MSDSTerminology Definition Precautionary Action

Avoid ContactGeneral rule for all chemicals, even ifthey are considered nonhazardous.

Do not breathe vapors and avoid contactwith skin, eyes and clothing for allchemicals.

Carcinogen

Substances that are suspected or known tocause cancer. Some may have thresholdlimits of exposure. Multiple exposure tosuspected carcinogenic materials for evena low dose may be worse than a singlemassive exposure.

Exercise extreme care when handling. Donot breathe vapors and avoid all contactwith skin, eyes and clothing by wearingsuitable protective equipment.

CorrosiveLiving tissue as well as equipment isdestroyed on contact with thesechemicals.

Do not breathe vapors and avoid contactwith skin, eyes and clothing. Use suitableprotective equipment.

SkinA notation on the MSDS for substancesthat can be absorbed sufficiently throughthe skin as to cause toxic effects.

Do not allow contact with skin, eyes, orclothing.

DangerSubstances that can have serious harmfuleffects.

Considered dangerous chemicals. Thereare serious hazards associated with thesechemicals.

ExplosiveSubstances known to explode under someconditions.

Avoid shock (dropping), friction, sparksand heat. Isolate from other chemicalsthat are hazardous when spilled.

Flammable orCombustible

Substances that give off vapors that canreadily ignite under usual workingconditions.

Keep chemicals away from heat, sparks,flames and other sources of ignition.

Table A.1

Common Terms Used in an MSDSTerminology Definition Precautionary Action

Irritant Substances that have an irritant effect onskin, eyes, etc.

Do not breathe vapors and avoid contactwith skin and eyes.

Lachrymator

Substances that have an irritant orburning effect on skin, eyes or respiratorytract. These are dangerous in very smallquantities.

Only open in a hood. Do not breathevapors. Avoid contact with skin and eyes.Avoid heating.

MutagenChemical or physical agents that causegenetic alterations.

Handle with extreme care. Do not breathevapors and avoid contact with skin, eyesand clothing.

Peroxide FormerSubstances that form peroxides orhydroperoxides upon standing or when incontact in air.

Many peroxides are explosive.

Poison

Substances that have very serious andoften irreversible effects on the body.These substances are hazardous whenbreathed, swallowed, or in contact withthe skin.

Avoid all contact with the body and usesuitable protective equipment.

Stench Substances that have or generate odors. Open only in a hood.

TeratogenSubstances that cause the production ofphysical defects in a developing fetus orembryo.

Handle with extreme care. Do not breathevapors and avoid contact with skin, eyesand clothing. Use protective clothing.

Toxic

Substances that are hazardous to healthwhen breathed, swallowed, or are incontact with the skin. There is danger ofserious damage to health by short orprolonged exposure.

Avoid all contact with the body. Do notbreath vapors, dust or mist. Use suitableprotective equipment.

Table A.1 (continued)

Wet Chemical SafetyWhen working with corrosives:

• Clearly identify all chemicals before use (e.g., HF looks like H2O). Do not mix incompatible chemicals (see Table A1.3).

• Wear eye protection and a face shield at all times.

• Wear body and arm protection, including acid-resistant apron and sleeve guards.

• Wear gloves and boots suitable for the type of chemical.

• Do not breathe vapors. Use only under a fume hood.

• Store and use HF only in plastic containers – HF attacks glass.

Incompatible Chemicals

Table A.2

Chemical DO NOT MIX WITH:Acetone Bromine, chlorine, nitric acid and sulfuric acid

Ammonium Fluoride Acid solutions

Antimony Trioxide Metals and reducing agents

Arsine Oxidizing compounds

Boron Trichloride Moisture in air or water

Flammable Liquids Ammonium nitrate, chromic acid, hydrogen peroxide, nitric acid, sodiumperoxide and halogens

Hydrofluoric Acid Ammonia solutions

Hydrogen Peroxide Copper, chromium, iron, most metals or their salts, alcohols, acetone,organic materials, aniline, nitromethane, flammable liquids andcombustible materials

Nitric Acid Acetic acid, aniline, chromic acid, hydrocyanic acid, hydrogen sulfide,flammable liquids and flammable gases

Oxygen Flammable gases, liquids or solids such as acetone, acetylene, grease,hydrogen oils and phosphorus

Sulfuric Acid Potassium chlorate, potassium perchlorate, potassium permanganate, andcompounds with light metals such as sodium and lithium

Precautions When Working With Solvents

• Wear eye protection (face masks), appropriate gloves and protective clothing.

• Avoid breathing vapors. Use only under a hood or in a well-ventilated area.

• Keep solvents away from heat, sparks and open flame. Know the fire extinguisher location.

• Do not pour solvents into acid sinks or drains. Pour solvents into waste solvent containers.

• Keep solvents in a flammable materials storage cabinet.

• Do not mix acid waste with solvent waste - could produce dangerous exothermic reaction.

Special Precautions with Chemicals(Refer to p. 606 for details)

• Hydrofluoric Acid (HF)

• Sulfuric Acid (H2SO4)

• Chemical Hazards

Gas Detection and Monitoring

Some recommended safety procedures:

• Conduct formal safety reviews and inspections

• Implement regular gas safety training programs

• Limit the number of cylinders stored on-site through just in time deliver

Gas Detection and Monitoring(continued)

Important gas system design features:• Select components and materials suitable for reactive gases• Double containment for gas lines, where appropriate• Good ventilation around piping• Leak testing prior to use• Appropriate use of check valves and flow limiting orifices• Automatic shutoff valves• Pressure and vacuum-cycle purge on process stations• Backup power for fire protection and exhaust systems• Gas detection and alarm system appropriately placed, as

defined in the Uniform Fire Code and local ordinances• Steel gas cabinets with locks and external emergency

shutoff valves

Commonly Used Fab Chemicals and Their Safety Hazards

Note: Process applications are listed here only for reference and are described in the appropriate chapters.

Table A.3

A: annealing E/C: etch/clean

CVD: chemical vapor deposition I: ion implant

CG: crystal growth P/B: purge/blanket

Di: diffusion S: sputtering

Do: doping TO: thermal oxidation

TLV-TWA: Threshold limit values – time weighted average. Nearly all workers could be repeatedly exposed, day after day, without an adverse affect.

TLV-STEL: Threshold limit values – short term exposure limit. Exposures at the STEL should not be longer than 15 minutes, and should not be repeated more than 4 times per day.

IDLH: Immediately dangerous to life and health.


ChemicalName

Symbol Combustibleor Explosive

Healthhazardclass

TLV –TWA

(ppm)

TLV -STEL

(ppm)

IDLH(ppm)

Process Applications

(see note below)

Ammonia NH3 X 2 25 35 500 CVD

Argon Ar 0 - - - A.,CVD,CG,Di,E/C,I,P/B,S,TO

Arsine AsH3 X 4 0.05 - 6 CVD, CG, Di, Do, I

Boron trichloride BCl3 3 1 - 100 Di, Do, E/C, I

Boron trifluoride BF3 3 1 - 100 Di, Do, I

Chlorine Cl2 3 0.5 1 30 E/C, TO

Carbon dioxide CO2 1 5000 30000 50000 P/B

Diborane B2H6 3 0.1 0.3 40 CVD, Di, Do

Dichlorosilane SiH2Cl2 3 5 - 100 CVD

Helium He 0 - - - A, CVD, CG, E/C, I, P/B

Hydrogen H2 X 0 - - - A,CVD,CG,Di,E/C,I,P/B,TO

Hydrogen bromide HBr 3 3 - 50 E/C



ChemicalName

Symbol Combustibleor Explosive

Healthhazardclass

TLV –TWA

(ppm)

TLV -STEL

(ppm)

IDLH(ppm)

Process Applications

(see note below)

Hydrogen chloride HCl 3 5 - 100 TO

Nitrogen N2 0 - - - A, CVD, E/C ,I, P/B, TO

Nitrogen trifluoride NF3 3 10 15 2000 E/C, TO

Nitrous oxide N2O X 2 50 - - E/C, TO

Oxygen O2 X 0 none none None CVD, Di, E/C, S, TO

Phosphine PH3 X 4 0.3 1 200 CVD, CG, Di, Do, I

Silane SiH4 X 4 5 - - CVD, Di

Silicon tetrachloride SiCl4 3 5 - 100 CVD, E/C

Sulfur hexafluoride SF6 3 100 1250 - E/C

Tetrafluoromethane CF4 X E/C

Tungstenhexafluoride WF6 3 3 6 - CVD

Tetraortho-

Silicate (TEOS)(C2H5)4SiO4 X 2 10 - 1000 CVD


Other Safety Hazards(Refer to p. 608-609 for details.)

• Photo Light Source Safety

• Ion Implantation Safety

• Chemical Recycling


Appendix B

Contamination Controls in Cleanrooms


Appendix B

Contamination Controls in Cleanrooms

Evolution of Chip Feature Sizes and Contamination Control

Year of MassProduction 1980 1984 1987 1990 1993 1995 1997

Wafer Diameter (mm) 75 100 125 150 200 200 200

DRAM MemoryTechnology

(increasing value hasmore memory)

64K 256K 1M 4M 16M 64M 256M

Chip Size (cm2) 0.3 0.4 0.5 0.9 1.4 2.0 3.0

Minimum Feature Sizeon Chip (µm)

2.0 1.5 1.0 0.8 0.5 0.35 0.25

Number of ProcessSteps 100 150 200 300 400 450 500

Class of Cleanroom

(smaller value iscleaner)

1,000-100 100 10 1 0.1 0.1 0.1 and mini-

environment

Chemical Impurity(ppb) 1,000 500 100 50 5 1 0.1

Table B.1

Human Contamination

• Saliva and Lung Particles– talking– sneezing

• Contents of Saliva – Dissolved minerals– Salts– Elements (Na, Ca, Fe, Mg, Cl, Al, S, K, P)

• Other Body Contaminants

Evolution of Federal Standard 209 Specifications for Cleanliness of Air

Table B.2

Date FederalStandard Highlights of Original and Revised Contents

Dec. 1963 209 Cleanroom operation principles.

Aug. 1966 209A Cleanroom design and testing methods:

Defined air cleanliness classifications as class 100, 10,000, and100,000: specified as the number of particles at sizes largerthan 0.5 micron per cubic foot.

Defined air flow pattern of laminar flow and turbulent flow.

Specified air velocity at 90 +/- 20 ft/min.

Specified pressure, temperature, humidity and vibration.

Specified audio frequency noise & air exchange rate.

Apr. 1973 209B Changed air velocity from 90 +/- 20 ft/min to 90 +/- 20%ft/min and changed humidity from 45% to 40 +/- 5%.

May 1977 209B (amend) Added cleanliness class 1,000.

Oct. 1987 209C Major revision of cleanroom classification and testing method:

Added air cleanliness classes 1 and 10.

Extended the particles measurements from 5 micron and 0.5micron down to 0.3 micron and 0.2 micron for class 100, anddown to 0.3, 0.2 and 0.1 micron for class 10 and class 1.

Clearly defined particulate sampling locations and numbers ofsampling and measuring time.

June 1988 209D Corrected several typographical errors found in 209C.

Sep. 1992 209E Adapted the metric system.

Added descriptor to specify the maximum allowable number ofultrafine particles per cubic meter.

Added sequential airborne particle sampling plan to the singleair sampling plan specified in 209D.

Metric Definitions of Airborne Particulate Cleanliness Classes Per Federal Standard 209E

Table B.3

Particles/m3

Class 0.1 µµµµm 0.2 µµµµm 0.3 µµµµm 0.5 µµµµm 5 µµµµmM1 3.50 x 102 7.57 x 101 3.09 x 101 1.00 x 101

M1.5 1.24 x 103 2.65 x 102 1.06 x 102 3.53 x 101

M2 3.50 x 103 7.57 x 102 3.09 x 102 1.00 x 102

M2.5 1.24 x 104 2.65 x 103 1.06 x 103 3.53 x 102

M3 3.50 x 104 7.57 x 103 3.09 x 103 1.00 x 103

M3.5 2.65 x 104 1.06 x 104 3.53 x 103

M4 7.57 x 104 3.09 x 104 1.00 x 104

M4.5 3.53 x 104 2.47 x 102

M5 1.00 x 105 6.18 x 102

M5.5 3.53 x 105 2.47 x 103

M6 1.00 x 106 6.18 x 103

M6.5 3.53 x 106 2.47 x 104

M7 1.00 x 107 6.18 x 104

Cleanroom Glove Characteristics

Table B.4

Glove Desirable Characteristics UndesirableCharacteristics

PVC (vinyl) cleanroom glove • Barrier to skin contaminants

• Flexible; inexpensive

• Low level of contaminants

• Low particle levels

• Excessive sweating

• Tears/splits easily

• Not acid or solventresistant

Latex cleanroom glove • Inexpensive • Often irritates skin

Orange latex acid glove • Excellent acid protection

• Low particle levels

• Slippery

• Too warm

• Chemical extractables toohigh (e.g., chloride)

Green nitrile solvent glove • Adequate solvent protection formany solvents

• Not resistant to all solvents

• Chemical extractables toohigh (e.g., sulfur)

Silver mulitlayered PVAsolvent glove for specialsolvents (e.g., dimethyl

acetamide)

• Excellent Solvent Protection

• Low level of extractablecontaminants & particles

• Lacks dexterity

• Expensive

Specification for DI Water

Two primary specifications for electronic grade DI water:

• American Society for Testing and Materials (ASTM)– ASTM D-19 Standard Guide for Electronic

Grade Wafer D512-90 (1990)

• Semiconductor Equipment and Materials International– SEMI Suggested Guidelines for Pure Water for

Semiconductor Processing (1989)

Charge Generation Capability of Common Materials

Figure B.1

Positive (+)

Negative (-)

AirHuman skinGlass, quartzAluminumPaperHard rubberCopperPolyester (mylar)Polystyrene (styrofoam)PVC (vinyl)TeflonSilicone rubber

Electrostatic Voltages at Different Relative Humidity Levels

Table B.5

Means of Static Generation10% to 20%

Relative Humidity15% to 90%

Relative Humidity

Walking across carpet 35,000 V 1,500 V

Walking over vinyl floor 12,000 V 250 V

Worker at bench 6,000 V 100 V

Work chair padded withpolyurethane foam

18,000 V 1,500 V


Appendix C

Units


Appendix C

Units

The International System of Units (SI)

Quantity Unit Abbreviation UnitsLength meter mMass kilogram KgTime second sTemperature kelvin KCurrent ampere AFrequency hertz Hz 1/sForce newton N Kg-m/s2

Pressure pascal Pa N/m2

Energy joule J N-mPower watt W J/sElectric charge coulomb C A-sPotential volt V J/CConductance siemens S A/VResistance ohm Ω V/ACapacitance farad F C/VMagnetic flux weber Wb V-sMagnetic induction tesla T Wb/m2

Inductance henry H Wb/A

Table C.1

SI Prefixes

Table C.2

Prefix Symbol Valuefemto- f 10-15

pico- p 10-12

nano- n 10-9

micro- m 10-6

milli- m 10-3

centi- c 10-2

deci- d 10-1

deka- da 10hecto- h 102

kilo- k 103

mega- M 106

giga- G 109

tera- T 1012

Unit Conversions

A meter is the basis for metric units of measure.

1 Å = 10-10 m1 nm = 10-9 m1 µm = 10-6 m1 mm = 10-3 m1 cm = 10-2 m

Metric Equivalents to the Angstrom

The angstrom is a common thickness unit of measure.

1 Å = 10-1 nm

1 Å = 10-4 µm

1 Å = 10-8 cm

1 Å = 10-10 m

Conversion Between Common and SI Units

Physical Property Common Unit SI Unit1 in. 2.54 cm0.001 in (1 mil) 25.4 microns (µm) ≈ 25 µm0.039 in (about 4 mils) 0.1 mm

Length

39.3 microinches (µ inches) 1 µm2.205 pounds (lb) 1.000 kg1.000 lb 453.6 g

Mass

1 ounce (oz) 28.35 g1.000 gallon (gal) 3.785 liter (L)Volume1.00 quart (qt) 0.946 L1 eV 1.6022 x 10-19 JEnergy1 kWh 3.600 x 103kL

Table C.3


Appendix D

Color as a Function of Oxide Thickness


Appendix D

Color as a Function of Oxide Thickness

Color Chart for Thermally Grown Oxide Films

FilmThickness

(µµµµm)Color & Comments

FilmThickness


0.050.07

TanBrown

0.630.68

Violet-redBluish

0.100.120.150.17

Dark violet to red-violetRoyal blueLight blue to metallic blueMetallic to very light yellow-green

0.720.77

Blue-green to greenYellowish

0.200.220.250.27

Light gold or yellowGold with slight yellow-orangeOrange to melonRed-violet

0.800.820.850.860.870.89

OrangeSalmonDull, light red-violetVioletBlue-violetBlue

Table D.1

Color Chart for Thermally Grown Oxide Films

Table D.1 (continued)

FilmThickness


FilmThickness


0.300.310.320.340.350.360.370.39

Blue to violet-blueBlueBlue to blue greenLight greenGreen to yellow-greenYellow-greenGreen-yellowYellow

0.920.950.970.99

Blue-greenDull yellow-greenYellow to yellowishOrange

0.410.420.440.460.470.480.49

Light orangeCarnation pinkViolet-redRed-violetVioletBlue-violetBlue

1.001.021.051.061.07

Carnation pinkViolet-redRed-violetVioletBlue-violet

0.500.520.540.560.570.580.6

Blue-greenGreen (broad)Yellow-greenGreen-yellowYellow to “yellowish”Light orange or yellowCarnation pink

1.101.111.121.181.19

GreenYellow-greenGreenVioletRed-violet


Appendix E

Overview of Photoresist Chemistry


Appendix E

Overview of Photoresist Chemistry

Diagram and Symbol of Simple Benzene Aromatic Ring

Figure E.1

Carbon atom

Hydrogen atom

Benzene aromatic ring

Redrawn from S. Campbell, The Science and Engineering of Microelectronic Fabrication (New York: Oxford University Press, 1996), p. 183.

Aromatic Compounds

Toluene Naphthalene

C HH

H

Figure E.2


Polyethylene Polymer and Cross Linking

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

Polyethylene polymer

C

H

H

C

H

H

C

H

H

C

H

C

H

H

C

H

H

C

H

H

H

C

C

H

HC

H

H

C

H

HC

H

HCross linkingC

H

H

Figure E.3


Common Photoactive Compound of Diazonaphthoquinone (DNQ)

Figure E.4A

C

CH3

CH3

SO 2

O

N 2


Common Photoactive Compound of Diazonaphthoquinone (DNQ)

C

CH3

CH3

SO2

O

N2

R =

O

N2

R

Figure E.4B


Novolak Polymer

CH3HO

CH 2

HO

CHCH 2

CH3

CHCH 2

Figure E.5


Reactions of DNQ After Exposure to UV Light

Figure E.6

+ UV Light

R

N2

O

Photo active componentR

OHC

O

+N2

Dissolution enhancer

Through a cascade of reactions involving light

Redrawn from S. Campbell, The Science and Engineering of Microelectronic Fabrication (New York: Oxford University Press, 1996), p. 185

Chemical Amplification of Photoresist with tBOC Deprotection Reaction

Figure E.7

Redrawn from T. Ueno, “Chemistry of Photoresist Materials”, Edited by J. Sheats and B. Smith, Microlithography, Science and Technology (New York: Marcel Dekker, 1998), p. 465. Adapted by S. Postnikov

S+ –X + UV light H+ –X

Acid catalystOnium salt

–— (CH2 CH) –—n

Heat

OH

+ CO2

PHS

O

O –— C –— O –— C –— CH3

CH3

CH3H+

Protecting group

–— (CH2 CH) –—n

tBOC

Isobutelene (escapes polymer)

H+ + C

CH3

CH3

CH2+


Appendix F

Etch Chemistry


Appendix F

Etch Chemistry

Etch Chemistries of Different Etch ProcessesEtched

Material Conventional Chemistry NewChemistry Benefits

PolySi Cl2 or BCl3/CCl4Cl2 or BCl3/CF4 sidewallCl2 or BCl3/CHCl3 passivatingCl2 or BCl3 /CHF3 gases

SiCl4/Cl2BCl3/Cl2HBr/Cl2/O2

Br2/SF6

SF6

CF4

No carbon contamination.

Selectivity to SiO2 & resist.No carbon contamination.Higher etch rate.

Al. Cl2

BCl3 + sidewall passivating gasesSiCl4

SiCl4/Cl2BCl3/Cl2HBr/Cl2

Improved profile control.No carbon contamination.

Al with 1% Siand 0.5% Cu

Same as Al BCl3/Cl2 + N2 N2 accelerates Cu etch rate.

Al with 2% Cu BCl3/Cl2/CCl4 SF6 onlyWSi2, TiSi2,CoSi2

CCl2F2 CCl2F2/NF3

CF4/Cl2

Controlled etch profile.No carbon contamination.

Single-crystal Si Cl2 or BCl3 + sidewall passivatinggases

CF3BrHBr/NF3

Higher selectivity for trenchetch.

SiO2 (BPSG) CCl2F2CF4

C2F6

C3F8

CCl2F2

CHF3/CF6

CHF3/O2

CH3CHF2

Environmentally improvedalternatives.

Si3N4 CCl2F2

CHF3

CF4/O2

CF4/H2

CHF3

CH3CHF2

Environmentally improvedalternatives.

Y. Lii, “Etching,” ULSI Technology, ed. C. Chang and S. Sze (New York: McGraw-Hill, 1996), p. 354.

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IA_Safety Issues for MicroFabrication