A Primer on Contamination Control 

and Electrostaticsand Electrostatics 

Scott Mackler, Principal Consultant

Tom Albano, Certified Electrostatics Engineer

Cleanroom Consulting, LLC

www.cleanroom‐consulting.com

How Small Is Small?

Human Hair One Micron Equals

0 00003937 I h1/10,000

of an inch

• 0.00003937 Inches

• 1/1,000,000 Meter

1/1,000of an inch

of an inch

• 1/25,400 Inch

25 i 1 MilOne Micron • 25 microns = 1 Mil

3

Settle‐out Contamination(on witness wafers ‐ New)

Settle‐out Contamination(Class 100 – 6 day exposure)

l i iSettle‐out Contamination(Class 100/1000, 4 day exposure, operational)

H Cl i Cl ?How Clean is Clean?Class 100,000 ‐ 1 Day

Particle Settling Rates

Size µm Time to fall one meterSize, µm Time to fall one meter0.1 36 days0.5 1.4 days0.5 1.4 days1 8.6 hours5 21 mins10 5.2 mins15 2.3 mins20 1.3 mins25 50 secs

Particles Generated (0.3 micrometers / minute / activity)

Motionless, sitting or standing 100,000

Head, arm, neck, leg motion 500,000

All above w / foot motion 1,000,000

Standing to siting & vice versa 2,500,000

Walking at 2 mph 5,000,000

Walking at 3.5 mph 7,500,000

Walking at 5 mph 10,000,000

Room Cleanliness after a contamination excursion

E ffect o f A C P H o n R eco very R ate

6 7 5 A C P H 3 0 A C P H T im e (sec)

P artic les T im e (sec)

P artic les

0 1 00 0 0 00 0 1 0 0 0 0 000 1 ,0 0 0 ,0 00 0 1 ,0 0 0 ,0 005 .3 3 1 0 ,0 0 0 1 2 0 1 0 ,0 0 0

1 0 6 6 1 0 0 2 4 0 1 0 01 0 .6 6 1 0 0 2 4 0 1 0 01 5 .9 9 1 3 6 0 1

Typical  Electrostatic Charges  Found  In Work Areas   

• Components ‐ Ceramic  5 kV• Components – Plastic 2.5kVComponents  Plastic    2.5kV• Plastic Film 20 kV• Polyethylene Parts 5 kV• Glass Plates 5 kV• Teflon® Subassemblies  25 kV• Fiberglass 2.5 kV• Silicon Wafers 5 kV

DischargeofanIsolatedPlate

Cleanrooms Generate Static  Charge and Hold it Efficiently

Discharge of an Isolated Plate

50005500

• Low Humidity• Low Surface Contamination 

Ai C diti i R

al V

olta

ge

25003000350040004500 • Air Conditioning Removes 

Natural Air Ions• Use of Insulators

– Teflon®

Res

idu

5001000150020002500

500 V

Teflon– Quartz– Glass– Plastic

Time (hours)

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 340 Plastic

– Oxide‐Coated silicon

What Happens When a Surface is Charged?

Gravitational

Aerodynamic

q q For electric fields

Aerodynamic

Fq q

r 1 2

4 02

For electric fields of 1000 V/inch, the greatest force is electrostatic!

Electrostaticis electrostatic!

Effect of Static Charge on Wafer Contamination

200 mm Wafer in a Class 1 Mini-Environment200 mm Wafer in a Class 1 Mini Environment

Wafer at 0 VClass 1 mini-environment for 6 weeks

Wafer at 2000 VClass 1 mini-environment for 6 weeks

Water

Why do Cleanrooms Develop Such High Levels of Charge?

Charge Generation:The Materials Used

Latex

Human Hands

Quartz

Positive+

Encourage Transfer:Nylon

Aluminum

Steel

P l hPolyurethane

Polyethylene

Polypropylene

PVC (Vinyl)

Triboelectric Charging

PVC (Vinyl)

Silicon

Mylar®

Teflon®

Negative-

17

Teflon

Processing of Plastic Film over Rollers  Contact of Dissimilar Materials Pressure of ContactPressure of Contact

Separation after Contact Vibration Friction between Objects

IV Bags, Photographic Film, and Cleanroom Packaging Materialsand Cleanroom Packaging Materials

++++++++++++++++++++++++++++++++++++

Electrostatic Problems in Polymer Processing

Conveyance and blending issues withpolymer pellets/extrusions, both in compounding and in injection moldingHigh electric fields: particle attraction and Electrostatic Bonding to molded parts, some ofcritical surfaces, applications.

Conventional cleaning methods ineffective