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Lecture 3 : Cleanroom Technology(Contamination Control)

The topics covered the following:Cleanroom DefinitionStandards and ClassificationsContamination: Types, Effects, and SourcesCleanroom Systems

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What is a Cleanroom?Two Definitions:( a ) Federal Standard 209 Defines a Clean Room

"A Clean Room is an enclosed area employing control over the particulate matter in air with temperature, humidity and pressure control as required. To meet the requirements of a 'Clean Room' as defined by this standard, all Clean Rooms must not exceed a particulate count as specified in the air cleanliness class." This standard, first issued in 1963, has been used in the current version 209B amendment 1 since 1976. It is shortly to be re-issued, entitled "Airborne Particulate Cleanliness Classes for Clean Rooms and Clean Zones".

( b ) BS 5295 Definition"Environmental cleanliness in enclosed spaces". "A Clean Room is a room with environmental control of particulate contamination, temperature and humidity, constructed and used in such a way as to minimize the introduction, generation and retention of particles inside the room." This standard dates from 1976 and falls into 3 parts. Part 1: Specification for controlled environment Clean Rooms, workstations and clean air devices. Part 2: Guide to the construction and installation of Clean Rooms, workstations and clean air devices. Part 3: Guide to operational procedures and disciplines applicable to clean rooms, workstations and clean air devices.

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Federal Standard 209D Class Limits

MEASURED PARTICLE SIZE (MICROMETERS)CLASS

0.1 0.2 0.3 0.5 5.0

1 35 7.5 3 1 NA

10 350 75 30 10 NA

100 NA 750 300 100 NA

1,000 NA NA NA 1,000 7

10,000 NA NA NA 10,000 70

100,000 NA NA NA 100,000 700

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Federal Standard 209E Airborne Particulate Cleanliness Classes

Class Name Class Limits

0.1m m 0.2m m 0.3m m 0.5m m 5m m

Volume Units Volume Units Volume Units Volume Units Volume Units

SI English (m^3) (ft^3) (m^3) (ft^3) (m^3) (ft^3) (m^3) (ft^3) (m^3) (ft^3)

M 1 350 9.91 75.7 2.14 30.9 0.875 10.0 0.283 -- --

M 1.5 1 1 240 35.0 265 7.50 106 3.00 35.3 1.00 -- --

M 2 3 500 99.1 757 21.4 309 8.75 100 2.83 -- --

M 2.5 10 12 400 350 2 650 75.0 1 060 30.0 353 10.0 -- --

M 3 35 000 991 7 570 214 3 090 87.5 1 000 28.3 -- --

M 3.5 100 -- -- 26 500 750 10 600 300 3 530 100 -- --

M 4 -- -- 75 700 2 140 30 900 875 10 000 283 -- --

M 4.5 1 000 -- -- -- -- -- -- 35 300 1 000 247 7.00

M 5 -- -- -- -- -- -- 100 000 2 830 618 17.5

M 5.5 10 000 -- -- -- -- -- -- 353 000 10 000 2 470 70.0

M 6 -- -- -- -- -- -- 1 000 000 28 300 6 180 175

M 6.5 100 000 -- -- -- -- -- -- 3 350 000 100 000 24 700 700

M 7 -- -- -- -- -- -- 10 000 000 283 000 61 800 1 750

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Clean Room Class Ratings

from ULSI Technology by Chang and Sze

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BS 5295 Environmental Cleanliness Classes

Class of environmental

cleanliness0.3 m m 0.5 m m 5 m m 10 m m 25 m m

Between classified areas and unclassified

areas (Pa)

Between classified area and adjacent

areas of lower classification (Pa)

C 100 35 0 NS NS 10 15 10D 1 000 350 0 NS NS 10 15 10E 10 000 3 500 0 NS NS 10 15 10F NS 3 500 0 NS NS 25 15 10G 100 000 35 000 200 0 NS 25 15 10H NS 35 000 200 0 NS 25 15 10J NS 350 000 2 000 450 0 25 15 10K NS 3 500

000 20 000 4 500 500 50 15 10

L NS NS 200 000 45 00 5 000 50 10 10M NS NS NS 450 000 50 000 50 10 NA

Maximum permitted number of particles per m^3 (equal to, or greater than, stated size)

Maximum floor area per

sampling position for cleanrooms

(m^2)

Minimum pressure difference*

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ISO 209 Airborne ParticulateCleanliness Classes

Numbers(N)

Maximum concentration limits (particles/m^3 of air) for particles equal to and larger than the considered sizes shown below

0.1m m 0.2m m 0.3m m 0.5m m 1m m 5.0m m

ISO 1 10 2

ISO 2 100 24 10 4

ISO 3 1 000 237 102 35 8

ISO 4 10 000 2 370 1 020 352 83

ISO 5 100 000 23 700 10 200 3 520 832 29

ISO 6 1 000 000 237 000 102 000 35 200 8 320 293

ISO 7 352 000 83 200 2 930

ISO 8 3 520 000 832 000 29 300

ISO 9 35 200 000 8 320 000 293 000

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Industrial Application of Cleanroom10 100 1,000 10,000 100,000

High Reliable

Tube

Cleanliness Level - Class ( Fed Std. 209E)

Inspection

Assembly

IC Chip Manufacture

Photolithography

Wafer Processing

Diffusion

Silicon Crystallization

Wafer Manufacturer

Industry

Semiconductor Manufacturer

Electronics

Optical, Printing

Others

Lens

LSI Mask

Magnetic Drum Tape

Shadow Mask

Laser Generator

Printer Circuit Board

Film

Precision Print

Laundry for Clean Garments

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Contamination Control

The most important aspect of microfabricationis control of dirt Processes killed by very small contaminants

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Types of Contamination

Particulates– semiconductor devices very vulnerable– Rule of thumb: killer particle size < 1/10 min feature– Feature size ↓, particle # and size must ↓Metallic ions - mobile ions (Na+, K+) can cause failureUnwanted chemical traces cause unwanted etch, nonuniformity in processingBacteria grow in water and on wafer surfaces, not cleaned well

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Effects of Contamination

Device processing yieldDimension of deviceSurface cleanlinessPitted layersQuality check (QC) required

Device performanceDevice reliability

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Sources of Contamination

Air: class #: # of particles/ square areaProduction facilityClean-room personnelProcess waterProcess gasStatic charge

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Sources of Contamination

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Particle Sizes in

Air

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Human Activities and Contamination

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Clean Room Garments

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Contamination Reduction Strategies

Level 1 – Clean factoriesClean air strategies

Level 2 – Wafer CleaningDeionized water (DI water)Chemical cleaning

Level 3 – GetteringRemove metal ions and alkali ions

from device active regions

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Clean Room Air Filters

HEPA stands for High Efficiency Particulate Air.It means a filter must be capable of capturing 99.97% of particles as small as .3 µm (microns).

– most common type of clean room air filter– high efficiency, low pressure drop, good loading

characteristics– uses glass fibers in a paper-like medium– are rated by their particle retention.

ULPA stands for Ultra Low Particulate Air.This means the filter is capable of capturing 99.999% of particles as small as .12 µm (microns).

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HEPA Filter Types

Type Application PerformanceA Industrial, noncritical > 99.97 % @ 0.3 µm

(MIL-STD-282)B nuclear containment > 99.97 % @ 0.3 µm

(certified by DOE)C laminar flow > 99.97 % @ 0.3 µm

(MIL-STD-282)D ultra-low penetration air > 99.9995 % @ 0.12 µm

(ULPA)E toxic, nuclear, and MIL-F-51477

biohazard containment MIL-F-51068(classified performance)

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HEPA Filter Construction

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DeionizedWater

Water contamination as important as air •Use Deionized (DI) water systems • Removes heavy elements and biologicals

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Cleanroom Systems

Option 1from ULSI Technology by Chang and Sze

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Cleanroom Systems

Option 2from ULSI Technology by Chang and Sze

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Cleanroom Systems

Option 3from ULSI Technology by Chang and Sze

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Cleanroom Systems

Option 4from ULSI Technology by Chang and Sze

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Specifications for Clean Room

Utilities

Air, Water, Chemicals, Gases are common utilities • All must meet specifications listed