Lecture 3 : Cleanroom Technology (Contamination Control)

Transcription

1 Lecture 3 : Cleanroom Technology (Contamination Control) The topics covered the following: Cleanroom Definition Standards and Classifications Contamination: Types, Effects, and Sources Cleanroom Systems 1

2 Two Definitions: What is a Cleanroom? ( 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 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. 2

3 Federal Standard 209D Class Limits CLASS MEASURED PARTICLE SIZE (MICROMETERS) NA NA 100 NA NA 1,000 NA NA NA 1, ,000 NA NA NA 10, ,000 NA NA NA 100,

4 Class Name Federal Standard 209E Airborne Particulate Cleanliness Classes 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 M M M M M M M M M M M M

5 Clean Room Class Ratings from ULSI Technology by Chang and Sze 5

6 BS 5295 Environmental Cleanliness Classes Class of environmental cleanliness Maximum permitted number of particles per m^3 (equal to, or greater than, stated size) 0.3 m m 0.5 m m 5 m m 10 m m 25 m m Maximum floor area per sampling position for cleanrooms Minimum pressure difference* Between classified areas and unclassified areas (Pa) Between classified area and adjacent areas of lower classification (Pa) (m^2) C NS NS D NS NS E NS NS F NS NS NS G NS H NS NS J NS K NS L NS NS M NS NS NS NA 6

7 ISO 209 Airborne Particulate Cleanliness 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 ISO ISO ISO ISO ISO ISO ISO ISO

8 Industrial Application of Cleanroom Industry Cleanliness Level - Class ( Fed Std. 209E) ,000 10, ,000 Silicon Crystallization Wafer Manufacturer Semiconductor Manufacturer Diffusion Wafer Processing Photolithography IC Chip Manufacture Inspection Assembly Magnetic Drum Tape Electronics Optical, Printing LSI Mask High Reliable Tube Shadow Mask Lens Printer Circuit Board Film Precision Print Others Laser Generator Laundry for Clean Garments 8

9 Contamination Control The most important aspect of microfabrication is control of dirt Processes killed by very small contaminants 9

10 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 failure Unwanted chemical traces cause unwanted etch, nonuniformity in processing Bacteria grow in water and on wafer surfaces, not cleaned well 10

11 Effects of Contamination Device processing yield Dimension of device Surface cleanliness Pitted layers Quality check (QC) required Device performance Device reliability 11

12 Sources of Contamination Air: class #: # of particles/ square area Production facility Clean-room personnel Process water Process gas Static charge 12

13 Sources of Contamination 13

14 Particle Sizes in Air 14

15 Human Activities and Contamination 15

16 Clean Room Garments 16

17 Contamination Reduction Strategies Level 1 Clean factories Clean air strategies Level 2 Wafer Cleaning Deionized water (DI water) Chemical cleaning Level 3 Gettering Remove metal ions and alkali ions from device active regions 17

18 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 % of particles as small as.12 µm (microns). 18

19 HEPA Filter Types Type Application Performance A Industrial, noncritical > µm (MIL-STD-282) B nuclear containment > µm (certified by DOE) C laminar flow > µm (MIL-STD-282) D ultra-low penetration air > µm (ULPA) E toxic, nuclear, and MIL-F biohazard containment MIL-F (classified performance) 19

20 HEPA Filter Construction 20

21 Deionized Water Water contamination as important as air Use Deionized (DI) water systems Removes heavy elements and biologicals 21

22 Cleanroom Systems Option 1 from ULSI Technology by Chang and Sze 22

23 Cleanroom Systems Option 2 from ULSI Technology by Chang and Sze 23

24 Cleanroom Systems Option 3 from ULSI Technology by Chang and Sze 24

25 Cleanroom Systems Option 4 from ULSI Technology by Chang and Sze 25

26 Specifications for Clean Room Utilities Air, Water, Chemicals, Gases are common utilities All must meet specifications listed 26