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SEMI F5-1101 © SEMI 1990 , 2001 3 may be as lo w as 10% ). Additio nal by-prod ucts will h a ve different an d so metimes m o re hazardous properties. 7.2 Considerable research h as been con ducted into various hazardous…

SEMI F5-1101 © SEMI 1990, 2001 2

4 Referenced Standards

4.1 SEMI Standards

SEMI S2 — Environmental, Health, and Safety

Guideline for Semiconductor Manufacturing Equipment

SEMI S5 — Safety Guideline for Flow Limiting

Devices

SEMI S8 — Safety Guidelines for Ergonomics

Engineering of Semiconductor Manufacturing

Equipment

4.2 Code of Federal Regulations — United States

Environmental Protection Agency

40 CFR Part 63 (Clean Air Act 112 (b)(1))

4.3 Uniform Codes

Uniform Fire Code — Article 80 — Hazardous

Material

NOTE 1: Unless otherwise indicated, all documents cited

shall be the latest published versions.

5 Terminology

5.1 Abbreviations and Acronyms

5.1.1 CVD — Chemical Vapor Deposition

5.1.2 EPI — epitaxial deposition

5.1.3 HAP — Hazardous Air Pollutants [as defined by

40 CFR Part 63 (Clean Air Act 112 (b)(1))

5.1.4 PFC — perfluorocompounds

5.1.5 POU — Point of use

5.1.6 VOC — Volatile Organic Compounds

5.2 Definitions

5.2.1 classification of emissions — understanding the

composition of process exhausts.

5.2.2 efficiency — the ratio (or fraction or proportion)

of removed chemical species to its input amount

5.2.3 End-of-Pipe Abatement — abatement

technologies that can be fitted at the discharge point of

the exhaust system.

5.2.4 flow capacity — the maximum flow any specific

equipment can handle.

5.2.5 occupational exposure limits (OELs) — for the

purpose of this document, OELs are generally

established on the basis of an eight-hour workday.

1 United States Government Code of Federal Regulations, free from

the web site at http://www.epa.gov

2 International Conference of Building Officials (ICBO), 5360

Workman Mill Road, Whittier, CA 90601-2298

Various terms are used to refer to OELs, such as

permissible exposure levels, Threshold Limit Values®,

maximum acceptable concentrations, maximum

exposure limits, and occupational exposure standards.

However, the criteria used in determining OELs can

differ among the various countries that have established

values. Refer to the national bodies responsible for the

establishment of OELs. (Threshold Limit Value is a

registered trademark of the American Conference of

Governmental Industrial Hygienists.)

5.2.6 Point-of-Use Abatement — abatement

technologies that can be fitted at the point of discharge

of the gaseous emission from semiconductor process

equipment. These devices are also called exhaust

conditioners.

5.2.7 removal capacity — amount of a species which

can be removed.

5.2.8 usage reduction — reducing the total volume of

process chemicals requiring abatement.

6 Philosophy

6.1 Gaseous mixtures potentially emitted from

numerous processes could also produce hazards within

exhaust ducts.

6.2 With increasing legal requirements worldwide on

both worker safety and general environmental

protection, more effective exhaust management is

required.

6.3 This demands a detailed understanding of the

chemical and physical properties of the chemical

compounds being emitted from processes, and of the

conditions under which they are released.

6.4 Careful design of the abatement systems is required

to attain both high efficiency and maximum economy.

7 Classification of Emissions

7.1 The following fundamental points regarding

exhaust emissions should be considered:

• Exhaust contaminants might be solely the material

used in the process (e.g., isopropyl alcohol (IPA)

from a rinse chamber)

• In plasma and thermal chambers many reactions

occur, both those desired and others; therefore by-

products are also key components of exhaust

emissions.

• In theory, most possible combinations of the

elements in the input gases may be found as

compounds in the exhaust. In practice, the main

components will be the unused process gas (the

percentage consumed in the process varies, and

SEMI F5-1101 © SEMI 1990, 20013

may be as low as 10%). Additional by-products

will have different and sometimes more hazardous

properties.

7.2 Considerable research has been conducted into

various hazardous by-products of processes, from

explosive solids to organochlorine compounds with

mutagenic properties. (See Sections 13.1 through

13.3.)

7.3 In considering selection of exhaust systems and

abatement technology, it is essential to review all the

materials likely to be present in the exhaust.

7.4 Contributions from the materials on the wafer must

also be considered, as they often cause blocked

exhausts (e.g., aluminum etches produce aluminum

chloride (a by-product of removal of aluminum from

the wafer with chlorinated gases)).

7.5 Processes that produce specific hazardous by-

products should be evaluated for appropriate point-of-

use abatement technology before discharge to an

exhaust system.

7.6 Gaseous and particulate contaminants emitted from

semiconductor manufacturing can be divided

conveniently into nine major groups, each of which

might justify its own exhaust system.

7.6.1 Group-1 Acid — Easily hydrolyzable acids, (e.g.,

hydrogen chloride hydrolyzes into hydrochloric acid.)

7.6.2 Group-2 Acid aerosols (“difficult–to-scrub”) —

This group includes acids that generate aerosols and

that are not easily removed by simple water scrubbers

(e.g., aqua regia, sulfuric and nitric).

NOTE 2: High concentrations of easily soluble acids will also

fall into the “difficult-to-scrub” category.

7.6.3 Group-3 Ammonia — Exhaust streams

containing ammonia

7.6.4 Group-4 Volatile Organic Compounds (VOCs)

— Exhausts containing volatile organic compound

vapors or flammable gas discharge requiring

destruction.

7.6.5 Group-5 Pyrophoric — Exhausts containing

pyrophoric gases.

7.6.6 Group-6 Emergency Release Discharges —

Enclosures are provided with additional exhausts to

contain sudden unanticipated releases of gas from

cylinders, etc.

7.6.7 Group-7 Special/Direct — Additional exhausts

used to keep specific gases separate for recovery

purposes (e.g., hydrogen (H

) reclamation from EPI or

PFC reclamation from CVD tools, Oxides of Nitrogen

(NO

)).

7.6.8 Group-8 General Exhaust Systems without End-

of-Pipe Treatment — Exhaust of heat or post-treatment

exhaust from POU abatement systems.

7.6.9 Group-9 Highly Toxic Gas Exhaust — Highly

toxic gases especially those with poor warning

properties (e.g., arsine, phosphine, diborane, germane).

The end user has a primary responsibility to prevent

discharge of these gases above a regulated level (e.g.,

usually one-half (1/2) of Immediately Dangerous to

Life and Health (IDLH) levels).

NOTE 3: Facility exhaust systems may be called by a number

of different names such as: Acid, Corrosive, Ammonia,

Scrubbed, VOC, Solvent, Incinerated, Highly Toxic, Toxic,

Dedicated, Special, PFC, General, Heat, Treated, or others.

The actual facility exhaust system name, and what groups are

routed to each system, will vary by factory and by country.

7.7 The groups listed in Section 7.6 are not a definitive

division, but represent a summation of common

industry practice for separation. The division is based

on three basic principles:

• avoiding mixing of incompatible gases in the

exhaust,

• potential need for different end-of-pipe abatement

technologies, and,

• keeping materials separate for recovery.

7.8 The number of separate exhaust systems used is

entirely a decision for each facility, based on the

following:

• processes and chemicals used,

• the number of each type of process,

• whether recovery of gases is required,

• whether point-of-use (POU) abatement is installed,

and

• compatibility of emissions with each other or the

effluent handling system.

7.9 In theory, if POU abatement systems are fitted to

all sources of gaseous effluent all exhaust could then be

combined into a single exhaust system.

7.9.1 In practice most facilities operate a compromise

between the two extremes with two to four separate

exhaust systems and point-of-use abatement systems

fitted only to certain sources. The decision (as to which

combination to use) will often be based on economic

and space constraints.

7.9.2 Safety and environmental factors listed below,

should always be considered first when determining

specific gaseous sources that require POU abatement

systems.

SEMI F5-1101 © SEMI 1990, 2001 4

7.10 Many types of process equipment use and exhaust

incompatible gases sequentially (e.g., silane and then

nitrogen trifluoride (NF

) as elements of a deposition

and cleaning cycle).

7.10.1 With more than one of these processes being

discharged asynchronously into a common exhaust

duct, undesired reactions may occur.

7.10.2 It is possible to avoid this problem by fitting the

equipment outlet with three-way valves to divert the

discharge to the correct exhaust system, depending on

equipment process step. Three-way valves may not be

necessary if pump ballast-gas flow is increased to dilute

gases.

7.10.2.1 Switching must accurately account for the gas

transmission times from process chamber inlet to the

exhaust valve.

7.10.2.2 Introduction of additional mechanical devices

could create major hazards, reliability, and service or

maintenance issues.

7.10.2.3 Valves must incorporate failsafe designs to

ensure pump outlet is not shut off.

7.10.3 An alternative solution is to fit a local POU

abatement system that treats at least one component and

is not adversely affected by the other components.

7.11 Point-of-Use (POU) Abatement Devices

7.11.1 POU abatement devices are designed to operate

at the process tool or pump outlet, and to remove

hazardous gases BEFORE they enter the exhaust

ductwork.

7.11.2 An end-of-pipe scrubber does not protect the

facility from reactions in the ductwork. Reactions

between process gases, as discussed above, or reactions

with other process by-products within the ductwork

itself are not prevented by end-of-pipe systems either.

7.11.3 POU abatement devices may be appropriate

wherever the exhaust gases can react in the ductwork.

7.11.4 If process systems are not treated with POU

abatement devices, the higher concentrations of

hazardous gases will present a higher risk during a leak

into the facility space.

7.11.5 Improperly functioning POU abatement devices

can create backpressure that can increase the risk of a

leak.

7.12 Four significant consequences can be foreseen

from effluent gas reactions in the ductwork:

7.12.1 Blocked Ducts — Reactions between gases, or

condensation of vapors, can produce solids and semi-

solids (such as crystals, slurries or gels) that will block

the ductwork.

7.12.1.1 Collection of solids can create dead leg

sections that may contain reactive byproducts or unused

raw materials. Catastrophic release of these trapped

materials could generate a significant hazard.

7.12.1.2 Extensive downtime (for clean out, or ducts

collapsing under the weight of accumulated solids) is a

possible undesirable outcome of this condition.

7.12.1.3 Solids deposited (such as from metal etching)

can, themselves, be both corrosive and hazardous,

leading to health risks for people performing cleaning

in ductwork. (See Related Documents 13.1 through

13.3).

7.12.1.4 Blocked ducts may result in toxic process

gases or by products escaping into the work area.

7.12.2 Duct Corrosion — Etching and some chamber

cleaning process emissions are corrosive. Both metallic

(including stainless steel) and plastic ducting can be

attacked, resulting in the release of hazardous gas or

condensed liquids into the workplace.

7.12.3 Duct Fires or Explosions — Flammable and

pyrophoric gases can ignite in the ductwork. If the

ductwork is combustible or has flammable or

combustible deposits in it (e.g., hydrocarbon pump oil),

facility fires can result.

7.12.4 Additional information on protection of

Industrial Exhaust systems from fires may be found in

FM Global Loss Prevention Data Sheet 7-78,

“Industrial Exhaust Systems”.

NOTE 4: Destruction of whole production lines with multi-

million dollar cost impact has resulted from such incidents.

7.12.5 Formation of Ammonium Compounds — If

ammonia is discharged into a duct with acid

compounds, a sub-micron ammonium compound fume

can be generated, that is not easily removed by end-of-

pipe systems.

7.12.5.1 The result is visible discharges.

7.12.5.2 Ammonium compounds produce solids in the

duct.

7.13 If any of the above reactions can occur in the

process exhaust, POU abatement should be considered.

7.14 Exhausts of oil-lubricated vacuum pumps should

be fitted with well-maintained oil mist separators/

filters.

7.15 POU abatement devices may also be needed

upstream of the recovery device for the recovery of

some gaseous compounds (e.g., hydrogen (H

), PFC

gases).