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SEMI F51-0200 © SEMI 2000 2 5.2.3 cation  a positively charged i o n; an io n that is attracted to th e cathode in electrolysis. These are typically ions o f metallic elements. 5.2.4 chem ical/mechani cal wear  i n ju …

SEMI F51-0200 © SEMI 20001

SEMI F51-0200

GUIDE FOR ELASTOMETRIC SEALING TECHNOLOGY

This guide was technically approved by the Global Facilities Committee and is the direct responsibility of the

North American Facilities Committee. Current edition approved by the North American Regional Standards

Committee on December 15, 1999. Initially available on www.semi.org February 2000; to be published

February 2000.

1 Purpose

1.1 The purpose of this document is to introduce a

basic guide for the use of seals in semiconductor

fabrication equipment. Also, to introduce the diverse

chemical and physical requirements for the many

process applications, and to reduce cost of ownership

and improve up-time through the use of appropriate

sealing materials. It is important that equipment users,

suppliers, OEMs, and seal manufacturers use the same

terminology and that communication can take place at

the same level so that actual performance of the

equipment can be discussed.

2 Scope

2.1 This guide is applicable to the use of seals in

specific operating environments used in the fabrication

of semiconductor devices. The guide will aid in

defining the seal parameters for the various process

environments. It includes those elastomeric seals that

come in contact with process liquids and or gases.

2.2 This guide does not purport to address safety

issues, if any, associated with its use. It is the

responsibility of the users of this guide to establish

appropriate safety and health practices and determine

the applicability of regulatory limitations prior to use.

3 Limitations

3.1 The application of this guide is limited to

elastomeric sealing technology performance as used in

semiconductor manufacturing and related process

equipment.

4 Referenced Standards

4.1 SEMI Standards

SEMI C3 — Specifications for Gases

SEMI D9 — Definitions for Flat Panel Display

Substrates

SEMI E45 — Test Method for the Determination of

Inorganic Contamination from Minienvironments

SEMI F21 — Classification of Airborne Molecular

Contaminant Levels in Clean Environments

SEMI P5 — Specification for Pellicles

SEMI S4 — Safety Guideline for the

Segregation/Separation of Gas Cylinders Contained in

Cabinets

NOTE 1: As listed or revised, all documents cited shall be the

latest publications of adopted standards.

5 Terminology

5.1 Abbreviations and Acronyms

5.1.1 ATM — Atmospheric

5.1.2 BCD  Bulk Chemical Dispensing System

5.1.3 CVD — Chemical Vapor Depo sition

5.1.4 DI — De-ionized

5.1.5 HDP — High Density Plasma

5.1.6 HF — Hydrofluoric Acid

5.1.7 LPCVD — Low Pressure Chemical Vapor

Deposition

5.1.8 MOCVD — Metal Organic Ch emical Vapor

Deposition

5.1.9 OEM — Original Equipment Manufacturer

5.1.10 PPB — Parts per Billion

5.1.11 PVD — Physical Vapor Deposition

5.1.12 RF — Radio Frequency

5.1.13 RTP — Rapid Thermal Process

5.1.14 T.O.C. (total organic carbons)  hydrocarbons

which can appear in a process from a variety of sources

including breakdown of O-ring materials.

5.1.15 UPDI — Ultra Pure De-ionize d

5.1.16 UV — Ultraviolet

5.2 Definitions

5.2.1 acid



a corrosive material whose chemical

reaction characteristic is that of an electron acceptor

(SEMI F21, SEMI S4).

5.2.2 anion  a negatively charged ion that is

attracted to an anode in electrolysis.

SEMI F51-0200 © SEMI 2000 2

5.2.3 cation  a positively charged ion; an ion that is

attracted to the cathode in electrolysis. These are

typically ions of metallic elements.

5.2.4 chemical/mechanical wear  injury to the

surface of an object or partial obliteration of or altering

caused by rubbing, stress or chemical/mechanical use.

5.2.5 chemical breakdown  the degradation of a seal

as the result of a chemical reaction.

5.2.6 chemical property



chemical durability is a

measure of corrosion or attack of a glass surface when

subjected to a specific reagent, such as acid, base, or

water at a specific concentration for a specific time and

temperature (SEMI D9).

5.2.7 chemical reaction  a process that involves

change in the structure of ions or molecules.

5.2.8 compatibility  the ability of the molecules of a

seal to coexist with process chemistries without the

degradation of either.

5.2.9 corrosives  a chemical that c auses visible

destruction of, or irreversible alterations in, living tissue

by chemical action at the site of contact. A chemical is

considered to be corrosive if, when tested on the intact

skin of albino rabbits by the method described in the

U.S. Department of Transportation in Appendix A to 49

CFR 173, it destroys or changes irreversibly the

structure of the tissue at the site of contact following an

exposure period of four hours. This term shall not refer

to action on inanimate surfaces (SEMI S4).

5.2.10 de-ionized water



(specified with specific

resistivity ≥ 18 MΩcm, cations: Na, Fe, Ca ≤ 0.2 µg/l)

(SEMI E45).

5.2.11 degradation  a chemical reaction leading to

the reduction to a simpler molecular structure. See also

chemical breakdown.

5.2.12 ion  an atom or group of ato ms that has lost

or gained one or more electrons.

5.2.13 leachables  atoms or molecules which escape

from the body of a material under vacuum, heat or

chemical attack.

5.2.14 leak rate  rate at which an e nvironment loses

a vacuum (Millitorr litres/second).

5.2.15 outgassing  process whereby molecules of air

or other gases adhere to the surface of the vacuum

vessel or component therein and become liberated

under vacuum conditions. Sometimes known as

degassing.

5.2.16 oxidizer gas  a gas which will support

combustion or increase the burning rate of a

combustible material with which it may come in contact

(SEMI S4).

5.2.17 particle  materials which can be

distinguished from the film whether on the film surface

or embedded in the film (SEMI P5).

5.2.18 particle generation  molecu les of material

generated due to degradation of a material.

5.2.19 permeation  the tendency for a gas or liquid

to pass through a seal structure by osmosis or diffusion.

5.2.20 silica  silicon dioxide, occur ring as quartz,

etc.

5.2.21 swell resistance  the ability of a material to

resist increasing its volume when it has been immersed

in a liquid or exposed to vapor.

5.2.22 temperature  a measure of h eat usually

expressed in degrees Celsius or Fahrenheit.

Temperature values shall be expressed in degrees

Celsius (SEMI C3).

5.2.23 weight loss  reduction in ma ss of a sealing

compound through the result of a chemical or physical

reaction.

5.2.24 vacuum integrity  a subjecti ve measure of the

efficiency of a vacuum vessel.

6 Related Documents

6.1 SEMI Standard

SEMI E49  Guide for Standard Performance,

Practices, and Sub-Assembly for High Purity Piping

Systems and Final Assembly for Semiconductor

Manufacturing Equipment

SEMI F40  Practice for Preparing Liquid Chemical

Distribution Components for Chemical Testing

6.2 Other Documents

Millipore 9

Annual Microelectronics Technical

Symposium, May 20, 1991, “Contamination Derived

from O-Rings”, Robert Matthews

RTP’97 5

International Conference on Advanced

Thermal Processing of Semiconductors, “Sealing

Technology for the Semiconductor Industry”, Dalia

Vernikovsky

1 Millipore Corporation, 80 Ashby Road, Bedford, MA, USA, 01730-

2271

2 Greene, Tweed & Co., 2157D O’Toole Avenue, San Jose, CA,

USA, 95131

SEMI F51-0200 © SEMI 20003

7 Considerations for Use in Ultra Pure De-

ionized Water (UPDI)

NOTE 2: See Figure 1.

7.1 De-ionized water is used in ma ny wafer processing

steps and shall not contribute any contaminants to the

processes. The most common sealing requirements in

DI water systems are filters, valves, flow and pressure

regulators, and fittings.

7.2 Contaminants in DI water fall primarily into three

categories. They are ion contamination, T.O.C.’s and

bacterial growth. Contaminant levels are usually

measured in parts per billion (PPB).

7.3 Ion contamination problems are caused by anionic

and cationic elements in DI water such as fluorides,

chlorides, sulfates, etc. These can be leached from

seals as well as the DI plumbing.

7.4 Cations (mostly metallic ions) are leached from

seals as well as the plumbing that delivers the DI water.

In order to kill bacteria which have a propensity to

grow in DI water, the water is either heated (80°C+),

ozonated, or bombarded with UV light, or possibly a

combination of these three elements. This poses unique

problems for seals used in the DI system and can cause

the following problems: Contamination of the DI water

caused by T.O.C.’s being leached from the seals and

plumbing.

7.5 Seal breakdown caused by ozone attack, or seal

deterioration due to UV exposure. T.O.C.’s are of great

concern since they can adhere to wafers and result in

degraded oxide quality and hazy films. Ozone and UV

deterioration of the seals usually leads to particulate

contamination. These can be as small as single atoms

or molecules to gross particle size contamination.

7.6 Considerations:

• What method of sterilization (i.e., chemical,

thermal or radiation)?

• Concerns for cations, anions, or T.O.C.’s?

• Seal life expectation?

8 Considerations for Use in Corrosives

(Acids, Bases), Oxidizers, and Solvents

NOTE 3: See Figure 2.

8.1 Inorganic wet chemicals at hig h concentration

levels and in some cases at elevated temperatures are

readily used in front-end semiconductor processing in

the fabrication of semiconductor devices. Most

common sealing requirements are in acid recirculation

and chemical distribution systems (mostly BCD’s).

Component systems include pumps, filters, megasonic

seals, gaskets for pipeline interfaces and valves.

8.2 Of primary concern when spec ifying a specific

seal for an application are issues relating to resistance

to chemical reaction. Design considerations should

include resistance to chemical breakdown, static vs.

dynamic environments, pressure, temperature,

leachables, particle generation.

8.3 Chemical and Thermal Degrad ation involves the

incompatibility of the seals to the process chemistries.

An example is Hydroflouric Acid (HF) dissolves

silicone elastomers. The same is true of temperature

degradation (i.e., Piranha or Phosphoric Acids) where

the process temperature causes thermally and

chemically induced effects on the seal. That also

contributes to the mechanical failure of the seal.

8.4 Leaching is most commonly a ssociated with metal

filler systems of the seal, which usually introduce

metallic ions. This is a continuous occurrence as long

as the seal is in the system.

8.4.1 Particles  Particles can be th e result of

mechanical damage of the seal or as a result of leaching

or chemical degradation or foreign material present on

the seal surface. Particles can end up on the wafer and

cause defects.

8.4.2 Summary  All cases of the above

contamination can create electrical shorts, voids, and

unwanted doping.

8.4.3 Solvents  Incompatibility of elastomers or

seals with solvent chemistries may cause

contamination.

8.4.3.1 For example, there are degrees of

incompatibility:

8.4.3.1.1 If the seal is dissolved by the solvent, then a

catastrophic failure occurs where the solvent leaks out

of the liquid process loop. This is associated with mis-

processed wafers.

8.4.3.1.2 Another type of solvent seal interaction is the

swelling of the elastomer or the leaching of small

amounts of elastomer. Excessive swelling of the

elastomer can result in premature seal failures and a

higher cost of ownership caused by increased frequency

of seal change outs.

9 Considerations for Use In Thermal

Processes

NOTE 4: See Figure 3.

9.1 Diffusion processes are used p rimarily for growth

of oxide layers and to anneal crystal damage caused by

implant. Diffusion furnaces are usually batch process

equipment where the process atmosphere is constrained

within quartz tubes. The seals of these tubes are

exposed to temperatures of 250–300°C. This requires