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SEMI E108-0301 © SEMI 2001 2 NOTE 1: A s listed or revised, all d ocuments cited shall be the latest public ations of adopted standards. 5 Terminology 5.1 anal ytical environme n t — env i r on ment w here all analytical…

SEMI E108-0301 © SEMI 20011

SEMI E108-0301

TEST METHOD FOR THE ASSESSMENT OF OUTGASSING ORGANIC

CONTAMINATION FROM MINIENVIRONMENTS USING GAS

CHROMATOGRAPHY/MASS SPECTROSCOPY

This test method was technically approved by the Global Metrics Committee and is the direct responsibility

of the European Equipment Automation Committee. Current edition approved by the European Regional

Standards Committee on December 20, 2000. Initially available at www.semi.org February 2001; to be

published March 2001.

1 Purpose

1.1 The purpose of this standard is to define a test

method for the determination of the outgassing organic

contamination from minienvironments used for storage

and transport of wafers using gas chromatography/mass

spectroscopy (GC/MS).

1.2 This test method is intended as an alternative to

SEMI E46. The main difference between SEMI E46

and this document is that SEMI E46 defines a test

method which is based on ion mobility spectroscopy

(IMS) as the measurement technique while this

standard is based on gas chromatography/mass

spectroscopy in combination with thermal desorption.

Additionally, this test method provides a procedure for

testing the outgassing of organic compounds in a

complete minienvironment. The results of SEMI E46

and this document are given in different units.

2 Scope

2.1 The test method provided in th is document is

applicable to the assessment of the outgassing of

organic contamination from minienvironments.

2.2 Gas chromatography/mass spe ctroscopy is chosen

as the method to determine organic contamination

because it is commonly used for characterization and

quantification of organic compounds. In combination

with thermal desorption, it provides a method for the

identification of organic compounds in the atmosphere

(i.e., inside the minienvironment) as well as directly

from source materials, and transferred contaminants.

This method can also be used to evaluate materials and

processes used in semiconductor industry.

2.3 This test method is based on ASTM F1982.

2.4 This standard does not purport to address safety

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

responsibility of the users of this standard to establish

appropriate safety health practices and determine the

applicability or regulatory limitations prior to use.

3 Limitations

3.1 The test methodologies, metric s and applications

provided in this standard are limited by the following

constraints:

3.1.1 The specific recovery of comp ounds by the

proposed standard method strongly depends on the

setup of the apparatus used. This has been taken into

account by the use of the “reference-cocktail”, see

Section 9.2.

3.2 Identification of the source of organic compounds

inside the minienvironment is out of the scope of this

test method. For a procedure for the analysis of

outgassing organic compounds from individual

materials using gas chromatography/mass spectroscopy,

see IDEMA M11-99.

3.3 This test method does not prov ide a procedure how

to use the obtained data for assessing the risks that

come from individual compounds.

4 Referenced Standards

4.1 SEMI Standards

SEMI E46 — Test Method for the Determination of

Organic Contamination from Minienvironments

SEMI F21 — Classification of Airborne Molecular

Contaminant Levels in Clean Environments

4.2 ASTM Standard

ASTM F1982 — Standard Test Methods for Analyzing

Organic Contaminants on Silicon Wafer Surfaces by

Thermal Desorption Gas Chromatography.

4.3 IDEMA Standard

IDEMA M11-99 — General Outgas Test Procedure by

Dynamic Headspace Analysis

1 American Society for Testing and Materials, 100 Barr Harbor

Drive, West Conshohocken, PA 19428-2959, website: www.astm.org

2 International Disk Drive Equipment and Materials Association,

3255 Scott Blvd., Suite 2-102, Santa Clara, CA 95054-3013, website:

www.idema.org

SEMI E108-0301 © SEMI 2001 2

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

latest publications of adopted standards.

5 Terminology

5.1 analytical environment — environment where all

analytical measurements are taking place.

5.2 headspace sampling — in this standard defined as:

collecting volatile organic compounds in an enclosed

volume by means of a silicon wafer or silicon wafer

chips.

5.3 minienvironment — A localized environment for

transport and storage created by an enclosure to isolate

the product from contamination and people.

5.4 sample — wafer or wafer chip s used for the

headspace sampling of organic contaminants.

5.5 static storage conditions — co nditions excluding

any active movement of test specimens.

5.6 thermal desorption tube — Analytical equipment

capable of collecting organic compounds of interest

(i.e., adsorbent filled glass tube).

5.7 wafer — Object made of semiconducting material

to be processed, handled or stored in the

minienvironment to be tested (i.e., prime or processed

silicon wafer).

6 Summary of Method

6.1 This test method comprises sto rage tests of wafers

in minienvironments under static storage conditions.

The contamination is directly measured from the silicon

wafer surface. Three important aspects are covered:

a) Contamination due to the minienvironment alone,

b) Contamination from the use of minienvironments for

wafer processing, and

c) Contamination from future materials to be used in

semiconductor technology.

6.2 The setup for each test compri ses an analytical

equipment in the analytical environment as well as a

test equipment in the test environment. Each

environment has to fulfill the following requirements:

6.2.1 Analytical Environment — shall be clean enough

with respect to airborne organic contamination:

recommendation is less than 100 pptM for organic

compounds with boiling points > 150°C (Class MC-

100, according to SEMI F21).

6.2.2 Test Environment — shall equ al the environment

in which the test specimen will be used.

6.3 Silicon wafers are placed in the minienvironment

or used for headspace sampling experiments. These

wafer samples are then analyzed by gas chromatogra-

phy/mass spectrometry to determine the amount of

contaminants.

6.4 The wafers or wafer chips to b e used for the test

method are decontaminated as described in ASTM

F1982 for bare silicon wafers. The surface condition of

the wafer (hydrophobic or hydrophilic) has to be

adjusted in a reproducible way and has to be the same

for all comparative measurements.

6.5 The wafer or the wafer chips are placed in the

minienvironment and are left there under static

conditions for the chosen static storage time (depending

on the intended use of the minienvironment to be tested,

a time between 1 h and 28 d may be used). When

loaded into the minienvironment the wafer may have a

temperature which reflects production circumstances

(i.e., 80°C when unloading from furnace processes). In

some situations wafers may be exposed to severe

thermal conditions. The minienvironment should be

evaluated under the conditions exposed to. Be sure that

the material to be tested does not undergo phase

transitions under the chosen temperature conditions.

6.6 After the static storage test per iod, the wafer is

returned to the analytical equipment and the organic

contamination on the wafer is measured immediately.

6.7 The quantitative value for the total amount of

outgassed and adsorbed organics from the minienviron-

ment is calculated as the difference between the

detected amount of contamination on a blank sample

vs. the amount on the exposed sample.

7 Interferences

7.1 The presence of organic conta mination in the

atmosphere of the test environment may lead to a

significant contribution to the detected total amount of

organic compounds on the test wafers or wafer chips.

Care has to be taken when subtracting the blank value

from the test value. Transport times from test

environment to analytical environment have to be as

short as possible.

8 Apparatus

8.1 For the analysis of organic compounds on wafers a

gas chromatography/mass spectroscopy apparatus with

thermal desorption unit is required: A gas

chromatography (GC) instrument, which utilizes a

capillary column to separate a wide variety of organic

compounds, combined with mass spectrometer (MS). A

thermal desorption unit is used to desorb organics from

sample thermal desorption tubes and collect them in a

trap. Two types of trapping may be used:

SEMI E108-0301 © SEMI 20013

a) cooling the trap down to a minimum of -150°C does

not require any adsorbent (glass wool may be used) or

b) a Tenax® filled trap has to be cooled down to a

minimum of -25°C.

8.1.1 The thermal desorption unit is coupled to the gas

chromatography instrument via a heated transfer line.

This apparatus may be used directly for the desorption

from wafer chips which are put in empty glass (or

stainless steel) thermo desorption tubes (method A).

8.1.2 A desorption unit for complete wafers is

specified in ASTM F1982. In this case sample thermal

desorption tubes packed with adsorbent have to be used

to trap compounds desorbed from the wafer. These

thermal desorption tubes are analyzed within the

thermal desorption unit (method B).

8.2 The analysis of outgassing org anic contamination

from minienvironments requires an extremely sensitive

analytical equipment. Recovery and limit of detection

for the different classes of compounds must be

evaluated carefully in order to ensure reliable results.

9 Reagents and Materials

9.1 For the materials used for hand ling and transport

of wafers clean, decontaminated equipment has to be

used, e.g. tweezers heated in a propane flame. Refer to

the reagent and materials described in SEMI E46 and

ASTM F1982.

9.2 Test Mixture — For the calibra tion of equipment

and the quantification of the amount of contamination a

test mixture (”cocktail”) is used. This mixture was

chosen in order to give an ”average” over typical

substance classes present in semiconductor production

lines, which have high sticking factors to the wafer

surface. The response factor of the MS-detection for

organics varies significantly. As this is true for all

contaminants, the method gives a realistic trustworthy

quantitative correlation to a ”typical average compound

mixture” of contaminants on wafer surfaces.

9.3 Preparation of Test Mixture

9.3.1 The mixture consists of triethyl phosphate,

ε-caprolactam, palmitic acid and diethylhexyl phthalate

each 0.5 µg/µl in isooctane (as solvent). The

preparation has to be done according to SEMI E46.

NOTE 2: A similar test mixture is suggested by the working

group WG 031 of the Institute for Environmental Science and

Technology (IEST)

10 Safety Precautions

10.1 All preparation and analytical work has to be

done according to local safety regulations.

11 Preparation of Minienviro nment and

Sample

11.1 Minienvironment — The minie nvironment to be

tested has to be used as received from the supplier. A

cleaning step can be added but there must be no

contribution from the cleaning procedure to the

outgassing of organic compounds from the

minienvironment. The cleaning method has to be

defined by the supplier or agreed upon between supplier

and user of the tested minienvironment.

11.2 Sample — The wafers shall be made organic-free

before using them to monitor organic contamination.

The surface condition of the wafer (hydrophobic or

hydrophilic) has to be adjusted in a reproducible way

and has to be the same for comparative measurements.

Refer to SEMI E46 and ASTM F1982.

12 Procedure

12.1 The procedure described below is used for

obtaining the baseline value of the method (method

blank) as well as the test value for outgassing organic

compounds of the minienvironment within a defined

static storage time (storage time t

= 1 h - 28 d).

12.1.1 Choose that static storage time according to the

intended use of the minienvironment (i.e., if the

maximum sit time of wafers in a process where the

minienvironment is to be used is 4 h then choose a

static storage time of 4 h). If no static storage time

related to processes can be defined, a recommended

value for the first static storage time is 1 day.

NOTE 3: Composition of adsorbed compounds may vary with

static storage time.

12.2 For transport store the wafers or wafer chips used

for testing in decontaminated, organic-free petri-dishes

wrapped in organic-free aluminum foil. Refer to SEMI

E46.

12.3 Loading Procedure

12.3.1 For tests at room temperature: open a

minienvironment to be tested and load it with a

decontaminated wafer using decontaminated handling

tools (i.e., tweezers). Default storage location is the

center slot of the minienvironment. Close the

minienvironment. Leave the minienvironment closed

for the chosen static storage time.

12.3.2 For tests at elevated temperatures using a

wafer furnace: place the decontaminated wafers in a

clean furnace used for production processes and heat

the wafers under inert gas to a temperature > 120°C.

Turn off the heating. When the temperature of the

furnace has reached (90±10)°C open the

minienvironment to be tested and fully load it with the