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SEMI MF1982-1103 © SEMI 2003 4 7.1.2.3 Cleave the waf er sample into strips abo ut 5 to 7 mm wide by scri bing a line on the wafer where one wants it to brea k and then placing i t on a straight wire and breakin g it alo…

SEMI MF1982-1103 © SEMI 2003 3

atomic emission detector (AED). The

nitrogen/phosphorus thermionic ionization detector

(NPD) also responds to nitrogen containing

compounds.

NOTE 1: A nitrogen/phosphorus thermionic ionization

detector (NPD) may also be used as a phosphorus selective

detector. This type of detector also responds to nitrogen

containing compounds. If an NPD is used, the total

organophosphorus reported should exclude any signals due to

nitrogen containing compounds. Often, identification from

the mass spectra can be used to determine whether compound

contains nitrogen or phosphorus, or both.

6.1.2 Sample Thermal Desorption Tubes — Stainless-

steel tubes packed with adsorbent medium, are used to

trap compounds of interest and release them onto a

thermal desorption unit.

NOTE 2: Note that stainless steel is catalytically active and

can corrode with time, affecting recovery for some

compounds. In this case, deactivated stainless steel, glass, or

quartz tubes also can be used. Several adsorbent materials

can be used for trapping organic compounds desorbed from

silicon wafer samples. Some examples are activated carbon,

graphitized carbon, and poly (2,6-diphenyl-p-phenylene

oxide).

6.1.3 Thermal Desorption Unit — Used to desorb

organics from sample thermal desorption tubes. The

thermal desorption unit is coupled to the GC instrument

via a heated transfer line, for example, heated to 225°C

or above.

6.1.4 Thermal Annealer — Or a high temperature

furnace used to obtain a blank wafer (see Section

7.1.1.2 ).

6.1.5 Temperature Controllable Wafer Desorption

Oven — Used to hold and heat a wafer desorption tube.

6.1.6 Wafer Desorption Tube — Stainless-steel tube

with an approximate dimension: 12.7 mm (0.5 in.) in

outer diameter, 9.53 mm (0.375 in.) in inner diameter

and 254 mm (10 in.) in length (see Figure 1), used to

desorb organics from cleaved wafers. Larger tubes may

be used for larger wafer sizes and to increase the

sensitivity of the test (see Note 2).

6.1.7 Analytical Balance

6.1.8 Quartz Plate and Carbide-Tipped Scribe — Used

to cleave wafer samples.

6.1.9 Quick Connect — Used to connect a nitrogen line

to the wafer desorption tube.

6.2 Method B

6.2.1 GC Instrument — Utilizes a capillary column to

separate a wide variety of organic compounds, coupled

to a mass spectrometer (MS) or a phosphorus selective

detector, or both. Examples of phosphorus selective

detectors are flame photometric detector (FPD), atomic

emission detector (AED), or nitrogen/phosphorus

thermionic ionization detector (NPD). The

nitrogen/phosphorus thermionic ionization detector

(NPD) also responds to nitrogen containing compounds

(see Note 1).

6.2.2 Quartz Chamber Unit — Used to desorb organic

contaminants from the wafer surface and transfer them

to a glass TD tube (see Figure 2).

6.2.3 Quartz Chamber — May be used also to purge

out any organic contaminants from a blank wafer.

6.2.4 Glass TD Tube — Packed with adsorbent

medium used to trap compounds of interest and release

them onto a cold trap. Several adsorbent materials can

be used for trapping organic compounds desorbed from

silicon wafer samples. Some examples are activated

carbon, graphitized carbon, and poly (2,6-diphenyl-p-

phenylene oxide).

6.2.5 Cold Trap — Used to concentrate organics

desorbed from glass TD tube and release the organics to

a GC instrument by rapid heating.

7 Procedure

7.1 Method A

7.1.1 Sample Handling and Preparation

7.1.1.1 At all times, avoid manual handling of samples

for analysis to prevent any secondary contamination of

samples. Use stainless steel tweezers for sample

preparation. Use a propane torch to flame stainless

steel tweezers, weigh boats, and other accessories that

come into direct contact with the sample before their

usage.

7.1.1.2 Thermally debsorb any organics from blank

wafers in a rapid thermal annealer or a high temperature

furnace. In order to desorb any organics from blank

wafers, the temperature of a rapid thermal annealer is

kept at 900°C for 15 s, or the temperature of a high

temperature furnace is kept at 700°C for 30 min.

Heating under air or oxygen will make a consistent

organic-free SiO

surface. Place the thermally treated

blank wafers directly into petri dishes and wrap the

dishes with organic-free aluminum foil.

7.1.2 Wafer Desorption

7.1.2.1 Clean and precondition sample thermal

desorption tubes in accordance with ASTM Practice

D 6196 prior to attaching to the wafer desorption tube.

7.1.2.2 Turn on the temperature controller for the wafer

desorption oven and wait for the temperature to reach

275°C.

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7.1.2.3 Cleave the wafer sample into strips about 5 to 7

mm wide by scribing a line on the wafer where one

wants it to break and then placing it on a straight wire

and breaking it along the scribed line. The portion of

the wafer sample needed for the analysis changes with

the size of the wafer. For a 100-mm wafer, about half

of its surface area is needed. Larger samples (having

larger surface area) may be used to increase the

sensitivity of the test.

7.1.2.4 Place the wafer strips of wafer into the wafer

desorption tube. Attach a sample thermal desorption

tube to the side of the wafer desorption tube. Connect

the other end of the wafer desorption tube to a nitrogen

line with a flow of 15 to 100 mL/min.

7.1.2.5 Place the wafer desorption tube in the oven and

heat it for 30 min at 275°C. This allows the volatile

organics to be thermally desorbed from the sample

wafer and transferred to the sample thermal desorption

tube.

7.1.2.6 Seal both ends of the sample thermal desorption

tube into the thermal desorption unit or by using caps if

the thermal desorption-GC system is automated. Tubes

must not be left open and exposed to the laboratory

atmosphere. The end caps should be made of a material

that has low outgassing and low reactivity properties,

such as poly tetrafluoroethylene (PTFE), or stainless

steel.

7.1.2.7 Analyze a blank wafer at least daily. Use a

blank wafer treated with the same desorption procedure

just described. Report blank data with the sample data.

7.1.3 GC Analysis

7.1.3.1 Place the sample thermal desorption tube,

which contains organic contaminants desorbed from the

wafer, onto the thermal desorption unit. Enter the

sample information into the computer, and start the GC

analysis.

7.1.3.2 Flow the helium carrier gas through the sample

thermal desorption tube during primary desorption.

Heat the sample thermal desorption tube and sweep out

the target organics contained in the sample to a cold

trap where they are preconcentrated. Two

recommended conditions for heating the sample

desorption tube are as follows. When graphitized

carbon is used as adsorbent material, heat the tube to

400°C and hold at 400°C for 15 min. When poly (2,6-

diphenyl-p-phenylene oxide) is used as adsorbent

material, heat the tube to 270°C and hold at 270°C for

15 min. Cold trap parameters, that is, sorbent, sold

temperature, etc., should be selected such that all target

analytes are retained quantitatively throughout the tube

desorption process, for example, using a cold trap

temperature of −30°C. Refer to ASTM Practice D 6196

for a method for testing desorption efficiency and

analyte recovery. At the end of this period, heat the

cold trap rapidly to 300°C to release the target organics

to the GC column head.

NOTE 3: For higher sensitivity analysis, larger sample sizes

can be used, but clogging by water is possible. In this case, a

subambient cold trap with an adsorbent may be used and

maintained higher than 0°C during trapping to prevent freeze-

up of trap.

7.1.3.3 Separate volatile organics desorbed from the

sample thermal desorption tube by an appropriate

column temperature program. Two recommended

temperature programs are as follows. For high

resolution analysis, using polydimethylsiloxane-coated

column (60 m by 0.25 mm by 0.25–µm film thickness),

heat the column from 40 to 280°C at a rate of 10°C/min

and hold the temperature at 280 °C for 16 min. For

rapid analysis, using polydimethylsiloxane-coated

column (25 m by 0.32 mm by 0.52–µm film thickness),

heat the column from 30 to 265°C at a rate of

12.5°C/min and hold the temperature at 265°C for 16

min.

7.1.3.4 Use n-Hexadecane, n-C

), as a standard

for total organic analysis 4

. Use tris (2-chloroethyl)

phosphate, (ClCH

PO (TCEP) or tributyl

phosphate, (C

PO (TBP), as a standard for

organophosphorus analysis (see Section 6.1.1 ). These

standards are introduced into the GC system from a

precleaned sample thermal desorption tube. Two-point

calibration method is recommended for checking the

instrument performance. Recommended standards are

two different concentrations of n-C

) for total

organic analysis; and, two different concentrations of

tris (2-chloroethyl) phosphate (TCEP) for total

organophosphorus analysis. Recommended frequency

of these measurements is at least once a week.

NOTE 4: AED and FID are recommended for accurate total

carbon quantification.

7.1.4 Quantification

7.1.4.1 Obtain each area below for the calculation of

total organic contaminants. Obtain total organic

contaminants of the sample wafer (A

) by summing up

all the peak areas integrated from GC-AED, FID, or

MS chromatogram of the sample wafer. Obtain total

area of the blank wafer (A

) by summing up all the peak

areas integrated from GC-AED, FID, or MS

chromatogram of the blank wafer. Obtain the area of

the standard peak (A

) integrated from GC-AED, FID,

or MS chromatogram of the standard sample.

7.1.4.2 Obtain each area below for the calculation of

total organophosphorus (TP). Obtain total area of

phosphorus compounds of the sample wafer (A

) by

SEMI MF1982-1103 © SEMI 2003 5

summing up all the peak areas integrated from GC-

(phosphorus selective detector) chromatogram of the

sample wafer. Obtain total area of the blank wafer (A

)

by summing up all the peak areas integrated from GC-

(phosphorus selective detector) chromatogram of the

blank wafer. Obtain the area of the standard peak (A

)

integrated from GC-(phosphorus selective detector)

chromatogram of the standard sample.

7.1.4.3 Before starting analysis, weigh and get the total

weight of each sample wafer to be tested, and also the

weight of unused part of each wafer. These weights are

used for the calculation of total organic contaminants

and total organophosphorus (TP).

7.2 Method B

7.2.1 Sample Handling and Preparation

7.2.1.1 At all times, avoid manual handling of samples

for analysis to prevent any secondary contamination of

samples. Use stainless steel tweezers for sample

preparation. Use a propane torch to flame stainless

steel tweezers and other accessories that come into

direct contact with the sample before their usage.

7.2.1.2 Thermally desorb any organics from blank

wafers in the quartz chamber unit. Recommended

conditions for preparing blank wafers are to heat them

for 30 min in the quartz chamber kept at 700°C.

Usually, helium is used as purge gas. Heating under air

or oxygen will make a consistent organic-free SiO

surface.

7.2.2 Wafer Desorption

7.2.2.1 Enter the analytical information into the quarts

chamber unit, cold trap and GC. Wait for the system to

be stabilized. Place the sample wafer into the quartz

chamber unit and start it. Supply helium gas into the

quartz chamber and heat the chamber from initial

temperature (40°C or lower) to 400°C at a rate of 10 to

30°C/min, and hold the temperature for 15 min. Sweep

out the volatiles contained in the sample to a glass TD

tube where they are adsorbed.

7.2.2.2 Analyze a blank wafer at least daily. Report

blank data with the sample data.

7.2.3 GC Analysis

7.2.3.1 Heat the glass TD tube and sweep out the target

organics adsorbed in the tube to a cold trap where they

are preconcentrated. Two recommended conditions for

heating the glass TD tube are as follows:

• When graphitized carbon is used as adsorbent

material, heat the tube to 400°C and hold at 400°C

for 15 min.

• When poly (2,6-diphenyl-p-phenylene oxide) is

used as adsorbent material, heat the tube to 270°C

and hold for 15 min.

7.2.3.2 Select cold trap parameters, that is, sorbent,

cold temperature, etc., such that all target analytes are

quantitatively retained throughout the tube desorption

process, for example using a cold trap temperature of

–130°C. Refer to ASTM Practice D 6196 for a method

for testing desorption efficiency and analyte recovery.

At the end of this period, heat the cold trap rapidly to

300°C to release the target organics to the GC column

head.

7.2.3.3 Separate volatile organics desorbed from the

glass TD tube by an appropriate column temperature

program. Two recommended temperature programs are

as follows. For high resolution analysis, use

polydimethylsiloxane coated column (60 m by 0.25 mm

by 0.25-µm film thickness), heat the column from 40 to

280°C at a rate of 10°C/min and hold the temperature at

280°C for 16 min. For rapid analysis, use

polydimethylsiloxane coated column (25 m by 0.32 mm

by 0.52-µm film thickness), heat the column from 30 to

265°C at a rate of 12.5°C/min and hold the temperature

at 265°C for 16 min.

7.2.3.4 Use n-Hexadecane, n-C

), as a standard

for total organic analysis (see Note 4). Use tris (2–

chloroethyl) phosphate, (ClCH

PO (TCEP) or

tributyl phosphate, (C

PO (TBP), as a standard

for organophosphorus analysis (see Section 6.1.1).

These standards are introduced into the GC system

from a precleaned wafer. A two-point calibration

method is recommended for checking the instrument

performance. Recommended standards are two

different concentrations of n-C