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SEMI M30-0997 © SE MI 1997 5 12 Calculatio ns 12.1 C alculate the absorption coeffi c i e nt, = α , using the expres sion: α = 1X ⋅ 1n ( Ι 0 / Ι ) = 1/X ⋅ 2.303 ⋅ (peak height of absorption ) where : α = absorption coeff…

SEMI M30-0997 © SEMI 1997 4

8.3 Holders for these test and refer ence specimens that

prevent any source of infrared radiation from bypassing

the specimen.

8.4 For use at 77K, low-temperature cryostat capable

of maintaining the specimen and reference at 77K

temperature with suitable window materials (refer to

ASTM Practice F 120).

8.5 Equipment and materials for s licing and polishing

GaAs to a final thickness tolerance of 0.005 mm or less,

and a total thickness variation of 0.01 mm or less.

9 Sampling

Unless otherwise specified, a GaAs slice used for the

carbon test is to be measured at the nominal slice

center. And if a slice is to be reduced in area prior to

test, it is shaped such that the original slice center area

is that which is tested.

10 Test Specimens

10.1 A single crystal slice of GaAs with a thickness

from 3 to 6 mm must be used for carbon determination.

10.2 The test specimen must be carefully shaped to the

following criteria:

10.2.1 Thickness variation over the m easurement area

of 0.005 mm or less.

10.2.2 Same surface preparation on both front and

back surfaces. For room temperature measurement,

surface preparation of specimen should be same with

reference sample. For 77K measurement, mirror

polishing on both surface or same surface preparation

with standard sample is recommended.

10.2.3 Final thickness agreement betw een specimen

and reference samples of 0.1 mm.

10.2.4 Surface area large enough such that with

respect to the holders no incident radiation can bypass

either specimen or reference.

11 Procedure

11.1 Prepare FT-IR in accordance with the

manufacture’s instructions.

11.2 Determine the differential tran smission spectrum

from 700 to 500 cm

-1

in accordance with of ASTM

Practice F 120.

11.2.1 The FWHM must not exceed 2 cm

-1

to achieve

reliable results. If this is not met, recheck test and

reference specimen mechanical properties, use slower

scan speed, or longer measuring time, and reverify FT-

IR operating conditions.

11.2.2 Reference to Figure 1 and Recommended

ASTM Practice E 168, Section 7, for assistance in

establishing a baseline on the finished spectrogram.

Baseline determination is very important to this

method, and becomes more critical as the measured

carbon level decreases (refer to ASTM Practice E 168).

11.2.3 For room temperature meansurement, the

following conditions are recommended:

• Detector : Broadband MCT (or TGS) (see Sections

4.1.3 and 4.1.4)

• Resolution : 0.5 cm

-1

• S/N ratio : > 3

• Range of wave number : including 700 – 500 cm

-1

• Aperture : Optimum for each FT-IR

• Apodization function : Triangle

• Smoothing : Not applicable

• Reference : Air, reference sample

• Temperature : 290 ~ 300K

11.2.4 Make the determination at low temperature

(77K) if increased sensitivity is required. Follow the

same test conditions as described in Sections 11.1 and

11.2 except reference and temperature.

11.3 Determination of the calibratio n coefficient

should be done once or more times per year. Four or

more secondary standard samples should be used for

this calibration. The user of this method can have and

use the internal standard samples to check the

spectrometer frequently.

SEMI M30-0997 © SEMI 19975

12 Calculations

12.1 Calculate the absorption coefficient,=α, using the expression:

= 1X ⋅1n (Ι0/Ι) = 1/X ⋅2.303 ⋅(peak height of absorption

)

where :

= absorption coefficient

X = specimen thickness, cm,

Ι = transmitted intensity at peak absorption (580 cm

-1

for room temperature, 582 cm

-1

for 77K, and

Ι0 = baseline intensity at peak absorption, Ι.

12.2 Determine the calibration coefficient of each FT-IR using the least square method in the following equations:

[C0]=

⋅

0 ⋅

∆

0 or [C0]=

⋅

where :

[C0] = already known carbon concentration in standard samples

0 = absorption coefficient of standard samples

∆ 0 = FWHM of standard samples

= calibration coefficient of each FT - IR

12.3 Calculate the concentration of s ubstitutional carbon in atoms/cm

with the use of the following equations:

[C]=

⋅

⋅∆ or [C] =

⋅

where :

[C] = carbon concentration in test specimen

= absorption coefficient of test specimen

∆ = FWHM of test specimen

= calibration coefficient of each FT - IR, determined in 12.2

13 Report

13.1 The following information shall be included in the report for referee and research measurements:

13.1.1 Instruments used, detector, resolution, measurement time, range of wave number, aperture, apodization

function, smoothing, specimen measurement temperature (room temperature or 77K).

13.1.2 Specimen thickness, and identification.

13.1.3 Calibration coefficient of FT-IR used, width of base line.

13.1.4 FWHM in cm

-1

, calculated absorption coefficient or absorption, and carbon concentration.

13.1.5 Date of measurement, organization performing test, and location.

13.1.6 Use of any special techniques, such as beam condenser, scale expansion, scan suppression, etc.

NOTICE: These standards do not purport to address

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appropriate safety and health practices and determine

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