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SEMI MF1630-0704 © SEMI 2004 5 Table 1 Peak Location, Baseline an d Integration Limits, and Calibration Facto rs Baseline Limits Integration Limits Element Peak cm − 1 Upper Lower Upper Lower Factor A f(mm-cm) Aluminum (…

SEMI MF1630-0704 © SEMI 2004 4

10.2 Check for detector linearity.

10.2.1 Examine one of the two single-beam (unratioed)

spectra obtained in Section 10.1.1 for nonzero response

at wavenumbers where the detector is known to have

zero response (below 200 cm

−1

for the zinc doped

germanium detector with a CsI window). The observed

response in this region should be less than 1.0% of the

maximum response over the 1200 to 250 cm

−1

region.

If not, take corrective action before proceeding.

10.2.2 Alternatively, collect a spectrum with a CaF

crystal wafer, 5 mm-thick, in the IR beam. Ratio this

spectrum relative to one of the background spectrum

obtained in Section 10.1.1 to obtain a transmittance

spectrum. CaF

is totally opaque below 800 cm

−1

. The

spectrum must give 0.0 ± 0.5% transmittance from 800

to 250 cm

−1

. If not, take corrective action before

proceeding.

11 Procedure

11.1 Measure the thicknesses to ± 0.02 mm and load all

the sample specimens to be examined onto the sample

specimen holder leaving at least one open slot. Include

a reference specimen to serve as an audit to ensure that

the entire instrument is performing correctly.

11.2 Mount them in the cryostat and cool the samples to

less than 15 K.

11.3 Set instrumental parameters to give a resolution of

1.0 cm

−1

or better.

11.4 Select the reference specimen as the first sample to

be measured.

11.5 Collect 1000 scans of an empty sample chamber

slot and use this as the background spectrum.

11.6 Move the sample specimen into position.

11.7 Turn on the incident white-light source and ensure

that the sample specimen is fully illuminated with white

light and properly aligned relative to the IR beam (see

Figure 1).

11.8 Collect a minimum of 300 scans of the sample.

11.9 Zero-fill, apodize, and transform the interferogram

into a spectrum and then ratio it to the background

spectrum.

11.10 Covert to an absorbance spectrum and use as the

sample specimen spectrum.

6 Chase, D. B., “Nonlinear Detector Response in FT-IR,” Applied

Spectroscopy 38(4), 491–494 (1984).

11.11 Store this spectrum and subsequent ones for

further manipulation and measurement of the peak

areas.

11.12 Repeat Sections 11.5 through 11.11 for each

sample specimen.

12 Data Reduction

12.1 This test procedure requires the measurement of

the areas of the absorption bands before calculation of

the concentration of each element. The absorption

bands are very sharp, especially for the Group V

elements, and therefore peak height measurements are

difficult to reproduce from instrument to instrument.

Use of peak areas greatly reduces this variability.

12.1.1 Establish baselines for each peak before

measurement of the area. Use only the area above the

established baseline in the calculations. Several

algorithms are available on various commercial FT-IR

instruments to obtain the desired baseline corrected

areas. The following is one suggested method:

12.1.1.1 Retrieve the sample absorbance spectrum

from the computer storage disk. With the wavenumber

expand commands available, zoom in on the region of

the absorption band(s) of interest. Expand until this

region is only slightly larger than the baseline limit

regions given in Table 1.

12.1.1.2 Employ the interactive baseline correction

routine to bring the spectral baseline to coincide with

the 0.0 absorbance line. Refer to Table 1 for the upper

and lower wavenumber regions for guidance in

adjusting the baseline. Expand in the absorbance scale

as necessary to improve the observation of the noise

and fine features of the spectrum in order to provide the

best placement of the baseline. Apply only linear

corrections with the fit of the straight line through the

points on both sides of the absorption peak(s). Note

that the peaks for boron and phosphorus are very close

together and thus only one baseline is obtained

surrounding both peaks. Figures 2 and 3 show spectra

before and after, respectively, baseline correction for

boron and phosphorus spectral region.

12.1.2 Measure the area for the absorption peak

between the upper and lower wavenumbers given in

Table 1 for the integration limits. Most computer

algorithms handle this nicely. However, disable the

automatic zeroing of the baseline at the integration

limits. If not disabled, the integration would not

represent the baseline as established in Section 12.1.1

and may result in errors.

12.1.3 Repeat Sections 12.1.1 and 12.1.2 for each

component desired for each specimen measured.

SEMI MF1630-0704 © SEMI 2004 5

Table 1 Peak Location, Baseline and Integration Limits, and Calibration Factors

Baseline Limits Integration Limits

Element

Peak cm

−

Upper Lower Upper Lower

Factor

f(mm-cm)

Aluminum (Al) 473.2 479 467 475.2 471.2 32.7

Antimony (Sb) 293.6 296 289 295.1 292.1 10.6

Arsenic (As) 382.0 385 379 383.5 380.5 8.96

Boron (B) 319.6 323 313 321.5 318.0 9.02

Gallium (Ga) 548.0 552 544 549.5 546.5 42.4

Indium (In) 1175.9 1181 1169 1177.4 1174.4 244.0

Phosphorus (P) 316.0 323 313 317.5 314.5 4.93

The factors given here do not all have the same degree of certainty. The factors for boron, phosphorus, and arsenic are

believed to be correct to better than ± 10%. The other factors should be considered approximations and used for

estimations only. A discussion of the origin of these factors is given in Related Information 1.

13 Calculation

13.1 Calculate the concentration of each of the

electrically active impurity/dopant in each specimen

measured according to the following equation:

C = (1)

where:

= concentration of impurity/dopant element i,

ppba, in sample specimen j,

= integrated area of component i,

= thickness of sample specimen j, mm, and

= calibration factor for component i, mm-cm.

13.2 The concentration may be expressed as density in

units of atoms/cm

as follows:

ijij

100.5 ×= (2)

Figure 2

Typical Infrared Spectrum in the Spectral Region

for Aluminum, Arsenic, Boron, and Phosphorus at

11 K

Figure 3

Boron and Phosphorus Region Expanded and

Baseline Corrected

14 Report

14.1 Report the following information:

14.1.1 The instrument used, the operator, and the date

of the measurements,

14.1.2 Identification of specimens,

14.1.3 The results of the audit reference specimen on a

control chart or other suitable form,

14.2 For each sample specimen report the following

information:

14.2.1 The concentration of each impurity/dopant or the

detection limit if no peaks can be identified,

14.2.2 Sample thickness,

14.2.3 The FWHM for each absorption peak,

14.2.4 The apodization function used, and

14.2.5 The amount of zero-fills and resulting number of

data points/cm

−1

15 Precision

15.1 A within-laboratory precision was determined by

measurement of boron and phosphorus in a reference

specimen by multiple operators over a period of one

year. The relative precision was determined to be 8.5%

and 9.7% for boron and phosphorus, respectively, at

nominal concentrations of 0.095 and 0.072 ppba.

16 Bias

16.1 The bias of this test method is not known but

believed to be within ± 10% of an accepted reference

value.

17 Keywords

17.1 analysis of silicon; determination of dopants;

determination of impurities; electrically active

impurities; Fourier transform infrared; impurities;

silicon.