Determination of Various Elements in Semiconductor-Grade Phosphoric Acid by ICP-OES

APPLICATION NOTE
ICP-Optical Emission Spectroscopy
Author:
Kenneth Ong
PerkinElmer, Inc.
Shelton, CT
Determination of Various
Elements in SemiconductorGrade Phosphoric Acid
by ICP-OES
Introduction
In the manufacture of semiconductor
products, the purity of the reagents
is of utmost importance since the
presence of contaminants can affect the performance of the final products.
Phosphoric acid is commonly used in the production of various semiconductor
materials and, therefore, requires trace levels to be measured as specified in the
SEMI C36-1107 Grade 3 requirements. Phosphoric acid presents an analytical
challenge due to its viscosity, composition, and concentration. The combination of
matrix composition and measurement levels make phosphoric acid an ideal
candidate for analysis by ICP-OES. This work describes the analysis of phosphoric
acid with ICP-OES to meet the SEMI requirements.
Experimental
Results and Discussion
All analyses were carried out on a PerkinElmer Optima 8300
ICP-OES which uses flat induction plates (Flat Plate™ plasma
technology) instead of the traditional helical load coil. This
innovative technology delivers a plasma generation system that
does not require coil cooling and is capable of operating at a
plasma argon flow as low as 8 L/min. The operating conditions are
listed in Table 1.
®
To avoid contamination from the lab environment, samples were
prepared in a clean hood, and the autosampler was covered. All
sample preparation was done in PFA bottles which were pre-soaked
in 5% (v/v) nitric acid for 24 hours, then filled with ultra-pure water
for storage before use. In order to eliminate contamination from the
pump tubing, self-aspiration was used.
All measurements were made against calibration curves using the
Method of Additions Calibrations, with 5 ppb, 10 ppb and 20 ppb
standards. For analysis, ultra-pure grade phosphoric acid (H3PO4)
was diluted ten times with deionized water.
Table 1. Sample introduction system and plasma parameters
Parameter
Injector:
Spray chamber:
Cyclonic
Nebulizer:
Meinhard
Sample tubing:
Capillary
Drain tubing:
1.14 mm i.d.
Quartz torch:
Single slot
Sample capillary:
PTFE 1 mm i.d.
Sample vials:
Polypropylene
Equilibrium delay:
Plasma aerosol type:
RF power:
15 sec
Wet
1300 W
Nebulizer flow:
0.55 L/min
Auxiliary flow:
0.2 L/min
Plasma flow:
8 L/min
Sample uptake:
Self aspiration
Plasma viewing:
Axial
Processing mode:
Peak area
Auto integration:
5 - 10 sec
Replicates:
Background correction:
2
Condition
Alumina 2 mm i.d.
3
1 or 2-point
Table 2 shows the elements, wavelengths, correlation coefficients,
and detection limits of the method. The detection limits,
determined from 25 replicate measurements of the sample, are
within the SEMI 36-1107 criteria. The low detection limits are an
indication of the system’s short-term stability. The elevated Pb
detection limit results from the higher level of Pb in the acid.
Table 2. Elements, wavelengths, correlation coefficients, and detection limits
Analytes and
Wavelengths (nm)
Al 396.153
Correllation
Coefficients
0.997
Detection
Limits (ppb)
1.86
Ba 233.527
0.999
0.529
Be 313.107
0.999
0.119
Ca 317.933
0.999
0.640
Cd 228.802
0.996
0.909
Co 228.616
0.998
0.794
Cr 205.560
0.999
0.838
Cu 327.393
0.999
0.953
Fe 239.562
0.999
0.736
K 766.490
1.000
8.71
Li 670.784
0.997
0.205
Mg 285.213
0.998
0.253
Mn 257.610
0.999
0.176
Mo 202.031
0.999
1.86
Na 589.592
0.999
0.523
Ni 221.648
0.999
1.22
Pb 220.353
1.000
8.56
Sn 189.927
0.999
3.83
Ti 334.940
0.999
0.172
V 290.880
0.999
0.690
Zn 202.548
0.999
0.527
To ascertain the accuracy and robustness of the method, a spike
recovery test was carried out. The H3PO4 was divided into three
containers, and each analyzed. A 5 µg/L spike was then added to
each container and re-analyzed. The spike recoveries, shown in
Table 3 (Page 3), ranged from 90-111%, well within the SEMI
requirement of 75%-125%.
Table 3. Repeatability and recovery of 5 µg/L spikes
Analyte and
Wavelength
Al
Sample 1
Sample 2
Sample 3
Sample Avg
Spike 1
Spike 2
Spike 3
Spike Avg
Recovery
396.153
0.161
0.586
-0.039
0.236
5.58
5.07
6.09
5.59
107%
Ba 233.527
1.01
0.660
0.869
0.848
5.74
5.82
5.88
5.81
99.3%
Be 313.107
0.076
0.071
0.067
0.071
5.00
4.99
4.99
4.99
98.4%
Ca 317.933
0.604
0.776
0.719
0.700
5.58
5.21
5.80
5.53
96.6%
Cd 228.802
11.7
11.6
11.8
11.7
16.6
16.6
16.8
16.7
99.6%
Co 228.616
6.11
6.06
6.11
6.09
11.1
11.1
11.2
11.1
101%
Cr
205.560
5.41
5.38
5.47
5.42
10.9
10.4
10.4
10.6
103%
Cu 327.393
3.08
2.87
2.56
2.84
7.77
7.76
7.69
7.74
98.1%
97.7%
Fe
239.562
1.36
1.62
1.71
1.56
6.17
6.60
6.57
6.45
K
766.490
-9.72
-9.50
-9.24
-9.49
-4.14
-3.67
-3.98
-3.93
111%
Li
670.784
1.31
1.25
1.16
1.24
6.15
6.10
6.11
6.12
97.6%
Mg 285.213
-0.071
0.069
-0.013
-0.005
5.06
5.11
5.14
5.10
102%
Mn 257.610
0.581
0.591
0.602
0.591
5.53
5.49
5.51
5.51
98.4%
Mo 202.031
-1.39
-1.68
-1.56
-1.54
4.11
3.61
4.03
3.92
109%
Na 589.592
0.424
0.590
0.498
0.504
5.49
5.46
5.44
5.46
99.2%
Ni
221.648
-1.41
-1.06
-1.11
-1.19
3.71
3.63
3.86
3.74
98.5%
Pb 220.353
21.0
21.3
23.1
21.8
26.2
25.9
26.8
26.3
89.5%
Sn 189.927
-0.667
0.175
-0.088
-0.193
4.66
4.20
4.49
4.45
92.9%
Ti
334.940
0.276
0.354
0.292
0.307
5.26
5.28
5.30
5.28
99.4%
V
292.402
0.218
0.008
0.124
0.117
5.08
5.18
5.04
5.10
99.6%
Zn 202.548
-0.695
-0.806
-0.605
-0.702
4.33
4.129
4.20
4.22
98.4%
To verify the stability of the method, a 5 µg/L spike solution was
aspirated continuously for an hour, with measurements being made
consecutively. Figure 1 shows the resulting stability plot, where
results were normalized to the average reading. The variations were
generally less than ± 10%, indicating no significant drift. This result
demonstrates the robustness of the Optima 8300’s Flat Plate plasma
to handle a complex matrix at a low plasma gas flow.
Conclusion
This work has demonstrated that the Optima 8300 ICP-OES can
effectively analyze phosphoric acid to meet the specifications of
SEMI 36-1107. Utilizing Flat Plate plasma technology, only 8 L/min
of argon gas are needed, significantly reducing operating costs.
Even with low argon consumption, a robust plasma is produced,
which results in signal stability in complex matrices and low
detection limits. The combination of low argon consumption and
robustness makes PerkinElmer’s Optima 8300 ICP-OES ideally
suited for the analysis of complex samples, while minimizing
operating costs.
References
SEMI C10-1109–Guide for Determination of Method
Detection Limits
SEMI C1-0310 – Guide for the Analysis of Liquid Chemicals
SEMI C36-1107– Specification for Phosphoric Acid
Figure 1. Stability plot for continuous aspiration of a 5 µg/L spike in H3PO4 measured
over one hour.
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