We have developed improved analyzer multilayers for the detection
of aluminium (Al) and boron (B) on silicon (Si) wafers with
wavelength-dispersive x-ray fluorescence spectrometers. For the
detection of Al on Si wafers we show that WSi2/Si and
Ta/Si multilayers provide detection limits that are 42% and 60%
better, respectively, than with currently used W/Si
multilayers. For the detection of B on Si wafers we show that
La/B4C multilayers improve the detection limit by ∼28%
compared with a conventionally used Mo/B4C
multilayer.
Jeroen Bosgra, Erwin Zoethout, Ad M. J. van der Eerden, Jan Verhoeven, Robbert W. E. van de Kruijs, Andrey E. Yakshin, and Fred Bijkerk Appl. Opt. 51(36) 8541-8548 (2012)
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Calculated Reflectivities RAl and
RSi for Unpolarized Radiation of Al Kα
(1487 eV) and Si Kα (1740 eV), at the Respective Angle Where
the Reflectivity for Al Kα Reaches Its
Maximuma
Multilayer
θ (deg)
RAl (%)
RSi (%)
WSi2/Si
6.436
51.44
0.031
Ta/Si
6.452
49.65
0.021
W/Si
6.464
52.32
0.102
Si was chosen as the top layer.
Table 2
Theoretically Predicted Values for the Reflectivity of
Unpolarized Radiation of B Kα (183 eV), Si L (90 eV), P L
(122 eV), C Kα (277 eV), and O Kα (525 eV) at the
Respective Angle Where the Reflectivity for B Kα Reaches Its
Maximuma
Multilayer
θ (deg)
RB (%)
RSi (%)
RP (%)
RC (%)
RO (%)
La/B4C
24.578
63.99
0.88
6.208
0.020
0.006
Mo/B4C
24.308
38.13
4.96
0.686
0.022
0.024
W/C
24.974
11.59
5.32
1.505
0.162
0.290
The spacers were chosen as top layers.
Table 3
Parameters Characterizing the Multilayers Produced for the
Detection of Al on Si Wafers
Multilayer
N
d (nm)
Γ
σ (nm)
Ta/Si
100
3.74
0.39
0.34
WSi2/Si
100
3.78
0.43
0.30
W/Si
100
3.82
0.45
0.33
Table 4
Experimental Peak Intensities (P),
Backgrounds, (B) and
/(P - B) Obtained with
WSi2/Si, Ta/Si, and W/Si Mirrors, with a Si Wafer
Coated with 12-nm Al as the Sample
Multilayer
P (cps)
B (cps)
/P - B) (10-3/cps1/2)
WSi2/Si
154
82
125.8
Ta/Si
160
66
86.4
W/Si
212
155
218.4
Table 5
Parameters Characterizing the Multilayers Fabricated for
the Detection of B
Multilayer
N
d (nm)
Γ
σ (nm)
La/B4C
40
8.57
0.49
0.37
Mo/B4C
40
8.52
0.41
0.44
Table 6
Theoretically Predicted (for Ideal, Semi-Infinite
Multilayers) and Experimentally Verified Values for the Reflectivity
of s-Polarized Radiation of B Kα (183 eV), Si L (90
eV), and P L (122 eV)a
Multilayer
RB (%)
RSi (%)
RP (%)
Theory
Experim.
Theory
Experim.
Theory
Experim.
La/B4C
69.4
50.8
1.2
1.2
8.1
6.8
Mo/B4C
46.2
31.5
6.1
3.1
0.9
0.3
At an angle of 24.5°, where the
reflectivity for B Kα is maximum. B4C was chosen as the
top layer.
Table 7
Experimental Peak Intensities (P),
Backgrounds (B), and
/(P - B) of
La/B4C and Mo/B4C for the Detection of B in
Two Different Samples: B4C and BPSG
Multilayer
Sample
P (cps)
B (cps)
/(P - B) (10-3/cps1/2)
La/B4C
B4C
15139
243
1.047
Mo/B4C
B4C
8635
156
1.473
La/B4C
BPSG
502
191
44.438
Mo/B4C
BPSG
277
108
61.493
Tables (7)
Table 1
Calculated Reflectivities RAl and
RSi for Unpolarized Radiation of Al Kα
(1487 eV) and Si Kα (1740 eV), at the Respective Angle Where
the Reflectivity for Al Kα Reaches Its
Maximuma
Multilayer
θ (deg)
RAl (%)
RSi (%)
WSi2/Si
6.436
51.44
0.031
Ta/Si
6.452
49.65
0.021
W/Si
6.464
52.32
0.102
Si was chosen as the top layer.
Table 2
Theoretically Predicted Values for the Reflectivity of
Unpolarized Radiation of B Kα (183 eV), Si L (90 eV), P L
(122 eV), C Kα (277 eV), and O Kα (525 eV) at the
Respective Angle Where the Reflectivity for B Kα Reaches Its
Maximuma
Multilayer
θ (deg)
RB (%)
RSi (%)
RP (%)
RC (%)
RO (%)
La/B4C
24.578
63.99
0.88
6.208
0.020
0.006
Mo/B4C
24.308
38.13
4.96
0.686
0.022
0.024
W/C
24.974
11.59
5.32
1.505
0.162
0.290
The spacers were chosen as top layers.
Table 3
Parameters Characterizing the Multilayers Produced for the
Detection of Al on Si Wafers
Multilayer
N
d (nm)
Γ
σ (nm)
Ta/Si
100
3.74
0.39
0.34
WSi2/Si
100
3.78
0.43
0.30
W/Si
100
3.82
0.45
0.33
Table 4
Experimental Peak Intensities (P),
Backgrounds, (B) and
/(P - B) Obtained with
WSi2/Si, Ta/Si, and W/Si Mirrors, with a Si Wafer
Coated with 12-nm Al as the Sample
Multilayer
P (cps)
B (cps)
/P - B) (10-3/cps1/2)
WSi2/Si
154
82
125.8
Ta/Si
160
66
86.4
W/Si
212
155
218.4
Table 5
Parameters Characterizing the Multilayers Fabricated for
the Detection of B
Multilayer
N
d (nm)
Γ
σ (nm)
La/B4C
40
8.57
0.49
0.37
Mo/B4C
40
8.52
0.41
0.44
Table 6
Theoretically Predicted (for Ideal, Semi-Infinite
Multilayers) and Experimentally Verified Values for the Reflectivity
of s-Polarized Radiation of B Kα (183 eV), Si L (90
eV), and P L (122 eV)a
Multilayer
RB (%)
RSi (%)
RP (%)
Theory
Experim.
Theory
Experim.
Theory
Experim.
La/B4C
69.4
50.8
1.2
1.2
8.1
6.8
Mo/B4C
46.2
31.5
6.1
3.1
0.9
0.3
At an angle of 24.5°, where the
reflectivity for B Kα is maximum. B4C was chosen as the
top layer.
Table 7
Experimental Peak Intensities (P),
Backgrounds (B), and
/(P - B) of
La/B4C and Mo/B4C for the Detection of B in
Two Different Samples: B4C and BPSG
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