Borophosphosilicate glass component analysis using secondary neutral mass spectrometry
In the present study the SNMS technique for the quantitative component analysis of the borophosphosilicate glass layers was used. These layers were deposited on the silicon substrate by chemical vapor deposition method. The charge-up of the surface is compensated by plasma gas electrons in the high...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2002
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| Zitieren: | Borophosphosilicate glass component analysis using secondary neutral mass spectrometry / O. Oberemok, P. Lytvyn // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2002. — Т. 5, № 1. — С. 101-105. — Бібліогр.: 11 назв. — англ. |
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irk-123456789-1211242017-06-14T03:06:27Z Borophosphosilicate glass component analysis using secondary neutral mass spectrometry Oberemok, O. Lytvyn, P. In the present study the SNMS technique for the quantitative component analysis of the borophosphosilicate glass layers was used. These layers were deposited on the silicon substrate by chemical vapor deposition method. The charge-up of the surface is compensated by plasma gas electrons in the high frequency mode sputtering. It is shown that modes of such sputtering significantly influence on the macro- and microrelief of the crater during the process of the depth component distribution analysis. An on-off time ratio change of the voltage applied to the sample results in changing the crater shape. At the same time the increase of the sputtering frequency results in appearance of thin protrusions at the crater bottom. Improvement of the depth resolution requires optimization both on-off time ratio and frequency of voltage applied to the sample. 2002 Article Borophosphosilicate glass component analysis using secondary neutral mass spectrometry / O. Oberemok, P. Lytvyn // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2002. — Т. 5, № 1. — С. 101-105. — Бібліогр.: 11 назв. — англ. 1560-8034 PACS: 68.49.S, 82.80.M, 61.72.T, V, W, 73.20.H, 68.37.P, 61.43.F http://dspace.nbuv.gov.ua/handle/123456789/121124 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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In the present study the SNMS technique for the quantitative component analysis of the borophosphosilicate glass layers was used. These layers were deposited on the silicon substrate by chemical vapor deposition method. The charge-up of the surface is compensated by plasma gas electrons in the high frequency mode sputtering. It is shown that modes of such sputtering significantly influence on the macro- and microrelief of the crater during the process of the depth component distribution analysis. An on-off time ratio change of the voltage applied to the sample results in changing the crater shape. At the same time the increase of the sputtering frequency results in appearance of thin protrusions at the crater bottom. Improvement of the depth resolution requires optimization both on-off time ratio and frequency of voltage applied to the sample. |
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Oberemok, O. Lytvyn, P. |
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Oberemok, O. Lytvyn, P. Borophosphosilicate glass component analysis using secondary neutral mass spectrometry Semiconductor Physics Quantum Electronics & Optoelectronics |
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Oberemok, O. Lytvyn, P. |
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Oberemok, O. |
| title |
Borophosphosilicate glass component analysis using secondary neutral mass spectrometry |
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Borophosphosilicate glass component analysis using secondary neutral mass spectrometry |
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Borophosphosilicate glass component analysis using secondary neutral mass spectrometry |
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Borophosphosilicate glass component analysis using secondary neutral mass spectrometry |
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Borophosphosilicate glass component analysis using secondary neutral mass spectrometry |
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borophosphosilicate glass component analysis using secondary neutral mass spectrometry |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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2002 |
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Borophosphosilicate glass component analysis using secondary neutral mass spectrometry / O. Oberemok, P. Lytvyn // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2002. — Т. 5, № 1. — С. 101-105. — Бібліогр.: 11 назв. — англ. |
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Semiconductor Physics Quantum Electronics & Optoelectronics |
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AT oberemoko borophosphosilicateglasscomponentanalysisusingsecondaryneutralmassspectrometry AT lytvynp borophosphosilicateglasscomponentanalysisusingsecondaryneutralmassspectrometry |
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2025-07-08T19:13:55Z |
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1837107288015372288 |
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101© 2002, Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
Semiconductor Physics, Quantum Electronics & Optoelectronics. 2002. V. 5, N 1. P. 101-105.
PACS: 68.49.S, 82.80.M, 61.72.T, V, W, 73.20.H, 68.37.P, 61.43.F
Borophosphosilicate glass component analysis
using secondary neutral mass spectrometry
O. Oberemok, P. Lytvyn
Institute of Semiconductor Physics, NAS of Ukraine, 45 prospekt Nauky, 03028 Kyiv, Ukraine
Phone: +380 (44) 265 5940; e-mail: plyt@isp.kiev.ua, obez@isp.kiev.ua
Abstract. In the present study the SNMS technique for the quantitative component analysis of the
borophosphosilicate glass layers was used. These layers were deposited on the silicon substrate by
chemical vapor deposition method. The charge-up of the surface is compensated by plasma gas electrons
in the high frequency mode sputtering. It is shown that modes of such sputtering significantly influence
on the macro- and microrelief of the crater during the process of the depth component distribution
analysis. An on-off time ratio change of the voltage applied to the sample results in changing the crater
shape. At the same time the increase of the sputtering frequency results in appearance of thin protrusions
at the crater bottom. Improvement of the depth resolution requires optimization both on-off time ratio
and frequency of voltage applied to the sample.
Keywords: borophosphosilicate glass, secondary neutral mass spectrometry, atomic force microscopy,
crater shape, roughness, depth profile, depth resolution.
Paper received 31.01.02; revised manuscript received 14.02.02; accepted for publication 05.03.02.
1. Introduction
Borophosphosilicate glass (BPSG) is an impor-
tant component of the silicon-based semiconductor
technology. BPSG have been used as interlevel di-
electric films for planarization and passivation of
device surfaces. An essential feature of the BPSG
layers is reflow [1,2,3] for at relatively low tem-
peratures and small flow angles. As it is shown in
[4], the B2O3 and P2O5 presence increase the ther-
mal expansion coefficient of SiO2, reducing the
stress caused by thermal mismatch with the Si
substrate. Layer properties depend on its composi-
tion. The phosphorus concentration defines the glass
reflow temperature [5]. The boron concentration
limits the overmuch reflow providing the better sur-
face planarization. There exists an optimum phos-
phorus concentration for any given boron concen-
tration to achieve the lowest possible reflow, the
minimum flow angles, and hence to obtain the best
gap-filling glass. Advanced technology of ultra shal-
low junctions demands the process temperature to
decrease for the dopant diffusion suppression. The
optimal temperature range for the advanced tech-
nology processes are 700÷900°Ñ. It is this range
that used to provide the high reflow level of the
BPSG layers. For the BPSG quantitative analysis
some methods, such as SIMS- [6,7], XRF- [8], IR-
[9,10] spectroscopies are used.
SIMS analysis of the BPSG layers is complicated
by charge-up of the sample surface. Sometimes, the
charge-up compensation is reached by the electron
beam processing or by the metal layer deposition
on the surface. In the last case, it is impossible to
perform the thick dielectric layer analysis. Besides,
the crater effect is the significant problem of the
sputtering. The non-rectangular crater shape results
in the depth resolution decreasing.
102 SQO, 5(1), 2002
O. Oberemok et al.: Borophosphosilicate glass component analysis...
a)
b)
U
U
HPM
DBM
Aperture
Mask
Fig. 1. Voltage shape applied to the sample (a) and schematic
crater shape of the dielectric films in the DBM mode and at non-
optimal p value in the HFM mode.
The dielectric layer analysis demands the elimi-
nation of disadvantages referred above. The SNMS
method with high frequency mode (HFM) sputter-
ing is more acceptable for this analysis [11]. Since
sputtering and ionization processes are separated
in SNMS, the dependence of results from the sam-
ple composition is smaller than in SIMS, and use of
HFM sputtering enables to minimize the crater ef-
fect. In the work we have investigated an influence
of the HFM sputtering on accuracy of the quantita-
tive depth component analysis of BPSG.
Experimental and results
BPSG layers (1.2µm thick) were deposited on the
Si substrate by the CVD technique at 450°C. A
dopant depth distribution quantitative analysis was
performed by INA3 instrument (Leybold-Heraues,
Berlin, Germany). The primary ion beam was
formed by applied square-wave voltage (HFM) be-
tween plasma wall and the sample. During the nega-
tive pulse (UHFM=500 V), Ar+ ions from low-pressure
(3.26×10-3 mbar), high-frequency (27 MHz) Ar plasma
are accelerated to the sample and sputter it. Plasma elec-
trons neutralize the accumulated positive surface charge
while the voltage is absent. HF-generator was used as a
high-frequency voltage source with adjustable frequency
(f) and on-off time ratio (p) of pulses. The voltage shape
applied to sample is shown in Fig. 1a.
The plasma potential and electron-ionization
current, measured by the Langmuir probes, are of
3 V and 0.35 mA, respectively. The DEKTAK 3030
(Veeco) profilometer was used for the crater shape
and sputtering rate measurements. We investigated
the uniformity and structureof the sample surface
after 10 min sputtering at different conditions by
the atomic force microscopy (AFM). The dopant
concentration quantitative analysis on the depth was
carried out taking into account relative sensitivity
factors (RSF). For RSF determination, the SiO2/Si
structure was implanted by boron and phosphorus.
We evaluated RSF�s from the expression:
SiCXI
XCSiI
RSF )(
)(1
0
0
=
where I(Si0) � secondary neutrals intensity for bulk
silicon (reference element),
I(X0) � secondary neutrals intensity for the
element X
ÑX � X concentration,
ÑSi � Si concentration
The RSF for oxygen was determinted from its known
concentration in the SiO2 film (2.45×1022 at/cm3). Re-
sults of these calculations are shown in Tab.1.
Element Å implant. keV Dose, cm-2 RSF
P 180 1×1016 0.380
B 50 6×1015 1.012
O - - 0.012
Si - - 1
The depth resolution was evaluated by the ex-
pression:
RF =∆Z/Z × 100 %,
where ∆Z � difference of depths at the 16 and
84% of signal intensity;
Z � depth at the 50% signal intensity;
F � frequency of sputtering.
1. Crater shape dependence on the sputter-
ing modes
During the dielectric or semiconductor film sput-
tering in the direct bombardment mode (DBM), the
crater shape is essentially non-uniform (Fig. 1b.).
The crater shape and sputtering rate depend on the
voltage (UDBM) applied to the sample.
The sputtering rate is higher in areas close to
the crater edges that are limited by a metal mask.
O. Oberemok et al.: Borophosphosilicate glass component analysis...
103SQO, 5(1), 2002
a)
-500
0
-1000
-1500
-2000
500 1500 2500 3500 4500 5500
M
µm
M
-500
0
-1000
-1500
-2500
-2000
50004000300020001000
µm
b)
Fig. 2. The crater profiles in the BPSG film after 10 min sputtering at f=50 kHz (a- p=0.5; b- p=0.7).
a)
c)
µm
2
1
10 n m
0
µm
2
1
10 n m
0
b )
µm
2
1
10 n m
0
d )
µm
2
1
10 n m
0
Fig. 3. Surface micro-relief of the as-deposited BPSG film (a), obtained after 10 min sputtering by SNMS at p=0.5 for f=50 kHz - (b),
at p=0.7 for f=50 kHz - (c) and at p=0.7, f=400 kHz - (d).
104 SQO, 5(1), 2002
O. Oberemok et al.: Borophosphosilicate glass component analysis...
50 100 150 200 250 300 350 400
0.30
0.32
0.34
0.36
0.38
0.40
Frequency, kHz
R
ou
gh
ne
ss
, n
m
a ) b )
50 100 150 200 250 300 350 400
50
100
150
Frequency, kHz
N
um
be
r
of
t
he
p
ro
tr
us
io
ns
>
1
n
m
Fig. 4. Frequency dependences of the roughness (a) and number (b) of the protrusions (>1nm).
Moreover, the shape of crater bottom has the hemi-
sphere form. These non-uniformities are connected
with the surface charge-up during the sample sput-
tering. Use of HFM sputtering is one of the possi-
bilities to compensate the surface charge-up [11].
For realization of this mode, high-frequency volt-
age (UHFM) is applied between the sample mask and
the aperture (Fig. 1b). The crater shapes obtained
at different p values are shown in Fig. 2. The ob-
tained results show that on-off time ratio essentially
influence the crater shape in BPSG layers. Fitting of on-
off time ratio of applied voltage is possible to receive the
almost rectangular crater shape. Thus at f=50 kHz and
p=0.5, the crater shape is more uniform as compared with
the DBM mode but has the non-uniform residual pattern
(Fig. 2a.).
At p=0.7, the crater shape is close to the rectan-
gular one (Fig. 2b.). At this p value for f=50 kHz
(optimal sputtering conditions for BPSG film), in-
crease of the sputtering frequency does not result in
essential modifications of the crater shape. It is nec-
essary to note that during the sputtering time, the
crater shape is not changed at optimal conditions.
Non-optimal conditions lead to the increase of the
distance between depths of central and peripheral
parts of the crater during sputtering.
2. Surface structure on the crater bottom
Microrelief of as deposited BPSG films is shown
in Fig. 3a. The surface has a significant roughness
(0.93 nm). The maximal height of protrusions
reaches 13.07 nm. After sputtering at f=50 kHz and
p=0.5 the roughness is less (0.72 nm) but the maxi-
mal height of protrusions increases to 13.88 nm (Fig. 3b).
At p increase up to 0.7, surface shape becomes nearly
3. Dopant distributions in the BPSG/Si struc-
ture
Fig. 5 illustrates the BPSG depth profiles for B,
P, O, Si measured at f=50 kHz (solid lines) and 400 kHz
(dashed lines). Thickness of BPSG layer was 1.2 µm.
More overextended tails (dashed lines) of the boron
and phosphorus indicates the depth resolution de-
crease (R50=7.9% and R400=8.6% for phosphorus).
Obviously, mechanism of this phenomenon is con-
nected to charge transfer. Some plasma gas elec-
trons have no time to reach the surface sample. Thus,
the frequency increase results in the decrease of the
charge-up compensation. In this case, ∆R is 0.7%.
Estimated element concentrations of B, P, O and Si
near the BPSG/Si interface are 24, 12, 30, 34 %,
respectively.
Conclusion
In the present study, the analysis of the influ-
thick and high protrusions at optimal sputtering condi-
tions. The reasons of this phenomenon demand additional
investigations.
In Fig. 4, the change of structural properties of
the surface on sputtering frequency are shown.
At p=0.7, increase of the sputtering frequency
from 50 kHz to 400 kHz results in the surface rough-
ness increase from 0.35 nm to 0.39 nm (Fig. 4a.).
Also, it results in the increase of the small protru-
sion number with the height larger than 1 nm (Fig.
4b.) on the 3µm×3µm area (Fig. 3d.). Thus, sput-
tering frequency increase leads to the essential mi-
cro-relief evolution and, therefore, to decrease of
the depth resolution.
O. Oberemok et al.: Borophosphosilicate glass component analysis...
105SQO, 5(1), 2002
,
Fig. 5. Dopants distribution in BPSG/Si structure.
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pp. 1676�1682, (1997).
ence of HFM sputtering mode on the BPSG micro-
and macrorelief was carried out. It is shown that
the change of the sputtering voltage on-off time ra-
tio enables to reach the near-rectangular crater
shape. But it does not provide the microuniformity
of the BPSG sputtering. Increase of the frequency
sputtering leads to the evolution of the BPSG
microrelief. There is a plenty of fine protrusions
higher than 1nm at the bottom of a sputtering sur-
face. Presence of these protrusions results in the
depth resolution worsening. The latter is confirmed
by the R increase. In order to obtain the high depth
resolution and, accordingly, high-quality concen-
tration analysis of BPSG layers, the sputtering
parameters (p, f) should have the optimum values.
Thus, not only on-off time ratio of applied voltage,
but also the frequency influences on accuracy of
concentration measurements, which was not speci-
fied earlier for INA3 SNMS instrument.
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