In situ barrier formation using rapid thermal annealing of a tungsten nitride/polycrystalline silicon structure

Article abstract of DOI:10.1063/1.126401

This letter describes the use of rapid thermal annealing (RTA) to form a barrier layer applicable to the gate electrode in dynamic random access memory devices with a stacked structure [tungsten nitride (WN_x)/polycrystalline Si (poly-Si)]. After RTA, the reactively sputtered amorphous WN_x film on the poly-Si was transformed to a low-resistive α-phase W and nitrogen-segregated layer. Most of the nitrogen in the WN_x film was dissipated and a relatively small amount of the nitrogen was segregated at the interface of the α-phase W and poly-Si. The segregated layer was estimated to be 2 nm thick and revealed a silicon nitride (Si-N) bonding status. More importantly, we found that this thin segregated layer successfully protected the formation of tungsten silicide, even after RTA at 1000°C for 2 min in a hydrogen environment.

Full text of DOI:10.1063/1.126401

In situ barrier formation using rapid thermal annealing of a tungsten
nitride/polycrystalline silicon structure
Byung Hak Lee, Kee Sun Lee, Dong Kyun Sohn, Jeong Soo Byun, Chang Hee Han, Ji-Soo Park, Sang Beom
Han, and Jin Woon Park
Citation: Applied Physics Letters 76, 2538 (2000); doi: 10.1063/1.126401
View online: http://dx.doi.org/10.1063/1.126401
View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/76/18?ver=pdfcov
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APPLIED PHYSICS LETTERS
VOLUME 76, NUMBER 18
1 MAY 2000
In situ barrier formation using rapid thermal annealing of a tungsten
nitrideÕpolycrystalline silicon structure
a)
b)
c)
d)
Byung Hak Lee, Kee Sun Lee, Dong Kyun Sohn, Jeong Soo Byun,
Chang Hee Han, Ji-Soo Park, Sang Beom Han, and Jin Woon Park
R&D Division, Hundai MicroElectronics Company Ltd., 1 Hyangjeong-dong, Cheongju-si 361-480, Korea
͑
Received 16 February 1999; accepted for publication 10 March 2000͒
This letter describes the use of rapid thermal annealing ͑RTA͒ to form a barrier layer applicable to
the gate electrode in dynamic random access memory devices with a stacked structure ͓tungsten
nitride (WN )/polycrystalline Si ͑poly-Si͔͒. After RTA, the reactively sputtered amorphous WN
x
x
film on the poly-Si was transformed to a low-resistive ␣-phase W and nitrogen-segregated layer.
Most of the nitrogen in the WN film was dissipated and a relatively small amount of the nitrogen
x
was segregated at the interface of the ␣-phase W and poly-Si. The segregated layer was estimated
to be 2 nm thick and revealed a silicon nitride ͑Si–N͒ bonding status. More importantly, we found
that this thin segregated layer successfully protected the formation of tungsten silicide, even after
RTA at 1000 °C for 2 min in a hydrogen environment. © 2000 American Institute of Physics.
͓
S0003-6951͑00͒03418-5͔
As ultra-large-scale integrated circuit devices are scaled
down to a deep submicron regime, the gate resistance/
capacitance time delay limits the speed of metal–oxide–
semiconductor devices. To reduce this delay, a gate structure
with a low-resistive material has been widely investigated.1
A stacked gate structure, tungsten ͑W͒/barrier/polycrystalline
Si ͑poly-Si͒, is considered to be a promising candidate to
Therefore, a highly reliable diffusion barrier layer is essential
between W and poly-Si.
In this study, we propose a method of forming a barrier
layer for the W/poly-Si gate structure with a WN film on
x
–3
poly-Si by rapid thermal annealing ͑RTA͒. To make the
sample structure, the WN film ͑100 nm͒ was reactively
x
sputtered on a doped poly-Si film that had been cleaned by
HF. Then, RTA was performed at temperatures ranging from
600 to 1000 °C under nitrogen atmosphere for 1 min. Ruth-
erford backscattering spectroscopy was employed to quantify
the composition of the WNx film, and secondary ion mass
spectroscopy ͑SIMS͒ was used for compositional analysis.
Electrical resistivity was evaluated using a four-point-probe
method was phase identification was carried out using ⌰–2⌰
x-ray diffraction with a scan rate of 0.2°/min. Also, the mi-
crostructure and chemical status at the interface of W and
poly-Si were analyzed by transmission electron microscopy
replace the tungsten silicide (WSi ) or a self-aligned silicide
x
͑
salicide͒ gate, due to its low electrical resistance and high
4
,5
resistance against agglomeration during annealing. For ex-
ample, the sheet resistance of the gate structure of
W͑100 nm͒/WN (5 nm)/poly-Si͑100 nm͒ was estimated to
x
be 1.5 ⍀/sq, which is lower by one order of magnitude com-
pared with that of the conventional gate structure of
WSi (100 nm)/poly-Si͑100 nm͒. Moreover, this low sheet
x
resistance was able to reserve even at a narrow gate line-
6
width of 0.12 ␮m.
͑TEM͒ and x-ray photoelectron spectroscopy ͑XPS͒.
Because direct contact of W to poly-Si results in the
Figure 1 shows the variation of the resistivity and the
formation of WSi during annealing at temperatures above
x
6
00 °C, a barrier layer such as titanium nitride ͑TiN͒ and
7
–9
tungsten nitride (WN ) jams in between them.
The W
x
film in the W/WN /poly-Si structure revealed a lower sheet
x
6
resistivity than that in the W/TiN/poly-Si structure. In addi-
tion, better oxide integrity at the edge of the W/WN /poly-Si
x
gate was shown compared with the W/TiN/poly-Si structure
after selective Si oxidation that was conducted for etch dam-
1
0
age recovery. However, WN is known to be unstable and
x
easily transform to W and nitrogen at temperatures above
8
00 °C, resulting in the formation of WSi at the interface of
x
W/WN and poly-Si during the next high-temperature pro-
x
1
1
cess, such as selective Si oxidation and dopant activation.
a͒
Electronic mail: wgate@hmec.co.kr
b͒
Present address: Department of Materials Science Engineering, Kongju
National University, 182 Shinkwan-Dong, Kongju City 314-701, Korea.
Present address: Basic Research Laboratory, Electronics and Telecommu-
nications Research Institute, Yusong P.O. Box 106, Taejon City 305-600,
Korea.
c͒
FIG. 1. Resistivity and x-ray diffraction spectra of WNx as a function of
nitrogen content in as-deposited film.
d͒
Present address: Applied Materials Inc., Santa Clara, CA 95054.
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003-6951/2000/76(18)/2538/3/$17.00 2538 © 2000 American Institute of Physics
42.104.240.194 On: Tue, 16 Dec 2014 16:29:59
0
1

Appl. Phys. Lett., Vol. 76, No. 18, 1 May 2000
Lee et al.
2539
FIG. 2. X-ray diffraction spectra of W N /poly-Si ͑inset͒ and resistivity as
6
7
33
a function of RTA temperature in nitrogen for 1 min.
phase of the WN film as a function of the nitrogen content
x
in the as-deposited films. The resistivity of the WN films
x
increased gradually with increasing nitrogen content up to
about 10%, and then leveled off with further increments of
nitrogen content by 45%. With further increments of nitro-
FIG. 4. TEM micrograph of W67N33 on poly-Si after RTA at 1000 °C for 1
min: ͑a͒ uniform interface of a W/poly-Si structure and ͑b͒ amorphous layer
between W and poly-Si.
gen content, above 45%, the resistivity of the WN films was
drastically increased. In the case of 10%–45% of nitrogen
x
the as-deposited film was 175 ␮⍀ cm and decreased with
higher RTA temperatures. After RTA at 1000 °C for 1 min,
the resistivity was lowered to 15 ␮⍀ cm, which is compa-
rable to the value of the sputtered W, 13 ␮⍀ cm. As can be
seen in the inset of Fig. 2, the amorphous structure of the
content, the as-deposited WN was an amorphous structure,
x
as shown in the inset of Fig. 1. To the contrary, the WNx
films containing 50% of nitrogen were polycrystalline. Af-
folter reported that the amorphous WN film containing 33%
x
as-deposited W N films transformed to W N and ␣-phase
of nitrogen was easily crystallized into W N during vacuum
67 33
2
2
annealing at 600 °C for 30 min.11 Also, this WN film depos-
W after RTA at 600 °C. As the RTA temperature was in-
x
creased to 900 and 1000 °C, W N peaks disappeared and a
ited on SiO was transformed to a low-resistive ␣-phase W
2
2
new peak of ␣-phase W appeared. Also, higher RTA tem-
peratures yielded a higher peak intensity of ␣-phase W.
by annealing at 800 °C for 30 min, while the polycrystalline
WN film containing 50% of nitrogen was not completely
x
Therefore, we may insist that a lower resistance of W N
transformed to the ␣-phase W, even after annealing at
67 33
on poly-Si by RTA is mainly caused by the transformation of
8
00 °C. Therefore, WN films composed of W N were
x 67 33
amorphous WN films to ␣-phase W.
used in this work.
x
It is well known that W reacts easily with Si at tempera-
Figure 2 shows the resistivity of the W N film on
6
7
33
7
,8
tures above 600 °C, resulting in the formation of WSix .
poly-Si as a function of RTA temperatures. The resistivity of
However, it is interesting to note that we were not able to
FIG. 3. SIMS depth profiles of W N on a poly-Si substrate: ͑a͒ as-
6
7
33
deposited and ͑b͒ after RTA at 1000 °C. The intensities of nitrogen were
normalized by an intensity of ͑a͒ tungsten and ͑b͒ silicon indicated on the
FIG. 5. XPS spectra of W N on poly-Si after annealing at 1000 °C: ͑a͒
6
7
33
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right-hand axis.
as-received, ͑b͒ after sputtering for 5 s, and ͑c͒ after sputtering for 10 s.
42.104.240.194 On: Tue, 16 Dec 2014 16:29:59
1

2540
Appl. Phys. Lett., Vol. 76, No. 18, 1 May 2000
Lee et al.
Si, the W layer was removed using a boiling H O solution,
2
2
before XPS analysis. Before sputtering the surface of the
sample, a strong peak of Si in the SiO peak was detected,
2
probably due to the oxide formed during the H O treatment.
2
2
However, a peak indicating the silicon nitride ͑Si–N͒ bond-
ing status was clearly seen after sputtering the sample for 5 s,
and a peak of pure silicon appeared with further sputtering.
This result implies that the segregated nitrogen has a Si–N
bonding status.
The thermal stability of the W N /poly-Si structure
6
7
33
treated by RTA at 1000 °C under nitrogen atmosphere was
evaluated at the annealing temperatures of 850, 1000, and
1
050 °C in a hydrogen environment for 2 min. It was found
that the RTA-treated W N /poly-Si structure was stable up
6
7
33
to 1000 °C for 2 min annealing, as shown in Fig. 6, due to
the nitrogen-segregated layer acting as a barrier between W
and poly-Si.
FIG. 6. X-ray diffraction spectra of the rapidly thermal annealed
W N /poly-Si structure after hydrogen annealing at temperatures of ͑a͒
67
33
8
50, ͑b͒ 1000, and ͑c͒ 1050 °C for 2 min.
In summary, the structure of W N /poly-Si converted
6
7
33
into ␣-phase W/nitrogen-segregated layer/poly-Si layers by
RTA at 1000 °C for 1 min. The ␣-phase W layer was used as
a low-resistive electrode, and the nitrogen-segregated layer at
the interface of W/poly-Si acted as an in situ formed diffu-
sion barrier, which successfully suppressed the silicidation
between W and poly-Si. The nitrogen-segregated layer was
an amorphous structure and revealed a Si–N bonding status.
observe any peaks on WSi with the samples tested, even
after high-temperature annealing at 1000 °C ͑Fig. 2͒. To in-
x
vestigate the causes of the lack of formation of WSi , the
x
behavior of nitrogen was investigated using SIMS analysis.
Ϫ3
Equilibrium solubility of nitrogen in W is about 10 at. %
at 1000 °C. This indicates that excessive nitrogen in the
W N films may be diffused out and also redistributed after
6
7
33
RTA at 1000 °C.
Figure 3 shows the SIMS depth profiles of tungsten,
oxygen, silicon, and nitrogen before and after RTA at
1
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ized by the intensity of tungsten and silicon on the right axis.
In the case of the as-deposited film, the concentration of
nitrogen was uniformly distributed in depth, but after RTA at
1000 °C, most of the nitrogen atoms were dissipated and par-
5
6
tially segregated at the W/poly-Si interface, as in Fig. 3͑b͒.
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and poly-Si, TEM analysis was conducted with the sample
annealed at 1000 °C. As shown in Fig. 4͑a͒, the interface of
W and poly-Si was extremely uniform and there was no
layer of WSi . The nitrogen-segregated layer is clearly seen
x
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