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Indian Journal of Materials Science

Volume 2013, Article ID 725975, 6 pages
http://dx.doi.org/10.1155/2013/725975

Research Article
Structure and Thermal Stability of Copper Nitride Thin Films

Guangan Zhang,1 Zhibin Lu,1 Jibin Pu,1 Guizhi Wu,1 and Kaiyuan Wang2
1
State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences,
Lanzhou 730000, China
2
School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237, China

Correspondence should be addressed to Guangan Zhang; gazhang@licp.cas.cn

Received 26 June 2013; Accepted 4 August 2013

Academic Editors: Y. Habibi and A. Sotelo

Copyright © 2013 Guangan Zhang et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Copper nitride (Cu3 N) thin films were deposited on glass via DC reactive magnetron sputtering at various N2 flow rates and partial
pressures with 150∘ C substrate temperature. X-ray diffraction and scanning electron microscopy were used to characterize the
microstructure and morphology. The results show that the films are composed of Cu3 N crystallites with anti-ReO3 structure. The
microstructure and morphology of the Cu3 N film strongly depend on the N2 flow rate and partial pressure. The cross-sectional
micrograph of the film shows typical columnar, compact structure. The thermal stabilities of the films were investigated using
vacuum annealing under different temperature. The results show that the introducing of argon in the sputtering process decreases
the thermal stability of the films.

1. Introduction partial pressure, sputtering pressure, substrate temperature,

and substrate bias voltage. The electrical resistivity of the films
Transition metal nitrides show a wide variety of properties varied from 2 × 10−3 Ω cm to about 103 Ω cm, and the optical
and have lots of applications, and some of them have acquired band gap of the films increased from 0.8 eV to 1.9 eV with
a large number of industrial application. Among them, the various sputtering process parameters [12–15]. Liu et al.
copper nitrides have attracted considerable attention as a [5] and Ji et al. [16] have studied thermal stability of the
new material for optical storage devices and high speed films. Yue et al. [1, 17] have studied the structure, thermal
integrated circuits, based on its unique properties, such as properties, optical properties, and Hall effects of the Cu3 N
rather low thermal decomposition temperature, excellent films. The mechanical properties of the copper nitride films
electrical properties, and optical qualities [1, 2]. All of these were also studied by Pierson [4, 14, 15]. However, the structure
properties are due to its special cubic anti-ReO3 structure. A and thermal properties of the films, which may influence
number of nonequilibrium techniques, such as RF reactive significantly on the applications of electronic and optical
sputtering [1, 3–7], DC magnetron sputtering [8], ion assisted storage, were found to be dependent on substrate, growth
vapor deposition [9], reactive pulsed laser deposition [10], technologies, and preparation process.
and other methods [11], are currently used for the preparation However, the influence of the formation process on the
of Cu3 N films. In recent years, Terada et al. [3] prepared structure, morphology, and thermal properties of copper
oriented epitaxial films by the reactive rf magnetron sputter- nitride is still not very clear. It was therefore decided to study
ing method on the Pt/MgO and Al2 O3 substrates. They also the formation and stability of copper nitride films. In prepa-
reported that copper nitride films were amorphous on glass, ration of the films, the DC magnetron sputtering method
MgO, and SrTiO3 substrates. Maruyama and Morishita [12] was used in which the influences of N2 flow rate and N2
have studied the electrical and optical characteristics of the partial pressure on the copper nitride films prepared at 150∘ C
films prepared by rf reactive sputtering. And the electrical substrate temperature were investigated systematically. In a
and optical properties of the copper nitride films critically thermal stability study, the vacuum annealing process was
depended on the sputter process parameters such as nitrogen used, with our objective being to describe the decomposition
2 Indian Journal of Materials Science

111 The Ar and N2 gas flow rate were adjusted by independent

100
mass-flow controllers. The partial pressures of Ar and N2 in
N2 50
the chamber were estimated by their respective flow rates
measured by the mass-flow controllers. The total sputtering
pressure was maintained at 1 Pa by controlling the pumping
rates during the sputtering. The substrate temperature during
Intensity (a.u.)

the sputtering maintained at 150∘ C. The power applied to the

N2 30
target is fixed at 1000 W throughout the study.
The film thickness was determined using a long scan
profiler (2206, Harbin, China). The crystalline structures
of the films were identified with an X-ray diffractometer
(D/Max-2400X, Rigaku Co., Japan) using Cu K𝛼 radiation.
N2 10
Scanning electron microscopy (JSM-5600LV, Electron Opti-
cal Co., Japan) and atomic force microscopy (SPM-9500,
Shimadzu, Japan) were performed to investigate the state of
20 30 40 50 60 70 80 the surface and the cross-section of the specimens and to
2𝜃 (deg) search for characters that have occurred in the deposited
films. In order to study the thermal stability of Cu3 N thin
Figure 1: The X-ray diffraction spectra of Cu3 N films with different
N2 flow rates. films, the as-deposited samples were annealed in vacuum
(pressure = 3.0 × 10−3 Pa) for 1 h at a temperature ranging
from 150∘ C to 300∘ C. Then the samples were cooled to room
100 temperature under same vacuum conditions.
0.8 Pa
111
3. Results and Discussion
3.1. Film Deposition and Structure. The deposition rate was
0.6 Pa
estimated from the film thickness and the corresponding
Intensity (a.u.)

deposition time. The deposition rate of the mixture N2

30 sccm/Ar 20 sccm was 66.7 nm/minute, while for pure N2
30 sccm flow rate was only 38.3 nm/minute. The deposition
0.4 Pa rates of the films decrease dramatically in a pure reactive
N2 atmosphere. This is partly due to the poor sputtering
capability of nitrogen compared to argon and partly from the
Cu4 N 111
target poisoning effects (induced by the reactive N2 atmo-
0.2 Pa sphere) where the sputtering yield for nitride is much smaller
than the metal, and partly due to that these compounds
have higher secondary electron emission yields than metal
20 30 40 50 60 70 80 targets [19]. The additional Ar can dramatically increase the
2𝜃 (deg) sputtering of Cu and Cu3 N and have a negative influence of
forming nitride compound layer on the target surface and
Figure 2: The X-ray diffraction spectra of Cu3 N films with different
consequently results in a large increase of the deposition rate.
N2 partial pressure.
Figure 1 shows the X-ray diffraction (XRD) spectra of
Cu3 N films prepared on glass at different N2 flow rates of 50,
30, and 10 sccm with pressure of 1 Pa. The XRD spectra are
process of the films in detail so that a critical decomposition corresponding to the cubic anti-ReO3 structure of Cu3 N, and
temperature could be found. no Cu peaks are found in all the films. The films formed under
50 sccm N2 flow rates had grown with an obviously preferred
2. Experiment orientation of [111]. The preferred growth orientation of the
film changed gradually to [100] as N2 flow rates decreased
Thin copper nitride films were prepared with a DC reactive to 30 sccm, and the diffraction peaks of (111) and (200) are
magnetron sputtering with a columnar target (99.99% pure also very strong. The XRD spectra of the films deposited at
copper) on glass. The experimental equipment has been N2 flow rate of 10 sccm are preferred to [100] orientation and
described in detail elsewhere [18], so only a brief description almost the same as the films deposited at 30 sccm N2 flow rate.
of experiment is given here. The glass wafers were ultrasoni- However, the (111) diffraction peak of the films that deposited
cally cleaned in acetone and methanol and finally dried with N2 flow rates is even weaker than that of films deposited at
blowing gas. The substrate was placed parallel to the target 30 sccm N2 flow rate.
at 150 mm. Before sputtering, the chamber was evacuated to Figure 2 shows the XRD spectra of the films prepared at
less than 1.0 × 10−3 Pa. The working gas (99.999% pure argon different N2 partial pressure with total pressure of N2 and
and 99.999% pure nitrogen) was introduced to the chamber. Ar gas mixture maintained at 1 Pa. The sputtering lasted for
Indian Journal of Materials Science 3

1 𝜇m 1 𝜇m

(a) (b)

1 𝜇m

(c)

Figure 3: The SEM image of Cu3 N film deposited under various N2 flow rate 50 sccm; 30 sccm; 10 sccm.

20 min. The XRD spectra of the films prepared at 0.8 Pa N2 (Figure 3(c)), grains on the surface appeared obviously as
partial pressure show a strong [100] orientation. The XRD uniformly nodular-like morphology.
spectra also show that the films prefer [100] orientation, The topography shown in Figure 4 suggests that the film is
but the (111) and (200) peaks become stronger at the N2 prepared with mixture of N2 and Ar. The grain size of the films
partial pressure of 0.6 Pa. For the films prepared at 0.4 Pa N2 increases with the argon introduced in the reactive atmo-
partial pressure, the [100] peaks disappeared. For the films sphere. The copper nitride films prepared at 0.8 Pa N2 partial
prepared at 0.2 Pa N2 partial pressure, the Cu4 N (111) peaks pressure also show pyramid cone morphology (Figure 4(a)).
were observed [12, 20]. The preferred orientation of the However, the film prepared at 0.6 Pa N2 partial pressure is
as-deposited copper nitride films is interpreted to depend composed of large polygonal grains (of up to micrometer
mainly on the mobility of the Cu and N atoms participating scale) with irregular tops separated by a large number of
in the film growth process [2]. Such mobility is expected to porous boundaries (Figure 4(b)). The additional Ar gas can
be a function of the ratio between the number of N and Cu dramatically increase the deposition rate of the films, and
atoms reaching the substrate and also of the kinetic energies high deposition rate may cause larger grain size and sharp
of these atoms. The preferred orientation transformed from grain boundaries.
Cu-rich orientation [111] to N-rich orientation [100] as N2 Difference in crystallite orientation and deposition rate of
partial pressure increased, which indicates that large amount adatoms is believed to be responsible for the great changes
of Cu and N atoms formed N-rich orientation at higher N2 in morphology. For the Cu3 N films prepared at N2 flow
partial pressure. rate of 10 sccm, the crystallite orientation [100] is much
stronger, while other orientations are very weak. This fine
3.2. Morphology. Figure 3 shows the surface morphology of [100] preferred orientation caused nodular-like morphology
the Cu3 N films deposited at different N2 flow rates. It is as a result of isotropic growth. While at higher N2 flow rate
obvious that all the films are extremely smooth, compact, and the argon introduction the pyramid cone morphology
and uniform. It can be found that the N2 flow rates had appeared. This phenomenon can be attributed to the multi-
no significant influence on the grain size of the Cu3 N plicate crystallite orientation. In the deposition process, [111]
films; however, the grain shapes were influenced obviously. and [100] orientation had a competitive growth and thus
Pyramid cone structure was found in Cu3 N films and presented complicated pyramid cone morphology.
deposited at 50 sccm N2 flow rate (Figure 3(a)). Figure 3(b) is In order to understand more details of the grains, we use
also the pyramid cone morphology of Cu3 N film deposited atomic force microscopy images. Figure 5 shows the image of
at 30 sccm N2 flow rate. For the N2 flow rate of 10 sccm film deposited under N2 flow rate of 50 sccm. We can clearly
4 Indian Journal of Materials Science

1.5

(𝜇m)
1

1 𝜇m
0.5
(a)

0
0 0.5 1 1.5 2
(𝜇m)

0.00 116.02
(nm)
(a)
1 𝜇m
80
(nm)

(b)
0
Figure 4: The SEM image of Cu3 N film deposited under various N2
partial pressure 0.8 Pa; 0.6 Pa. 0.5

(𝜇m) 1.0
1.5 0
0.5
see that several small grains of size ∼50 nm agglomerated 1.5
1.0
together and formed a big grain boundary (grains as seen in (𝜇m)
SEM images). (b)
A typical cross-sectional micrograph is also shown in
Figure 6, where the formation of columnar grains perpen- Figure 5: The AFM image of Cu3 N film deposited under N2 flow
dicular to the substrate surface and a smooth film surface rate of 50 sccm.
morphology is clearly shown. It is known that the columnar
structure formed due to the high deposition rate and low
lateral adatoms mobility. The columnar boundary is due to evolution of the phase structure and decomposition temper-
an accumulation effect of the crystallographic flaws that are ature of the film deposited at mixed N2 and Ar atmosphere is
built into the thin films during deposition and then enriched unlike the film deposited at pure N2 atmosphere (Figure 8).
in the boundary. When the heating temperature at 150∘ C, the intensity of Cu3 N
(111) diffraction peaks increased and the intensity closed to
3.3. Thermal Stability. The Cu3 N films deposited at N2 that of (100). At 200∘ C heating temperature, the intensity
flow rate of 10 sccm and N2 partial pressure of 0.8 Pa were of (100) peaks is stronger than the (111) peaks. However,
annealed in vacuum (pressure = 3.0 × 10−3 Pa) for 1 h at at 250∘ C heating temperature, Cu peaks appeared without
a temperature ranging from 150∘ C to 300∘ C. Figures 7 and obvious Cu3 N peaks. This indicates that Cu3 N phase has been
8 show the XRD spectra of the heat treated Cu3 N films transformed into Cu phase completely through annealing
compared with as prepared films. For the film prepared at treatment at a temperature of 250∘ C. The color change of
pure nitrogen atmosphere (Figure 7), it is found that as the Cu3 N films also can provide information of phase transform.
heating temperature at 150∘ C, the intensity of Cu3 N (111) and The decomposition temperature of Cu3 N in our experiment
(200) diffraction peaks decreased and almost disappeared, is higher than Cu3 N annealing in vaccum as reported [5].
and when the heating temperature reached 200∘ C and 250∘ C, One possibility of this difference of decomposition tem-
the diffraction peaks did not show obviously changes. Further perature is the structure. The films prepared at pure nitrogen
increase the heating temperature to 300∘ C, the Cu (111) peaks atmosphere show a small particle size with a relative compact
appeared, which indicated that decomposition took place at texture, while the films prepared at mixed nitrogen and argon
the temperature ranges from 250∘ C to 300∘ C, lower than the atmosphere show a larger particle size with obvious large
decomposition temperature (about 360∘ C) [6]. However, the number of void boundaries with a looser texture. And the
Indian Journal of Materials Science 5

Cu (200)
Cu (111)
300∘ C

250∘ C

Cu3 N (100)

Cu3 N (111)
Intensity (a.u.)

Cu3 N (200)
1 𝜇m

200∘ C
Figure 6: The typical cross-sectional SEM image of Cu3 N film.

150∘ C

Sample

20 30 40 50 60 70 80
2𝜃 (deg)

Figure 8: The X-ray diffraction spectra of Cu3 N films prepared

with N2 and Ar mixture atmosphere annealing at different annealing
temperature.

significant influence on the grain size of the Cu3 N films

except the grain shapes. For a lower N2 flow rates, grains
on the surface appeared obviously as uniform nodular-like
morphology. While the high N2 flow rates and the addition
of the Ar, grains presented pyramid cone morphology due to
multiple growth orientations. The cross-sectional micrograph
of the film shows typical columnar, compact structure. The
decomposition temperature of the mixed argon and nitrogen
atmosphere is lower than the film prepared at pure nitrogen
atmosphere. The results show that the introducing of argon
Figure 7: The X-ray diffraction spectra of Cu3 N films prepared with in the sputtering process decreases the thermal stability
pure N2 atmosphere annealing at different annealing temperature. properties due to its looser texture.

References
decomposition process may begin at these void boundaries.
Finally, the film shows a lower decomposition temperature. [1] G. H. Yue, P. X. Yan, J. Z. Liu, M. X. Wang, M. Li, and X. M.
Yuan, “Copper nitride thin film prepared by reactive radio-fre-
quency magnetron sputtering,” Journal of Applied Physics, vol.
4. Conclusion 98, Article ID 103506, 2005.
[2] K. J. Kim, J. H. Kim, and J. H. Kang, “Structural and optical char-
Copper nitride (Cu3 N) thin films were deposited on glass acterization of Cu3 N films prepared by reactive RF magnetron
via DC reactive magnetron sputtering at various N2 flow sputtering,” Journal of Crystal Growth, vol. 222, no. 4, pp. 767–
rates and partial pressures with 150∘ C substrate temperature. 772, 2001.
X-ray diffraction measurements show that the films are [3] S. Terada, H. Tanaka, and K. Kubota, “Heteroepitaxial growth
composed of Cu3 N crystallites with anti-ReO3 structure. of Cu3 N thin films,” Journal of Crystal Growth, vol. 94, no. 2, pp.
The preferred growth orientation of the film turned from 567–568, 1989.
[111] to [100] as N2 flow rates decrease. And the preferred [4] J. F. Pierson, “Structure and properties of copper nitride films
orientation also transformed from orientation [111] to [100] formed by reactive magnetron sputtering,” Vacuum, vol. 66, no.
as N2 partial pressure increased. The N2 flow rates had no 1, pp. 59–64, 2002.
6 Indian Journal of Materials Science

[5] Z. Q. Liu, W. J. Wang, T. M. Wang, S. Chao, and S. K. Zheng,

“Thermal stability of copper nitride films prepared by rf
magnetron sputtering,” Thin Solid Films, vol. 325, no. 1-2, pp.
55–59, 1998.
[6] T. Nosaka, M. Yoshitake, A. Okamoto, S. Ogawa, and Y.
Nakayama, “Thermal decomposition of copper nitride thin
films and dots formation by electron beam writing,” Applied
Surface Science, vol. 169-170, pp. 358–361, 2001.
[7] J. Wang, J. T. Chen, X. M. Yuan, Z. G. Wu, B. B. Miao, and P.
X. Yan, “Copper nitride (Cu3 N) thin films deposited by RF
magnetron sputtering,” Journal of Crystal Growth, vol. 286, no.
2, pp. 407–412, 2006.
[8] L. Maya, “Deposition of crystalline binary nitride films of tin,
copper, and nickel by reactive sputtering,” Journal of Vacuum
Science and Technology A, vol. 11, p. 604, 1993.
[9] M. Asano, K. Umeda, and A. Tasaki, “Cu3 N thin film for a new
light recording media,” Japanese Journal of Applied Physics, vol.
29, pp. 1985–1986, 1990.
[10] G. Soto, J. A. Dı́az, and W. de la Cruz, “Copper nitride films
produced by reactive pulsed laser deposition,” Materials Letters,
vol. 57, no. 26–27, pp. 4130–4133, 2003.
[11] M. Sıcha, Z. Hubicka, L. Soukup, L. Jastrabık, M. Cada, and P.
Spatenka, “Low-pressure RF multi-plasma-jet system for depo-
sition of alloy and composite thin films,” Surface and Coatings
Technology, vol. 148, no. 2–3, pp. 199–205, 2001.
[12] T. Maruyama and T. Morishita, “Copper nitride thin films pre-
pared by radio-frequency reactive sputtering,” Journal of
Applied Physics, vol. 78, p. 4104, 1995.
[13] Z. Liu, X. Li, A. Zuo, Z. Yuan, J. Yang, and K. Yao, “Effect of N2 -
gas partial pressure on the structure and properties of copper
nitride films by DC reactive magnetron sputtering,” Plasma Sci-
ence and Technology, vol. 9, no. 2, article 147, 2007.
[14] K. Venkata Subba Reddy, A. Sivasankar Reddy, P. Sreedhara
Reddy, and S. Uthanna, “Copper nitride films deposited by dc
reactive magnetron sputtering,” Journal of Materials Science, vol.
18, no. 10, pp. 1003–1008, 2007.
[15] K. V. S. Reddy, T. K. Subramanyam, and S. Uthanna, “Nitro-
gen partial pressure influence on physical properties of DC
magnetron sputtered copper nitride films,” Optoelectronics and
Advanced Materials, vol. 1, pp. 31–35, 2007.
[16] Z. Ji, Y. Zhang, Y. Yuan, and C. Wang, “Reactive DC magnetron
deposition of copper nitride films for write-once optical record-
ing,” Materials Letters, vol. 60, no. 29–30, pp. 3758–3760, 2006.
[17] G. H. Yue, J. Z. Liu, M. Li, X. M. Yuan, P. X. Yan, and J. L. Liu,
“Hall effect of copper nitride thin films,” Physica Status Solidi
(a), vol. 202, no. 10, pp. 1987–1993, 2005.
[18] Z. G. Wu, W. W. Zhang, L. F. Bai, J. Wang, and P. X. Yan, “Pre-
paration and properties of nano-structure Cu3 N thin films,”
Acta Physica Sinica, vol. 54, pp. 1689–1692, 2005 (Chinese).
[19] Z. Han, J. Tian, Q. Lai, X. Yu, and G. Li, “Effect of N2 partial
pressure on the microstructure and mechanical properties of
magnetron sputtered CrN𝑥 films,” Surface and Coatings Tech-
nology, vol. 162, no. 2-3, pp. 189–193, 2003.
[20] J. Blucher and K. Bang, “Preparation of the metastable inter-
stitial copper nitride, Cu4 N, by d.c. plasma ion nitriding,”
Materials Science and Engineering A, vol. 117, pp. L1–L3, 1989.
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