1.deposition of tantalum nitride thin films by d.c. magnetron sputtering
TRANSCRIPT
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Thin Solid Films 475
Deposition of tantalum nitride thin films by D.C. magnetron sputtering
S.K. Kim*, B.C. Cha
School of Materials Science and Engineering, University of Ulsan, Ulsan 680-749, South Korea
Available online 28 September 2004
Abstract
Thin films of tantalum nitride (TaN) were deposited on SKD11 tool steel substrate by a D.C. magnetron sputtering system. The influence
of the N2/Ar gas ratio of the inlet gases on the structure, hardness, adhesion and wear resistance was investigated. The X-ray diffraction data
showed that TaN deposited at low N2/Ar gas ratio, tetragonal h-Ta(330) and hexagonal TaN(101) were observed. Orthorhombic TaN(110)
and orthorhombic Ta3N5 were formed with the increase of the N2/Ar gas ratio. High hardness of the films was observed at the low N2/Ar gas
ratio. The films deposited at N2/Ar gas ratio of 0.3 showed good adhesion, wear resistance and hardness of Hv0.05 1450. The films deposited
with etching time of 30 min at 133.32 Pa gave good adhesion. Thickness of the films decreased with applying the bias voltage. As the bias
potential was increased, the hardness of the film increased and then decreased. The films with fine dome structure showed good wear
resistance.
D 2004 Elsevier B.V. All rights reserved.
Keywords: TaN; D.C. magnetron sputtering; Wear resistance; Adhesion
1. Introduction
Transition metal nitrides are well known for their
remarkable physical properties including high hardness
and mechanical strength, chemical inertness, and high
temperature stability. They are widely studied and have
become technologically important for applications such as
wear resistant coatings [1], protective coatings with func-
tional optical properties [2] or for specific metallization
properties in microelectronics [3].
Tantalum nitride (TaN) thin films are attractive for use as
structural elements in integrated circuits. Most of the works
on TaN have been done on their application in thin film
resistors and diffusion barriers [4,5]. Very little work has
been done on their application in hard wear resistant
coatings. In this work, we report the effects of the N2/Ar
gas ratio of inlet gases, the etching pressure and time and
bias voltage on the structural and mechanical properties of
magnetron-sputtered TaN thin films.
0040-6090/$ - see front matter D 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.tsf.2004.08.059
* Corresponding author. Tel.: +82 522592228; fax: +82 522591688.
E-mail address: [email protected] (S.K. Kim).
2. Experimental procedures
The TaN films were produced in an unbalanced D.C.
magnetron sputtering equipment. A circular sputter source
(2005) 202–207
Fig. 1. X-ray diffractograms of TaN films deposited with various N2/Ar
gas ratios of inlet gases ((a) N2/Ar=0.1, (b) N2/Ar=0.2, (c) N2/Ar=0.3, (d)
N2/Ar=0.4).
Fig. 2. Hardness of TaN films deposited at various N2/Ar gas ratio.
Fig. 3. Optical micrographs of scratch tracks of TaN films deposited at various N2/
Fig. 4. Optical micrographs of wear tracks of TaN films obtained at various N2/A
S.K. Kim, B.C. Cha / Thin Solid Films 475 (2005) 202–207 203
was fixed to the lid of the chamber. A tantalum target (99.98%
pure) of diameter 76.2mmwas attached to the sputter source.
A sample holder, which can rotate and enabled bias
voltage, was located at the center of the chamber. Substrate
to target distance was 55 mm. After the chamber was
evacuated to 1.3�10�4 Pa using a rotary pump and a
diffusion pump, argon was introduced to maintain working
pressure. The SKD11 steel (1.5% C, 11.5% Cr, 0.8% Mo,
0.9% V) specimens were polished and degreased ultrasoni-
cally in alcohol. Before deposition, the specimens were
plasma etched for 10 to 60 min with 370 V, 600 mA at the
pressure of 133.32 Pa.
To determine the effect of nitrogen partial pressure, the
N2/Ar gas ratio of inlet gases was varied from 0.1 to 0.4.
Target power was fixed to 200 W. Before the deposition
of the TaN, an interlayer of tantalum was deposited at 0.8
Ar gas ratios ((a) N2/Ar=0.1, (b) N2/Ar=0.2, (c) N2/Ar=0.3, (d) N2/Ar=0.4).
r gas ratios ((a) N2/Ar=0.1, (b) N2/Ar=0.2, (c) N2/Ar=0.3, (d) N2/Ar=0.4).
Fig. 5. Micrographs of etched surface morphology of the substrate at various pressure ((a) 37.33 Pa, (b) 68 Pa, (c) 133.32 Pa).
S.K. Kim, B.C. Cha / Thin Solid Films 475 (2005) 202–207204
Pa for 20 min. Then TaN layer was deposited at the same
pressure for 60 min. X-ray diffractometer (Rigaku, RAD-
3C) was used to determine the phases of the films. Field
emission scanning electron microscope (JSM-650F) was
used to observe the surface morphology of the films. The
hardness of films was measured by a Vicker’s hardness
tester using a 50-g load. Adhesion was evaluated by a
scratch tester (Revetest, CSEM). When wear resistance
was measured by a ball-on-disc type wear tester, the test
condition was a 3-N load, 121 rev./min, 60–65% relative
humidity. Test duration was up to 1000 cycle. Bearing
steel ball which contained 10% Cr was used as a
counterpart. Wear track was examined by an optical
microscope.
Fig. 6. Optical micrographs of scratch tracks of TaN films deposited with v
3. Results and discussion
X-ray diffractograms of TaN films deposited using
various N2/Ar gas ratio of inlet gases are shown in Fig. 1
The other deposition parameters kept constant were the
deposition pressure of 0.53 Pa and the target power of 220
W. At low N2/Ar gas ratio, tetragonal h-Ta(330) [JCPDS 25-
1280] and hexagonal TaN(101) [JCPDS 39-1485] were
observed. With the increase of the N2/Ar gas ratio, hexagonal
TaN(110) [JCPDS 39-1485] and orthorhombic Ta3N5
[JCPDS 19-1291] were formed. At the N2/Ar gas ratio of
4, Ta3N5 phase was only present. Fig. 2 shows the hardness
of TaN films deposited at various N2/Ar gas ratios. High
hardness was observed at the N2/Ar gas ratio of 0.1 and 0.2
arious etching time ((a) 20 min, (b) 30 min, (c) 40 min, (d) 60 min).
Fig. 7. The hardness of the TaN films deposited at various bias potentials.
Fig. 8. SEM micrographs of the surface morphology of TaN films deposited at vario
S.K. Kim, B.C. Cha / Thin Solid Films 475 (2005) 202–207 205
although the data fluctuated significantly. At the N2/Ar gas
ratio of 0.3, hardness values did not fluctuate much and were
very stable. The hardness of the films decreased significantly
at the N2/Ar gas ratio of 0.4, this was due to the decrease
of the deposition rate and the formation of Ta3N5 phase.
Fig. 3 shows scratch tracks of thin films deposited at
various N2/Ar gas ratio. The films deposited at N2/Ar gas
ratio of 0.3 showed good adhesion whereas the films
deposited at other gas ratios cracked due to the residual
stress developed within the films. Wear tracks of TaN
films obtained at various N2/Ar gas ratios are shown in
Fig. 4. The films deposited at N2/Ar gas ratio of 0.3
showed best wear resistance. Although the films obtained
at N2/Ar gas ratio of 0.1 exhibited good wear resistance,
the films easily cracked with small shock due to high
residual stress. Fig. 5 shows SEM micrographs of etched
us bias voltage ((a) 0 V, (b) 50 V, (c) 100 V, (d) 150 V, (e) 200 V, (f) 300 V).
S.K. Kim, B.C. Cha / Thin Solid Films 475 (2005) 202–207206
surface morphology of the substrate at various pressure.
The pressure of 133.32 Pa produced very rough surface.
The surface was etched very densely at the pressure of
37.33 Pa. The surface was relatively smooth at the
pressure of 68 Pa. We cannot explain why such a smooth
surface was obtained at this intermediate pressure. This
increase in the etch rate with pressure is mainly due to the
increase in the concentration of neutrals with increasing
pressure. The scratch tracks of the TaN films deposited
with various etching time at 133.32 Pa with N2/Ar gas
ratio of 0.3 are shown in Fig. 6. TaN films deposited with
etching time of 30 and 40 min gave good adhesion
whereas 20- and 40-min etching time showed bad
adhesion. Short etching time did not produce rough
surface and prolonged etching time also made the surface
smooth which resulted in bad adhesion. Effect of the bias
voltage on the thickness and structure of the TaN films
was studied. The thickness of the film deposited without
Fig. 9. Optical micrographs of wear track of TaN films obtained at various
bias voltage was 4.5 Am. Thickness of the films deposited
with 50-, 100-, 150-, 200- and 300-V bias voltage were 2.5,
2.5, 2.5, 2.0 and 2.8 Am, respectively. Thickness of the films
decreased with applying the bias voltage. The increase of the
bias voltage did not affect the thickness of the film
significantly.
Fig. 7 shows the hardness of the TaN films deposited at
various substrate bias potentials. As the bias potential was
increased, the hardness of the film increased and then
decreased. SEM micrographs of the surface morphology of
each film are shown in Fig. 8. At low bias potentials, coarse
dome structures were developed. Fine dome structures were
observed with the increase of the bias voltage. Further
increase of the bias potential to �300 V collapsed the dome
structure which resulted in low hardness of the film. Similar
trend in the development of dome structures in the films
deposited with the increase of the bias voltage was also
observed previously at the NbN films deposited by D.C.
bias voltage ((a) 50 V, (b) 100 V, (c) 150 V, (d) 200 V, (e) 300 V).
S.K. Kim, B.C. Cha / Thin Solid Films 475 (2005) 202–207 207
magnetron sputtering [6]. Fig. 9 shows wear tracks of
TaN films deposited at various bias voltage. TaN films
with fine dome structures (Fig. 8d) exhibited good wear
resistance.
4. Conclusion
TaN thin films were deposited by D.C. magnetron
sputtering method. There was transition from a mixture of
h-Ta(330) and hexagonal TaN(101) to a mixture of
orthorhombic TaN(110) and orthorhombic Ta3N5 and
further to orthorhombic Ta3N5 with the increase of the
nitrogen partial pressure of the inlet gas. The hardness of
the film decreased significantly at high nitrogen gas ratio of
the inlet gas. The films deposited at N2/Ar gas ratio of 0.3
showed good adhesion and wear resistance. The pressure of
133.32 Pa and etching time of 30 and 40 min gave good
adhesion of the films. The thickness of the films decreased
with applying the bias voltage. The increase of the bias
voltage did not affect the thickness of the films signifi-
cantly. The films with fine dome structures exhibited good
wear resistance.
Acknowledgment
This research was supported by the 2004 University of
Ulsan Research Fund.
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