Thin Solid Films 443 (2003) 115–119
Deposition of permalloy films by filtered cathodic vacuum arc
J.S. Chen1, S.P. Lau*, Y.B. Zhang, Z. Sun, B.K. Tay, C.Q. Sun
Ion Beam Processing Laboratory, School of Electrical and Electronic Engineering, Nanyang Avenue, Nanyang Technological University,
Singapore 639798, Singapore
Received 11 February 2003; received in revised form 14 May 2003; accepted 16 July 2003
Abstract
The filtered cathodic vacuum arc technique was employed to deposit magnetic films such as FeNi on silicon substrate. Using
the normal cathode design, tetrahedral amorphous carbon and metals films can be deposited. If a magnetic target is used, the arc
spot always preferably moves to the edge of the target and then extinguishes. Therefore, the arc is not stable and no film can be
deposited. A cathode was designed to obtain stable and continuous arc and uniform erosion pattern. The atomic force microscopy,
grazing X-ray diffraction and vibrating sample magnetometry were used to characterize the morphological, structural and magnetic
properties of the FeNi film. When the film deposited at substrate bias of y100 V, it exhibits a square magnetization–hysteresis
loop, the lowest coercivity and the highest saturated magnetization among all the investigated samples, which may be related to
its good surface roughness and crystallinity.
䊚 2003 Elsevier B.V. All rights reserved.
Keywords: Permalloy; Filtered cathodic vacuum arc; Magnetic properties
1. Introduction
For many years there has been considerable interest
in producing films of magnetic materials because of
their many exclusive applications such as magnetic
recording, microactuation and sensors and so on. Many
techniques have been employed to synthesize the magnetic films with varying amounts of success, which
include evaporation, sputtering, pulsed laser deposition,
and molecular beam epitaxy w1–3x. Among them, the
evaporation and sputtering are predominant in industrial
application because of their economy and simplicity.
But the need for new, high performance materials in
magnetic recording entails the development of a new
deposition technology for magnetic films. It is well
known that cathodic vacuum arc technology has proven
to be a very promising method for ultrathin film deposition. It offers several advantages over evaporation and
*Corresponding author. Present address: Data Storage Institute, 5
Engineering Drive 1, NUS, Singapore 117608, Singapore. Tel.: q6567906439; fax: q65-67933318.
E-mail addresses: esplau@ntu.edu.sg (S.P. Lau),
chen_jingsheng@dsi.a-star.edu.sg (S.P. Lau).
1
Present address: Data Storage Institute, 5 Engineering Drive 1,
NUS, Singapore 117608.
sputtering, and the principal advantages are the high
percentage of ions in the emitted flux (approx. 100%),
high kinetic energy of these ions (20–200 eV) w4,5x. In
the present time, it has been in wide-scale industrial use
for producing wear protective coatings of TiN and
related materials on cutting and forming tools, as well
as decorative coatings on plumbing fixture and jewelry.
Adding a magnetized torus macroparticle filter the highly tetrahedrcally bonded amorphous carbon films can be
synthesized with high deposition rate (5 nmys) at room
temperature w6x. The filtered cathodic vacuum arc
(FCVA) technique has also been used for depositing
optical thin films of metal oxides (TiO2 and Al2O3) and
semiconducting thin films (amorphous Si and SnO2)
w7–9x. To our knowledge, however, no paper has been
reported on the deposition of magnetic films by FCVA
technique yet. In this paper, the FCVA technique was
used to deposit FeNi films on Si substrate. A modified
cathode design for depositing magnetic films was
presented.
2. Movement of cathode arc spot and cathode design
The typical FCVA system has been described elsewhere w10x. Generally, a conductive target mounted on
0040-6090/03/$ - see front matter 䊚 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0040-6090(03)01031-9
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J.S. Chen et al. / Thin Solid Films 443 (2003) 115–119
Fig. 1. The schematic diagrams of cathode (a) original and (b) modified design.
water-cooled copper block was used as a cathode as
shown in Fig. 1a. A tube-shaped stainless steel around
the outer of cathode was used as a shield to avoid
straying arcing and the space between them was approximately 2–3 mm. The cathodic arc is triggered with a
graphite electrode touching the cathode surface at an
initial background pressure of approximately 10y6 Torr
and the cathode is continuously water-cooled from the
back. The plasma beam produced by the cathode spots
passes through an off-plane double-bend macroparticles
filter into the deposition chamber w11x. This type of
filter bend has many advantages over the single bend,
for example, higher ion density, higher plasma transport
efficiency and significant reduction of macroparticles.
The anode is grounded and the shield and the bend are
under floating potential. The substrate can be biased up
to negative 400 V.
In such a cathode design, the arc spot on the surface
of magnetic materials moves away from the center to
the edge of the cathode after igniting the arc in the
center, and then the arc either sustains for a short time
(mostly less than a minute) or extinguishes immediately.
This is quite different from that of the Ti and Cu as a
cathode target. The behavior of the arc spot on the
surface of magnetic targets does not change even if the
filtering coils are not energized. It is well known that
the cathode spots apparently move randomly over the
cathode surface (Ti, Cu, Al, etc.) in the absence of a
magnetic field, but in the presence of a magnetic field
they have a direct velocity in the yJ=B direction, a
phenomenon known as ‘retrograde’ motion. At present,
most investigations on vacuum arc spot dynamics were
mainly focused on high current vacuum arc because of
its application for commercial vacuum circuit breakers.
Siemorth et al. have shown that the cathode spot at high
current should be considered as a multilevel organized
self-similar structure w11x. Sherman et al. w12x have
investigated the influence of self-generated magnetic
field on cathode arc spots movement for copper electrode at high current vacuum arc (2.7–6.9 kA), namely,
the influence of the magnetic field generated by other
vacuum arc spots on a vacuum arc. According to the
experimental results they derived a relationship between
the retrograde spot velocity (V) and magnetic flux
density (B), namely VsKØB, where K is the coefficient
depending on the cathode materials and is independent
of B. It has been generally believed that the arc current
self-generated magnetic field is a major factor that
governs the dynamics of arc spot in high-current vacuum
arc. However, it is believed that there is only a single
cathode spot with 10 mm in diameter in the low current
vacuum arc (approx. 100 A) w13x. For the arc spots on
the Ti and Cu cathodes there is no or little external
force imposed on them, so it moves randomly around
the surface of the cathode. The behavior of arc spot on
magnetic materials can be interpreted as follows: the
vacuum current is considered as a wire with current
flowing. According to Ampere’s law, vacuum arc current
generates an azimuthal magnetic field that can induce
magnetization of magnetic materials and then produce a
magnetic field. The magnetic field produced is due to
the magnetization of magnetic materials, which imposes
on the arc spot once it moves and makes a retrograde
motion, namely, the cathode arc spot moves outside in
the radial direction. In order to obtain continuous and
stable arc on magnetic materials and uniform erosion of
the target, it is necessary to re-design the configuration
of the cathode.
The cathode configuration designed for deposition of
magnetic materials is schematically shown in Fig. 1b.
A cylinder made of a soft magnetic material such as
pure Fe surrounds the magnetic target. A boron nitride
(BN) ceramic ring was placed on top of the magnetic
target. The design was mainly based on the following
principles: when a BN ring is placed on a magnetic
material, the arc spot moves randomly within the ring
and the target erosion is uniform. The BN ring is used
to confine the motion of arc spot within the ring. BN
ceramic has a low surface energy for most metals and
low emission efficiency of secondary electrons, which
can prevent the arc spot from moving on the surface of
the BN ring and reduce the deposition of the target
material on the surface of the BN ring. Using this new
cathode design, a stable and continuous arc can be
J.S. Chen et al. / Thin Solid Films 443 (2003) 115–119
117
Fig. 3. The surface roughness of the FeNi films as a function of
substrate bias.
Fig. 2. AFM images of FeNi films deposited at (a) y100 V and (b)
y400 V.
function of bias conditions. The rms roughness decreases
from floating condition (0 V) to y100 V, and then
increases as the bias increases from y100 to y400 V.
The XRD spectra of the films deposited at various
biases are shown in Fig. 4a. For the sample prepared at
floating condition, the FeNi(111) and (200) peaks are
observed. When a bias of y100 V is applied, the
intensity of FeNi(111) and (200) peaks increases. By
further increasing the substrate bias, the intensity of
obtained and the erosion pattern is uniform for magnetic
target.
3. FeNi films deposition and properties
In this work, permalloy Fe0.2Ni0.8 films were deposited on Si (100) substrate at room temperature using the
new cathode design and the arc current was set to 100
A. The toroidal magnetic field was fixed at 40 mT. The
substrate was negatively biased from y100 to y400 V
with respect to the ground (anode). The deposition rate
was approximately 0.1 nmys. The surface morphology
and roughness of the films were examined using atomic
force microscope (AFM, Digital Instruments) in tapping
mode. The value of root-mean-square (rms) surface
roughness was evaluated in the area of 2=2 mm. The
crystallographic structure of films was determined by
Rigaku grazing X-ray diffractometer (GXRD) with Cu
˚ at 50 kV and
Ka1 excitation (wavelength of 1.5406 A)
20 mA. The angle between the incident X-ray and the
surface of the films was fixed at 0.58 and the diffraction
pattern was obtained by changing the position of the
counter with a step of 0.058. Magnetic properties were
measured at room temperature by Lakeshore vibrating
sample magnetometer (VSM, Model 7300).
The typical AFM images of the films deposited with
the substrate bias of y100 and y400 V are shown in
Fig. 2. All of the images show island-like features. Fig.
3 shows the root mean square (rms) roughness as a
Fig. 4. (a) XRD spectra and (b) FWHM of peak (111) of FeNi films
deposited at various substrate bias.
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J.S. Chen et al. / Thin Solid Films 443 (2003) 115–119
FeNi(111) and (200) peaks decreases. Fig. 4b presents
the variation of the full width at half maximum
(FWHM) of peak (111) with the substrate biases. The
FWHM as a function of the substrate bias has a trend
similar to the roughness. With a bias of y100 V, the
FWHM reaches its minimum, reflecting the optimal
crystalline quality of the films. One of the most important factors affecting the morphology and structure of
the films is the lateral mobility of the adatoms on the
substrate. With a bias of y100 V, most of the ions
energy is changed into the lateral energy after bombardment on the substrate and adatoms mobility increases.
So the film at the bias of y100 V shows smoother
morphology and better crystallinity than that of the
sample under floating condition. Although lateral ion
energy also increases with further increase of the bias,
the ion energy along normal component is increased
more, which causes the increase of the roughness.
The magnetization–hysteresis (M–H) loops of FeNi
films with various substrate biases are shown in Fig. 5.
The films deposited at lower substrate bias (0 and
y100 V) have the expected square M–H loops while
the films deposited at higher substrate bias have poor
M–H loops with two distinctive slopes before saturation.
It has been recognized that the smaller slope before
saturation is due to a perpendicular anisotropy component normal to the plane of the film w14–16x. The
mechanisms for producing perpendicular anisotropy
include the following: (1) magnetocrystalline anisotropy—if the FeNi films is (100) textured, the film’s
normal is the easy axis in the absence of shape aniso-
Fig. 6. The saturated magnetization 4pMS and coercivity Hc of the
FeNi films as a function of substrate bias.
tropy; (2) microshape anisotropy—the columnar structure of the magnetic grains separated by a non-magnetic
phase or voids can produce a microshape anisotropy
along the column axis; (3) magnetoelastic anisotropy—
when the film is under a compressive stress, the magnetoelastic energy favors the magnetization orientated
out of the plane of the film. Further investigation is
currently under way to determine which kind of anisotropies play the dominant role.
The saturated magnetization 4pMS and coercivity Hc
as a function of substrate bias are shown in Fig. 6.
When the bias is y100 V, the film shows the lowest
coercivity and the largest saturated magnetization. The
X-ray photoelectron spectroscopy (XPS) results (not
shown) indicate that the composition of the films of
permalloy, fcc-FexNi1yx, where x ranging from 0.19 to
0.21, is nearly independent on the substrate bias. Thus
the changes in saturated magnetization and coercivity
Fig. 5. M–H loops of FeNi films deposited at various substrate bias, (a) 0; (b) y100 V; (c) y200 V; (d) y400 V.
J.S. Chen et al. / Thin Solid Films 443 (2003) 115–119
with bias are not induced by the slight variation of
composition. The film with good soft magnetic properties has the lowest surface roughness and better crystallinity, which are consistent with Fe films deposited by
dual ion beam sputtering w17x.
4. Conclusions
In summary, magnetic Fe0.2Ni0.8 films have been
successfully deposited on silicon substrate using the
modified cathode design. A stable and continuous arc
with uniform target erosion can be obtained. When the
substrate bias is y100 V, the film exhibits the lowest
coercivity and highest saturated magnetization among
all the investigated conditions, which may be related to
its good surface roughness and crystallinity.
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