New Deposition Technique for Nanocomposite Thin Film Growth at Ambient Temperatures

A.A. Bizyukov1, A.Y. Kashaba1, K.N. Sereda1, N.N. Yunakov1 and
E.V. Romaschenko2
1 Kharkiv National University, 31 Kurchatov Ave., 61108, Kharkiv, Ukraine
2 East-Ukrainian National University, 1 Vatutin Str., Lugansk, Ukraine
Abstract. The novel deposition process combining the ion beam sputtering and pulsed rf plasma CVD deposition is
proposed to prepare a new class of hard and chemically stable coatings consisting of nanocrystalline metal nitride phases
in a soft or crystalline diamond-like carbon phase matrix. In pursuit of this aim, we investigated simultaneous operation
of the Hall-type ion beam sputter system and pulse modulated rf plasma reactor in one deposition process and have
obtained encouraging results on deposition of metal nitrides and diamond-like carbon films onto temperature-sensitive
materials.
Keywords: ion beam sputtering, pulsed RF discharge, CVD deposition, nanocomposite thin film, metal nitride, diamonlike
carbon.
PACS: 81.07.Bc, 52.77-j, 52.80 Pi, 81.07-b, 81.15 Cd
INTRODUCTION
Nanocomposite coatings represent a new class of films, which are, in simplest case, composed of two
material phases concentrated in very small atomic domain dimensions below 100 nm, typically about 10 nm and
smaller. The main problem in formation of nanocomposite coatings is to stop the grain growth. There are several
methods to prevent the growth of grains in the alloy films: i) an addition of rare-earth (RE) elements into different
pure metals; ii) an addition of nitrogen into the film resulting in the formation of nanocrystalline nitride-alloy films;
and iii) selective reactive sputtering on a substrate heated up to 500 °C when one metal is converted into a nitride
while the second does not react [1].
Following the above requirements, we propose to combine ion beam sputtering with surface heating and CVD
deposition in pulse modulated RF discharge for preparation of nanocomposite coatings onto various materials,
including temperature-sensitive ones. It is expected that combining all these methods in one deposition process it
will be possible to prepare a new class of hard coatings consisting of nanocrystalline metal nitride phases in a soft or
crystalline phase matrix (a-SiNx, c-MSix, DLC) which will exhibit unique physical–chemical properties with a high
toughness.
EXPERIMENTAL
Since some years ago we are being concerned with development of ion beam sputtering system (IBSS) for
deposition of Si, SiO2, W and diamond-like carbon films (see. FIG. 1) [2].
The IBSS is a gas-discharge system with closed electron drift in crossed magnetic and electrical fields based on
an one stage Hall-type ion source. The cathode block of the IBSS serves as the basis of the accelerator, magnetic
circuit and cathode of the discharge gap. The magnetic field solenoid and system of working gas inlet are installed in
the cathode block. The solenoid provides creation of radial magnetic field in a ring aperture of the Hall accelerator.
The longitudinal electric field is created between the anode and cathode of the accelerator when accelerating voltage
is supplied to the anode. The beam of gas ions generated in the modified Hall source is guided to the surface of the
sputtered target at the glancing angle. The angle of incidence of the incoming beam can be adjusted from 30° to 80°
by moving the target and changing the magnetic intensity that in combination with adjustment of accelerating and The source allows one to sputter efficiently as conductive materials with low sputtering rate, such as graphite,
and dielectric materials due to utilization of self-compensation effect of the ion beam without use of neutralizers [3].
The deposition rate in the IBSS is controlled by changing energy, current and angle of incidence of ions bombarding
a sputtered target that is of particular interest with use the system at low deposition rates at low pressure. The
amount and energy of ions and secondary electrons from the sputtered target in the transport space of sputtered
atoms can be controlled by change of a bias voltage applied to the sputtered target. It allows to produce additional
ion, ion-electron or electron bombardment of deposited coatings.
The source was successfully used for deposition of various metal and insulating thin films (C, Ni, Cr, Ti, Co, W,
Cu, Al, Si, SiO2, DLC, etc). Deposition rate depends on target material, ion current to sputtered target, ion energy,
process pressure, distance between the sputtered target and substrate. For instance, the deposition rate of SiO2 films
can exceed 1 nm/s, diamond-like films up to 0.5 nm/s, W films up to 0.3 nm/s, Cu up to 2 nm/s.
The IBSS system provides many advantages over conventional sputtering systems, in particular:
• highly uniform target utilization;
• ability to sputter ferromagnetic materials efficiently;
• deposition of dielectric materials using ion-beam sputtering or reactive ion-beam sputtering;
• excellent control of deposition rates while maintaining film quality;
• low deposition rate work without the need for long-throw sputtering, in which the target is placed up to a
metre away from the substrate;
• low pressure sputter deposition down to 3×10-5 Torr.
Typical applications:
• deposition of metals including noble metals: Au, Pt…;
• ion-beam and reactive ion-beam sputtering deposition of diffusion barriers TiN, TiW, resistor films NiCr,
TaN, ceramics as Al2O3, nitrides, carbides etc.;
• reactive deposition of multilayer films: TiO2, SiO2;
• deposition of DLC films by reactive ion-beam sputtering from graphite target;
• decorative chromium coatings on plastics;
• deposition of highly conductive and highly insulating films;
• deposition of multilayered structures made of ferromagnetic materials for sensing applications;
• multilevel metallization;
• manufacturing waveguides for dense wavelength-division multiplexing (DWDM) (low rate deposition);
• production of hard drives and read-write heads;
• deposition of semiconductors, alloys and composite materials and high-temperature superconductors.
Recently we have been studying behavior of surface temperature of treated substrate at pulse modulated radiofrequency
(13.56 MHz) plasma processing. The calculation procedure of the dynamics and distribution of
temperature deep into near-surface layer of the material at pulsed vacuum – plasma processing at low-pressure in a
wide range of on-off time ratio of pulses and values of pulsed power for cooled and non-cooled samples was
developed [4]. Some interesting results for 1 μm SiO2 film for two values of on-off ratio are presented in FIG. 2 and
bias voltages allows

One can see that at small values of the on-off time ratio the average temperature of the surface and volume grows
linearly in time, however, the pulsed surface temperature can essentially exceed the temperature of the volume. At
large on-off time ratios at the intervals between the pulses, full cooling of the surface up to initial temperature due to
radiation and interaction of the surface with neutral gas occurs. At the same time, the temperature of the volume is
established at some constant level which considerably lower than the pulsed temperature of the surface. This
calculation procedure was used at development of plasma technology of deposition of SiO2, Si3N4 and diamond-like
carbon films onto temperature-sensitive small-sized samples in the pulse modulated rf discharge.
In the range of specific rf power density in a pulse of 0.5÷10 W/cm2 applied to the surface samples, the
theoretical and experimentally defined processing regimes are found to be in good agreement. For instance, for
efficient processing of temperature-sensitive small-sized samples like needles at specific rf-power density in a pulse
of 5 W/cm2 the pulse duration of rf-voltage applied to the samples should be in the range of 0.5÷1.5 μs at the
repetition rate of 10÷50 Hz. In this case the calculated pulsed surface temperature is in the range of 200÷400 ºC,
however, the bulk temperature does not exceed 50 °C at the exposure time of 30 min.
The proposed deposition method was successfully applied for plasma-enhanced CVD deposition of SiO2 films
using mixture of hexamethyldisiloxane (HMDSO) with oxygen onto small-sized (5×5×2 mm) semiconductor
detectors on the basis of CdTe and CdZnTe compounds. The interest to application of these detectors in different
devices for detection, X-ray and gamma ray spectroscopy has increased recently. The process was carried out
according to the reaction:
2 2 2 2
230 250
Si2O(CH3 )6 8O2 2SiO H O 6CO 8H o oC + − → ↓ + + +
The rf power was pulse modulated with a repetition rate of 30 Hz, pulse length of 1 μs and specific rf-power
density in a pulse of 5 W/cm2. The film was 5 μm and the deposition rate was 8÷10 nm/min.. In planar detectors
made of the CdZnTe on lateral surfaces the electric intensity can reach several kilovolts on centimeter. Therefore,
the surface current which depend on quality of surface processing can give the basic contribution to a dark current of
the detector. The dielectric coating were deposited to decrease surface component of the dark current and increase
stability of the characteristics of the CdZnTe detectors. Such processing is very important for high-resistance
materials, in which the contribution of surface dark currents to a total dark current can be appreciable and even
determining (as for the CdZnTe).
Comparison of dark currents of the detectors was carried out before and after deposition of the coating and also
with unprocessed reference sample. The important decrease (up to 100 times) of dark currents and, accordingly,
increase of resistance of the detector from initial resistance of 1010 Ω to 6×1011 Ω were observed. The CdZnTe
detectors after passivation have a dark current of ~1 nA at room temperature at field intensity of ~ 3000 V/cm.
Besides, the detectors with the coating have enhanced temporal stability.
At present, we attempt to combine the early developed technologies of ion beam sputtering and pulse modulated
RF plasma enhanced CVD deposition in one deposition process. The aim of this work is to develop novel deposition
process for preparation of a new class of hard nanocomposite coatings consisting of nanocrystalline nitride phases in
a soft or crystalline matrix which will exhibit unique physical–chemical properties, e.g. superior hardness,
magnetoresistance, chemical stability, low friction and wear-resistance along with a high toughness onto
temperature-sensitive materials. In pursuit of this aim, now, we investigate simultaneous operation of the IBSS and
pulse modulated RF plasma discharge in one vacuum chamber and have obtained some encouraging results on
deposition of metal nitrides and diamond-like carbon films with utilization of the IBSS.
OUTLOOK FOR FUTURE RESEARCH
In the nearest future our objectives are: i) Study an effect of the addition of the rare-earth elements into different
pure metals and addition of nitrogen on the growth of grains in alloy films. ii) Quantify the effect of the pulsing
waveforms, fast electron generation and bulk and surface heating on the arriving energy and flux of the ionic and
sputtered neutral species. iii) Define equivalent metrics for the pulse modulated rf discharge and sputtering system
that describe the interrelationships between material properties and ion-assisted parameters, and to express these
relationships in a universally applicable form. iv) Exploit the results by engineering 1) advanced materials;
specifically coatings with increased hardness and durability, reduced defect density, and enhanced adhesion and
tribological properties; and 2) advanced processes; specifically the design of the deposition system for a) energetic
deposition onto glass substrates, and b) low power deposition onto polymeric substrates.
The applications of the proposed technology can be the following: advanced hard and protective coatings; optical
coatings ranging from displays, ophthalmics, flexible transparent substrates for liquid crystal based devices to
DWDM telecommunication filters; development of nanostructured materials; mutilayer optics; high-density data
storage media making use of the major magnetoresistive properties of nano-scale granular magnetic materials.
REFERENCES
1 J. Musil, J. Vlcek, Surf. Coat. Technol. 112, 162-170 (1999).
2 A.A. Bizyukov, A.E.Kashaba, K.N.Sereda, Problems of Atomic Sci. Technol. 9, 144-148 (2003).
3 A.A. Bizyukov, A.E. Kashaba, K.N. Sereda, A.Ph. Tseluyko, Tech. Phys. Lett. 23, 403-408 (1997).
4 A.E. Kashaba, K.N. Sereda, E.V. Romaschenko, Proc.11th Conf. Vac. Sci. Eng., Sudak, Ukraine, 2004, pp. 176-179.

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