Nanotechnology for Fabrication of Film Elements, Powder-Like and Bulk
Materials Using Electroless Deposition and Surface Modification
T. N. Khoperia, T.I. Zedginidze, L.G. Maisuradze and N.T. Khoperia
Andronikashvili Institute of Physics, Georgian Academy of Sciences
6 Tamarashvili St.,Tbilisi GE-380077, Georgia
Fax: 995 (32) 53 6937
Abstract
The proposed nanotechnology for the first time allows fabrication of photomasks
and microdevices with nano-sized adjacent elements of different thickness made of
various materials by single conventional optical photolithography. These advantages
significantly extend functional capabilities of the device and simplify removal of
undesirable gases and heat dissipation. These nanotechnologies are promising for
production of unique photomasks with semitransparent nano-sized elements;
nanodevices; templates for fabrication of nanowires; microelectrodes for local microand nano- electrodeposition and etching techniques, etc. There are also proposed the
methods of fabricating the ultra-thin void-free and pore-free electroless coatings and
clusters on micro-, meso- and nano-sized particles. These methods allow us to obtain
nanostructured composite materials and coatings with the specified catalytic activity,
conductive nano-sized additives to plastics and rubber, nanoparticle-reinforced tires,
novel sensors, detectors of chemical and biological agents, adsorbents, hydrogen storage
materials, etc.
The method for fabrication of nanocavities, nano-sized holes in silicon photonic
crystals by conventional optical photolithography is under development.
Key words: Nanotechnology; Electroless deposition; Microelectronics; Piezoegineering;
Composites.
Introduction
One of the objectives of the work was fabrication of nano-sized films having
specified properties of various bulk materials and powder-like particles. One more
objectives was development of the methods of fabrication both continuous ultra-thin
pore-free coatings and clusters with specified properties on various nano-, meso- and
microparticles.
The proposed nanotechnologies using of electroless deposition are much more
advantageous and simpler than other expensive and complicated methods of
nanotechnologies.
For achieve theses purposes we proposed combination of novel approaches of
surface modification and electroless deposition with CMP techniques [1-3].
It was shown that electroless deposition of Ni-P and Ni-B alloys on various
materials can be successfully used in production of devices in piezoengineering,
microelectronics, electrotechnics, instrument – making, etc. [1-14]. The developed
electroless methods of metallization are widely used in industry [1-9].
Results and Discussion
For development of the optimum technology, we improved the entire cycle of
the metallization process: the preliminary treatment of various substrates (sensitization
and activation), the composition of solutions and the parameters of electroless
deposition, the parameters of heat treatment after deposition, the conditions of
photolithography, the selective etching processes, etc.[1-9].
It is shown that existence of the adsorbed tin ions on the glass provides both a
greater number of palladium ions on the glass and a greater strength of bonding of
2
palladium to the surface. The experimental results show that application of the
sensitization becomes less essential in case of electroless metal plating of non-metallic
materials with greater surface roughness. With the increase in the substrate roughness
(ground surface), the surface concentration of the adsorbed Sn and Pd ions increases [2,
3, 5, 6].
The conditions of activation such as pH of palladium chloride solution
concentration, temperature, and surface roughness determine whether the sensitization
is necessary or not [2 - 6]. The sensitization reduces the induction period of the nickel
deposition reaction, promotes complete coverage of the surface and improves the
coating quality.
There was established the mechanism of sensitization and activation, involving
the concept of an equilibrium shift towards formation of complex palladium anions and
predominance of the number of palladium ions over tin ions on the surfaces [2 – 6].
It was established that a part of the palladium ions, not reduced by sensitization
activation:
Sn(II)+Pd(II)=Sn(IV) + Pd,
(1)
can be partially reduced at subsequent interaction with hypophosphite in the solution of
electroless deposition according to the reaction:
PdCl42-+ H2PO2-+H2O=Pd+ H2PO3- + 2H + + 4Cl -
(2)
The results of investigation showed for the first time that, when the aqueousalcoholic solution is used as a solvent for tin chloride at the sensitization, at subsequent
activation, the amount of adsorbed palladium ions increases in comparison with
application of the aqueous solvent for tin chloride [4, 6]. That can be referred to the fact
that addition of the organic compound to the water changes the solvent configuration
and the solvation degree of the dissolved substances.
New Nanotechnology on the Basis of Single Conventional Optical Photolithography
The proposed nanotechnology for the first time allows one to produce nanosized adjacent elements of different thickness made of various materials (particularly of
Si) by single conventional optical UV photolithography (Fig. 1). These advantages
significantly extend functional capabilities of the devices and simplify removal of
undesirable gases and heat dissipation.
The proposed nanomethods are much more advantageous and simpler than other
expensive and complicated methods such as e-beam and X-ray lithography or
production of devices with nano-sized elements by a light phase shift photomasks [1, 2,
8]. The proposed method allows us to eliminate surface treatment by e-beam. It can save
about $4 000 000 (the price of e-beam exposure equipment). It also eliminates
application of X-ray masks with gold masking elements.
The developed nanotechnology is promising for production of nanodevices;
nanowires; microelectrodes for new local micro- and nano- electrodeposition and
etching techniques (Fig.2); press molds with nano-sized pillars for nanoimprint
lithography (NIL); quartz masks for laser-assisted direct imprint (LADI) of
nanostructures in silicon (a single excimer laser pulse melts a thin top surface layer of
silicon and the mask is pressed into the molten layer); tips of nanowidth for various
applications, etc.
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Preparation and Electroless Metallization of Nano-Sized Particles, Composites
Fabrication
The developed methods of fabricating the ultra-thin void-free and pore-free
electroless coatings and clusters on micro-, meso- and nano-sized particles (carbides,
borides, nitrides, oxides, diamond, graphite, zeolites, etc.). These methods allow us to
obtain nanostructured composite materials, coatings and clusters with the specified
catalytic activity, conductive nano-sized additives to plastics and rubber, nanoparticlereinforced tires, novel sensors, detectors of chemical and biological agents, unique
catalysts, adsorbents, hydrogen storage materials, etc. [1].
The method allows us to vary the electrical, optical, magnetic, mechanical properties
and melting points of the coatings in the wide range.
The great importance of deposition of void-free and pore-free films on powder-like
particles by the proposed method is emphasized also by the fact that the theoretical
strength of metals exceeds the strength obtained in practice 100 or even 1000 times. The
incorporation of metallized powder-like particles into metals, alloys, ceramics or
plastics can significantly increase their strength, microhardness, tribological properties,
wear resistance, temperature and radiation stability, and provide dry lubrication. This
point is very important for powder metallurgy; for increasing the toughness of metals,
(having high or low electrical resistance and melting points), ceramics and other
dielectrics; ecology (in the case of obtaining high-quality adsorbents); civil nuclear
techniques (at obtaining getters for ultra-high vacuum); electric-vacuum devices;
composites fabrication; power electronics; microelectronics; photonics; machine
building, etc.
The developed methods which allow us to substitute palladium chloride with
inexpensive non-precious substances for activation of non-metallic powder-like
particles and bulk dielectrics prior electroless metallization.
A gram of the powder-like particles having the 1 μm diameter contains 1012 particles
and their total surface area is 150 m2. The metallized micro-, meso- and nano-sized
particles having the specified catalytic activity and very large specific surface area can
be used for capturing toxic gases, cleaning the environment. The abovementioned
specified properties of metallized nano-sized particles provide great possibilities of their
application in a biomedical field, in medical practice, etc.
The proposed methods of obtaining nano-sized metallic particles with large surface
areas (Ag, Pd, Pt, Au, Cu and their alloys) and metallized nano-sized particles can be
used for reduction of the thermal boundary resistance between liquid helium and solids
(Kapitza resistance).
A method of local electroless deposition of metals on fine- grained photoelectrodes
(TiO2, CdS, InTaO4, etc.) for highly efficient splitting of water into hydrogen and
oxygen using solar energy is being developed. The proposed electroless method of local
deposition of catalyst metals (chemical metal-ion implantation) on nano-, meso- and
micro-sized photoelectrodes is very important for enhancing significantly their
photocatalytic activity in conversion of solar energy into electrical energy. Application
of such local coverage and doped photoelectrodes with a large surface area is promising
for improvement of the quantum efficiency of decomposition of toxic pollutants into
much less toxic forms using solar energy or a Xe arc lamp. The proposed method will
be promising to overcome the problem of the solar energy application - simultaneous
proceeding of oxidation and reduction reactions at the same sites of photoelectrodes,
and recombination of the photoexcited electron and its accompanying electron vacancy
(charge separation of a photogenerated electron-hole pair).
A method of production of novel Me-YSZ anodes for SOFCs are under
development. The proposed methods of deposition of metals and alloys with a higher
catalytic activity (for anodic oxidation of methane, hydrogen and carbon monoxide) and
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suitable electric properties allow one to overcome the major problems of available
SOFCs and cermet anodes such as 1) catalytic cracking of hydrocarbon reaction and
rapid deactivation due to carbon deposition on the Ni cermet anode; 2) prevention of
coagulation of particles; 3) weakening the adsorption forces of CO and so preventing
the retard of further adsorption and oxidation of methane; 4) increasing the maximum
power density due to the decrease in the anodic overvoltage of the fuel; 5) decreasing
the working temperature in fuel cells.
A cost-effective method for fabrication of metallized cermet membranes (on the
basis powder-like ZrO2) for hydrogen separation from mixed gases was developed.
Piezoengineering
A new method of production of precise piezoelectric quartz resonators and filters,
and monolithic piezoquartz filters with electrodes made of electroless Ni-P and Ni-B
alloys for spacecraft, hydroacoustics and communication devices was developed. As a
result of usage of the developed technology Au, Ag and Pd were adequately replaced by
non-precious metal alloys; a time for production of devices was reduced by a factor of
15 and labor intensity of the technology was reduced significantly; frequency stability
of piezoquartz devices was increased 1.8 times; an absolute value of dynamic resistance
of piezoquartz resonators became 30 % lower and scattering of the resistance became
about 40-50 % lower as compared to the resonators with silver-plated piezoelements [1,
2, 5-9]. Several tens million items were produced.
A technology of production of piezoceramic devices by electroless deposition of
electrode layers made of Ni-P or Ni-B for hydroacoustic equipment of submarines and
ships, delay lines of color TV sets (several hundred million items were produced), etc.
was developed [1, 2, 5, 6, 9,]. As a result of usage of the developed technology, the time
for production of the devices was reduced by a factor of 100 as compared to hightemperature fusing of silver-containing paste, and Ag was adequately replaced with
non-noble metals.
Photonics
The method for fabrication of nanocavities, nano-sized holes in (two-dimensional)
silicon photonic crystals (for application in photonic chips, nonlinear optics, ultra-small
filters, quantum information processing, etc.) by conventional optical photolithography
is under development.
A new Ductility Tester
A new device for precise determination of ductility by bending was designed
Fig.3). The developed ductility tester makes possible: to observe appearance of the
cracks and their propagation during bending, from start to finish, with the help of the
microscope; to photograph the shape of cracks, their density and geometry; to measure
the crack length and width, and to detect the moment of formation of a continuous crack
grid; to observe in-situ the cracks initiation, their growth and propagation rate at
different rates of specimen deformation. The abovementioned advantages allow
overcoming some problems related to cracking in micromechanics and flip chip
technology. The proposed tester is used in aerospace techniques and microelectronics.
The working drawings of the tester can be presented on request.
Conclusion
1. The mechanism of sensitization and activation of non-metallic materials have
been established involving the concept that a part of the palladium ions, not reduced by
sensitization-activation can be partially reduced at subsequent interaction with
hypophosphite in the solution of electroless deposition.
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2. A new nanotechnology for production of photomasks and microdevices with
nano-sized adjacent elements of different thickness made of various materials on the
basis of single conventional optical photolithography was developed for the first time.
These advantages significantly extend functional capabilities of the devices and simplify
removal of undesirable gases and heat dissipation.
3. The developed methods of fabricating the ultra-thin void-free and pore-free
electroless coatings and clusters on micro-, meso- and nano-sized particles (carbides,
borides, nitrides, oxides, diamond, graphite, zeolites, etc.).
4. As a result of usage of the developed technology Au, Ag and Pd were adequately
replaced with non-precious metal alloys; a time for production of devices was reduced
by a factor of 10 - 100 and labor intensity of the technology was reduced significantly;
frequency stability of piezoquartz devices was increased 1.8 times and an absolute value
of dynamic resistance of piezoquartz resonators became 30 % lower as compared to the
resonators with silver-plated piezoelements.
Acknowledgements
Thanks to the International Science and Technology Center for support.
References
1. Khoperia T.N., Electroless Deposition in Nanotechnology and ULSI, Microelectronic
Engineering, 69, Issues 2-4, September 2003, pp. 384-390 (2003).
2. Khoperia T.N., Electroless Metallization of Non-Metallic Materials and Ductility of
Ni-P Coatings, Proceedings of the International Conference Micro Materials, Berlin,
pp.771-787 (2000).
3. Khoperia T.N., Investigation of the Mechanism and Kinetics of Activation for
Electroless Plating and Competitive Submicron and LIGA Technologies, in
Fundamental Aspects of Electrochemical Deposition and Dissolution Including
Modeling, PV 99-33, The Electrochemical Society Proceedings Series, Pennington, NJ,
pp.251-262 (2000).
4. Khoperia T.N., Investigation of the Substrate Activation Mechanism and Electroless
Ni-P Coating Ductility and Adhesion, Microelectronic Engineering, 69, Issues 2-4,
September 2003, pp. 391-398 (2003).
5. Khoperia T.N., Tabatadze T.J. and Zedginidze T.I., Formation of Microcircuits in
Microelectronics by Electroless Deposition, Electrochimica Acta, 42 pp.3049-3055
(1997).
6. Khoperia T.N., Electroless Nickel Plating of Non-Metallic Materials (in Russian), p.
144, Metallurgia, Monograph, ed. K.M. Gorbunova, Moscow (1982).
7. Khoperia T.N., Investigation of Metal film Adhesion to Dielectrics and Production of
3-D Microdevices by Electroless Deposition, in Fundamental Aspects of
Electrochemical Deposition and Dissolution Including Modeling, PV 99-33, The
Electrochemical Society Proceedings Series, Pennington, NJ, pp.147-155 (2000).
8. Khoperia T. N., Electroless Deposition of Ni-P Alloy in Electronics, in Thin Film
Transistor Technologies, PV 2000-31, The Electrochemical Society Proceedings Series,
Pennington, NJ, pp.182-197 (2001).
9. Khoperia T.N., Physical and Chemical Bases of Substitution of Gold and Silver
Coatings by Non-noble Metals and New Technology for Micro- and Submicron
Miniaturization (in Russian), Georgian Academy of Sciences, Chemistry and Chemical
Technology, Proceedings, Metsniereba, Tbilisi, Georgia, pp.210-233 (2001).
10. Mallory G.O. and Hajdu J.B., Editors, Electroless Plating: Fundamentals and
Applications, AESFS, Orlando, Florida, EL (1990).
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Society of Electrochemistry Meeting, Kyoto, Japan (1989).
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Pellerin J., in Electrochemically Deposited Thin Films, M. Paunovic and D. A.
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(2000).
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4
3
3
5
3
5
4
1
1
1
2
(a)
2
(b)
Fig.1. Photomask with nano-sized semitransparent elements of different thickness
fabricated by single conventional optical photolitography:
(a) intermediate sample; (b) final product.
1- transparent substrate;
2- semitransparent masking elements of the first group;
3- boundary layers of the masking elements of the first group;
4- semitransparent masking elements of the second group;
5- nano-sized transparent sections.
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3
5
4
1
-+
2
Fig.2. Microelectrode for local micro- and nano- electrodeposition and etching
techniques:
1-substrate;
2- non-conducting elements of the first group;
3- conducting elements of the second group;
4- nano-sized sections;
5- electrolyte.
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Fig.3. The new device for determination of the ductility by bending (constructed by T. Khoperia)
1–wedge-shaped support; 2–pressure shafts; 3–arrows showing the bending of the specimen; 4–
scale calibrated in degrees; 5–flywheel by rotating of which the lowering of the pressure shafts
and bending of the specimen are provided from the opposite sides of the wedge-shaped support;
6–microscope; 7–the specimen under testing; 8–spring; 9–rod for pressure shafts; 10–support of
spherical shape.