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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 micro- and 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 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 aqueous-alcoholic 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 nano-sized 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.
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, nanoparticle-reinforced 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 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 high-temperature 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.
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).