Sputtering technique

Diode sputtering the simplest but requires an electrically conductive target it has low energy efficiency and electron bombardment may cause significant damage of the substrate. 

Radio-Frequency (RF) sputtering, using frequencies above 50 kHz, can sputter insulators but the process has low deposition rates. 

Triode sputteringxxsQS an additional cathode to sustain the plasma but is more complicated and may cause contamination of the deposit. 

In ion-plating deposition, the substrate and the deposited film (as it forms) are subj ected to bombardment by particles (ions, atoms, molecules) which alter the formation process and the properties of the coating.The process is also calltd ion-beam assisted deposition (TOAD). 

Two basic versions of the process plasma-based ion plating and vacuum-based ion plating. The coating material is vaporized in a manner similar to evaporation. Typically, the plasma is obtained by biasing the substrate to a high negative potential (5 kV) at low pressure. The constant ion bombardment of the substrate sputters off some of the surface atoms which results in improved adhesion and reduced impurities. Surface coverage of discontinuities is also improved. 

A number of variations have been introduced to improve the efficiency of the deposition process. Instead of a dc potential, a radio-frequency voltage can be used to maintain the plasma ( rf-sputtering ). Deposition rates may be increased by adding a focusing system or magnetron. Another improvement makes use of a separate anode to produce the plasma and to preserve the quality of the target. This system is known as a triode. 

Magnetite thin films have also been prepared by reactive sputtering (Ortiz et al, 1988). Fe was used as the target and the substrate was Si single crystals with (100) orientation, with O2 as the reactive gas. Polycrystalline films of magnetite were obtained with a thickness of 1000 A. The films obtained were further oxidised to y-Fc203 in a conventional furnace at 275-300 °C. 

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Aluminum, the most common material used for contacts, is easy to use, has low resistivity, and reduces surface Si02 to form interfacial metal-oxide bonds that promote adhesion to the substrate. However, as designs reach submicrometer dimensions, aluminum, Al, has been found to be a poor choice for metallization of contacts and via holes. Al has relatively poor step coverage, which is nonuniform layer thickness when deposited over right-angled geometric features. This leads to keyhole void formation when spaces between features are smaller than 0.7 p.m. New collimated sputtering techniques can extend the lower limit of Al use to 0.5-p.m appHcations. 

Fig. 3. Schematic configuration of (a) the 90° off-axis sputtering technique and (b) the system used to prepare multilayers.

Sample roughness also can produce problems in the interpretation of RBS spectra that are similar to problems encountered by sputtering techniques like AES,... 

Abstract The principles of coatings to either enhance reflectivity of mirrors or to enhance transmission of glass optics are described. Then the ion assisted deposition and ion beam sputtering techniques are addressed. Performances of these technique-sand their limitations are illustrated with the characteristics of the VIRGO mirrors coated at LMA. The importance of metrology is emphasized. 

We now describe the current techniques of deposition. A coating process involves several parameters. There is the nature of the substrate a crystal or an amorphous material, the quality of its polishing and its temperature. There are also the characteristics of the source, as temperature and emission law, and those of the medium in between, as its pressure and composition. In evaporation process the energy of particles is 0.1 eV, or 1100 K their impact velocity is in the range of m.s . With sputtering techniques, the energy lies in between 10-50 eV and the impact velocity is in the range of km.s . ... 

Work has also been conducted that involved the investigation, via infrared spectroscopy, of matrix-isolated, plutonium oxides (40), with the appropriate precautions being taken because of the toxicity of plutonium and its compounds. A sputtering technique was used to vaporize the metal. The IR spectra of PuO and PUO2 in both Ar and Kr matrices were identified, with the observed frequencies for the latter (794.25 and 786.80 cm", respectively) assigned to the stretchingmode of Pu 02. Normal-coordinate analysis of the PUO2 isotopomers, Pu 02, Pu 02, and Pu 0 0 in Ar showed that the molecule is linear. The PuO molecule was observed in multiple sites in Ar matrices, but not in Kr, with Pu 0 at 822.28 cm" in the most stable, Ar site, and at 817.27 cm" in Kr. No evidence for PuOa was observed. 

The Fe-N /Ti-N nano-multilayers were prepared by using the magnetron-sputtering technique [34]. Si (111) wafers are used as the substrate. The multilayers have a total thickness of about 500 nm with alternately Fe-N and Ti-N layers (shown in Fig. 38). The Fe-N layer was the outermost layer and the Ti-N layer was the iimermost layer. The thickness of each layer was strictly controlled by the sputtering time. Table 4 shows the thickness of each layer of the samples. Because the multilayer sample was supposed to be used as the magnetic write head, the thickness of the nonferromagnetic Ti-N layer was not changed. 

For comparison, a 20wt% Pt/XC72 catalysts prepared commercially by E-TEK had an average diameter of 2.6 nm. The sputter deposited Pt had a standard deviation between 0.42 and 0.49 nm, whereas the commercial E-TEK catalyst has a standard deviation of 0.79 nm. Thus, the sputtering technique creates smaller and more uniformly dispersed Pt particles than those prepared chemically. It should be noted that the Pt/C samples having low loadings prepared via sputtering did not uniformly coat... 

The magnetron sputtering technique can prepare supported metal nanoparticles on a wide variety of support materials including WO3 and carbon. 

The sputtering technique has been used in the preparation of SOFC electrodes, and is generally combined with photolithography in the production of thin-lilm patterned electrodes that are mainly used in fundamental reactivity and mechanistic studies [120], Although it is a versatile technique that allows for excellent control of composition and morphology, and relatively low temperatures that help to prevent unwanted reactivity observed at higher temperatures, its major limitations lie in the equipment costs and in the slow deposition rates ( 5 pm/h) [120],... 

One technique which has produced thin, but not epitaxial films of BaPbj.xBixOg, and which shows good promise is the use of laser evaporation methods (40). Since the compound is efficiently transported stoichiometrically from the target to the substrate at a high rate and does not require a vacuum, this method may be superior to sputtering techniques. 

The electrical (ohmic) contacts on the sNPS surface were made from aluminum by magnetron sputtering technique. It was found previously that the electrical contacts made from indium were unstable due to its mechanical softness. Their integrity was destroyed during measurements because of the porous surface underneath the contacts. In our investigations Al contacts with the thickness of about 3 pm were formed. 

The various methods of preparation employed to prepare nanoscale clusters include evaporation in inert-gas atmosphere, laser pyrolysis, sputtering techniques, mechanical grinding, plasma techniques and chemical methods (Hadjipanyas Siegel, 1994). In Table 3.5, we list typical materials prepared by inert-gas evaporation, sputtering and chemical methods. Nanoparticles of oxide materials can be prepared by the oxidation of fine metal particles, by spray techniques, by precipitation methods (involving the adjustment of reaction conditions, pH etc) or by the sol-gel method. Nanomaterials based on carbon nanotubes (see Chapter 1) have been prepared. For example, nanorods of metal carbides can be made by the reaction of volatile oxides or halides with the nanotubes (Dai et al., 1995). 

In many cases, particularly with evaporation and sputtering methods, adhesion of the deposited film to the substrate may be inherently poor. It is extremely desirable in such cases to deposit a thin layer of an intermediate material that has better adhesion to the substrate. Examples of appropriate adhesion layers are discussed after presentation of evaporation and sputtering techniques. 

Synthesis of niobates and tantalates of alkaline metals at high temperatures may result in the products with unintended stoichiometry because of high volatility of alkaline metal (especially lithium) oxides. Therefore, their synthesis in the form of efficiently sintering powders presents a serious problem. Films of alkaline niobates and tantalates can find wide range of applications in acousto- and optoelectronics and are usually prepared by rf-sputtering techniques, also giving rise to stoichiometry problems. 

The rapid development of solid state physics and technology during the last fifteen years has resulted in intensive studies of the application of plasma to thin film preparation and crystal growth The subjects included the use of the well known sputtering technique, chemical vapour deposition ( CVD ) of the solid in the plasma, as well as the direct oxidation and nitridation of solid surfaces by the plasma. The latter process, called plasma anodization 10, has found application in the preparation of thin oxide films of metals and semiconductors. One interesting use of this technique is the fabrication of complementary MOS devices11. Thin films of oxides, nitrides and organic polymers can also be prepared by plasma CVD. 

Fig. 11.3 (a) An rf-magnetron sputter technique with automated target... 

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