Sputtering

Sputtering is nowadays a common technique for thin film growth of complex oxides [74,75]. In particular, it is the most used technique in the field of 

However, while the sputtering technique is not very commonly used to study interlace effects in ionically conducting multilayer heterostructures, there are mmierous examples of thin film deposition. Actually, sputtering was the primary technique used for thin film deposition in the SOFC field, such as for Zr02 [84] and Ce02-based films [85]. The conducting properties were interpreted in terms of substrate-induced space charge effects, strain, or microstructure. 

o superiattice close to the (113) reflection of the STO substrate showing diffuse satellites around the superiattice Bragg peaks due to the periodic domain structure. (Adapted with permission from Ref. [78]. Copyright 2012, American Chemical Society.) 

Because sputtering deposition covers the sloped wall of vias, this technique is also suitable for the metallization of vias patterned in a photosensitive dielectric, vias formed through laser ablation, and wet-etched vias in poly-imide. However, it is difficult to sputter a thick metal film, because stress in the deposited film leads to poor adhesion. The typical metal thickness is around 2 pm. Therefore, the vias are partially filled and a staircase or staggered via layout is normally used, which limits interconnect density. In addition, the interconnect lines have sloped sidewalls because both vertical and lateral etching occur in the wet-etching process. 

Direct-current (DC) sputtering is not generally applicable for the preparation of thin-film soUd electrolytes since these compounds are electronic insulators. The target surface would be charged with the same polarity as that of the ions in the plasma, and the sputtering plasma would rapidly break down. 

In the FIM the ions are generated at the surface from incident neutrals. In other ion-probe methods the incident beam is already ionized and three major features may be distinguished when it interacts with a surface sputtering and desorption, ion neutralization, and ion scattering. Detection of secondary ions forms the basis of secondary-ion mass spectrometry (SIMS) which is well established as a technique for surface analysis (see ref 208 for a previous review in this series) while ion-neutralization spectroscopy (INS) yields both structural and bonding information on surface species (see ref 209). 

Barber and J. C. Vickerman, in Surface and Defect Properties of Solids , Specialist Periodical Reports, ed. M. W. Roberts and J. M. Thomas, The Chemical Society, 1977, Vol. 5, p. 162. 

Ions impacting onto the cathode during a discharge cause secondary electrons and other charged and neutral species from the electrode material to be ejected. Some of these other particles derived 

4 Pulsed laser ablation deposition technique (PLAI) technique) 

Laser ablation of TiC targets was studied by De Maria et al. (1997). TiC films were realized on oriented [111] silicon. During ablation the chamber was kept under a dynamic vacuum (1.5 10 4 Pa) the laser fluence was varied in the range 0-15 J/cm2. Different ablation mechanisms, corresponding to different film characteristics, were observed related to the laser fluence values. At low fluence values (0-3 J/cm2), a film of composition TiC2 was obtained. Films obtained at 3-8 J/cm2 showed a composition close to TiC they had the best characteristics of composition, crystallinity and compactness. 

In Chap. 2.3 the dissipation of the energy of the primary events by a collision cascade was mentioned. If a primary collision takes place near the surface, a part of this cascade may be directed to the surface. This leads eventually to the ejection of surface atoms from the solid as shown in Fig. 11. 

In addition to these factors, the elemental composition of the target plays a role. Tantalum or similar metals as targets have sputtering yields of 1 atom/ion, whereas metals like Ag, Au and Cd may have values from 10 — 100 atoms/ion. 

The sputtering effect has a number of practical consequences for ion bombardment experiments. 

There exist a number of investigations dealing with surface topography as a result of sputtering which we cannot treat in detail. Generally speaking, one would expect a smoothing of the surface. In practice this is only true for planar isotropic material. In a number of cases a new structure is produced  

Summarizing, one may say that sputtering has important consequences for the bombarded material and the surrounding area. It is widely applied for polishing and surface cleaning as well as for coating and thin film production. Some of its chemical aspects will be treated in Chap. 5.1. 

The exponential barometric decline of abundances with increasing mass generates an enormous range of elemental fractionations at the exobase using Jakosky et al. s (1994) estimate of -0.4 km/K for Martian Az/T, N(Az)/Nh is approximately 3 x 10 for °Ne 

10 and 10 ° for Kr and Xe respectively. Sputtering loss of the two heaviest noble gases is consequently extremely small, and isotopic fractionation in the process has negligible influence on the composition of their total atmospheric inventories. 

The electrical conductivity of sputtered CdS films varied according preparation conditions between 10 to lO cm .  

The size of crystallites was between 0.1 to 0.3 ym and demands further recrystallization processes for successful application in solar cell fabrication. 

It is used because of its high mass, which creates a high momentum and more ejected particles from the target. 

There are several characteristics of the sputtering process that need to be considered before using this technique for film growth  

As with CVD and evaporation, there are various types of sputtering. The process we have described so far is DC sputtering, also called diode or cathodic sputtering. It is the easiest process to visualize, but cannot be used for insulating targets. There are two approaches for ceramics  

MgO Dielectric films for multilayer optical coatings 

Yttrium aluminum garnet (YAG), Magnetic bubble memory devices 

TABLE 3.1 Surface Binding Energies and Cohesive Energies of Various Elements Present on Their Elemental Substrates. 

Element Substrate Binding Energy (eV) Cohesive Energy (eV) 

The sputter yield defines the absolute number of atoms, ions, or molecules removed per impinging primary ion. As discussed in Section 3.2.2, this absolute value is differentiated from the analytical value to avoid confusion. The absolute definition is used throughout this text unless otherwise specified. 

The sputter rate defines the sample removal rate resulting from sputtering. This can vary from less than a monolayer during the entire analysis to many monolayers per analytical cycle, with the rate depending heavily on the type of the primary ions and the conditions used, as this defines the energy transferred. How the sputter rate is determined is covered in Section 5.3.1. 

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After a heat treatment of several hours the electrodes are deposited by sputtering a 50 nm base layer of Ni/Cr or NiAVi followed by 1.5 pm Au-layer generated by galvanization. 

Ions are also used to initiate secondary ion mass spectrometry (SIMS) [ ], as described in section BI.25.3. In SIMS, the ions sputtered from the surface are measured with a mass spectrometer. SIMS provides an accurate measure of the surface composition with extremely good sensitivity. SIMS can be collected in the static mode in which the surface is only minimally disrupted, or in the dynamic mode in which material is removed so that the composition can be detemiined as a fiinction of depth below the surface. SIMS has also been used along with a shadow and blocking cone analysis as a probe of surface structure [70]. 

Figure Bl.17.8. Iron oxide particles coated with 4 nm of Pt in an m-planar magnetron sputter coater (Hennann and Mtiller 1991). Micrographs were taken in a Hitachi S-900 in-lens field emission SEM at 30,000 primary magnification and an acceleration voltage of 30 kV. Image width is 2163 nm.

The fonnation of clusters in the gas phase involves condensation of the vapour of the constituents, with the exception of the electrospray source [6], where ion-solvent clusters are produced directly from a liquid solution. For rare gas or molecular clusters, supersonic beams are used to initiate cluster fonnation. For nonvolatile materials, the vapours can be produced in one of several ways including laser vaporization, thennal evaporation and sputtering. 

The deposition of amoriDhous hydrogenated silicon (a-Si H) from a silane plasma doped witli diborane (B2 Hg) or phosphine (PH ) to produce p-type or n-type silicon is important in tlie semiconductor industry. The plasma process produces films witli a much lower defect density in comparison witli deposition by sputtering or evaporation. 

Harper J M E, Cuomo J J and Kaufman H R 1982 Technology and applications of broad-beam ion sources used in sputtering. Part II. Applications J. Vac. Sc/. Technol. 21 737-56... 

Barish E L, Vitkavage D J and Mayer T M 1985 Sputtering of chlorinated silicon surfaces studied by secondary ion mass spectrometry and ion scattering spectroscopy J. AppL Phys. 57 1336-42... 

Sigmund P 1969 Theory of sputtering. I. Sputtering yield of amorphous and polycrystalline targets Phys. Rev. 184 383-416... 

Thompson M W II 1968 The energy spectrum of e]ected atoms during the high energy sputtering of gold Phil. Mag. 18 377-414... 

Feil H, Dieleman J and Garrison B 1993 Chemical sputtering of Si related to roughness formation of a Cl-passivated Si surface J. Appi. Phys. 74 1303-9... 

Barone M E and Graves D B 1995 Chemical and physical sputtering of fluorinated silicon J. Appi. Phys. 77 1263-74... 

Back-sputtering Backswept turbine Backus process BaC12... 

Ion-beam lithography Ion beam mixing Ion beam processing Ion beams Ion-beam sputtering Ion channels Ion chromatogram Ion chromatography... 

Sputtered Co-Cr films Sputtered hard disks Sputtering... 

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