Thermal sputtering

Figure 8.2 The sputtering process in SIMS (a) direct collision sputtering (b) collision cascade and (c) thermal sputtering. (Reproduced with kind permission of Springer Science and Business Media from R. Behrisch, Ed., Sputtering by Particle Bombardment I, Springer-Verlag Gmbh, Berlin. 1981 Springer Science.)...

Uses. The chemical inertness, thermal stability, low toxicity, and nonflammability of PFCs coupled with their unusual physical properties suggest many useflil applications. However, the high cost of raw materials and manufacture has limited commercial production to a few, small-volume products. Carbon tetrafluoride and hexafluoroethane are used for plasma, ion-beam, or sputter etching of semiconductor devices (17) (see loN implantation). Hexafluoroethane and octafluoropropane have some applications as dielectric gases, and perfluorocyclobutane is used in minor amounts as a dielectric fluid. Perfluoro-1,3-dimethyl cyclohexane is used as an inert, immersion coolant for electronic equipment, and perfluoro-2-methyldecatin is used for... 

To examine the soUd as it approaches equUibrium (atom energies of 0.025 eV) requires molecular dynamic simulations. Molecular dynamic (MD) simulations foUow the spatial and temporal evolution of atoms in a cascade as the atoms regain thermal equiUbrium in about 10 ps. By use of MD, one can foUow the physical and chemical effects that induence the final cascade state. Molecular dynamics have been used to study a variety of cascade phenomena. These include defect evolution, recombination dynamics, Hquid-like core effects, and final defect states. MD programs have also been used to model sputtering processes. 

Radiation Sources. Ordinarily, electron beams are produced from soHds in vacuo by thermal or field-assisted processes. Plasmas also serve as electron sources, but are more uniquely used as ion sources. Whereas ions can be produced by sputtering and field assisted processes in the absence of plasmas, most ion sources involve plasmas (75). 

Characteristic Evaporation Ion plating Sputtering Chemical vapor deposition Electro- dep 0 sitio n Thermal spraying... 

Dielectric Deposition Systems. The most common techniques used for dielectric deposition include chemical vapor deposition (CVD), sputtering, and spin-on films. In a CVD system thermal or plasma energy is used to decompose source molecules on the semiconductor surface (189). In plasma-enhanced CVD (PECVD), typical source gases include silane, SiH, and nitrous oxide, N2O, for deposition of siUcon nitride. The most common CVD films used are siUcon dioxide, siUcon nitride, and siUcon oxynitrides. 

At aU but the lowest bombarding energies, the flux of atoms that are sputtered from the surface leaves the surface with a cosine distribution (Fig. 6). The sputtered atoms have kinetic energies higher than those of thermally vaporized atoms, as well as a high energy tail in the energy distribution that can be several tens of eV. 

In the sputtering process, each surface atomic layer is removed consecutively. If there is no diffusion in the target, the composition of the vapor flux leaving the surface is the same as the composition of the bulk of the material being sputtered, even though the composition of the surface may be different from the bulk. This allows the sputter deposition of alloy compositions, which can not be thermally vaporized as the alloy because of the greatly differing vapor pressures of the alloy constituents. 

The simple d-c diode sputtering configuration has the advantage that (/) large areas can be sputtered rather uniformly over long periods of time (2) the target can be made conformal with the substrate (J) the target-to-substrate distance can be made smaU compared to thermal vaporization and (4) the... 

The origin of the sputtered atoms may result from displacement below the surface of the source, a so-called thermal spike, as well as dhectly from the surface, depending on the incident energy of tire bombarding ions, ,. This must reach a tlrreshold value, before any atoms are dislodged from the target and... 

Because the energy which is imparted to the target by ion bombardment is Anally transformed into thermal energy, the target plate is normally water-cooled in a sputtering apparatus. 

Vacuum Deposition-also vapor deposition or gas plating the deposition of metal coatings by means of precipitation (sometimes in vacuum) of metal vapor onto a treated surface. The vapor may be produced by thermal decomposition, cathode sputtering or evaporation of the molten metal in air or an inert gas. 

Platinum coatings may also be thermally sprayed or sputtered onto the titanium, to provide uniform well-bonded coatings. Titanium rod may also be spiral wound with platinum wire. However, the use of these techniques is limited. 

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