The handbook deals with the general area of ion beam processing of materials: for basic sputter etching of samples, for sputter deposition of thin films, for the synthesis of materials in thin film form, and the modification of properties of thin films. The range of ion energies considered is from a few eV to about 10 keV, with the primary interest in the range of 20 eV to 1-2 keV, where implantation of the incident ion is a minor effect. This book principally examines broad beam ion sources, characterized by high fluxes and large work areas, including ECR ion sources, the Kaufman-type single and multiple-grid sources, gridless sources such as Hall effect or closed-drift sources, and hybrid sources such as ionized cluster beam (ICB) systems. Not discussed in this book are the type of ion sources typically used for surface analysis experiments, high energy ion implantation, or fusion-plasma heating.The use of ion beams for materials processing (in contrast to the directly extracting ions from a plasma to bombard a sample), has numerous advantages for the controlled processing of materials. Various parameters of the ion beam, such as, the flux, the energy, the species and charge state, and the direction (and divergence) are all easily quantified and controlled. The type of ion beams of interest in this book operates in the pressure range of 10~5 to 10" 3 torr, which makes them compatible with a number of other chemical and physical processes used in thin film materials processing. Ion beam processing is characterized by a high average energy (for the sputtered atoms), compared to plasma-based film deposition. This high energy results in improved film properties and increased film-substrate adhesion. The low pressure operation of these sources results in a line-of-sight film deposition due to low levels of gas scattering. The charge neutralization of the Kaufman-type ion sources permits the sputtering of insulating , or electrically isolated targets without charging. In addition, the problem of negative ion formation encountered in plasma based sputter deposition of some alloys and compounds is not encountered due to the lack of a significant electric field at the target surface.
The technology of broad-beam ion sources used in sputtering applications is reviewed. The most frequently used discharge chambers are described, together with procedures for predicting performance. A new, compact ion source is described. Ion acceleration is reviewed, with particular emphasis on recent low-energy techniques. Some of these techniques include three-grid, small-hole two-grid, and one-grid ion optics. A new material for fabrication of high-precision ion optics is silicon. Because no stresses are introduced with the etching techniques used, the finished grid can be held to very close tolerances. A recent innovation for sputtering applications is the use of Hall-current acceleration. This technique uses a magnetic field interacting with an electron current to provide the accelerating electric field, thereby avoiding the usual space-charge limit on ion current density that is associated with gridded optics. Electron emission is also reviewed, with new hollow cathodes promising improved lifetimes. The overall picture is one of greatly improved ion source capability, with particularly large improvements in low-energy ion current densities.
Based on air annealing studies at 1500°C, it appears that bulk and surface mechanical damage in sapphire and normalMgAl spinel false(MgAl2O4false) may be greatly minimized. Such annealed surfaces can then be effectively polished chemically leaving essentially featureless surfaces. Preannealed sapphire orientations can be polished at 285°C in a 1:1 H2SO4:H3PO4 mixture for 15 min while normalMgAl spinel orientations may be treated in a 3:1 H2SO4:H3PO4 mixture at 250°C for the same length of time. (111) normalMgAl spinel and false(10true1¯4false) sapphire cannot be chemically polished by the procedures described but are presumably amenable to removal of most surface and mechanical saw and polish induced bulk damage via the high‐temperature annealing process.
The developments in broad-beam ion source technology described in the companion paper (Part I) have stimulated a rapid expansion in applications to materials processing. These applications are reviewed here, beginning with a summary of sputtering mechanisms. Next, etching applications are described, including microfabrication and reactive ion beam etching. The developing area of surface layer applications is summarized, and related to the existing fields of oxidation and implantation. Next, deposition applications are reviewed, including ion-beam sputter deposition and the emerging technique of ion-assisted vapor deposition. Many of these applications have been stimulated by the development of high current ion sources operating in the energy range of tens of hundreds of eV. It is in this energy range that ion-activated chemical etching is efficient, self-limiting compound layers can be grown, and the physical properties of vapor-deposited films can be modified. In each of these areas, broad ion beam technology provides a link between other large area plasma processes and surface analytical techniques using ion beams.
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