Ion Beam Deposition: Damage and Epitaxy
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ION BEAM DEPOSITION:
DAMAGE AND EPITAXY
D G ARMOUR Department of Electronic and Electrical Engineering and Centre for Thin Film and Surface Research, University of Salford, Salford M5 4WT, UK.
ABSTRACT The bombardment of solid surfaces with ions in the energy range below about 150 eV, depending on the ion-substrate combination, results in a net growth of material on the surface. An ion beam facility capable of producing highly uniform, low energy beams of current densities in the 2 range 10-2 to 1 Am. has been developed to study the potential of this growth technique for the fabrication of thin epitaxial films at low temperatures. The energy deposition associated with ion bombardment, which is considered to be responsible for the low temperature epitaxy capability, can also cause atomic displacements on the surface and near-surface regions of the substrate during initial growth and in the growing film. A study of the growth processes thus requires investigation of the damaging effects of low energy ion bombardment. In the present paper, fundamental aspects of the implantation and deposition of materials using very low energy ions will be discussed.
INTRODUCTION The interaction of very low energy ions with solid surfaces is of both scientific and technological interest. Low energy ion beams or ion bombardment in a plasma have the potential to enable very thin layers to be doped to high concentrations (1,2], to etch the surface with minimal damage and to lead to the growth of epitaxial layers at low temperatures [3,4,5. Effective use of the technique, however, requires that the equipment used must meet highly demanding specifications concerning the purity, uniformity and energy distribution of the beam and the quality of the vacuum environment in the target chamber. The availability of systems capable of meeting these specifications enables the full range of applications of low energy ion beams to be investigated and, by combining the bombardment system with an appropriate surface analytical system, the fundamental factors which affect ion collection and damage build-up can be evaluated. The experimental system used for the present experiments comprises an ultra-high vacuum implanter combined with a low and medium energy ion scattering facility. Bombarded surfaces can be transported directly between the chambers without removal from uhv. The system has been used to study ion implantation, radiation damage and film growth using energies in the 10 eV to 10 keV range with the region below 500 eV being of major interest. In the present paper, theoretical and experimental studies of 300 eV Sb implantation into Si will be described to illustrate the capabilities of low energy implantation to produce extremely highly doped, shallow layers. The need to provide atomically clean, flat surface for either implantation or film growth, requires the development of in-situ preparation methods. The role of low energy ion bombardment in this application and in the more general area of ion etching, has been investigated for a GaAs
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