Analysis and design of ion-beam deposition apparatus
In order to establish an upper limit on the practicality and usefulness of ion-beam deposition of thin films, an experimental beam-deposition system was assembled which was capable of producing an ideally focused ion beam. The system was designed under the assumptions that the final beam diameter is limited by the thermal velocity spread of the ions and the spherical aberration of the final lens of the optical column. Theoretically, this apparatus is capable of producing a 0.01-cm-diam 6×10-8-A indium ion beam at 100-eV energy. Under these conditions, the predicted deposition sweep velocity would be 0.016 cm/min to produce a 2×10-6-cm-thick indium film. Chromatic aberration was the factor that limited the actual measured spot diameter to 0.075 cm for a beam current of 10-8 A and ion energy of 100 eV. Indium films were deposited in this apparatus with ion energies ranging from 100 to 500 eV (total dose of 7×1017 atom/cm2). Interferometric measurements indicated that these films retained, to some extent, the shapes of the ion distributions across the beam. Sputtering, however, inhibited the complete vertical growth of the deposits. Measurements of the sputtering yield indicated that unity sputtering yield occured at an ion energy of 550 eV, as compared with the predicted energy of 200 eV. © 1971 The American Institute of Physics.
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