Partially ionized beam deposition of oriented films
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M. Madden Intel Corporation, Santa Clara, California 95051 (Received 21 July 1988; accepted 1 November 1988)
The microstructure of Al films deposited on SiO2 using the partially ionized beam (PIB) deposition technique is studied. It is shown that by employing less than 1% ions (ion-to-atom ratio) derived from the evaporated material and about 1-2 kV bias voltage at the substrate during deposition, one can grow highly (111) oriented Al films at room temperature. For a fixed bias potential, the value of the ion-to-atom ratio to achieve the optimum orientation effect is determined. At the optimum condition for the (111) preferred orientation growth, no significant enhancement in the grain size is observed. It is also found that a drastic reduction in the degree of the preferred orientation occurs when the films are deposited at a substrate temperature greater than 150 °C. I. INTRODUCTION The use of ion bombardment during deposition to modify thin film properties is the basic notion of the diverse variety of ion-assisted deposition techniques.1 One of the most important features in the ion-assisted techniques is the fact that additional deposition parameters related to ion bombardment are provided to give additional degrees of freedom to control the film properties. In principle, both foreign ions such as Ar + ' or ions derived from the evaporated materials2"7 can be used to bombard the surface during deposition. The latter technique, in which self-ions bombardment is used, has enjoyed some successes in growing low temperature epitaxial films2'8'9 and high-efficiency dopant incorporation.5 We shall call the method the partially ionized beam (PIB) technique. Also falling in this class is the ionized cluster beam (ICB) technique.4 In the ICB technique, the deposited material is evaporated through a small nozzle to produce metal clusters resulting from condensation during a supersonic jet expansion. Although considerable data have shown the ability of the ICB technique to grow high quality films, the issue of the formation of large metal clusters (~ 1000 atoms/cluster) during the expansion is still a controversial subject.10"14 Setting aside the issue of cluster formation, from the application standpoint, the ICB source crucible with a small nozzle cap is undesirable since it puts a severe limitation on the deposition rate.15 Our newly developed PIB source was designed to address the above problem; no small nozzle cap was used.7 Our PIB setup also allowed us to produce at least one order of magnitude higher ion-to-atom ratio in the beam than the conventional ICB setup. A wide range of studies carried out by our group showed no significant difference in the film properties deposited using an open cap or a nozzle cap crucible. We believe that the properties of the film deposited using either PIB or ICB configuration depend primarily on J. Mater. Res., Vol. 4, No. 2, Mar/Apr 1989
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the deposition parameters such as the percentage of ions in the beam and the bias voltage
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