Influence of deposition parameters on the microstructure of ionplated films

Ion plating is essentially vapor deposition onto a substrate which is the cathode of a glow discharge. The most important characteristic of the technique is that the growing film is subjected to a flux of high energy particles (neutrals and ions). In this study we report information about the effect of ion plating parameters on grain diameter and crystallite size distribution. At a constant potential grain size remains constant with the increase of ion density. On the other hand, at a constant ion density the grain size decreases with the substrate potential increment. Ion bombardment also has an effect on the crystallite size distribution. The ion plated films show a higher degree of uniformity in grain size than vacuum evaporated films. In contrast with vacuum evaporated films, where the grain size is proportional to the thickness, no variation of grain size with film thickness has been observed for the ion-plated films. Electron ~ o n patterns have shown that the orientation remains near random over the entire J and V range studied. INTRODUCTION Ion plating, generally defined as a plasma or ion activated deposition technique, is essentially vapor deposition onto a substrate which is the cathode o f a glow discharge. The most important characteristic o f the technique is that the growing film is subjected to a flux of high energy particles (neutrals and ions)O). Despite the widespread attention paid to technological applications of ion plating since the introduction o f the technique in 1963 (2), very little work has been done on the correlation between the deposition parameters and the microstructure of the restflting films (3-7). In previous work (8) we have shown that nucleation and growth o f thin films deposited by ion-plating teelmique are quite different from vacuum evaporated films; a continuous fine grained film is obtained at a lower thickness. The structural properties of the films have been explained on the basis of the special characteristics o f the method: permanent bombardment of the growing film and a © 1996 American Institute of Physics 356 Downloaded 12 Dec 2011 to 130.236.169.5. Redistribution subject to AIP license or copyright; see http://proceedings.aip.org/about/rights_permissions higher kinetic energy of the evaporant. Epitaxial growth at substrate room temperature was observed. In this work we report the result of an analysis of grain diameter and crystallite size distribution, with changes in ion current density and ion energy. E X P E R I M E N T A L The samples have been prepared by vacuum evaporation and the ion-plating technique. The deposition system used in these experiments has been described in detail elsewhere (8). Ion bombardment of the growing film is supplied by the glow discharge plasma of argon. Control over ion energy is provided by the substrate potential, and ion current is controlled by substrate potential and pressure. The gold films were deposited onto Coming 7059 glass substrates. For microstrucUtral examination by transmission electron microscopy (TEM) and high energy electron diffraction (HEED), an aqueous HF solution (1:1) was used to separate the filing from the glass. The average grain diameter and crystallite size distribution were determined directly from TEM micrographs. For comparison, vacuum evaporated tilm~ of the same thicknesses were obtained. The thicknesses were measured by multiple beam interferometry. R E S U L T S A N D D I S C U S S I O N Figure 1 shows grain size versus current density (J) for films obtained at constant substrate potential (V). At the two observed potentials no decrease in grain size with increased current density is seen. On the other hand, at a constant current density, a substantial grain size decrease with increased substrate potential has been observed. Figure 2 shows the