Control of Metal Film Properties by Ion Assisted Deposition
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CONTROL OF METAL FILM PROPERTIES BY ION ASSISTED DEPOSITION RONNEN A. ROY, DENNIS S. YEE, and JEROME J. CUOMO, IBM Research Division, Watson Research Center, P.O. Box 218, Yorktown Heights, N.Y., 10598 ABSTRACT Ion-assisted deposition allows for independent control of ion energy, ion flux, and adatom flux incident on the growing film. We describe herein general trends in property and structure modification of thin film metals using this technique. INTRODUCTION Ion bombardment of films during growth has long been recognized as an important tool in modifying resultant film properties. Beginning with bias sputtering and techniques such as ion plating, researchers have sought to control film properties by varying the amount of bombardment (1-4). With the advent of broad beam ion sources the ability to modify and reproducibly control film properties (5-7) has improved due to several factors. A major advantage is that ion energy and ion flux are decoupled, allowing for independent variation of either parameter. Another advantage is that the plasma is contained in the ion source, providing a much simpler deposition environment near the substrate. Thus, one can better quantify the amount and energy of the various species incident on the film/substrate during growth, making the interpretation of data much simpler. In this paper, we focus on the application of ion-assisted deposition (IAD) for property modification of various metal films (6-10). Based on the results of niobium, chromium, copper, and tungsten, we shall highlight the importance of parameter selection, such as ion energy, in controlling property changes. Furthermore, the modifying effects of substrate temperature (TJ) on film properties will be described. A review of film physical property changes, microstructure changes, and their interrelation will be given. EXPERIMENTS All of the results described herein are obtained from films deposited by electron beam evaporation with concurrent argon ion bombardment of the growing film using small Kaufman ion sources, described in detail elsewhere (6-10). RESULTS Property Modification Film properties such as stress, microhardness and electrical resistivity, have been modified by concurrent bombardment during deposition. In the case of Cu, the resistivity and nmicr-ohardnes-s behavi-or have shown a strong energy dependence (8). At 600 eV ion energy, the resistivity of films rises steeply with ion flux, surpassing 1OpLI-cm at high flux levels (fig 1). On the other hand films deposited with concurrent 125 and 62 eV Ar ion bombardment (also shown in Fig. la) show only a small increase in resistivity from about 2 41-cm at low levels to 2.6 41-cm at high levels. Qualitatative differences were also seen in microhardness changes under ion bombardment as the primary
Mat. Res. Soc. Symp. Proc. Vol. 128. ;1989 Materials Research Society
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ion energy is lowered. At 600 eV energy microhardness in copper films was found to increase rapidly with increased ion flux, while at 62 eV ion energy decreases in hardness were seen at low t
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