Aluminum Atom Surface Mobility on SiO 2 During Ionized Cluster Beam Deposition
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ALUMINUM ATOM SURFACE MOBILITY ON SiO 2 DURING IONIZED CLUSTER BEAM DEPOSITION LEONARD L. LEVENSON*, AMY B. SWARTZLANDER**, HIROAKI USUI***, ISAO YAMADA***, AND TOSHINORI TAKAGI*** *Department of Physics and Energy Science, University of Colorado, Colorado Springs, CO 80933-7150 **Solar Energy Research Institute, 1617 Cole Boulevard, Golden, CO 80401 ***Ion Beam Engineering Experimental Laboratory, Kyoto University, Kyoto 606, Japan ABSTRACT An ionized cluster beam (ICB) source was used to deposit Al onto Si0 2 substrates. A 60 gtm diameter wire held at the substrate served as a mask. After Al deposition, the wire was removed and the masked area was examined by scanning electron microscopy (SEM) and by scanning Auger microprobe (SAM). The ICB source was operated at 0, 3, and 6 kV acceleration voltages. The substrate was held at 800, 2000, and 400'C during Al depositions. The Al deposition rate averaged 240 A per min. The chamber 6 pressure during deposition was 2x10- Torr. The diffusion distance of Al under the mask edge was determined from the SEM micrographs and SAM line scans. The maximum diffusion distance for all 0 acceleration voltages occured at a substate temperature of 200 C. The maximum diffusion distance at 0 200'C was 29 p.m at 6 kV acceleration voltage. The minimum diffusion distance was 12 pin at 400 C for an acceleration voltage of 6 kV. INTRODUCMION The dependence of the microstructure of thin films on deposition conditions has been studied both experimentally and theoretically [1-51. One primary parameter governing film structure is the substrate temperature ratio T/Tm, where T is the substrate temperature and Tm is the melting point of the film material, both in absolute units. The other primary parameter is the kinetic energy of the impinging atoms, or a quantity which is proportional to the kinetic energy. Both of these factors are related to the surface mobility of surface atoms. However, surface mobility on semiconductor surfaces has not been measured until recently in the case of Ag on Si(1 11) [6,7] and Al on Si(1 11) [8,9]. The surface mobility of Al atoms on Si and SiO 2 surfaces is of interest because Al contacts and interconnections are commonly made on Si based integrated circuits. Here, we report on the measurement of the surface mobility of Al atoms deposited from an ionized cluster beam (ICB) source onto SiO 2 surfaces for various substrate temperatures. EXPERIMENTAL The construction and operating conditions of ICB sources have been described previously [10]. The source used in this work is similar to that illustrated by Takagi [11]. The graphite crucible was heated to 15000 C by electron bombardment, and the vacuum chamber was shielded by a water cooled thermal radiation shield. The crucible orifice was 2 mm in diameter and 2 mm in length. During Al deposition, t6j. 6 vacuum chamber was held at a pressure of 2x 10- Torr by a liquid nitrogen trapped oil diffusion pi,,'-.1Mat. Res. Soc. Symp. Proc. Vol. 128. 11989 Materials Research Society
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The deposition target was a Si bar 6
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