Structural Characterization and Schottky Barrier Height Measurements of Epitaxial NiSi 2 on Si
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. Res. Soc. Symp. Proc. Vol. 54. 1986 Materials Research Society
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and the related interface, but will also discuss the electrical results and the implications of those measurements. EPITAXIAL GROWTH The NiSi 2 epitaxy was done in asycuum Generators Si NBE system with a base pressure of approximately 2xlO "-mbar. The substrates were 3 inch Si wafers phosphorous-doped to a resistivity of 2.5-50-cm and oriented within 0.350 of the (111) axis. Before growth, three of the ten wafers processed were backside-implanted with P for later ohmic contacts, and had windows from 20 to 260pm in diameter etched into a 0.6pm thick field oxide. These wafers were used for some of the I-V measurements. The remaining wafers were unprocessed except for cleaning before entering the NBE system. All wafers went through a chemical degreasing step before loading, but the primary cleaning procedure was an in-situ Ar ion sputter-clean at lkeV followed by an 800-8500C anneal. After cooling to room temperature, the Ni templates were deposited by e-'bam evaporation at rates of .5-1.01/s followin; the procedures of Tung. 2. The type A templates were formed using a 16-18 Ni layer, while the type B templates consisted of a 201 Ni layer overlayed by a 30-401 Si film. The templates were then annealed to a temperature of 500±25 C for a period of 5 minutes. For final NiSi 2 thicknesses greater than 701, a further Ni deposition or Ni/Si codeposition 0 was carried out at a temperature of 650 C. Film thicknesses ranged from
70-6001. STRUCTURAL CHARACTERIZATION Detailed knowledge of the epitaxial films and interfaces is crucial for understanding Schottky barrier formation in the NiSi /Si system. For 2 this reason, thorough structural characterization of the NiSi 2 layers was done using transmission electron microscopy (TEM) and high energy ion channeling measurements. Cross-sectional TEM studies were performed on ýhree type A and four type B samples using conventional sample preparation and imaging techniques. In addition, high resolution TE_ (HRTEM) was done on one sample of each orientation using a Philips EM430 electron microscope at a 300keV beam energy. Fig. 1 shows cross-sectional TEM micrographs of type A and type B NiSi 2 epitaxial layers. It is clear from these pictures that the silicide/Si interfaces are extremely flat and regular over extended
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Fig. 1. Cross-sectional TEM micrographs. (a) 6001 type A NiSi 2 . (b) 6001 type B NiSi . (c) HRTEM micrograph of a type A NiSi 2 /Si interface. (d) HRTEM micrograph of a type B NiSi 2 /Si interface.
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distances, and that the boundary between the layers is atomically abrupt. An HRTEM survey of approximately one micron of each silicide orientation indicated that the interfaces shown in Figs. lc) and ld) were representative of more than 80% of the respective boundaries. However, there were occasionally small regions, typically less than 1001 in extent, in which there appeared to be an extra atomic plane inserted at or near the interface. The average spacing of the defect regions was app
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