THE GROWTH, STRUCTURE, AND ELECTRICAL TRANSPORT PROPERTIES OF MOLYBDENUM/TANTALUM SUPERLATTICES.

Abstract

We use high rate magnetically-confined-plasma-triode sputtering guns in a diffusion pumped vacuum chamber to fabricate metal-metal superlattices. By feedback control of the sputtering rates and microprocessor control of the substrate rotation the individual layer thicknesses were kept constant to within ±0.3% over the entire sample thickness ∼0.5 μm. We describe in detail the results of a number of structural characterization techniques applied to these materials, including Bragg Θ-2Θ x-ray diffraction, transmission and reflection Laue diffraction, wide film Debye-Scherrer diffraction, and Rutherford Backscattering Spectrometry (RBS). By depositing Ta onto freshly deposited Mo surfaces and using RBS to measure the resultant Ta coverage we determined the dependence of the Ta sticking coefficient on coverage. The same was done for Mo deposited on Ta surfaces. We grew a series of Mo/Ta superlattices with superlattice wavelengths covering the range from 10 to 120 Å. A number of four-wire resistance measuring patterns were etched in each superlattice using standard photolithographic techniques. Resistivities of the superlattice films of various layer thicknesses were then measured to a relative precision of 0.01% and an absolute accuracy of 1%. The layer thickness dependence and temperature coefficient of the resistivity of these superlattices was analyzed using grain and size effect theories.