The Origin of Anomalous Strain in Thin Sputtered Mo Films on Si(100)
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THE ORIGIN OF ANOMALOUS STRAIN IN THIN SPUTTERED Mo FILMS ON Si(100) J. TAO, D. ADAMS, S. M. YALISOVE AND J. C. BILELLO Department of Materials Science & Engineering, University of Michigan, Ann Arbor, MI 48109-2136, U.S.A.
ABSTRACT Stress and structure evolution in thin films of sputtered Mo on Si(100) substrates has been studied, as a function of microstructure, by x-ray diffraction, transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy (RBS). Double crystal x-ray diffraction topography (DCDT) has been employed to determine film stress as a function of thickness. High compressive stress, about 1000 MPa, is found for the thinnest Mo film. With increasing film thickness a minimal residual stress level is reached. Low incidence angle x-ray diffraction patterns indicated that crystalline Mo is present even in the thinnest films. Line broadening of the Mo(l 10) diffraction peak has shown that the grain dimension is comparable to the film thickness over the range studied. Plan view TEM observations of films less than 20nm demonstrated the presence of continuous film with grain dimensions on the order of film thickness, in good agreement with the x-ray results.
INTRODUCTION Thin film refractory metal coatings on Si substrates are of interest for a variety of purposes, including protective coatings, diffusion barriers in devices, high temperature contacts, and potential x-ray lithography masks. Dimensional stability of the film-substrate couple is an important consideration in processing and ultimate utilization. Characterization studies, beginning at a very early stage of film growth, under non-UHV (eg. sputtering) conditions, would permit an understanding of the mechanisms controlling the microstructure of the film expediting the eventual design of film properties for a wide variety of industrial applications. The major tool for assessing the residual stress as a function of film growth thickness is a non-destructive x-ray analysis technique which uses a modified high sensitivity asymmetric double crystal diffraction topography camera (DCDT), in conjunction with advanced image processing, to quantitatively measure strains and map them out in two dimensions over large sample areas (= 2500 mm 2 ).[ 1,2,3,] This measurement is not affected by surface roughness: since the curvature of the crystal lattice planes is determined (with sensitivity of 0.1 km- 1) and not that of the physical surface of the specimen. Low incidence angle x-ray diffraction is used to evaluate the degree of crystallinity and assess the microstructure of the film. Line broadening analysis of the associated diffraction peaks provides information on grain size of the Mo film.[4,5] Finally, transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy (RBS), are used as additional probes to achieve a comprehensive understanding of the evolution of the film microstructure as a function of growth thickness.
Mat. Res. Soc. Symp. Proc. Vol. 239. @1992 Materials Research Society
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