Evolution of Intrinsic Stress During Nucleation and Growth of Polycrystalline Tungsten Films by Chemical Vapor Depositio
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EVOLUTION OF INTRINSIC STRESS DURING NUCLEATION AND GROWTH OF POLYCRYSTALLINE TUNGSTEN FILMS BY CHEMICAL VAPOR DEPOSITION. G.J. Leusink, T.G3.M. Oosterlaken, G.C.A.M. Janssen and S. Radelaar Delft Institutefor Microelectronicsand Submicron technology (DIMES), Delft University of Technology, P.O. Box 5046, 2600 GA, Delft, the Netherlands
Abstract We present in situ measurements of the intrinsic (growth) stress during nucleation and growth of thin tungsten films by chemical vapor deposition. It is shown that interfering stress sources, as recrystallization or plasic flow, do not contribute to the intrinsic stress in these films. This makes W-CVD a model system for the experimental study of the relation between the evolution of microstructure and the development of growth stress. Introduction Stresses in thin films on silicon substrates are a major concern in I.C. technology. Stress can affect both the mechanical and electrical properties. High stress in thin films can cause a film to crack, peel off or lead to stress induced transport phenomena. When the silicon crystal is distorted by a stress in the film the band gap will change. Stresses in thin films are usually divided in two categories: 1) extrinsic stresses which are stresses due to external effects (e.g. change in temperature), 2) intrinsic or growth stresses which are determined by material properties (e.g. the elastic constants, surface energy, interface energy, misfit in lattice spacing of film and substrate, grain boundary energy and defect density) and by the growth mode (i.e. layer by layer growth, Stranski-Krastanov growth or island growth in cases of epitaxial growth). For the case of nucleation and growth of polycrystalline thin films the grain boundary density [1,21 and recrystallization [3,4] may, for example, play an important role in the development of growth stress. The study of the mechanisms behind the sources of intrinsic stress development is complicated due to superimposition of various effects. In order to study the structure dependence of stress in a polycrystalline transition metal film a model system consisting of a well defined growth mechanism and a material with properties that do not change after deposition are necessary. In contrast to physical deposition techniques, polycrystalline films grown by surface reaction rate limited chemical vapor deposition have excellent step coverage. This means that the growth rate is independent of the angle of the growing surface and shadowing effects, characteristic for physical deposition methods, are avoided. This makes CVD the best candidate for the deposition technique in the model system for the evolutionary selection of grains during the nucleation and growth of polycrystalline films on a substrate. Because of the high melting temperature of W and the relatively low deposition temperature during W-CVD, mechanisms like recrystallization or defect annihilation can be expected not to make a significant contribution to stress development during growth. The high melting temperature, combined wit
