Underlayer Effects on the Growth Stress of Titanium Films
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ABSTRACT: The growth stress of titanium films was measured in situ with a cantilever beam technique under UHV conditions at Ts >! 130'C. The substrate used in these experiments was a double layer consisting of a base layer of A120 3 or of MgF 2 and as a second layer a titanium film evaporated at different H20-partial pressures (Tif/iOx). With both base layers the growth stress of the substrate Ti/TiOx layer is similar. The main objective of this paper was the investigation of the effect of a variation in the chemical composition of the substrate Ti/TiO, layer on the growth stress and by way of our stress model - on the growth mode of a clean titanium film always evaporated under identical vacuum conditions onto this bilayered substrate. At low water content of the substrate titanium layer (the substrate layer still consists of metallic titanium) the growth of the clean titanium film is a continuation of the growth of the second substrate layer. As soon as the substrate titanium film contains only a few percent of water the initial compressive stress is overcompensated by a tensile stress contribution which increases as the water content of the substrate is
increased. We interprete this to indicate renewed nucleation for the clean titanium
film on the substrate surface. A small part of the tensile stress is also due to gas interdiffusion (hydrogen) from the substrate film. This effect is rather small when the second substrate film consists of stoichiometric oxide. With a MgF 2 base layer in the substrate bilayer the results indicate a diffusing species from the MgF 2 base layer into the Ti/TiOx layer. This interdiffusion from the substrate significantly affects the growth stress of the clean titanium film on this substrate bilayer. However, the general trends due to the incorporation of water in the substrate Ti/TiOx film, seen in case of the A120 3 base layer, are the same. INTRODUCTION: Stresses in thin films, built up during or after their deposition are a major concern in technical applications, since they may affect their function and life time. Thus measurements of these stresses are of technical interest. We have demonstrated in the past, that such stress measurements can also successfully be used for in situ 173 Mat. Res. Soc. Symp. Proc. Vol. 356 @1995 Materials Research Society
studies of thin film growth [1,2]. By measuring the internal stress, built up in a film during its deposition as a function of film thickness and thereafter as a function of time, we were able to study the influence of various deposition parameters on the growth stress of a number of film materials. Using a model for the origin of the film stress [3-7] we were able to interprete this film stress in terms of the film microstructure and changes in this microstructure. The work presented in this paper is part of a longrange investigation on the growth of titanium films [8,9]. In particular we present recent results of experiments in which we have investigated the effect of a variation in the chemical composition of the substrate fi
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