In Situ Investigation of Ti x Al y Film Growth As A Function of Substrate Temperature and Film Stoichiometry
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IN SITU INVESTIGATION OF TixAly FILM GROWTH AS A FUNCTION OF SUBSTRATE TEMPERATURE AND FILM STOICHIOMETRY St. LACKNER and R. ABERMANN Institute of Physical Chemistry, University of Innsbruck, Austria. ABSTRACT The growth of TixAly-alloy films was investigated by measuring the film stress during as well as after the film deposition under UHV-conditions with a cantilever beam technique. The alloy films were deposited on alumina substrates from two separate evaporation sources. The substrate temperature was varied from room temperature to 500°C and the alloy stoichiometry from Ti25Al75 to Ti75Al25. At a substrate temperature of 200°C the dependence of the growth stress of the alloy film on stoichiometry is pronounced and varies from tensile stress in the case of titanium rich alloyfilms to compressive stress in aluminium rich films. The stress changes after deposition at 200°C are negligible for titanium rich alloys but in the case of aluminium rich alloys small tensile stress changes are measured. At a substrate temperature of 500°C the film stress is compressive and the dependence on stoichiometry is rather small. The stress vs. thickness curves of Ti25Al75-films, however, show unexpected oscillations during growth while at lower aluminum content stable stress curves are measured. The stress changes after deposition are large in each case, interpreted to indicate film recrystallisation and/or continued alloy formation. In a second series of experiments we have measured the internal stress changes in Ti25Al75-alloy films during annealing. It can be shown that the changes in the film stress can be correlated with changes in the film microstructure seen in the electron microscope (TEM). INTRODUCTION Thin films of titanium, aluminum and TixAly-alloys are used in a large number of technological applications due to their unique physical and chemical properties, i.e., mechanical strength, specific weight as well as corrosion and temperature resistance. In the past we have demonstrated that the mechanical properties of thin one component films are closely related to their microstructure and that internal stress measurements can be used for the in situ study of film growth [1]. In continuation of earlier work, we present results of experiments in which we have studied the stress evolution in TixAly-alloy-films during deposition as a function of alloy stoichiometry at two selected substrate temperatures. Due to a substantial improvement in the experimental setup we are now able to measure the internal stress changes in a film during annealing. First results for one typical example (Ti25Al75) are presented. EXPERIMENTAL The stress measuring apparatus is mounted in a diffusion pumped ultra high vacuum (UHV) system with two liquid nitrogen cooled titanium sublimation pumps. The base pressure is better than 2x10-10 mbar and the pressure during evaporation is better than 1x10-9 mbar. The residual gas composition is analysed with a quadrupole mass analyser. P3.20.1
The film stress (i.e., film force normalized to substrate width) i
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