A method for the in situ measurement of mechanical stress in thin films deposited in a vacuum system is presented. The bending of the substrate, a measure for mechanical stress in the deposited layer, is detected by reflecting two parallel laser beams off the surface of the substrate and measuring the angle between the two reflected beams. A hollow mirror in the path of the reflected beams acts as an ‘‘optical cantilever’’ and increases the sensitivity of this method. In the present setup it is possible to detect the difference between a flat substrate and a substrate with a radius of curvature of 6.5 km.

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The kinetics of the hydrogen reduction of tungsten hexafluoride were studied. The growth rate was measured as a function of the process conditions, which were determined in situ by means of laser Raman scattering. The partial pressures were measured at a height of 17 mm above the center of a 100 mm wafer in a cold-wall single-wafer low-pressure chemical vapor deposition reactor. The hydrogen reduction reaction was on the order of 1/6 in WF, and 1/2 in 113. The activation energy was equal to 64 kJ mol'. An analysis of available reaction paths revealed that either the formation or the desorption of HF is the rate-limiting step. Since only one activation energy is present, the rate-limiting step is valid for the complete regime that was investigated.

An in situ study of the evolution of the biaxial state of intrinsic stress during nucleation and growth of polycrystalline tungsten chemical vapor deposition films deposited by the hydrogen reduction of tungsten hexafluoride is presented. The evolution of biaxial stress was determined from in situ wafer curvature measurements. It is shown that the intrinsic stress is a growth stress, i.e., a stress developing in close vicinity to the advancing surface of the film due to metastable film growth processes. The stress developing depends strongly on the thickness of the film. High tensile stress (≊4 GPa) is observed during the initial stage of growth, compressive stress (up to −1 GPa) is observed in an intermediate thickness regime after film closure and tensile stress (0.1–1 GPa) is observed in the thick film regime. The associated stress gradients in the film are preserved during and after growth. The development of growth stress is determined by deposition temperature and growth rate. The tensile stress in the thick film regime is larger at a higher growth rate or a lower deposition temperature, while the compressive stress in the intermediate thickness regime showed the opposite dependency. Film properties as the evolution of grain size, impurity content, and resistivity are found not to vary significantly with the growth conditions. Therefore, the development of growth stress is ascribed to kinetical processes. The development of tensile stress in the thick film regime is described with a (kinetic) grain boundary formation and relaxation model. The compressive stress in the intermediate thickness regime is tentatively ascribed to compressive coherency strains induced by interfacial tensions of the grains in the stage of island growth.

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