Structure of LPCVD Tungsten Films for IC Applications

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Abstract
Because of the widespread potential use of CVD tungsten films in integrated circuit applications, the structural properties of these films were examined over a range of deposition conditions and with different nucleating layers. When tungsten is deposited on a chromium nucleating layer on an oxidized silicon wafer, the stress is not a strong function of film thickness, and most of it is caused by the difference in the thermal coefficients of expansion of tungsten and silicon. The surface roughness increases almost linearly with increasing film thickness. The grain size also increases with increasing film thickness, with the diameters of the largest grains comparable to the film thickness. The structure is equiaxed, rather than columnar. The (100) texture is dominant near the normal deposition temperature of 300°C for different film thicknesses and nucleating layers, but the dominant orientation changes at higher deposition temperatures. The structure develops as the film is deposited, rather than being determined by the nucleation.

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