Influence of dopants and deposition temperatures on the properties of TaSi2/polysilicon films and their thermal oxides

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Abstract
Tantalum silicide films were prepared by sputtering from compound targets. The influence of various deposition and process parameters on the TaSi2/poly-Si film properties and on the quality of thermal oxides grown by dry and steam oxidation on top of the polycide was investigated. In particular, the cleaning procedure of the poly-Si surface prior to TaSix-sputtering was varied and elevated substrate temperatures were adjusted during deposition. Furthermore, As- or P-implantations were inserted at various stages of the process sequence to study the properties of oxidized polycide structures present within actual devices. The polycide films were characterized by measurements of the sheet resistivity as well as by x-ray microprobe analysis and x-ray diffraction, while the thermal oxides were investigated by cross-sectional TEM and breakdown strength measurements. At the elevated substrate temperatures during TaSix-deposition, the sheet resistivity of the as-deposited and the sintered films decreases and the quality of the thermal oxides increases. At the maximum temperature of 400 °C, best results were obtained for the oxidized polycide structures. The preferential orientation of the TaSi2 crystallites within the polycrystalline layer depends on the process stage of the implantation. These implantations cause an increase of the quality of the thermal oxides on top of the polycides. Best oxides with mean breakdown fields of up to 5 MV/cm—even better than for oxides grown on polysilicon—were obtained by an As implantation process after sintering. Finally, the results were compared with those for TaSi2/poly-Si films prepared by cosputtering.

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