Thermal stability of thin poly-Si/Ta2O5/TiN capacitors for dynamic random access memory applicationsThe properties of Ta 2 N and TaN compound films as a diffusion barrier between Cu and Si have been investigated by examining compositional depth profiles obtained by Auger electron spectroscopy. The use of a Ta 2 N barrier is effective for improving the thermal stability of the contact system by raising the silicide formation temperature as compared with the use of a Ta barrier. The contact system of Cu/TaN/Si is fairly stable due to annealing for 1 h even at 750°C. This is interpreted by the stability of the TaN compound, which is chemically inert to Si as well as Cu at this temperature. Eliminating the grain growth of TaN due to annealing is also effective for suppressing the physical diffusion through the barrier.

A thermally stable Cu/ZrN/Si contact system using a ZrN diffusion barrier of low resistivity was developed. In the contact system, the growth of an oriented ZrN(100) layer on Si(100), and subsequent growth of a Cu(110) layer on ZrN(100) were observed. The obtained contact system was fairly stable after annealing even at 750 °C for 1 h without any diffusion and/or reactions at either the interface of Cu/ZrN or ZrN/Si. It was revealed that the ZrN layer with low electrical resistivity showed a high performance as a diffusion barrier, and was one of the excellent materials for the use in ultralarge scale integration technology.

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Low-temperature deposition has been required for preparing SiNx films of high density, high refractive index, and low hydrogen content for various applications. We examine the characteristics of SiNx films deposited at low temperature by reactive sputtering and plasma-enhanced CVD under different conditions. The results reveal that we can give an outline of the preparation conditions that provide the properties of SiNx films required for various applications. The pretreatment of the Si target improves the properties of the sputter-deposited SiNx films by reducing the amount of oxygen incorporation.

Thin nanocrystalline vanadium nitride (VN) films of low resistivity were examined as an extremely thin diffusion barrier to provide thermal stability in Cu∕VN∕SiO2∕Si systems. A 10-nm-thick VN barrier with grains ranging from several to ∼10nm in diameter provided excellent barrier properties. After annealing at 600°C for 1h, the barrier showed scarcely any change in structure and absence of Cu diffusion and/or decisive interfacial reaction in the system. This was interpreted to mean that the present barrier, which is made of a thermochemically stable δ-VN compound phase with a slightly nitrogen-rich composition and a nanocrystalline structure, was preferable to suppress the solid-phase reaction and/or diffusion, as well as the structural change upon annealing. It was revealed that the nanocrystalline VN barrier is an excellent candidate as a barrier in a forthcoming Cu metallization scheme.

The results of analyses by X-ray diffraction, transmission electron microscopy, and grazing incidence X-ray reflectivity measurement indicate that a 5-nm-thick ZrN film interposed between Cu and SiO2 shows excellent barrier properties, tolerating annealing up to at least 500 °C for 30 min. The X-ray diffraction pattern reveals a decrease in the intensity of the Cu(111) reflection upon annealing at 800 °C, suggesting a failure of the thin barrier due to Cu diffusion through the barrier. We are confident that the formation of a continuous nanocrystalline ZrN film in a uniform fashion in a stable phase with a slightly nitrogen-rich composition is a cause of the excellent features obtained. The formation process of the ZrN film is discussed in terms of the nucleation process of reactive sputtering at a low deposition temperature.

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