Conventional Si or SiGe epitaxy via chemical vapor deposition is performed at high temperatures with a large amount of hydrogen gas using silane (SiH4) or dichlorosilane (SiCl2H2) precursors. These conventional precursors show low growth rates at low temperatures, particularly below 500 °C although a low thermal budget becomes more important for modern fabrication techniques. High-order silane precursors, such as disilane, trisilane, and tetrasilane, are candidates for low-temperature epitaxy due to the lower strength of the Si-Si bonds compared to that of the Si-H bonds. In addition, the consumption of vast amounts of hydrogen gas is an additional burden of the low-temperature process due to its low throughput. In this study, we explored Si and SiGe epitaxial growth behaviors using several high-order silanes under ultra-high vacuum chemical vapor deposition (UHVCVD) and low-pressure chemical vapor deposition (LPCVD) conditions without a carrier gas. Disilane showed high-quality epi-growth under both pressure conditions, whereas trisilane and tetrasilane showed enhanced growth rates and lower quality.
The effects of CeO2 addition on the microstructural change of a Ta diffusion barrier film and thermal stability of the Cu/Ta/Si system were investigated. When a Ta layer was prepared with CeO2 addition, the silicide formation was retarded up to 800 °C. The Cu/Ta+CeO2/Si system retained its structure up to 800 °C without an increase in stack resistivity, while the Cu/Ta/Si structure degraded after annealing at 550 °C. The Ta+CeO2 diffusion barrier showed an amorphous microstructure and chemically strong bonds with Ta–Ce–O. It appeared that the thermal stability of the Cu/Ta+CeO2 interface as well as the Ta+CeO2/Si interface was higher than that of both Cu/Ta and Ta/Si interfaces. Therefore, the Ta film prepared by CeO2 addition effectively prevented the interdiffusion of Cu and Si through the diffusion barrier up to 800 °C.
The diffusion barrier properties of Ta, both as deposited without ion bombardment and deposited concurrent with iou energy, were investigated in the Cu/Ta/Si contact system using Auger electron spectroscopy, x-ray diffraction, optical microscopy, transmission electron microscopy, and sheet resistance measurements. It was found that the ion bombardment during deposition of Ta films influenced the microstructural characteristics, such as the packing density of grain boundaries, the grain size, and the preferred orientation of Ta grains. The Ta film deposited concurrent with 150 eV ion energy (0.13 mA/cm2) showed the increased packing density of grain boundaries, low resistivity, and preferred orientation. The densification of grain boundaries of the Ta barrier layer followed by an increase of silicide formation temperature, significantly enhanced the barrier property of Ta in the Cu/Ta/Si system.
InfroductionRecently, Cu has attracted attention as a new material because of its lower bulk resistivity and superior resistance to electromigration than Al and its alloy.1-2 However, to be used as a metallization material for the development
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