The authors have fabricated thin films of alpha tantalum (α-Ta) with crystalline and amorphous structures by nonequilibrium pulsed laser deposition techniques, and compared their electrical properties and diffusion characteristics with those of polycrystalline beta tantalum (β-Ta) films produced by magnetron sputtering. The microstructure and atomic structure of these films were studied by x-ray diffraction and high-resolution electron microscopy, while elemental analysis was performed using electron energy-loss spectroscopy and x-ray dispersive analysis. The α-Ta with body-centered-cubic structure was formed only under clean, impurity-free conditions of laser molecular beam epitaxy. The resistivity measurements in the temperature range of 10–300K showed room-temperature values to be 15–30μΩcm for α-Ta, 180–200μΩcm for β-Ta, and 250–275μΩcm for amorphous tentalum (a-Ta). The temperature coefficients of resistivity (TCRs) for α-Ta and β-Ta were found to be positive with characteristic metallic behavior, while TCR for a-Ta was negative, characteristic of high-resistivity disordered metals. The authors discuss the mechanism of formation of a-Ta and show that it is stable in the temperature range of 650–700°C. Electron energy-loss spectroscopy (EELS) and Rutherford backscattering measurements showed oxygen content in a-Ta films to be less than 0.1%. The secondary ion mass spectrometry, scanning transmission electron microscope Z-contrast imaging, and EELS studies show that, after 650°C annealing for 1h, a-Ta films have less than 10nm Cu diffusion distance while polycrystalline Ta films have substantial Cu diffusion. The superior diffusion barrier properties of a-Ta for Cu metallization have been attributed to the lack of grain boundaries which usually lead to enhanced diffusion in the case of polycrystalline α-Ta and β-Ta films. Thus, superior diffusion properties of a-Ta provide an optimum solution for copper metallization in next-generation silicon microelectronic devices.

No abstract

No abstract

W/B4C multilayers (MLs) consisting of ten layer pairs with varying boron carbide layer thicknesses have been investigated. The ML structures were characterized using grazing‐incidence hard X‐ray reflectivity (GIXR), resonant soft X‐ray reflectivity (RSXR), hard X‐ray photoelectron spectroscopy (HAXPES) and X‐ray absorption near‐edge spectroscopy (XANES). Depth‐resolved spectroscopic information on the boron carbide layer in W/B4C MLs was extracted with sub‐nanometre resolution using reflectivity performed in the vicinity of the B K‐edge. Interestingly, these results show that the composition of boron carbide films is strongly dependent on layer thicknesses. HAXPES measurements suggest that most of the boron is in the chemical state of B4C in the multilayer structures. XANES measurements suggest an increase in boron content and C—B—C bonding with increase in boron carbide layer thickness.

No abstract