2006 journal article

Methods for processing tantalum films of controlled microstructures and properties

JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A, 24(5), 1948–1954.

By: J. Narayan n, V. Bhosle n, A. Tiwari n, A. Gupta n, P. Kumar* & R. Wu

co-author countries: United States of America 🇺🇸
Source: Web Of Science
Added: August 6, 2018

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.