Methods for processing tantalum films of controlled microstructures and properties
- Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7916 and NSF Center for Advanced Materials and Smart Structures, North Carolina State University, Raleigh, North Carolina 27695-7916 (United States)
The authors have fabricated thin films of alpha tantalum ({alpha}-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 ({beta}-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 {alpha}-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 10-300 K showed room-temperature values to be 15-30 {mu}{omega} cm for {alpha}-Ta, 180-200 {mu}{omega} cm for {beta}-Ta, and 250-275 {mu}{omega} cm for amorphous tentalum (a-Ta). The temperature coefficients of resistivity (TCRs) for {alpha}-Ta and {beta}-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 deg. 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 deg. C annealing for 1 h, a-Ta films have less than 10 nm 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 {alpha}-Ta and {beta}-Ta films. Thus, superior diffusion properties of a-Ta provide an optimum solution for copper metallization in next-generation silicon microelectronic devices.
- OSTI ID:
- 20853545
- Journal Information:
- Journal of Vacuum Science and Technology. A, International Journal Devoted to Vacuum, Surfaces, and Films, Vol. 24, Issue 5; Other Information: DOI: 10.1116/1.2335863; (c) 2006 American Vacuum Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1553-1813
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ANNEALING
BCC LATTICES
COPPER
DIFFUSION
ELECTRIC CONDUCTIVITY
ENERGY BEAM DEPOSITION
GRAIN BOUNDARIES
LASER RADIATION
OXYGEN
POLYCRYSTALS
PULSED IRRADIATION
RUTHERFORD BACKSCATTERING SPECTROSCOPY
TANTALUM
TANTALUM 180
TEMPERATURE RANGE 0273-0400 K
THIN FILMS
TRANSMISSION ELECTRON MICROSCOPY
X RADIATION
X-RAY DIFFRACTION