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Kinetics of the tungsten hexafluoride-silane reaction for the chemical vapor deposition of tungsten

Tungsten has been used for multilevel metallization in very large scale integration (VLSI) technology. Reduction by silane has been considered as a high-rate, low-temperature process alternative to hydrogen reduction of tungsten hexafluoride in the chemical vapor deposition of W. In the present study, the kinetics of the low pressure chemical vapor deposition (LPCVD) of tungsten by silane reduction of tungsten hexafluoride on Si(IOO) surfaces was studied. A single-wafer, cold-wall reactor was used for the experiments. The SiH4/WF6 ratio was 1.0. The pressure and temperature range were 1-10 torr and 137-385°C, respectively. Kinetic data were obtained in the absence of mass transfer effects. The film thicknesses were measured by gravimetry. Scanning electron microscopy (SEM), Auger electron spectroscopy (AES), x-ray diffraction (XRD), and resistivity measurements were used to analyze the W films. For the horizontal substrate position and 4-minute reaction times, the apparent activation energies were determined to be 0.35 eV/atom for 10 torr, 0.17 eV/atom for 3 torr, and 0.08 eV/atom for 1 torr. Lower temperatures and higher pressures produced porous films, while higher temperatures and lower pressures resulted in continuous films with smoother surfaces. At the Si-W interface, a W(110) preferential orientation was observed. As the W films grew thicker, W orientation switched from (110) to (100). Apparent activation energy seems to change with thickness. Si and F contents of the films were within the noise level for Auger detection. Porosity was found to be influential in the film resistivity. The higher activation energy observed at higher pressure was deduced to be a result of limitations in the rate of SiH4 adsorption and subsequent adatom surface diffusion. The domination of W(100) orientation for thick films at high temperatures was attributed to a reconstruction of W(100) surfaces on which adatom surface diffusion is easier. KINETICS OF THE TUNGSTEN HEXAFLUORIDE-SILANE REACTION FOR THE CHEMICAL VAPOR DEPOSITION.OF TUNGSTEN