Deposition of Tungsten Boride by Ion Beam Sputtering

Abstract

ABSTRACTRefractory metal compounds, such as nitrides or borides, are attractive candidates for diffusion barrier between silicon and aluminium in VLSI technology. We studied tungsten boride films deposited on silicon (100) by ion beam sputter deposition (IBSD).The tungsten boride films were prepared by sputtering a W2B5 target by argon ions with energy ranging from 0.5 to 2keV. The substrate temperature was varied from room temperature to 630°C. Finally, the films were patterned by selective wet etching in order to characterize the resulting Schottky diodes. We observed that a boron loss occurs during deposition, probably due to the backscattering of sputtered boron on previously deposited W atoms. By in situ AES analysis, we verified that a 5 nm thick layer acts as a diffusion barrier for silicon up to about 630°C, for all deposition conditions. The films properties were found to depend weakly on the primary ion energy and on the substrate temperature. All the films have resistivity at room temperature in the range of about 250 µΩ cm. The measured density, in the range of 12 g/cm3, is very close to that of WB2 bulk material, while the intrinsic stress of the films remains compressive and in the range of -lGPa. This value is notably lower than what we measured for pure tungsten prepared under similar deposition conditions.