A novel multilevel metallization scheme has been developed that uses tungsten for the primary levels of interconnection. 1-ym-wide 2.0-pm-deep grooves, corresponding to a level of line conductor interconnection, are pattern etched into a planar layer of oxide dielectric. Grooves are filled by isotropically depositing a blanket layer of pure tungsten using low-pressure CVD, followed by etch-back of the tungsten to produce a filled interconnect groove (FIG) conductor structure. Fabricated FIG conductors display an average sheet resistivity of 48 mQ/square, comparable to conventional aluminum conductors. In addition, FIG metallization provides excellent planarity, greatly improved electromigration strength, and facilitates the use of stacked vias.

A rapid thermal anneal (RTA) in an NH3 ambient has been found to increase the thermal stability of W films chemically vapor deposited (CVD) on Si. W films deposited onto single-crystal Si by low-pressure CVD were rapid thermal annealed at temperatures between 500 and 1100 °C in NH3 and Ar ambients. The reactions were studied using Rutherford backscattering spectrometry, x-ray diffraction, Auger electron spectroscopy, transmission electron microscopy, and four-point resistivity probe. High-temperature (≥1000 °C) RTA in Ar completely converted W into the low resistivity (31 μΩ cm) tetragonal WSi2 phase. In contrast, after a prior 900 °C RTA in NH3, N inclusion within the W film and at the W/Si interface almost completely suppressed the W-Si reaction. Detailed examination, however, revealed some patches of WSi2 formed at the interface accompanied by long tunnels extending into the substrate, and some crystalline precipitates in the substrate close to the interface. The associated interfacial contact resistance was only slightly altered by the 900 °C NH3 anneal. The NH3-treated W film acted as a diffusion barrier in an Al/W/Si contact metallurgy up to at least 550 °C, at which point some increase in contact resistance was measured.