High-temperature stability of chemically vapor-deposited tungsten-silicon couples rapid thermal annealed in ammonia and argon

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 0C 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 0C) RTA in Ar completely converted W into the low resistivity (31 μΩ cm) tetragonal WSi2 phase. In contrast, after a prior 900 0C 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 0C NH3 anneal. The NH3-treated W film acted as a diffusion barrier in an Al/W/Si contact metallurgy up to at least 550 0C, at which point some increase in contact resistance was measured