Metal film characterization with qualified spreading resistance

The spreading resistance probe (SRP) tool is widely used for obtaining the electrically active dopant profile in silicon. In this work, the capabilities of SRP for thin metal film (Cu/Al/TaN) characterization are investigated. It is well known that quite large correction factors (∼500) are involved in sub-100 nm silicon SRP profiling to extract the underlying carrier depth profiles from the measured raw resistances. These large correction factors also allow, in principle, for the characterization of sub-100 nm metal layers, as their measured resistances will fall in the 1–100 ohm range. Structures consisting of Cu or Al metal layers, respectively, with different thicknesses (25–400 nm) on a Ta/TaN barrier layer (∼20 nm) on SiO2 have been characterized with SRP. For calibration, the characteristics of the probe imprints have been measured with atomic force microscopy. Present results indicate that for the thinnest Cu films, it is possible to obtain a resistivity depth profile in good agreement with available theoretical predictions, based on the impact of an electron mean-free-path length of 39 nm.