ALD and PVD Tantalum Nitride Barrier Resistivity and Their Significance in via Resistance Trends

Abstract

Tantalum nitride (TaN) processes for barrier applications in advanced dual damascene Cu interconnect metallization schemes were developed and compared in order to study their electrical properties and the impact on via resistance. The limits of various physical vapor deposited (PVD) TaN processes in terms of resistivity were characterized, showing a rapid increase in TaN resistivity when DC sputtering is conducted with high nitrogen flow rates in an Ar/N2 plasma. More incorporation of nitrogen into TaN is observed at low PVD TaN deposition rates, established by applying low DC power sputtering conditions. Via resistance measurements were performed on dual damascene via structures built with either Ta-rich PVD TaN films with a resistivity of ~240 μΩcm, or ALD TaN films with a resistivity of ~5000 μΩcm as barriers. Even though the resistivity of ALD TaN blanket films is significantly higher than PVD TaN, reduced via resistance values were observed as a larger fraction of PVD TaN in the barrier stack was replaced by ALD TaN. For a TaN barrier at 3nm thickness, the via resistance measured for ALD TaN was ~28% lower than its PVD counterpart.