Microstructural evolution of tantalum nitride thin films synthesized by inductively coupled plasma sputtering.

Tantalum nitride (TaN) thin films were grown utilizing an inductively coupled plasma (ICP) assisted direct current (DC) sputtering, and 20-100% improved microhardness values were obtained. The detailed microstructural changes of the TaN films were characterized utilizing transmission electron microscopy (TEM), as a function of nitrogen gas fraction and ICP power. As nitrogen gas fraction increases from 0.05 to 0.15, the TaN phase evolves from body-centered-cubic (b.c.c.) TaN, to face-centered-cubic (f.c.c.) δ-TaN, to hexagonal-close-packing (h.c.p.) ε-TaN phase. By increasing ICP power from 100 W to 400 W, the f.c.c. δ- TaN phase becomes the main phase in all nitrogen fractions investigated. The higher ICP power enhances the mobility of Ta and N ions, which stabilizes the δ-TaN phase like a high-temperature regime and removes the micro-voids between the columnar grains in the TaN film. The dense δ-TaN structure with reduced columnar grains and micro-voids increases the strength of the TaN film.