Control of bombardment energy and energetic species toward a superdense titanium nitride film

TiN deposited by dc magnetron sputtering has been widely used as a hard mask material for dielectric patterning in multilevel Cu interconnects. Typically inside a “poison-mode” regime, the film density is $4.5–4.9g/cm3$⁠. The microstructure, varying from columnar structure to nanocrystalline, is controlled by both thermodynamics and surface kinetics through ionization, substrate bias, target voltage, etc. A relatively low density film can be correlated with a porous columnar structure, low mechanical robustness, and weak resistance to plasma etching. However, with controlled growth, an applied substrate bias does not create resputtering and crystal defects. Instead, the authors create film with a maximum density of $5.3g/cm3$⁠. In this high density film, carrier scatterings through grain boundary are greatly suppressed and the film resistivity is as low as $95μΩcm$⁠, which brings additional benefits as a conductive capping layer. As it is deposited at room temperature, the process minimizes the thermal budget to the underlying low-$k$ dielectric materials to be patterned.