Fabrication of TiN metal hard masks via very-high-frequency-direct-current superimposed sputtering

In high-end logic devices, TiN films have attracted increasing attention as metal hard masks (MHMs) for scaling trenches and vias of Cu back-end of line. In this study, we investigated the application of very-high-frequency-direct-current (VHF)-DC superimposed magnetron sputtering for fabricating TiN MHM films and compared these films with TiN MHM films deposited via DC magnetron sputtering. The X-ray diffraction (XRD) pattern of deposited TiN MHs showed crystalline orientations corresponding to the (111), (200), and (220) orientations of NaCl TiN. The films deposited using DC magnetron sputtering exhibited high density (<5.2 g/cm³) and significant compressive stress (1.477 GPa) when the TiN film thickness ranged from 29 to 30 nm. The films deposited via VHF-DC superimposed sputtering exhibited a higher density (5.25 g/cm³) and tensile stress (0.928 GPa). As revealed by XRD, the films deposited via DC sputtering exhibited the (111) crystal orientation, whereas those deposited via VHF-DC superimposed sputtering exhibited the (200) crystal orientation. The film deposited by VHF-DC superimposed sputtering at a frequency of 60 MHz and a substrate temperature of 350 °C exhibited good resistivity (93.0–143.3 μΩ cm). Furthermore, the TiN films exhibited exceptional smoothness with a surface roughness of less than 0.5 nm. These results show that VHF-DC superimposed sputtering is a promising technique for fabricating TiN-based MHMs.