Influence of high power impulse magnetron sputtering plasma ionization on the microstructure of TiN thin films

HIPIMS (High Power Impulse Magnetron Sputtering) discharge is a new PVD technology for the deposition of high-quality thin films. The deposition flux contains a high degree of metal ionization and nitrogen dissociation. The microstructure of HIPIMS-deposited nitride films is denser compared to conventional sputter technologies. However, the mechanisms acting on the microstructure, texture and properties have not been discussed in detail so far. In this study, the growth of TiN by HIPIMS of Ti in mixed Ar and N2 atmosphere has been investigated. Varying degrees of metal ionization and nitrogen dissociation were produced by increasing the peak discharge current (Id) from 5 to 30 A. The average power was maintained constant by adjusting the frequency. Mass spectrometry measurements of the deposition flux revealed a high content of ionized film-forming species, such as Ti(1+), Ti(2+) and atomic nitrogen N(1+). Ti(1+) ions with energies up to 50 eV were detected during the pulse with reducing energy in the pulse-off times. Langmuir probe measurements showed that the peak plasma density during the pulse was 3×016 m^-3 Plasma density, and ion flux ratios of N1þ: N2 1þ and Ti1þ: Ti0 increased linearly with peak current. The ratios exceeded 1 at 30 A. TiN films deposited by HIPIMS were analyzed by X-ray diffraction, and transmission electron microscopy. At high Id, N(1+): N2 (1+)>1 and Ti(1+): Ti(0)>1 were produced; a strong 002 texture was present and column boundaries in the films were atomically tight. As Id reduced and N1þ: N21þ and Ti1þ: Ti0 dropped below 1, the film texture switched to strong 111 with a dense structure. At very low Id, porosity between columns developed. The effects of the significant activation of the deposition flux observed in the HIPIMS discharge on the film texture, microstructure, morphology and properties are discussed.