Effect of ambient gas on structural and optical properties of titanium oxynitride films

Titanium oxynitride films have been deposited on glass substrates by reactive RF magnetron sputtering of titanium target. The influence of oxygen partial pressure in N₂ + Ar and N₂ + He mixtures was examined on structural and optical properties of titanium oxynitride films. The prepared samples were characterized by X-ray diffraction, EDS, surface profilometer, AFM and contact angle measurement system. With increase in oxygen partial pressure, the grain size decreases from ∼70 nm to ∼50 nm in N₂ + Ar mixture, while from ∼60 nm to ∼37 nm in N₂ + He mixture. The thickness calculated from optical transmission data and surface profilometer is in good agreement with each other. The deposited samples are hydrophobic by nature and the contact angle was found to decrease with increase in oxygen partial pressure. Samples prepared in oxygen partial pressure ≥5.5% show transmittance of about 97% in the visible region of the spectrum in both N₂ + Ar and N₂ + He mixtures. The atomic mass of the sputtering gas (Ar and He) significantly affects the primary crystallite size, orientation as well as band gap. We were able to relate the better crystallisation of titanium atoms with low partial pressure of oxygen when films are deposited in helium instead of argon due to Penning ionization.