Effects of arrival rate and gas pressure on the chemical bonding and composition in titanium nitride films prepared on Si(100) substrates by ion beam and vapor deposition

Abstract

Thin titanium nitride films were prepared at room temperature by titanium metal vapor deposition on silicon substrates with simultaneous irradiation by a 2 keV nitrogen ion beam. Arrival rate ratios, ARR(N/Ti), defined as the ratio of the flux of incident atomic nitrogen particles in the ion beam relative to the flux of titanium atoms transported to the substrate, ranged from 0.17 to 2.5. The gas pressure in the vacuum chamber was maintained at 1.3×10−3 or 6.7×10−3Pa during the deposition and irradiation process. Analyses of Ti 2p x-ray photoelectron spectroscopy spectra indicated the presence of metal Ti0, nitride TiN, oxide TiO2, oxynitride TiNxOy, and carbide TiC phases. The Ti0 phase was observed exclusively and predominantly in the films prepared at 1.3×10−3Pa and ARR(N∕Ti)=0.17, 0.21, and 0.28, and the TiN phase is major in the others, as confirmed by the x-ray diffractometry analyses. The chemical composition ratio N/Ti in the films prepared at 1.3×10−3Pa increased linearly with increasing ARR(N/Ti) up to ARR(N∕Ti)=0.42 and tended to be constant with further increase in ARR(N/Ti), while this ratio in the films prepared at 6.7×10−3Pa was almost constant independently of ARR(N/Ti), similar to the constant value observed at 1.3×10−3Pa and higher ARR(N/Ti). This dependence may be understood by comparison with the flux of evaporated titanium atoms, the flux of nitrogen in the beam, and the impingement rate of nitrogen gas in the vacuum chamber, evaluated through the kinetic theory of gases. On the other hand, titanium is known to be one of the chemically active materials which form stable compounds with gases by chemisorption, this fact leading to considerable incorporation of contaminant oxygen and carbon in the depositing titanium film.