Investigation of the valence band states of reactively sputtered carbon nitride films

Abstract

The variation in the electrical properties of carbon nitride films deposited by a Penning-type opposed target reactive sputtering technique as a function of nitrogen incorporation was recently described (1) M.A. Monclus, D.C. Cameron, R. Barklie, M. Collins, Electrical properties of reactively sputtered carbon nitride, Journal of Vacuum Science and Technology, in press. It was shown that the resistivity and activation energy of the films increase with nitrogen incorporation and this was related to a transition from metallic to semiconducting behaviour. In this paper X-ray photoemission spectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS) are used to study the valence band spectra of the films. XPS studies do not give a good indication of the states responsible for conduction in the films due to cross-section modulation effects. On the other hand, UPS is more useful for measuring the binding energies of the valence electrons and should give a better approximation of the actual valence band spectra of the films. It is also found that the resistivity of carbon nitride films decreases with negative substrate bias. Infrared Spectroscopy is used to investigate the structural modification of the carbon nitride films occurring by changing the substrate bias. The resistivity is found to correlate with the amount of CN triple bonds. Electron spin resonance spectroscopy (ESR) is used to investigate how substrate bias affects the spin concentration in the films. The spin concentration decreases with increasing substrate bias, as the amount of CN bonds linked to aromatic rings decreases. The decrease in resistivity with negative substrate bias is then related to the increase in conduction paths by cross-linking.