Microstructure of amorphous carbon nitride films fabricated by facing-target reactive magnetron sputtering

Abstract

Carbon nitride films have been fabricated by a dc facing-target reactive sputtering system for various N2 fractions (PN) in the gas mixture. Complementary measurement techniques, including atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and high-resolution transmission electron microscopy (HRTEM), were used to systematically study the morphology and microstructure of the films. AFM images show that the average surface roughness increases with increasing PN. XPS analyses indicate that the concentration of N is not directly proportional to PN, and it rises quickly to a saturated value of ∼33 at% at a PN of 20%, which can be attributed to the chemical sputtering effect. The ratio N–C(sp2)/N–C(sp3) increases with increase in PN from 0% to 20%, and then decreases with further increase in PN. However, the number of sp2-hybridized C atoms continues to increase over the whole range of PN, as evidenced by Raman and FTIR measurements. The growth of a disordered sp2 C structure at PN below and above 20% can be attributed to the incorporation of N and the compressive stress relaxing, respectively. Raman scattering and HRTEM analyses reveal an incomplete ordering process of the sp2 C structure with increase in PN.