Silicon carbonitride (SiCN) thin films have drawn considerable interest among the ternary compounds due to the combination of unique properties such as high hardness, wide band gap, high photosensitivity in the ultraviolet (UV) region and low dielectric coefficient (k). In the last few decades various fabrication methods including reactive sputtering and plasma-enhanced chemical vapour deposition (PECVD) have been intensively studied to achieve SiCN thin films having attractive mechanical, tribological and optoelectronic features. Applications range from hard, wear-resistant coatings, low-k interconnects, UV photodetectors to gas separation membranes .
The properties of thin films are not only influenced by the deposition method, which mainly determines the energy of bombarding ions, but also the choice of source gas . In PECVD processes, silicon (Si), carbon (C) and nitrogen (N) can either be introduced separately as silane (SiH4), methane (CH4), and molecular nitrogen (N2) or ammonia (NH3), or alternatively using organic single precursors such as methylsilazanes . In this work we deposited our thin films with the electron cyclotron resonance (ECR) PECVD method, which differs from other PECVD methods due to it is capability of generating a dense, highly ionized plasma (1011 ions/cm3) and ion impingement energies on the substrate as low as 20 eV . We present the compositional and mechanical properties of hydrogenated SiCN (SiCN:H) thin films which were deposited with two different C precursors, acetylene (C2H2) and ethane (C2H6). The stoichiometry, density of the thin film, optical constants, and the bonding structure of SiCN:H thin films as a function of hydrocarbon carbon gas source have been explored. Due to the hydrogen-containing precursors used, the silicon carbonitride films deposited by CVD methods contain a significant amount of hydrogen (H). From Rutherford backscattering spectrometry (RBS), elastic recoil detection (ERD) analysis, quantitative elemental composition distributions including H were found for films deposited with both carbon sources. For further investigation of bonding structure of SiCN:H, Fourier Transform Infrared (FTIR) Spectroscopy and X-ray Photoelectron Spectroscopy (XPS) measurements were performed. Furthermore, we studied the hardness and Young’s modulus by nanoindentation, and variable angle spectroscopic ellipsometry (VASE) measurements were performed to extract optical constants. To interpret the measurements further, nearly stoichiometric silicon nitride and silicon carbide thin films were also prepared.
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