Investigation Of Preparing Nanocrystalline Carbon Nitride Thin Film

In this paper, preparing nanocrystalline carbon nitride thin films has been investigated by using Arc Discharge and dc Hollow Cathode Discharge (HCD). HCD, as a new method of preparing carbon nitride thin films, has been studied specially. In addition, as my previous work, the emission spectra of He plasma were measured by using three kinds of experiment devices: Dielectric Barrier Discharge, HCD and Penning Discharge.At the beginning of our research, we applied Arc Discharge to prepare carbon nitride films successfully. But the quality of the films is not satisfying because of too excessive discharge current and too strong sputtering to form uniform films. To solve this problem, a new type plasma source device, HCD, has been designed and set up. By studying the relationship among discharge current, discharge voltage and air pressure, we find that the dc HCD operates in a special glow mode, which is an intergrade between normal and abnormal glow discharge. It has the characteristic of working on higher pressure and lower voltage and having a high cathode sputtering rate. The most appropriate pressure for forming film is between 90Pa and 160Pa. Plasma diagnostics has been performed using optical emission spectroscopy and Langmuir probe. The spectra are dominated by N₂⁺, N₂⁺, C₂ and CN bands. The electron temperature is between 1.7eV and 2.6eV by analyzing and calculating the emission spectra of Argon plasma. Depending on discharge voltage and air pressure, the density of electron and ion varied from 10⁷cm^-3 to 10⁸cm^-3.High quality carbon nitride thin films were synthesized on Si(100) substrates at room temperature by using HCD plasma sputtering technique. The surface morphology of the film indicated that very smooth and uniform CNx films have been fabricated. The averagesize of particles is about 0⁵0nm. When bias voltage is used on substrates, the deposition rate increased and the surface of the film became more compact. In order to understand their structure, X-ray photoelectron, XRD, Raman and Infrared spectra were investigated. X-ray photoelectron spectroscopy showed that synthesized films were constructed primarily from sp² CN and sp³ CN bonds. The fact that N content is very high in the films is associated with the intension of the films. The ratio of N/C is close to that of C₃N₄. Obvious variations of component ratio among C-C, sp² CN, and sp³ CN bonds were also observed by XPS. The results show a obvious evidence that the modes of the film can be controlled by variations of bias voltage. The XRD feature of the films indicates one diffraction peak at 29=68.8°, which was assumed to correspond to (211) reflection for the crystalline P-C3N4 material. Infrared and Raman spectra indicate the existence of C-N, C=N, C≡N, β-C₃N₄ and α-C₃N₄.All results indicate that the HCD technique is a very effective way to fabricate carbon nitride films. The synthesized films have a multi-crystal structure and a high N content. The HCD has the merits of simple structure, low discharge voltage, and high ion density. As a plasma source, it can be used to prepare carbon nitride films on big sized products, so it has a good prospect in industry application.