The Structural And Optical Properties Of SiN_x Prepared By Radio Frequency (r.f.) Magnetron Sputtering

One of the most important manufacturing steps of crystalline silicon solar cells is to prepare an antireflection coating, Which is not only reducing surface reflectance but simultaneously providing surface passivation. Silicon nitride films explore by PECVD using of mixtures based on silane, ammonia and nitrogen, which present a security hidden trouble in the process resulting in growing interest in different deposition techniques. R.F. magnetron sputtering has been regarded as one of the promising ways to produce the nitrogen silicon films at a low temperature, which have been extensively studied in many domains. It is well known that the r.f. magnetron sputtering can prepare amorphous film of very important characteristic in advance applications. By controlling the deposition conditions, it is possible to get the different stoichiometric films. Here, the optical properties and photoluminescence of the films were studied in this paper.Another aspect, the properties of photoluminescence was explored, because of the downconverter possibilities of such layers, which could be integrated in third generation solar cells.Silicon nitride thin films were prepared by radio frequency(r.f.) magnetron reactive sputtering with different Ar / N₂ flow ratio at 80℃temperature. The polished silicon wafers were used as the substrate materials in order to make surfaces of the sample smooth. The influence of working gas on structures and optical properties of silicon nitride thin films were studied. From X-ray photoelectron spectroscopy (XPS) experiments, the bonding structure of Si-N appeared in the film which were confirmed by two peaks in standard binding enery. The atomic force microscope(AFM) images show that the films deposited on the silicon wafers were flat and compact. The experiment shows that some micropores and defects existed in the films accompanied with increasing of N₂ flow, which have a great impact on the properties of the films. And the content of SiN_x in the films prepared in puried N₂ gas is higher than that deposited in the Ar:N₂ mixtures ambience.Subsequently the samples were annealed in pure N₂ ambience. Influences of the Ar:N₂ gas flow ratio as well as annealing on the structure were studied. The composition of the samples was investigated by Fourier transform infrared (FTIR) spectra. Microstructure of the films was investigated using atomic force microscope (AFM). The films after annealing compared to former present a more compact construct, which is very dependent on the hydrogen concentration in the film.Also, the influences of annealing and sputtering ambience on the photoluminescence of silicon nitride thin films were studied. The silicon nitride films with different Si-rich degrees were obtained by changing the flow ratio of Ar:N₂, subsequently the samples were annealed at a high temperature in pure N₂ ambience. The influence of annealing on the properties of films was investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and photoluminescence (PL). The appearance of Si-N bonds can be confirmed by the XPS, from which the ratio of Si/N can be rough estimated. Therefore, the XPS reveals that the sample before annealing has a high content of Si which is the premise to come into being nanometer Si. However, the PL of the films after annealing in the visible light region can be observed obviously. The XRD results indicate that the presence of Si clusters buried in the films after annealing are confirmed by the novel diffraction peak, which are related to nanometer Si. The PL productions were considered to quantum confinement effect and defect states in the film. Thus, the UV response of standard solar cells could be improved by controlling the annealing condition.