Etude et caractérisation de matériaux à base d’oxyde de Silicium pour applications en microtechnologies

Abstract

This thesis is devoted to the study of thin films silicon oxynitride SiOxNy characteristics. Currently, silicon oxynitride SiOxNy is considered the most appropriate material for the manufacture of electronic and optoelectronic devices, since it presents several advantages and the ability to obtain intermediate properties between silicon oxide SiO2 and silicon nitride Si3N4, while being compatible with the standard technology of the microelectronic industry. The main purpose of this thesis is to study the optical and physico-chemical properties of SiOxNy films before and after annealing, using analysis techniques such as ellipsometry, FTIR and RBS technique. The films involved in this study were deposited on (100) silicon single-crystal wafer by low pressure chemical vapour deposition (LPCVD) technique at temperature of about 8500C from a mixture of dichlorosilane (SiH2C12), nitrous oxide (N2O) and ammonia (NH3). The optical properties, film thickness and composition of the oxynitride layers were studied by spectroscopic ellipsometry. For ellipsometry analysis, the application of Bruggeman effective medium approximation theory BEMA and the Tauc-Lorentz dispersion model has allowed us to calculate the refractive index, the volume fractions, the optical gap and thickness of silicon oxynitride films. The physico-chemical properties of the as deposited SiOxNy (not annealed) films were essentially studied using Fourier-Transform Infra-Red spectroscopy (FTIR). Based on the deconvolution of the FTIR spectra, we have identified the vibration modes of Si-O and Si-N bonds. To improve the deconvolution method and the interpretation of FTIR results, we proposed a novel method based on the correlation between the obtained results by BEMA model (derived from the analysis ellipsometry) and FTIR measurements. This method allowed a satisfactory and accurate estimatation of the SiOxNy films stoichiometry and their atomic concentrations. Additional measurements were obtained by the RBS technique to access to the volume fractions values [O]/[Si] and [N]/[Si]. By using these characterization techniques on thermally annealed samples at high temperatures, we have found that a suitable thermal annealing of the SiOxNy film can, on the one hand, almost completely releases the nitrogen atoms, on the other hand, causes the formation of a certain amount of silicon clusters in these films. Finally, in the last part of this thesis, we presented an application of SiOxNy films in the field of microelectronics technology, such as the submicron MOSFET with silicon oxynitride as gate material. The study was carried out using TCAD -SILVACO software. A comparison was made between the characteristics of a conventional gate transistor (based on silicon oxide SiO2) and a transistor gate made of SiOxNy. The obtained results showed that the use of silicon oxynitride as the gate of TMOS has enabled a significant improvement in the device performance in particular, the reduction of gate leakage current and the increase in current drain. These advantages allow the consideration of this material as a good candidate to replace conventional insulators used in the MOS technology.