Two-dimensional Simulation Of Pulse Modulated Radio-frequency SiH₄/N₂/O₂Discharge

In integrated circuits and electronic devices, silicon-oxynitride films are extensively used as dielectrics, diffusion barrers and passivation layer. This owes to good photoelectrical characteristics and stability, and this material possesses the most advantages of both SiO2and Si3N4. For that reason, processing techniques have in the previous decade, many been developed to form silicon-oxynitride films at low or high temperatures. For example, there are plasma enhanced chemical vapor deposition (PECVD) and ECR-PECVD techniques which belong to low-temperature processes, thermal CVD, sputtering from silicon target using various Ar-O2-N2atmosphere and nitridation of SiO2films which are high-temperature processes. Among these deposition methods, plasma enhanced chemical vapor deposition is, especially, already one of the most important processing techniques due to the low temperatures and the possibility of gaining excellent properties of the films. Accordingly, a lot of studies have been carried out on the SiOxNy material deposited by PECVD technique at low temperatures in silane plasmas mixed with other gas. Recently a pulsed-PECVD becomes the research hot spot, because it improves performance of films, compared with continuous discharge. Nevertheless, studies of the behaviors of silicon-oxynitride films in various pulsed plasma discharges is less in both experiments and theories, especially in SiH4/O2/N2discharges. This is due to the large amount of calculation and complex of chemical reaction. In previous studies, wang used a one-dimensional fluid model to study pulsed plasma in SiH4/N2/O2discharges. In order to more clearly understand process of pulsed plasma in SiH4/N2/O2discharges, it is essential to model realistic reactor geometries. In this paper, a self-consistent two dimensional fluid model is employed to investigate pulsed CCP in SiH4/O2/N2mixtures.Chapter I introduces the characteristics of low-temperature plasma and deposition techniques, then the progress of pulse discharge in the experiments and simulation aspects.Chapter II explains the fluid model and the numerical algorithms in the simulation, and gives the related reactions.Chapter III in this study, a two-dimensional fluid model is established to investigate the spatiotemporal dynamics of pulse modulated radio-frequency SiH4/N2/O2discharge sustained in a capacitively coupled plasma reactor. The influences of the pulse parameters and discharge parameters on the plasma properties, including electron, ions, radical, ion flux and deposition rate are quantified, as well as the electron temperature. Our simulation results show that for the same amplitude of the potential, when duty cycle increases, the plasma density in the bulk plasma and deposition rate and ion flux at the electrode increase. At the same time the variation of temperature with duty cycle causes constantly change of chemical ions in the discharge. If the rf voltage is kept constant, the maximum of electron density and negative density(O-) at the center of discharge is inversely proportional to pulse frequency, but the averaged negative density in the bulk plasma, voltage drop, deposition rate and ion flux at the plate is proportional to pulse frequency. When duty cycle and modulation frequency is fixed, the increased pressure improves plasma density, ion flux and deposition at the lower plate, but decreases ion energy at the lower plate. Higher voltage may promote the increase of plasma density, ion flux and energy on the plate, because the plasma may obtain more energy. Furthermore, we discuss the effect of the two kinds of chambers on plasma properties. The result implies that the presence of the media prevent edge effects and enhance the potential and deposition rate. At last, the effect of the gas percentage on the spatiotemporal dynamics of plasma properties is studied.In addition, no matter how the parameters of discharge change, when the power is off, the change of deposition rate is not large, the flux and energy on the substrate electrode will decrease. The uniformity of deposition during the off time is better. So utilizing pulsed power condition may almost maintain deposition rate under reducing ion bombardment of plate.Based on the above results, in the pulse modulation discharge by optimizing the various discharge parameters, on the one hand, the density of plasma may be improved and the magnitude and composition of the reactive fluxes to the wafer may be controlled, on the other hand, high quality thin film may be achieved due to the lower ion bombardment.