| Capacitively coupled plasmas maintained by silane mixture gases play a crucial role in depositing silicon-based films in the microelectronics industry.Therefore,studying the characteristics of capacitively coupled silane plasma and chemical reaction mechanism process of silane plasma are very important for optimizing silane discharge characteristics or developing new deposition processes.Numerical simulation methods are taken as one of the important methods for learning capacitively coupled discharges.In general,the commonly used numerical simulation methods for plasmas are fluid methods,Fluid/Monte Carlo(MC)and Particle-In-Cell/Monte Carlo(PIC/MC)methods.Compared with other methods,the fluid simulation can not only obtain the spatial-temporal transport process of kinds of species in plasmas but also be compatible with a large number of chemical reactions,as an important tool for studying complex chemical reaction plasmas.In particular,it has an irreplaceable role in the study of complex silane plasmas involving hundreds of chemical reactions.In addition,it is worth noting that in the silane involved discharges,dust particles will unavoidably appear under suitable discharge conditions,and affect the discharge characteristics.Therefore it is necessary to explore the interaction of dust particles with silane plasmas by numerical simulation.The research content of this paper is arranged as follows:The first chapter,as an introduction,introduces some of the challenges in the deposition and etching processes.Then,we discuss some key research interests involved in capacitively coupled plasmas and present the research progresses of related silane mixed gas discharges.At last,we also summariz overview of research on dust particles in silane discharges.In the second chapter,first,the two-dimensional fluid equations and the corresponding numerical solution algorithm are introduced.Subsequently,we investigate the spatial distribution of kinds of species and the influence of Ar or SiH4 gas content on the plasma sustained in the SiH4/N2O/Ar mixed gas.The simulation results show that the axial distribution of Ar metastable atoms satisfies the parabolic distribution at low pressure,while it forms a bimodal structure at high pressure.In addition,in this mixed gas,increasing the Ar content can increase the electron density in the plasma,while decreasing the Ar gas content can reduce the bombardment energy on the electode and improve the plasma radial uniformity.If the silane content is decreased at the fixed content of Ar,the plasma uniformity can be adjusted without increasing the bombardment energy.In addition,by analyzing the flux of neutral particles on the electrode,we find that the content of SiH3,O,SiH2,SiH3O and SiO may be the main gas precursors for the deposition of silicon oxide films,since their relatively higher content.In the third chapter,by using the two-dimensional fluid model,we study the influence of the dielectric layer upon the driven electrode on the plasma radial uniformity in the capacitively coupled plasma maintained by SiH4/N2/O2 mixture gases.At the same time,the possible chemical gas deposition precursors of this mixed gas are systematically studied by changing the external discharge parameters.The simulation results show that when a dielectric layer is applied to the lower electrode,the edge effect of the plasma is effectively suppressed,so that the radial uniformity of the plasma can be improved.However,by analyzing the spatial distribution of the deposition power density,the edge effect of plasma can not be completely eliminated.In addition,compared with the method of adjusting the gas pressure or the distance between the electodes,the dielectric layer can somewhat replace the above two methods to achieve the regulation of plasma uniformity.Finally,by analyzing kinds of species under different discharge conditions,we find that SiH3O,SiH2O,O,N and NO may be the main precursors of film deposition,rather than SiN and HSiNH2.In the fourth chapter,a two-dimensional fluid model is used to simulate the pulse moulated radio-frequency SiH4/N2/O2 plasma.In this discharge,we mainly focus on the influence of the pulse parameters on the transient characteristics and radial spatial distribution of the SiH4/N2/O2 plasma.The simulation results show that in the pulsed plasma,electrons,positive ions and negative ions can obtain a quasi-steady state which is similar to continuous discharge.And we also find that the quasi-steady state of plasma depends not only on the pulse discharge time,but also on the observed discharge position.In addition,the electron temperature,electron density and ionization rate will reach their maximum values during the pulse-on phase in which the electron density firstly attains a minimum value before reaching the maximum value,due to the electron generation term which is less than the loss process caused by electron diffusion.Further,although it is believed that the pulsed discharge can reduce the bombardment energy on the electrode,a high energy peak is still observed after pulse on,which would impair the performance of the substrate.Finally.The change of duty cycle,as one of two additional control parameters for the pulse modulation,compared with continuous discharge,can reduce the edge effect during the glow period and enhance the diffusion of the plasma to improve the radial uniformity of the plasma.In the fifth chapter,the Fliud/MC method combined with a dust model is used to study the interaction between dust and plasma.The simulation results show that dust particles with larger radius will cause a decrease in the electron density,accompanied by an increase in electron temperature.Moreover,lots of large dust particles can cause a brief rise in positive ion or negative ion densities before attaining steady state,and then the ion density decreases due to the decrease in electron temperature or the absorption of ions by dust particles.In addition,in the case of little effect of dust particles on the plasma,the heating mode in the silane plasma is dominated by the ? mode and the reversal field heating mode,and the decrease in the gas pressure,frequency and voltage can reduce the reversed field heating mode.However,by increasing the dust particle radius in the plasma,the drift field heating mode in the bulk is enhanced gradually and dominates the heating mechanism,mainly due to the consumption of electrons by the dust particles.Finally,a detailed study about the effects of the external parameters on the spatial distribution of dust particles,as well as electric field and ion drag forces acting on the dust particles,is also conducted. |
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