Research On Characteristic Of Plasma Sheath And Dust Particles In The Sheath

In the process of plasma material surface modification, synthesis film and etching, theplasma and the physical characteristic of the plasma sheath formed near the surface of thematerials directly affect the capability of the materials processed. Energy and densitydistribution of charged particle in the sheath, potential structure of sheath and magnetic fieldwill all decide the interactive process of plasma and material. Therefore, it is significant andworthy to research the plasma sheath. Meanwhile, the researches on the plasma sheath are notenough, especially the research on the sheath characteristic of the electronegative plasma. Forthe great amount of negative ions that exist in some plasmas' processes have impact on thestructure of the sheath dramatically. In addition, the charged dust particles exist widely inspace, laboratory as well as micro-electronics industry for plasma processes devices. Theresearch on characteristic of the dusty plasma or the dust in the plasma have explaineddifferent aspects, however, there are still many questions remaining unclear. This thesisresearches through simulation on the sheath of the electronegative plasma and the chargebehavior of dust with the ultraviolet radiation in the electronegative plasma, the plasma sheathof the cylindrical concave electrode and the distribution of the dust particles in the sheath, anddynamic behavior of the single dust particle in the plasma sheath within the magnetic field.The contents are:Firstly,basic concept and characteristic of plasma sheath and dusty plasmas, significance ofresearch and development actuality are introduced.Secondly,sheath structures of strong electronegative plasmas are investigated, using a fluidtheory. The effect of ultraviolet radiation to the charge behavior of dust particles in theelectronegative SiH₄ plasmas has been researched, using the OML model. The result showsthat presheath transition almost does not exist between bulk plasma and sheath and a purepositive ion sheath is formed near the electrode. Furthermore, the net charge has a peak nearthe sheath edge. The faster spatial potential falls, the thinner the sheath thickness becomes.UV photodetachment could significantly lower the dust negative charge and even make dustgrains positively charged under some special conditions.Thirdly,a fluid sheath model of a cylindrical concave electrode has been established and itstwo-dimension characteristic has been simulated. Based on that, a three dimensionaldynamics model describing dust particles has been established and their distributions have been studied. The result shows that the potential well formed by the electrode sheath couldscatter the dust particles. The sheath is thin if the density of the plasma is high; on thecontrary, the sheath is thick. One layer structure is formed if the number of the dust is small;while multilayer structure is formed if the number of the dust is large. With variant sizes ofthe electrode, the dust particles then form some complex and interesting structures. Whileconsidering the wake effect, it is found that in the sheath, the particles on the upper level areorientationally consistent to attract their counterparts on the lower level on the axialcomponent.Fourthly,dynamics of dust in a plasma sheath with magnetic field is investigated, using asingle particle model. The result shows that radius, original position and velocity of dustparticles and the magnetic field have effect on its movement and equilibrium position in theplasma sheath. The same size dust particles, whatever original velocity and position they have,finally will rest at the same position under the net actions of electrostatic, gravitational,neutral collisional,ion drag and Lorentz forces. But they will not rest in the plasma sheath iftheir radius is beyond certain size.Fifthly,the evolution of collisionless and collisional sheaths in different geometries andunder various gas pressures has been numerically studied, using a one-dimensional fluidmodel. Besides that, plots for the average kinetic energy as well as the current density of ionimplantations at the target surface are presented. For the collisional sheath, it is found that thefinal sheath thickness in planar, spherical or cylindrical geometries differs from each othersignificantly. Also, computational results of the collisional sheath in different geometries arein good agreement with those obtained by analytic models.Finally, conclusions and the future work are given in the thesis.