【作者】 田立成；

【导师】 李雪春；

【作者基本信息】 大连理工大学 ， 等离子体物理， 2010， 硕士

【摘要】 等离子体浸没离子注入(plasma immersion ion implantation,简称PⅢ)是一种新的离子注入工艺,具有成本低、操作简单、可以处理复杂形状样品等优点,在近年来受到了很多材料工程师和科研学者的青睐,并得到广泛的工业应用,比如材料表面改性、计算机芯片制造流程中的元素掺杂、绝缘体上的硅等。在实际应用中,空心圆柱形介质管内表面的离子注入问题比较复杂,一方面由于介质材料的导电性差导致电荷在表面积累而出现充电效应；另一方面由于放置在等离子体中的空心圆管相对表面的鞘层会随着时间的演化出现重叠,从而导致较低的离子注入剂量和注入能量。为解决上述问题,有必要从理论上深入研究空心圆柱形介质管PⅢ过程中鞘层的演化特性。因为在材料表面形成的鞘层的特性直接影响被加工材料的性能。并且,理论研究的结果可以揭示离子注入过程的物理机理,为实际离子注入工艺的优化提供一定的参考。本文主要采用流体动力学方法,对空心圆柱形介质管的内表面PⅢ过程中鞘层扩展规律进行了数值模拟研究,分析讨论了各种参数对鞘层演化过程的影响。首先,采用一维无碰撞流体动力学方法对圆柱形介质管内表面的PⅢ鞘层演化进行了数值模拟,得到了鞘层演化的规律,并且进一步讨论了各参数对注入效果的影响。结果表明,等离子体浸没离子注入圆柱形介质管内表面过程中,在脉冲持续时间内鞘层向中心电极方向扩展,在脉冲下降沿鞘层塌缩下来。在相同的参数条件下,与金属靶相比,介质靶表面附近的鞘层厚度变薄；在介质表面存在电荷积累引起的充电效应,这降低了介质表面电势和离子注入能量；各种参数对离子注入产生了一定影响,在实际注入工艺中,为了减小充电效应的影响,应尽量采用较薄的介质薄膜,同时适当延长脉冲上升时间和缩短脉冲下降时间。其次,本文采用双离子流体模型分析讨论了不同离子成分比对薄膜介质靶材鞘层演化的影响。结果显示,随着N+离子成分的增加,充电效应会越发明显。在实际的离子注入工艺中,为了抑制充电效应和增加离子注入剂量,应尽可能提高N2+离子的成分。最后,我们研究了施加轴向强磁场时圆柱形介质管内表面PⅢ鞘层时空演化规律,并揭示了轴向磁场的引入对鞘层演化特性的影响。结果表明,轴向磁场的引入,不会改变离子能量,但是会使径向离子能量和角向离子能量发生相互转移。轴向磁场的引入产生了角向离子速度,同时轴向磁场越强,径向离子能量分布高能峰越向低能量区移动。更多还原

【Abstract】 Plasma immersion ion implantation (PⅢ) is a new ion implantation processing, which possesses many advantages such as low costs, simple operation and the capability of processing complex-shaped objects etc. Presently, plasma immersion ion implantation as a new method is regarded by some material engineers and researchers. And it has been applied extensively in industry, such as the modification of materials, doping in the course of the manufacture of CMOS chip and silicon on insulating (SOI). In the actual application, the modification of the inner surface of a cylindrical dielectric tube is very complex. On the one hand, there exist the charging effects as a result of the charge accumulation at the dielectric surface because of low electrical conductivity of the dielectric. On the other hand, owning to overlapping of the converging plasma sheaths from the surfaces inside the hollow cylindrical dielectric tube in the plasma, thus makes the implant dose and energy decrease. In order to solve above problems, it is of necessity to investigate theoretically the sheath evolution next to the inner surface of a hollow cylindrical dielectric tube during the PⅢprocessing. Because the characteristics of the plasma sheath formed near the surface of the processed materials directly affect the final properties of the target materials in PⅢ. And then, theoretical research results can reveal the physical mechanism of ion implantation and provide some guidance for the actual processing of ion implantation optimization.In this thesis, we mainly adopt the fluid model to study the principles of PⅢand the expansion of the sheath in the inner surface of a hollow cylindrical dielectric tube. The influences of many parameters on the PⅢare then discussed.First of all, we apply the one-dimensional collision-less fluid sheath model to study the expansion dynamics of plasma sheath in the inner surface of a cylindrical dielectric tube. Then we can get the characteristics of sheath evolution, and the influence of other parameters including the thickness of dielectric-film, the shapes of pulse etc. on the ion implantation is disclosed in detail. It is disclosed that in the course of PⅢinto the cylindrical dielectric tube, the sheath expands towards the auxiliary central electrode in the pulse duration, and in the pulse fall time, the sheath collapses. Under the same parameters, the sheath near the dielectric surface is thinner than that near the metal surface. There exist the charging effects because of charge accumulation at the surface of dielectric, which decrease the dielectric surface potential and the ion implant energy. Various parameters have certain influence on the ion implantation. In the actual processing, we can thin the dielectric film and at the same time adopt suitably longer pulse rise time and shorter pulse fall time in order to reduce the influence of the charging effects.In the next place, we develop a two-ion fluid model describing nitrogen molecular ions N2+ and atomic ions N+ to investigate the influence of ion species ratio on the expansion dynamics of plasma sheath with dielectrics during PⅢ. The numerical results demonstrate that more atomic ions N+ in the plasma can make the charging effects increase. In the actual ion implantation, we had better raise the nitrogen molecular ions N2+ in PⅢwith dielectric-film in order to weaken the charging effects and improve the dose of ion implantation.In the end, we study the sheath evolution when applying strong magnetic field in the axis of the cylindrical dielectric tube, and the effects of strong magnetic field on the characteristics of sheath evolution are investigated. The results indicate that the ion energy would remain unchanged when introducing the magnetic field in the axis of a cylindrical dielectric tube. However, the magnetic field makes the ion energy shift between the radius direction and angle direction. The introduction of magnetic in the axis makes the ion velocity in the angle direction appear. At the same time, with increasing the strength of magnetic field, the high energy peak of ion energy distribution in the radius direction would move towards the low energy section.更多还原