Analyses of Reactive Plasma Dynamics by Particle Simulations

等离子体加工技术是包括半导体芯片和液晶显示在内的先进电子产品中最重要的技术之一，其中包括基于反应等离子体的薄膜形成和表面改性技术。在本研究中，我们采用基于粒子池（PIC）和蒙特卡罗碰撞（MCC）方法的粒子模拟来分析半导体制造中使用的等离子体处理工具。PIC和MCC方法是理想的反应等离子体模拟方法，前者可以解析电子速度分布函数，后者可以利用基本的物理数据（如反应碰撞截面）确定化学反应速率。1999年，我们开发了一个PIC/MCC代码来模拟二维圆柱形结构中电容耦合平行板氩放电。至于碰撞，我们包括了电子中性碰撞的电离、激发和弹性碰撞，以及离子中性碰撞的电荷交换和弹性碰撞。目前假定中性气体与室温是均匀的。在2000年，我们扩展了模拟代码来处理双频电容耦合放电，并为现实的等离子体处理工具引入了外部电路。此外，为了提高模拟代码的效率，我们还采用了加速方案进行离子动力学计算。在我们的模拟中，我们观察到，在单频和双频电容耦合放电中，随着气体压力的降低，电子加热机制从欧姆加热转变为无碰撞加热，并且由于Ar的弹性碰撞截面的Ramsauer最小值，电子能量分布函数呈现双麦克斯韦分布。

Plasma processing, such as thin-film formation and surface modification technologies based on reactive plasmas, is one of the most important technologies for the advanced electronics, including semiconductor chips and liquid-crystal displays. In the present research, we have employed particle simulations based on the Particle-in-Cell (PIC) and Monte-Carlo Collision (MCC) methods to analyze plasma-processing tools used in semiconductor manufacturing. The PIC and MCC methods are ideal for reactive plasma simulations as the former can resolve electron velocity distribution functions and the latter can determine chemical reaction rates using fundamental physical data such as reaction collision cross sections. In 1999, we have developed a PIC/MCC code to simulate capacitively coupled parallel-plate Ar discharges in 2D cylindrical geometry. As to collisions, we have included ionization, excitation, and elastic collisions for electron-neutral collisions, and charge exchange and elastic collisions for ion-neutral collisions. Currently the neutral gas is assumed to be uniform with the room temperature. In 2000, we have extended the simulation code to handle dual-frequency capacitively coupled discharges and also introduced external electrical circuits for realistic plasma processing tools. Furthermore, we have employed an acceleration scheme for ion dynamics calculations to increase efficiency of the simulation code. In our simulations we have observed that, in both single- and dual-frequency capacitively coupled discharges, as the gas pressure decreases, the electron heating mechanism changes from ohmic heating to collisionless heating, and the electron energy distribution function exhibits a bi-Maxwellian distribution due to the Ramsauer minimum of the elastic collision cross section for Ar.