双频容性耦合CF_4等离子体放电的二维混合模拟

Two-dimensional hybrid simulation of dual-frequency capacitively coupled CF_4 plasma

研究了等离子体反应装置内的等离子体密度、粒子能量与角度分布等参量在装置径向与轴向上的分布特性。在研究过程中应用二维混合模型对CF4气体放电进行模拟。计算结果显示:在电极表面与侧壁附近的鞘层区特性有明显的区别。由于装置侧壁处受电源产生的射频电场的影响较小,侧壁处的鞘层主要由双极扩散机制形成,其产生的径向电场强度较弱,鞘层厚度也较薄。而在电极附近,由于受到射频电场的影响,鞘层的厚度显著增加,指向电极方向的轴向电场强度也远大于指向侧壁方向的径向电场强度。在电极区域内,离子通量分布均匀;在电极边缘与侧壁的间隙内,因电场强度减小,离子通量则发生迅速衰减。在射频电极覆盖的范围内离子能量分布大体上保持不变,电极与侧壁的交界处,由于受到侧壁处径向电场的影响,离子能量分布略有不同。在放电装置的中心区域,入射到电极上的离子角度分布基本保持一致,而在电极边界与装置侧壁的交界处,由于径向电场的影响,离子的垂直入射角增加,以大角度轰击电极的离子数量也显著增加。

A two-dimensional hybrid model is used to study the two-dimensional characters of the plasma parameter such as the ion flux,the ion energy and angular distributions in radial and axial directions.It shows that the electric field and the sheath character at the center of the electrode are different from those at the area between the electrode and the side wall.At the area between the electrode and the side wall,the influence of the electrode is relatively small,and the sheath structure is determined by the ambipolar diffusion.Therefore,the axial electric field is small,the radial electric field is relatively stronger,and the sheath near the side wall is much thinner than that in the center of the RF electrode.The ion flux and the ion energy distributions on the electrode remain the same at the center area of the discharge chamber,however,the electric field in axial direction decreases between the side wall and the edge of electrode,which leads to a decrease of the ion flux in this region.The ion angular distributions also have little change at the center area of the discharge chamber.However,the radial electric field becomes stronger than the axial field between the side wall of the chamber and the edge of the electrode.This makes the ions in that area strike the lower electrode with a much larger angle.