In high aspect ratio (HAR) dielectric plasma etching, dual-frequency capacitively coupled radio-frequency plasmas operated at low pressures of 1 Pa or less are used. Such plasma sources are often driven by a voltage waveform that includes a low-frequency component in the range of hundreds of kHz with a voltage amplitude of 10 kV and more to generate highly energetic vertical ion bombardment at the wafer. In such discharges, the energetic positive ions can overcome the repelling potential created by positive wall charges inside the etch features, which allows reaching high aspect ratios. In order to increase the plasma density a high-frequency driving component at several 10 MHz is typically applied simultaneously. Under such discharge conditions, the boundary surfaces are bombarded by extremely energetic particles, of which the consequences are poorly understood. We investigate the charged particle dynamics and distribution functions in this strongly non-local regime in argon discharges by Particle-in-Cell simulations. By including a complex implementation of plasma-surface interactions, electron induced secondary electron emission (δ-electrons) is found to have a strong effect on the ionization dynamics and the plasma density. Due to the high ion energies at the electrodes, very high yields of the ion induced secondary electron emission (γ-electrons) are found. However, unlike classical capacitive plasmas, this high number of γ-electrons does not cause significant ionization directly, since upon High voltage low pressure dual-frequency CCPs 2 acceleration in the high voltage sheaths, these electrons are too energetic to ionize the neutral gas efficiently. These γ- and δ-electrons as well as electrons created in the plasma bulk and accelerated towards the electrodes to high energies by reversed electric fields during the local sheath collapse are found to induce the emission of a high number of δ-electrons, when they hit boundary surfaces. This regime is understood fundamentally based on the following approach: First, dual-frequency discharges with identical electrode materials are studied at different pressures and high-frequency driving voltages. Second, the effects of using electrodes made of different materials and characterized by different secondary electron emission coefficients are studied. The electron dynamics and charged particle distribution functions at boundary surfaces are determined including discharge asymmetries generated by using different materials at the powered and grounded electrodes.

中文翻译：

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在低频和高压下运行的低压双频电容耦合等离子体中的带电粒子动力学和分布函数

在高纵横比 (HAR) 电介质等离子体蚀刻中，使用在 1 Pa 或更低的低压下运行的双频电容耦合射频等离子体。这种等离子体源通常由电压波形驱动，该电压波形包括数百 kHz 范围内的低频分量，电压幅度为 10 kV 或更高，以在晶片上产生高能垂直离子轰击。在这种放电中，高能正离子可以克服蚀刻特征内部正壁电荷产生的排斥电位，从而实现高纵横比。为了增加等离子体密度，通常同时应用几个 10 MHz 的高频驱动分量。在这样的放电条件下，边界面被高能粒子轰击，其中的后果知之甚少。我们通过 Particle-in-Cell 模拟研究了氩放电中这种强烈非局域状态下的带电粒子动力学和分布函数。通过包括等离子体-表面相互作用的复杂实现，发现电子诱导的二次电子发射（δ-电子）对电离动力学和等离子体密度有很强的影响。由于电极处的高离子能量，发现离子诱导二次电子发射（γ-电子）的产率非常高。然而，与经典的电容等离子体不同，这种大量的 γ 电子不会直接引起显着的电离，因为在高压鞘中的高压低压双频 CCP 2 加速时，这些电子能量太大而无法有效地电离中性气体. 发现这些 γ 和 δ 电子以及在等离子体体中产生并在局部鞘层塌陷期间通过反向电场向电极加速到高能量的电子会诱导大量 δ 电子的发射，当它们击中边界面。从根本上理解该机制基于以下方法：首先，在不同压力和高频驱动电压下研究具有相同电极材料的双频放电。其次，研究了使用由不同材料制成并具有不同二次电子发射系数的电极的效果。