Capacitively coupled wafer-bearing cathodes are widely used in etching and deposition processes. Uniform electric field and plasma density across the wafer surface are necessary for process control all the way to the edge of the wafer. Terminating structures at the wafer edge such as focus rings are used to improve uniformity and minimize costly edge exclusion. The focus ring can be viewed as an arbitrary impedance element at the wafer edge that balances the sheath voltage above it and the region above the wafer, minimizing field variation at the wafer edge. To validate this assumption, a one-dimension circuit model with focus rings was developed. The simulations were compared to experimental results measured using hairpin probe, VI probe, and a retarding field energy analyzer (Impedans RFEA). It was found that the focus ring coupling acts as a voltage divider only in high voltage cases, and the sheath voltage drop over the focus ring will increase in low voltage cases and does not rigorously follow the voltage divider model typically used.

中文翻译：

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聚焦环几何形状对等离子工艺晶圆边缘电压分布的影响

电容耦合的承载晶片的阴极广泛用于蚀刻和沉积工艺。整个晶圆表面的均匀电场和等离子体密度对于一直到晶圆边缘的过程控制都是必要的。晶圆边缘的端接结构（例如聚焦环）用于提高均匀性并最大限度地减少昂贵的边缘排除。聚焦环可以被视为晶片边缘的任意阻抗元件，它平衡其上方的鞘电压和晶片上方的区域，最大限度地减少晶片边缘的场变化。为了验证这一假设，开发了一个带有聚焦环的一维电路模型。将模拟结果与使用发夹探针、VI 探针和阻滞场能量分析仪 (Impedans RFEA) 测量的实验结果进行比较。