Maintaining uniform sample etching during a plasma process is a critical requirement for applications in large-scale wafer processing. The interface between the plasma and the sample surface is defined by the plasma sheath, which accelerates ions toward the sample surface. In areas where the plasma sheath is not parallel to the sample surface, such as near the sample edges, the incident ions arrive at shallower, off-normal angles that can result in a greater etch yield relative to other areas of the sample. This phenomenon leads to nonuniform etching, along with characteristic surface morphology evolution. In this work, we utilized a combination of spatial ellipsometry for etching behavior, atomic force microscopy (AFM) for surface morphology evolution, and power spectral density (PSD) analysis to quantify the extent and spatial dependence of the nonuniform etching near the sample edges. The spatial ellipsometry indicated that a region extending for about 1000 μm from the sample edge experiences approximately 10%–15% more thickness loss (∼10–15 nm) relative to areas near the center of the sample under the tested processing conditions. Within this area, the greatest rate of change in the sample thickness occurs within 5 Debye lengths or ∼300 μm from the sample edge. Via AFM analysis, we detected the presence of ripple features that are consistent with directional ion impacts caused by deflection of ions from normal incidence on the surface morphology [Merkulov et al., Appl. Phys. Lett. 80, 4816 (2002)] AFM scans performed in two different sample orientations confirmed that the ripple features are oriented perpendicular to the direction of incident ions and propagate along the direction of the incident ions. Correspondingly, the magnitude of surface roughness decreases as the distance from the sample edge increases. The ripple features were quantified via PSD analysis, which found the presence of a greater population of long-wavelength roughness closer to the sample edge. The findings of this study provide insight into the influence of the plasma sheath distortions near sample edges on the extent of nonuniform sample etching and characteristic surface morphology evolution in plasma etching applications.

中文翻译：

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边缘效应引起的非垂直离子轰击对聚合物表面形貌演变和蚀刻均匀性的影响

在等离子体工艺过程中保持均匀的样品蚀刻是大规模晶圆加工应用的关键要求。等离子体和样品表面之间的界面由等离子体鞘限定，其将离子加速朝向样品表面。在等离子体鞘不平行于样品表面的区域，例如靠近样品边缘，入射离子以更浅的偏离法线的角度到达，这会导致相对于样品的其他区域更大的蚀刻产量。这种现象导致蚀刻不均匀，以及特征表面形态演变。在这项工作中，我们结合使用空间椭偏仪进行蚀刻行为，使用原子力显微镜 (AFM) 进行表面形态演变，和功率谱密度 (PSD) 分析，以量化样品边缘附近不均匀蚀刻的程度和空间依赖性。空间椭偏法表明，一个区域延伸约 1000 在测试处理条件下，相对于靠近样品中心的区域，距离样品边缘的μ m 经历大约 10%–15% 的厚度损失（~10–15 nm）。在该区域内，样品厚度的最大变化率发生在 5 个德拜长度或距样品边缘约 300微米的范围内 。通过 AFM 分析，我们检测到波纹特征的存在，这些特征与由离子从法向入射偏转到表面形态上引起的定向离子撞击一致 [Merkulov等人。，应用程序。物理。莱特。80, 4816 (2002)] 在两种不同的样品方向上进行的 AFM 扫描证实，波纹特征的方向垂直于入射离子的方向，并沿入射离子的方向传播。相应地，表面粗糙度的大小随着与样品边缘的距离增加而减小。纹波特征通过 PSD 分析进行量化，该分析发现在靠近样品边缘的地方存在更多的长波长粗糙度。这项研究的结果提供了深入了解样品边缘附近的等离子体鞘变形对等离子体蚀刻应用中不均匀样品蚀刻和特征表面形态演变程度的影响。