Ordered silicon nanocone fabrication by using pseudo-Bosch process and maskless etching

Zheng Yan, H. Ekinci, Aixi Pan, Bo Cui
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Abstract

Nanocone arrays are widely employed for applications such as antireflection structures and field emission devices. Silicon nanocones are typically obtained by an etching process, but the profile is hard to attain because anisotropic dry etching generally gives vertical or only slightly tapered sidewall profiles, and isotropic dry plasma etching gives curved sidewalls. In this work, we report the fabrication of cone structures by using masked etching followed by maskless etching techniques. The silicon structure is first etched using fluorine-based plasma under the protection of a hard metal mask, with a tapered or vertical sidewall profile. The mask is then removed, and maskless etching with an optimized nonswitching pseudo-Bosch recipe is applied to achieve the cone structure with a sharp apex. The gas flow ratio of C4F8 and SF6 is significantly increased from 38:22 (which creates a vertical profile) to 56:4, creating a taper angle of approximately 80°. After subsequent maskless etching, the sidewall taper angle is decreased to 74°, and the structure is sharpened to give a pointed apex. The effect of an oxygen cleaning step is also studied. With the introduction of periodic oxygen plasma cleaning steps, both the etch rate and surface smoothness are greatly improved. Lastly, it was found that the aspect ratio-dependent etching effect becomes prominent for dense patterns of cone arrays, with a greatly reduced etch depth at a 600 nm pitch array compared to a 1200 nm pitch array.
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利用伪博世工艺和无掩膜刻蚀技术制造有序硅纳米锥
纳米锥阵列广泛应用于抗反射结构和场发射装置等领域。硅纳米锥通常通过蚀刻工艺获得,但由于各向异性干法蚀刻通常会产生垂直或仅略带锥度的侧壁轮廓,而各向同性干法等离子体蚀刻则会产生弯曲的侧壁,因此很难获得轮廓。在这项工作中,我们报告了利用掩膜蚀刻技术和无掩膜蚀刻技术制造锥形结构的情况。首先,在硬金属掩膜的保护下使用氟基等离子体蚀刻硅结构,蚀刻出锥形或垂直的侧壁轮廓。然后移除掩膜,采用优化的非开关伪博世配方进行无掩膜蚀刻,以获得具有尖锐顶点的锥形结构。C4F8 和 SF6 的气体流量比从 38:22(形成垂直剖面)大幅提高到 56:4,形成约 80° 的锥角。在随后的无掩模蚀刻后,侧壁锥角减小到 74°,结构变得尖锐,形成一个尖尖的顶点。此外,还研究了氧气清洁步骤的效果。在引入周期性氧等离子清洗步骤后,蚀刻速率和表面光滑度都得到了极大改善。最后,研究发现,对于密集的锥形阵列图案,与长宽比相关的蚀刻效应变得非常突出,与 1200 nm 间距阵列相比,600 nm 间距阵列的蚀刻深度大大降低。
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