Zhang Yongkang, Hou Zhongxuan, Si Chaowei, Han Guowei, Zhao Yongmei, Lu Xiaorui, Liu Jiahui, Ning Jin, Yang Fuhua
Engineering Research Center for Semiconductor Integrated Technology, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China.
Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China.
Micromachines (Basel). 2023 Jan 25;14(2):306. doi: 10.3390/mi14020306.
The silicon etching process is a core component of production in the semiconductor industry. Undercut is a nonideal effect in silicon dry etching. A reduced undercut is desired when preparing structures that demand a good sidewall morphology, while an enlarged undercut is conducive to the fabrication of microstructure tips. Undercut is related to not only the production parameters but also the mask materials. In this study, five mask materials-Cr, Al, ITO, SiN, and SiO-are chosen to compare the undercut effect caused by the isotropic etching process and the Bosch process. In the Bosch process, the SiN mask causes the largest undercut, and the SiO mask causes the smallest undercut. In the isotropic process, the results are reversed. The effect of charges in the mask layer is found to produce this result, and the effect of electrons accumulating during the process is found to be negligible. The undercut effect can be enhanced or suppressed by selecting appropriate mask materials, which is helpful in the MEMS process. Finally, using an Al mask, a tapered silicon tip with a top diameter of 119.3 nm is fabricated using the isotropic etching process.
硅蚀刻工艺是半导体行业生产的核心组成部分。侧向腐蚀是硅干法蚀刻中的一种不理想效应。在制备需要良好侧壁形态的结构时，希望减小侧向腐蚀，而增大侧向腐蚀则有利于微结构尖端的制造。侧向腐蚀不仅与生产参数有关，还与掩膜材料有关。在本研究中，选择了五种掩膜材料——铬（Cr）、铝（Al）、氧化铟锡（ITO）、氮化硅（SiN）和二氧化硅（SiO）——来比较各向同性蚀刻工艺和博世工艺所引起的侧向腐蚀效应。在博世工艺中，SiN掩膜引起的侧向腐蚀最大，而SiO掩膜引起的侧向腐蚀最小。在各向同性工艺中，结果则相反。发现掩膜层中的电荷效应导致了这一结果，并且发现工艺过程中积累的电子效应可忽略不计。通过选择合适的掩膜材料可以增强或抑制侧向腐蚀效应，这对微机电系统（MEMS）工艺很有帮助。最后，使用铝掩膜，通过各向同性蚀刻工艺制造出了顶部直径为119.3纳米的锥形硅尖端。
