Wang Shuai, Wang Yaoyu, Zhang Shizhuo, Wang Lingfeng, Chen Shuai, Zheng Huai, Zhang Chen, Liu Sheng, Cheng Gary J, Liu Feng
Institute of Technological Sciences, Wuhan University, Wuhan 430072, China.
School of Power and Mechanical Engineering, Wuhan University, Wuhan 430072, China.
Micromachines (Basel). 2021 Sep 30;12(10):1188. doi: 10.3390/mi12101188.
Copper (Cu) is the main interconnect conductor for integrated circuits (IC), and its processing quality is very important to device performance. Herein, a hybrid process of plasma oxidation and femtosecond laser (fs-laser) ablation was proposed for the nanoscale precision removal of Cu in integrated circuits. In this hybrid process, the surface layer of Cu was oxidized to the copper oxide by plasma oxidation, and then the fs-laser with a laser fluence lower than the Cu ablation threshold was used to remove the copper oxide without damaging the underlying Cu. Theoretically, the surface temperature evolutions of Cu and copper oxide under the femtosecond laser were studied by the two-temperature model, and it was revealed that the ablation threshold of copper oxide is much lower than that of Cu. The experimental results showed that the ablation threshold of copper oxide is lower than that of Cu, which is consistent with the theoretical analysis. Using the hybrid process, a surface roughness of 3 nm and a removal accuracy of 4 nm were obtained in the process of Cu film processing, which were better than those obtained by fs-laser ablation. This demonstrated that the hybrid process has good application potential in the field of copper micromachining.
铜（Cu）是集成电路（IC）的主要互连导体，其加工质量对器件性能非常重要。在此，提出了一种等离子体氧化和飞秒激光（fs激光）烧蚀的混合工艺，用于集成电路中铜的纳米级精确去除。在这种混合工艺中，通过等离子体氧化将铜的表面层氧化为氧化铜，然后使用激光能量密度低于铜烧蚀阈值的飞秒激光去除氧化铜，而不会损坏下面的铜。理论上，利用双温模型研究了飞秒激光作用下铜和氧化铜的表面温度演变，结果表明氧化铜的烧蚀阈值远低于铜。实验结果表明，氧化铜的烧蚀阈值低于铜，这与理论分析一致。采用该混合工艺，在铜膜加工过程中获得了3nm的表面粗糙度和4nm的去除精度，优于飞秒激光烧蚀获得的结果。这表明该混合工艺在铜微加工领域具有良好的应用潜力。
