Abstract
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.
Highlights
Copper (Cu) is widely used in the fields of optics and micro-nano devices due to its low resistivity and superior resistance to electromigration, which can meet the requirements of high speed and low power consumption of the chip [1,2,3,4,5]
The main content of copper oxide generated in low-power oxygen plasma is Cu2 O, which is related to the low activation energy required for the formation of Cu2 O [32]
Combining the two-temperature model with the finite element analysis (FEA), it was confirmed theoretically that the ablation threshold of copper oxide is much lower than that of Cu, which was verified by experimental study
Summary
Copper (Cu) is widely used in the fields of optics and micro-nano devices due to its low resistivity and superior resistance to electromigration, which can meet the requirements of high speed and low power consumption of the chip [1,2,3,4,5]. It is necessary to develop a low-cost, low-defect, low-pollution, and high-precision Cu removal process for ICs. Micromachines 2021, 12, 1188. Many studies have been made on welding [23], drilling [24], cutting [25], and surface modification [26,27,28] by the fs-laser Surface defects such as pits, cracks, and molten particles are easy to occur during the fs-laser ablation [29], which makes it difficult to achieve nanometer-level processing quality. Laser ablation cannot meet the process requirements of Cu nano-precision removal in ICs. In this study, to obtain nanoscale Cu removal precision, a hybrid process of plasma oxidation and fs-laser ablation was proposed. It could be seen that the hybrid process can better meet the requirements of Cu processing in ICs than the fs-laser ablation can
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