Ant Colony Optimization-Based Freeform Sources for Enhancing Nanolithographic Imaging Performance

作者：Kuo Hung Fei^*; Frederick

来源：IEEE Transactions on Nanotechnology, 2016, 15(4): 599-606.

DOI：10.1109/TNANO.2016.2560221

• Ant colony optimization (ACO)
• depth of focus (DOF)
• exposure latitude (EL)
• mask error enhancement factor (MEEF)
• process window (PW)
• resolution enhancement technique (RET)
• source mask optimization (SMO)

As the complexity of mask patterns increases, the standard off-axis illumination in 193-nm immersion systems is increasingly becoming inadequate for high-quality lithography. In this study, a source optimization (SO) technique was employed for improving lithographic resolution. A pixel-based optimization process was developed for constructing freeform sources on a PC platform to enhance contrast and improve process window (PW). In the proposed SO algorithm, the metaheuristic binary ant colony optimization algorithm was applied for constructing the freeform sources. Moreover, the proposed algorithm converged to the optimal solution between the 300th and 400th iterations. The performance of this algorithm was assessed using the half pitch (hp) 45-nm line/space (L/S) and 55-nm SRAM contact hole (CH) patterns. The fitness function was quality of aerial image, exposure latitude (EL), and depth of focus (DOF); the constructed freeform sources enhanced the contrast and extended the PW for the patterns. The DOF increased from 0.91 to 1.1 mu m and 0.042 to 0.061 mu m for the L/S and SRAM CH patterns, respectively, at an EL of 5% when using the freeform source. Moreover, the freeform source improved the mask error enhancement factor by 22% for the SRAM pattern.

• 出版日期2016-7