Evaluating the impact of spherical aberration on sub-0.2-um contact/via hole patterning

Shuo-Yen Chou; Jen-Chung Lou; Chih-Ming Lai; Fu-Jye Liang; Li-Jui Chen

doi:10.1117/12.435668

14 September 2001 Evaluating the impact of spherical aberration on sub-0.2-μm contact/via hole patterning

Shuo-Yen Chou, Jen-Chung Lou, Chih-Ming Lai, Fu-Jye Liang, Li-Jui Chen

Proceedings Volume 4346, Optical Microlithography XIV; (2001) https://doi.org/10.1117/12.435668
Event: 26th Annual International Symposium on Microlithography, 2001, Santa Clara, CA, United States

Abstract

Several super resolution techniques, such as phase-shifting mask (PSM) and off-axis illumination (OAI), have been reported to extend the resolution limit and increase the depth-of-focus (DOF) of optical lithography. However, these techniques provide less immunity to spherical aberration than the conventional approaches like chrome binary mask and low coherent illumination. Best focus position shift is the most well known anomalous phenomenon resulted from spherical aberration. In this paper, the origin of best focus shift is explained in pictorial and analytical forms. The phenomenon is evaluated by observing the exposure-defocus windows of sub-0.2micrometers hole patterns from an 18% transmission rim-type attenuated PSM combined with several types of illumination. Under high coherent illumination, severe focus shift was observed in sparse patterns as strong phase-shifting effect is applied. For dense hole patterns, OAI results in abrupt focus position variation at specific pattern pitch. The experimental results show that spherical aberration would induce best focus shift, distortion of process windows, loss of DOF, and shrinkage of iso/dense process window overlap. Two approaches were proposed to suppress the impact of spherical aberration. One is introducing proper amount of phase bias in attenuated PSM to adjust the wave aberration in the lens. The other more feasible method is using a customized illumination. A synthesized illumination aperture was proposed to compensate the focus shift. Excellent lithographic performance was obtained in the experiment from this method.

Citation Download Citation

Shuo-Yen Chou, Jen-Chung Lou, Chih-Ming Lai, Fu-Jye Liang, and Li-Jui Chen "Evaluating the impact of spherical aberration on sub-0.2-μm contact/via hole patterning", Proc. SPIE 4346, Optical Microlithography XIV, (14 September 2001); https://doi.org/10.1117/12.435668

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