Influence of asymmetry of diffracted light on printability in EUV lithography

Minoru Sugawara; Iwao Nishiyama; Mikio Takai

doi:10.1117/12.598994

6 May 2005 Influence of asymmetry of diffracted light on printability in EUV lithography

Minoru Sugawara, Iwao Nishiyama, Mikio Takai

Proceedings Volume 5751, Emerging Lithographic Technologies IX; (2005) https://doi.org/10.1117/12.598994
Event: Microlithography 2005, 2005, San Jose, California, United States

Abstract

In EUV lithography, off-axis incident light on a mask can produce a printed image that is asymmetrical with respect to its center, even when a line and space pattern is perfectly symmetrical on the mask. A theoretical analysis of diffracted light shows that the asymmetry tends to occur, when diffracted rays of the 2nd order or higher pass through the pupil and are involved in creating the image on a wafer. In contrast, when only 0th- and 1st-order diffracted rays pass through the pupil, the printed image is always symmetrical regardless of any asymmetry in their amplitude and/or phase. In order to discover the causes of the asymmetry in aerial images, we used line-and-space line patterns with a pitch of 88 nm on a wafer, because this pattern pitch generates 0th-, 1st- and 2nd-order rays for the optical conditions of an NA of 0.25 and a σ of 0.80. Under these conditions, a thicker Ta absorber (107 nm) produces greater asymmetry than a thinner one (64 nm), especially when the target linewidth is around 44 nm (on wafer). An analysis of diffracted light and the combinations of diffraction orders involved in creating an aerial image reveals that asymmetry in a printed image is caused by 2nd-order diffracted rays.

Citation Download Citation

Minoru Sugawara, Iwao Nishiyama, and Mikio Takai "Influence of asymmetry of diffracted light on printability in EUV lithography", Proc. SPIE 5751, Emerging Lithographic Technologies IX, (6 May 2005); https://doi.org/10.1117/12.598994

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