Impact of the non-uniform intensity distribution caused by a meshed pellicle of extreme ultraviolet lithography

• The meshed pellicle can make the intensity distribution on the wafer non-uniform.
• Coherence radius and mesh pitch are key factor to reduce the non-uniformity.
• We develop physical optics simulation to simulate non-uniformity on the wafer.
• The non-uniformity is directly proportional to the CDU.
• We can optimize the mesh parameters which can meet the CDU allowance.

A physical optics simulation was performed to simulate intensity non-uniformity on a wafer passing through an extreme ultraviolet meshed pellicle. The non-uniformity is directly related to the coherence radius of the illumination and the mesh parameters. The intensity non-uniformity was reduced when using illumination conditions with a larger coherence radius in a fixed mesh pitch. The circular illumination σr=0.5σr=0.5 can accommodate a five times larger pitch than the dipole illumination σr=0.1σr=0.1. An aerial image simulation for a 16 nm half-pitch pattern was also performed to confirm the critical dimension uniformity (CDU) caused by the meshed pellicle. The CDU is directly proportional to the non-uniformity on the wafer in order to determine suitable mesh parameters that produce a small CDU through a non-uniform intensity distribution calculation. The non-uniformity on the wafer should be less than 0.2% in order to achieve the desired CDU less than 0.1 nm.

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