Two dimensional expansion effects on angular distribution of 13.5nm in-band extreme ultraviolet emission from laser-produced Sn plasma

The angular distribution of extreme ultraviolet emission at 13.5nm within 2% bandwidth was characterized for laser irradiated, planar, Sn targets at prototypic conditions for a lithography system. We have found that two dimensional plasma expansion plays a key role in the distribution of in-band 13.5nm emission under these conditions. The angular distribution was found to have two peaks at 45° and 15°. This complex angular distribution arises from the shape of both the emitting plasma and the surrounding absorbing plasma. This research reveals that the detailed angular distribution can be important to the deduction of conversion efficiency.