Effect of focal spot size on in-band 13.5 nm extreme ultraviolet emission from laser-produced Sn plasma.
The effect of focal spot size on in-band 13.5 nm extreme ultraviolet (EUV) emission from laser-produced Sn plasmas was investigated for an EUV lithography light source. Almost constant in-band conversion efficiency from laser to 13.5 nm EUV light was noted with focal spot sizes from 60 to 500 microm. This effect may be explained by the opacity of Sn plasmas. Optical interferometry showed that the EUV emission must pass through a longer plasma with higher density when the focal spot is large, and strong reabsorption of EUV light was confirmed by a dip located at 13.5 nm in the spectrum.
Tao
Y
Y
Department of Mechanical and Aerospace Engineering, and Center for Energy Research, University of California-San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0438, USA. yetao@ucsd.edu
Harilal
S S
SS
Tillack
M S
MS
Sequoia
K L
KL
O'Shay
B
B
Najmabadi
F
F