Characteristics Of Laser-produced Plasma EUV Emission Based On Several Targets

A laser-produced plasma extreme ultraviolet(EUV)source is quiet important for extreme ultraviolet lithography(EUVL),biological imaging,soft X-ray spectroscopy,and water-window imaging.Compare with other EUV source,laser-produced plasma owned the advantage of high brightness,stability,small volume and easy to control.So it is favoured by the researchers.The surface of the metal planar aluminum(Al),bismuth(Bi),and tin(Sn)targets were processed by laser ablation to fabricated the grooved structure targets.The grooved targets were irradiated by an ns laser,we obtained a higher EUV emission compare with the planar target in the same condition.The grooved targets parameters(groove depth and groove width)and the laser parameters(incident laser energy and focal spot size)are two important elements for the EUV emission from the grooved targets.These parameters required to be optimized for acquired the optimal condition for the EUV emission.Therefore,the paper was studied the effects of the grooved targets and the laser parameters for the EUV emission systematically.On the one hand,the grooved targets with various structured size were fabricated.The related EUV spectra were obtained.The EUV spectral relative intensity were optimized by changing the grooved parameters.Meanwhile the optimal groove depth and width of these three grooved targets were obtained.The optimal groove depth and width of the grooved Al target are 150?m and 100?m,with the optimal incident laser energy of 750 m J.The EUV emission enhancement was 2.03 with the use of the groove target,compare with the planar one.The optimal depth and width of the grooved Bi target are 100?m and 200?m,with the optimal incident laser energy of300 m J,the EUV emission enhancement was 1.44.The optimal depth and width of the grooved Sn target are 100?m and 300?m,with the incident laser energy of 500 m J,the EUV emission enhancement was 1.57.Meanwhile,the study figured out the optimal width of the grooved Al target was not related to the incident laser energy.When the optimal width of the grooved Bi target and groove Sn target were related to the incident laser energy,with the wider grooved,the corresponding incident laser energy was increased.On the other hand,on the basis of the optimal grooved parameters,the EUV emission was further optimized by adjusting the laser parameters.Firstly,the study found that the EUV emission of the Al,Bi,and Sn grooved targets were increased with the increasing incident laser energy.Secondly,to changed the focal spot diameter by adjusting the distance between the focal lens and the target,the EUV emission of the grooved Bi target and grooved Sn target were increased first and then decreased with the focal spot diameter increasing,when the emission of the grooved Al target was decreased.In addition,the temporal evolution of the laser-produced plasma were studied by using a ICCD.It was found that the plasma of the grooved target was higher than the planar one in the same delay time condition.It meant the grooved wall effectively controlled the expansion of the plasma leading to confinement which kept the high plasma concentration and increased the EUV emission.In conclusion,the grooved targets were an potential EUV source and were contributed to the higher EUV emission.This work laid the foundation for the laser-produced plasma EUV from grooved targets applied to the EUVL,biological imaging and soft X-ray spectroscopy.