Study On Out-of-band Radiation And Plasma Characteristics Based On 13.5 Nm Extreme Ultraviolet Light Source

The extreme ultraviolet lithography（EUVL）technology was used in the high-end chip manufacturing is the most important“bottleneck”technology in China,and it is also the most effective method to achieve chips with a feature node size of 7 nm and smaller.Extreme ultraviolet source plays a significant role in the EUVL system.High output power EUV source is the premise to realize the high volume manufacturing of chips.In addition,the out-of-band（OOB）radiation in the other wavelength will also be generated when generation the EUV source,which will cause deformation and damage of the optical components in the lithography system,reducing the lifetime of the EUVL system.In view of the above problems,the thesis used the solid Sn and low-density SnO₂targets to study the OOB radiation and plasma characteristics of 13.5 nm EUV source.The experimental results show that the laser irradiated on the low-density SnO₂target can generated high spectral efficiency EUV source and low OOB radiation.The specific research contents and main results of this paper as follows:Firstly,the 13.5 nm EUV radiation was studied.The results show that the strong EUV radiation was generated near the wavelength of 13.5 nm,and the EUV radiation intensity increases with an increaseof laser power density.When the size of focused spot is fixed,it was found that the EUV spectrum generated by the solid Sn target has a serious self-absorption effect,resulting in a dip phenomenon in the curve after the peak when changing laser energy.As the laser energy gradually increases,the dip phenomenon becomes more and more obvious,so that the radiation intensity at the 13.5 nm which was the opration wavelength of the EUVL system is located at the non-spectral peak.When the low density SnO₂target is used,the self-absorption effect is effectively reduced,and the EUV radiation peak position is just at 13.5 nm.At the same time,it was found that the spectral width of the low-density SnO₂target is 1/3 times narrower compare with the case of solid Sn target under the same laser energy,and the spectral efficiency is increased by about 20%.In addition,using the the interference method to measure the plasma electron density generated by the two targets.The results show that the plasma electron density generated by the low-density SnO₂target is lower than that of the solid Sn target.It can be further explained that the low-density SnO₂target can reduce the self-absorption effect and obtain higher spectral efficiency,thereby achieving higher EUV conversion efficiency.Secondly,the OOB radiation and plasma characteristics of the source are studied.The results show that the OOB radiation is mainly dominated by the continuous spectrum.Compared with the solid Sn target,due to the presence of oxygen element（Z=8）in the low-density SnO₂target,resulting in a lower OOB radiation due to the weaker continuous spectrum radiation in the case of low-density SnO₂target.At the same time,the results of the angle distributionds of the OOB radiation show that the OOB radiation of the two targets decreases when increasing the detection angle,and the peak intensity of the radiation signal generated by the two targets is similar under the same conditions.However,the signal duration in the case of low-density SnO₂target is short,which is another factor that causes weak OOB radiation of low-density SnO₂target.In addition,using the cosine function fitted to the angular distribution of the OOB radiation,it is found that the spatial distribution of the plasma radiation of the low-density SnO₂target is more uniform.Furthermore,the electron temperature and electron density in the visible wavelength of the plasma generated by the two targets was calculated.The results show that the electron temperature and electron density of the low-density SnO₂target are smaller than those of the solid Sn target.The maximum electron temperature of the solid Sn target laser plasma is about 1.3 e V,and the maximum electron density is about 6.5×10¹⁷cm^-3.