Study On The Generation Of Laser-produced Plasma Extreme Ultraviolet Radiation Source And Its Conversion Efficiency Enhancement

With the development of the times,the future will inevitably enter the smart society,and the microchip is the most fundamental core component hardware for building the future smart society.With the further miniaturization of chips,the preparation of microchips is now inseparable from the support of advanced EUV lithography technology.There are countless scientific and engineering problems involved in EUV lithography,one of which is the generation of EUV radiation sources.At present,the laser-produced plasma EUV light source has become the best EUV generation source due to its superior performance,such as its better controllability and stability and not only can it effectively reduce the heat load of the equipment,increase the operating frequency of the light source,reduce debris pollution,but also directly control the size and spatial stability of the plasma generation area.Therefore,the EUV radiation source of the current commercial EUV lithography machine is generated by laser plasma.a key issue that people are interested in laser-produced plasma EUV light source is to enhance the conversion efficiency of EUV light.This thesis focuses on this topic,combines theoretical analysis and numerical simulation methods,and mainly carries out the following work:Firstly,the plasma spectroscopic simulation code FLYCHK was used to systematically study the effects of plasma states on the Particle population and EUV radiation properties of high-temperature Sn/Li plasmas.It is found that in order to obtain EUV radiation with high flux and high spectral purity,the optimal electron temperature and density ranges for Sn plasmas are between 25～30 e V and 1×10¹⁹/cm³～1×10²⁰/cm³,respectively;and for Li plasmas,the optimal value ranges are between15～20 e V and 1×10²⁰/cm³～1×10²¹/cm³,respectively.Secondly,based on the spectral analysis of high-temperature Sn plasma,a new scheme for enhancing EUV conversion efficiency of Sn plasma by using 2μm wavelength laser is proposed,and detailed numerical simulation studies are carried out for this scheme by FLASH code and FLYCHK code.We found that the conversion efficiency（CE）reached as much as 3.38%with the 2μm laser,which is 1.48percentage points higher than the 1μm laser（CE=1.9%）.In addition,we analyzed the contribution of dominant ionization states to the emission spectrum for both lasers.We observed that the growths of the out-of-band emission eventually led to a broadening of the spectrum,resulting in a reduction of spectral purity for the 1μm laser.By contrast,the emission main peaks were all centered near 13.5 nm for the 2μm laser,which is beneficial for efficient emission of light with a 13.5 nm wavelength（relevant for nano-lithographic applications）.Thirdly,based on the spectroscopic analysis of high-temperature Li plasma,a new scheme to generate EUV radiation with high spectral purity by irradiating solid Li with a short-wavelength solid-state laser is proposed,which is carried out by coupling the Li average opacity parameters obtained by the FLYCHK code into the MULTI code.A self-consistent numerical simulation study was carried out.We found that the conversion efficiency（CE）reached as much as 2.19%with the 1μm laser with laser intensity I=2×10¹⁰W/cm²and 1.54%for the 2μm with laser intensity I=6×10⁹W/cm².Compare to Sn target,Li target has the advantage in term of improving the spectral purity（SP）under short-wavelength solid-laser irradiation.In addition,the lower off-band radiation emission and lower energy ion generation of Li target may minimize the heat and debris on the optical components in nanolithography machines.Based on these advantages,the Li target will provide a new target choice for the next generation of lithography machines.Finally,to explored next-generation soft X-ray radiation sources,a new scheme to improve the conversion efficiency of soft X-rays（0.1–1.5 ke V）is proposed by irradiating double-layer Au foils with colliding laser pulses.We carried out a simulation study of this scheme with the one-dimensional radiation hydrodynamics code MULTI.The results show that the total soft X-ray CE can be enhanced up to 71.5%by setting the foil thickness as d₁=0.3μm,and this is 20.3%higher than that for a single laser irradiating a single-gold-foil target.Most of the enhanced soft X-ray CEs are generated from a stagnation layer formed by plasma collisions.This soft X-ray generation scheme is simple and practical,and has certain reference value for the future soft X-ray lithography technology.