激光产生的锡、碘和金等离子体极真空紫外光谱的分析和模拟
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摘要
当一束高能脉冲激光作用到固体样品靶上时会产生激光等离子体,在膨胀过程会产生波段很宽的电磁辐射,其光谱一般由线状谱和连续谱构成。采用激光等离子体光谱技术,可以获得等离子体演化过程中大量有关原子结构及其相关动力学过程的信息,并且具有操作简单、发射波段宽、强度高、脉宽窄和重复性好等优点,是开展光谱研究的理想光源之一。因此,目前激光等离子体光谱已被广泛用于原子物理及其相关领域的应用研究。
本论文所涉及的工作主要集中在对XUV/EUV波段激光等离子体光谱的分析和模拟,主要包括以下三方面的内容:
(1)激光产生的锡等离子体作为EUV光刻光源的研究。在计算机芯片制造工业,激光烧蚀锡靶时产生的等离子体由于在13.5 nm附近2%带宽内的辐射在多层反射镜上具有高达70%以上的反射率,已被认为是下一代半导体光刻光源重要的候选光源之一。本文分析了9.5—18 nm波段范围内随激光功率变化的激光锡等离子体光谱,通过与HFCI计算结果及其他作者的实验结果比较,确定了光谱中由于不透明度效应引起的自吸收贡献及自吸收峰位置。并利用基于LTE模型的DCA/UTA程序计算了离子丰度并模拟了光谱。通过与实验光谱的比较,估算了等离子体核心和近边缘的电子温度和电子密度。
(2)激光产生的碘等离子体中的内壳层光吸收研究。利用双激光等离子体光谱技术,获得了70—127 eV波段范围的碘的4d光吸收光谱。利用HFCI方法,计算获得了相关的跃迁能、跃迁几率、统计权重和自电离宽度等原子数据,确定了其光谱主要由4d—nf的离散跃迁线和4d-εf的“扇形共振”构成。并确定了随离化度的增加,碘离子的离散跃迁线和“扇形共振”的演化情况。最后,基于归一化的玻尔兹曼分布假设和稳态碰撞辐射模型,获得了与实验光谱具有很好一致性的模拟光谱,确定了碘等离子体的参数条件。
(3)激光产生的金等离子体中的内壳层光吸收研究。本文利用与碘等离子体类似的处理过程,分析了XUV波段的Au~(2+),Au~(3+) and Au~(4+)离子的4f和5p内壳层光吸收光谱。激光产生的金等离子体光谱主要由大量的4f—5d,6d and 5p—5d,6s的共振跃迁及其单双6s旁观电子引起的伴线跃迁构成,其中伴线的贡献要远大于共振线,并随着离化度的增加,双6s旁观电子引起的伴线贡献逐渐大于单6s旁观电子的伴线贡献。同样,利用归一化的玻尔兹曼分布假设和稳态碰撞辐射模型,获得了与实验光谱具有很好一致性的模拟光谱。
对于上述激光等离子体光谱的分析和模拟,我们希望可以加深激光产生等离子体的物理特性的理解,还可以促进其在应用领域的发展。
Laser-produce plasmas(LPP),formed by focusing a beam from a pulsed laser onto solid sample targets,can emit an intense burst of radiation over a broad spectral range, making them ideally suited to spectroscopic studies.The spectra generally consist of lines and continuum,depending on factors such as the laser power density and the material used.Therefore,laser-produced plasma spectroscopy(LPPs) has been established as a versatile tool for atomic physics studies in the IR to X-ray regions because of its features, such as simplified production and operation,broad emission,high shot to shot intensity, short pulse duration,good reproducibility,lower costs and so on.Using LPPs,one can obtain lots of information about the atomic structure and related dynamics processes.
The work reported in this thesis consists of the investigation of laser-produced plasma as EUV lithography sources and inner-shell photoabsorption studies of laser-produced iodine and gold plasmas.The following studies focus mainly on the theoretical analysis and simulations of spectra mentioned above.
Laser-produced plasmas are considered to be important candidate sources of extreme ultraviolet(EUV) radiation for application in future lithography tools for the high-volume manufacturing of computer chips.In this work,extreme ultraviolet(EUV) emission spectra from laser-produced Sn plasmas have been experimentally investigated at different power densities in the 9.5-18 nm wavelength range.Experimental results indicate the presence of a broad reabsorption band and some pronounced dips because of opacity effects in the spectra.With increasing power densities,the reabsorption band shifts to the shorter wavelength side and the absorption dips become deeper.Theoretical calculations using the Cowan code show that the dips arise from the 4d-4f and 4p-4d transitions.Using detailed configuration accounting(DCA) with the term structures treated by the unresolved transition array(UTA) model,we analyze the opacity effects and simulate the spectra.By comparing the results of the simulations with experiments,it can be concluded that the plasma from a 5%Sn target gives essentially pure emission,while the spectra from a pure Sn target contains both emission and absorption,with electron temperatures ranging from 28 to 15 eV,and electron densities from 5.0×10~(20) to 3.7×10~(19) cm~(-3),in going from the core to the outer plasma region.
The 4d photoabsorption spectra of I~(2+),I~(3+) and I~(4+) have been obtained in the 70-127 eV region with the dual laser produced plasma technique at time delays ranging from 400 to 520 ns.With decreasing time delay,the dominant contribution to spectra evolves from I~(2+) to I~(4+) ions,and each spectrum contains discrete 4d-nf transitions and a broad 4d-εf shape resonance,which are identified with the aid of multiconfiguration Hartree- Fock calculations.The excited states decay by direct autoionization involving 5s or 5p electrons and rates fbr the different processes and resulting linewidths were calculated. With increasing ion stage,the 4d-εf shape resonance becomes intense and broader in going from I~(2+) to I~(3+),and then vanishes in I~(5+).In addition,the discrete structure of the calculated spectrum of each ion gradually approaches the corresponding shape resonance position.Based on the assumption of a normalized Boltzmann distribution amongst the excited states and a steady-state collisional-radiative(CR) model,we reproduced spectra which are in good agreement with experiment.
The photoabsorption processes of Au~(2+),Au~(3+),and Au~(4+) have been investigated experimentally and theoretically in the 70-127 eV region.Using the dual laser-produced plasma(DLP) technique,the 4f and 5p photoabsorption spectrum has been recorded at 50 ns time delay and was found to be dominated by a great number of transition lines from 4f-5d,6d and 5p-5d,6s transitions,which have been identified by comparison with the aid of Hartree-Fock with configuration interaction calculations.The characteristic feature of the spectrum is that satellite lines from excited configurations containing one or two 6s electrons are more important than resonance lines,and with increasing ionization,satellite contributions from states with one 6s spectator electron gradually become more important than those with two 6s spectator electrons.Based on the assumption of a normalized Boltzmann distribution among the excited states and a steady state collisional-radiative model, we succeeded in reproducing a spectrum which is in good agreement with experiment.
In a word,the main goals of the work presented in this thesis can be helpful to the further development of optical diagnostic methods fbr application to EUV producing discharges,and improving the understanding of the physical properties of these laser-produced plasmas.
本论文所涉及的工作主要集中在对XUV/EUV波段激光等离子体光谱的分析和模拟,主要包括以下三方面的内容:
(1)激光产生的锡等离子体作为EUV光刻光源的研究。在计算机芯片制造工业,激光烧蚀锡靶时产生的等离子体由于在13.5 nm附近2%带宽内的辐射在多层反射镜上具有高达70%以上的反射率,已被认为是下一代半导体光刻光源重要的候选光源之一。本文分析了9.5—18 nm波段范围内随激光功率变化的激光锡等离子体光谱,通过与HFCI计算结果及其他作者的实验结果比较,确定了光谱中由于不透明度效应引起的自吸收贡献及自吸收峰位置。并利用基于LTE模型的DCA/UTA程序计算了离子丰度并模拟了光谱。通过与实验光谱的比较,估算了等离子体核心和近边缘的电子温度和电子密度。
(2)激光产生的碘等离子体中的内壳层光吸收研究。利用双激光等离子体光谱技术,获得了70—127 eV波段范围的碘的4d光吸收光谱。利用HFCI方法,计算获得了相关的跃迁能、跃迁几率、统计权重和自电离宽度等原子数据,确定了其光谱主要由4d—nf的离散跃迁线和4d-εf的“扇形共振”构成。并确定了随离化度的增加,碘离子的离散跃迁线和“扇形共振”的演化情况。最后,基于归一化的玻尔兹曼分布假设和稳态碰撞辐射模型,获得了与实验光谱具有很好一致性的模拟光谱,确定了碘等离子体的参数条件。
(3)激光产生的金等离子体中的内壳层光吸收研究。本文利用与碘等离子体类似的处理过程,分析了XUV波段的Au~(2+),Au~(3+) and Au~(4+)离子的4f和5p内壳层光吸收光谱。激光产生的金等离子体光谱主要由大量的4f—5d,6d and 5p—5d,6s的共振跃迁及其单双6s旁观电子引起的伴线跃迁构成,其中伴线的贡献要远大于共振线,并随着离化度的增加,双6s旁观电子引起的伴线贡献逐渐大于单6s旁观电子的伴线贡献。同样,利用归一化的玻尔兹曼分布假设和稳态碰撞辐射模型,获得了与实验光谱具有很好一致性的模拟光谱。
对于上述激光等离子体光谱的分析和模拟,我们希望可以加深激光产生等离子体的物理特性的理解,还可以促进其在应用领域的发展。
Laser-produce plasmas(LPP),formed by focusing a beam from a pulsed laser onto solid sample targets,can emit an intense burst of radiation over a broad spectral range, making them ideally suited to spectroscopic studies.The spectra generally consist of lines and continuum,depending on factors such as the laser power density and the material used.Therefore,laser-produced plasma spectroscopy(LPPs) has been established as a versatile tool for atomic physics studies in the IR to X-ray regions because of its features, such as simplified production and operation,broad emission,high shot to shot intensity, short pulse duration,good reproducibility,lower costs and so on.Using LPPs,one can obtain lots of information about the atomic structure and related dynamics processes.
The work reported in this thesis consists of the investigation of laser-produced plasma as EUV lithography sources and inner-shell photoabsorption studies of laser-produced iodine and gold plasmas.The following studies focus mainly on the theoretical analysis and simulations of spectra mentioned above.
Laser-produced plasmas are considered to be important candidate sources of extreme ultraviolet(EUV) radiation for application in future lithography tools for the high-volume manufacturing of computer chips.In this work,extreme ultraviolet(EUV) emission spectra from laser-produced Sn plasmas have been experimentally investigated at different power densities in the 9.5-18 nm wavelength range.Experimental results indicate the presence of a broad reabsorption band and some pronounced dips because of opacity effects in the spectra.With increasing power densities,the reabsorption band shifts to the shorter wavelength side and the absorption dips become deeper.Theoretical calculations using the Cowan code show that the dips arise from the 4d-4f and 4p-4d transitions.Using detailed configuration accounting(DCA) with the term structures treated by the unresolved transition array(UTA) model,we analyze the opacity effects and simulate the spectra.By comparing the results of the simulations with experiments,it can be concluded that the plasma from a 5%Sn target gives essentially pure emission,while the spectra from a pure Sn target contains both emission and absorption,with electron temperatures ranging from 28 to 15 eV,and electron densities from 5.0×10~(20) to 3.7×10~(19) cm~(-3),in going from the core to the outer plasma region.
The 4d photoabsorption spectra of I~(2+),I~(3+) and I~(4+) have been obtained in the 70-127 eV region with the dual laser produced plasma technique at time delays ranging from 400 to 520 ns.With decreasing time delay,the dominant contribution to spectra evolves from I~(2+) to I~(4+) ions,and each spectrum contains discrete 4d-nf transitions and a broad 4d-εf shape resonance,which are identified with the aid of multiconfiguration Hartree- Fock calculations.The excited states decay by direct autoionization involving 5s or 5p electrons and rates fbr the different processes and resulting linewidths were calculated. With increasing ion stage,the 4d-εf shape resonance becomes intense and broader in going from I~(2+) to I~(3+),and then vanishes in I~(5+).In addition,the discrete structure of the calculated spectrum of each ion gradually approaches the corresponding shape resonance position.Based on the assumption of a normalized Boltzmann distribution amongst the excited states and a steady-state collisional-radiative(CR) model,we reproduced spectra which are in good agreement with experiment.
The photoabsorption processes of Au~(2+),Au~(3+),and Au~(4+) have been investigated experimentally and theoretically in the 70-127 eV region.Using the dual laser-produced plasma(DLP) technique,the 4f and 5p photoabsorption spectrum has been recorded at 50 ns time delay and was found to be dominated by a great number of transition lines from 4f-5d,6d and 5p-5d,6s transitions,which have been identified by comparison with the aid of Hartree-Fock with configuration interaction calculations.The characteristic feature of the spectrum is that satellite lines from excited configurations containing one or two 6s electrons are more important than resonance lines,and with increasing ionization,satellite contributions from states with one 6s spectator electron gradually become more important than those with two 6s spectator electrons.Based on the assumption of a normalized Boltzmann distribution among the excited states and a steady state collisional-radiative model, we succeeded in reproducing a spectrum which is in good agreement with experiment.
In a word,the main goals of the work presented in this thesis can be helpful to the further development of optical diagnostic methods fbr application to EUV producing discharges,and improving the understanding of the physical properties of these laser-produced plasmas.
引文
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