Extreme Ultraviolet Lithography Light Source Research Articles

RHDLPP: A multigroup radiation hydrodynamics code for laser-produced plasmas

In this paper, we introduce the RHDLPP, a flux-limited multigroup radiation hydrodynamics numerical code designed for simulating laser-produced plasmas in diverse environments. The code bifurcates into two packages: RHDLPP-LTP for low-temperature plasmas generated by moderate-intensity nanosecond lasers, and RHDLPP-HTP for high-temperature, high-density plasmas formed by high-intensity laser pulses. The core radiation hydrodynamic equations are resolved in the Eulerian frame, employing an operator-split method. This method decomposes the solution into two substeps: first, the explicit resolution of the hyperbolic subsystems integrating radiation and fluid dynamics; second, the implicit treatment of the parabolic part comprising stiff radiation diffusion, heat conduction, and energy exchange. Laser propagation and energy deposition are modeled through a hybrid approach, combining geometrical-optics ray-tracing in sub-critical plasma regions with a one-dimensional solution of the Helmholtz wave equation in super-critical areas. The thermodynamic states are ascertained using an equation of state, based on either the real gas approximation or the quotidian equation of state (QEOS). For ionization calculations, the code employs a steady-state collisional-radiation (CR) model using the screened-hydrogenic approximation. Additionally, RHDLPP includes RHDLPP-SpeIma3D, a three-dimensional spectral simulation post-processing module, for generating both temporally-spatially resolved and time-integrated spectra and imaging, facilitating direct comparisons with experimental data. The paper showcases a series of verification tests to establish the code's accuracy and efficiency, followed by application cases, including simulations of laser-produced aluminium (Al) plasmas, pre-pulse-induced target deformation of tin (Sn) microdroplets relevant to extreme ultraviolet lithography light sources, and varied imaging and spectroscopic simulations. These simulations highlight RHDLPP's effectiveness and applicability in fields such as laser-induced breakdown spectroscopy, extreme ultraviolet lithography sources, and high-energy-density physics.

High-Precision Spot Detection of Driving Laser for Extreme Ultraviolet Lithography Light Sources

High-Precision Spot Detection of Driving Laser for Extreme Ultraviolet Lithography Light Sources

Beam Pointing Stability of Extreme Ultraviolet Lithography Light Source System

Beam Pointing Stability of Extreme Ultraviolet Lithography Light Source System

Time-resolved spatial profiles of electron density and temperature in hydrogen plasmas induced by radiation from laser-produced tin plasmas for extreme ultraviolet lithography light sources

We observed the spatial and temporal changes of the electron density (n e) and the electron temperature (T e) of hydrogen plasmas around a laser-produced Sn plasma EUV source. The plasma parameters were measured by the laser Thomson scattering (LTS) method. In the experiment, the Sn plasmas are produced in H2 gas at a pressure of 50–200 Pa and the hydrogen plasmas were induced by radiation from the Sn plasmas. The LTS measurements were performed at distances 30–90 mm away from the Sn plasmas. In all cases, the strong bremsstrahlung radiation of the Sn plasmas easily overwhelmed the weak LTS signals. To suppress noise due to the radiation, the solid angle of radiation from the Sn plasmas was restricted. The experimental results show that the n e was in the order of 1017 m−3 and T e was around 0.7 eV.

Sensitivity enhancement of poly(methyl methacrylate) upon exposure to picosecond-pulsed extreme ultraviolet

Short-pulse extreme ultraviolet (EUV) of a free-electron laser (FEL) is a prime candidate as a next-generation EUV lithography light source. However, the physical events and chemical reactions in resist materials, induced by the short-pulse EUV, have not yet been elucidated. In this study, the morphological and chemical changes in poly(methyl methacrylate) (PMMA) induced by picosecond-pulsed EUV were investigated using an X-ray laser (XRL) as a touchstone for next-generation EUV-FEL lithography. The XRL is suitable for the evaluation of resist materials in next-generation EUV-FEL lithography because of its short pulse width (7 ps) and high intensity (approximately 200 nJ/pulse at a maximum). The sensitivity of PMMA upon exposure to a 7 ps XRL pulse was enhanced by approximately 50 times in comparison with using conventional EUV sources, which have a typical pulse width of the order of nanoseconds. X-ray photoelectron spectroscopy revealed the decomposition of both the main and side chains of PMMA after XRL irradiation. These changes only occurred for relatively high doses of EUV irradiation at picosecond timescales. Thus, the results suggest the importance of a specific resist design for next-generation EUV-FEL lithography.

Stagnation layer development from two colliding Sn plasmas for an efficient EUV source

The collision of two laser-produced plasmas (LPP), individually generated from the opposing faces of a tin wedge, was studied experimentally and through the HEIGHTS computer simulation package to explore onset and development of the stagnation layer and extreme ultraviolet (EUV) photoemission. The colliding Sn plasma offers promise for a powerful source of 13.5 nm light, the industry-identified wavelength being targeted for commercial EUV lithography light sources. A second laser pulse could efficiently couple with the material accumulated along the collision midplane to produce EUV with high power. Imaging of the LPP configuration is accomplished using an ICCD camera while electron temperature and density of the stagnation layer were determined using spectroscopic methods—both were verified using HEIGHTS which was also used to show the potential of an EUV source with 700 W power at the intermediate focus for efficient high-volume manufacturing.

Extreme-Ultraviolet Light Source for Lithography Based on an Expanding Jet of Dense Xenon Plasma Supported by Microwaves

We discuss a concept of a point-like source of the extreme ultraviolet (EUV) light based on a non-equilibrium microwave discharge in expanding jet of dense xenon plasma with multiply charged ions. A conversion efficiency of microwave radiation to EUV light is calculated, and physical constraints, and opportunities for future devices are considered. Special attention is given to trapping of spontaneous line emission inside a radiating plasma spot that significantly influences the efficiency of EUV light source.

Laser-produced plasma versus laser-assisted discharge plasma: physics and technology of extreme ultraviolet lithography light sources

Powerful extreme ultraviolet (EUV) sources at 13.5 nm are a prerequisite for the economical operation of lithography scanners for semi-conductor manufacturing. These sources have been under development for more than 10 years. At the beginning, many source concepts were considered. Compact technologies like dense plasma focus or capillary Z-pinch discharges reached very rapidly fundamental limits as far as power scalability and lifetime were concerned. Other complex technologies-like synchrotrons-eventually dropped out of the race as well, exceeding by far the footprint and cost targets. Over time, the technology solidified toward the two source concepts: on one hand, the discharge produced plasmas (DPP), which eventually led to the development of the current laser-assisted discharge plasma (LDP); on the other hand, the laser-produced plasmas (LPP). All these technologies generate hot and dense plasmas of similar properties, which emit EUV radiations efficiently as a black body radiator or Planck emitter, in a pulsed manner. The plasma generation method, however, is quite different. DPP uses a pulsed high-voltage current discharge to generate plasma heating a gaseous or vaporized material up to temperatures close to 200,000°C. As for LPP, microscopic droplets of molten tin are fired through a vacuum chamber, individually tracked, vaporized by a pre-pulse laser, and eventually irradiated by a pulsed high-power infrared CO2 laser at 50 to 100 kHz, creating a high-temperature tin plasma, which radiates EUV light. In the case of LDP the plasma is generated between two rotating discs. Partially immersed in baths filled with liquid tin, the discs are wetted and covered with a thin layer of liquid tin. A pulsed laser beam focused on one of the discs evaporates a small amount of tin and generates a tin cloud between the two discs. Next a capacitor bank, which is connected to the discs via the liquid tin, discharges and converts the tin cloud into a plasma heated up to 200,000°C as well.

Characterization of out-of-band radiation and plasma parameters in laser-produced Sn plasmas for extreme ultraviolet lithography light sources

Out-of-band (OOB) radiation, in contrast to the in-band radiation at 13.5 nm in a 2% bandwidth, emitted from dense tin plasmas generated by a laser was investigated for application as an extreme ultraviolet lithography light source. It was found that the continuum spectrum, which overwhelms the atomic and ionic line emissions, is responsible for the intense OOB radiation. The spectral distribution of the continuum emission matches that of blackbody radiation with a temperature of about 10 eV. The OOB radiation can be considerably suppressed by employing a minimum-mass target and short-pulse laser irradiation. Spectroscopic observations were made to examine the spatiotemporal behavior of the plasma immediately after laser irradiation. Prominent line broadening due to the Stark effect in the high-density plasma was observed, from which the variation of the electron density was deduced. The electron density and temperature on the target surface were 1017–1018 cm−3 and a few eV’s, respectively, in the first 200 ns after laser illumination. In addition, the expansion velocities of neutral and singly ionized tin atoms were deduced from time-of-flight transients in the spectral emission.

Emission characteristics of debris from CO2 and Nd:YAG laser-produced tin plasmas for extreme ultraviolet lithography light source

We describe a comparative study of the emission characteristics of debris from CO2 and Nd:YAG laser-produced tin plasmas for developing an extreme-ultraviolet (EUV) lithography light source. Tin (Sn) ions and droplets emitted from a Sn plasma produced by a CO2 laser or an Nd:YAG laser were detected using Faraday cups and quartz crystal microbalance (QCM) detectors, respectively. The droplets were also monitored by using silicon substrates as witness plates. The results showed higher ion kinetic energy and lower particle emission for the CO2 laser than the Nd:YAG laser for the same laser energy (50 mJ). The average ion energy was 2.2 keV for the CO2 laser-produced plasma (LPP), and 0.6 keV for the Nd:YAG LPP. The debris accumulation of the CO2 LPP detected by the QCM detectors, however, was less than one fourth of that of the Nd:YAG LPP for the same laser energy. Using ion energy data, the mirror lifetime is estimated for the CO2 and Nd:YAG lasers. In both cases, the upper limit of the number of shots was of the order of 106.

A New Light Source for EUV Lithography

A new type of X-ray laser could give hope to the semiconductor industry as it struggles to continue its march toward miniaturization. This next-generation chip-making tool was developed at the National Science Foundation's Engineering Research Center for Extreme Ultraviolet Science and Technology, located at Colorado State University, in Fort Collins.The laser operates at wavelengths of 18.9 and 13.9 nanometers, the latter fine enough for extreme ultraviolet (EUV) lithography, which will be needed to manufacture the generation of chips that are to become available around 2011.

Hydrothermal method grown large-sized zinc oxide single crystal as fast scintillator for future extreme ultraviolet lithography

The scintillation properties of a hydrothermal method grown zinc oxide (ZnO) crystal are evaluated for extreme ultraviolet (EUV) laser excitation at 13.9nm wavelength. The exciton emission lifetime at around 380nm is determined to be 1.1ns, almost identical to ultraviolet laser excitation cases. This fast response time is sufficiently short for characterizing EUV lithography light sources having a few nanoseconds duration. The availability of large size ZnO crystal up to 3in. is quite attractive for future lithography and imaging applications.

Effect of focal spot size on in-band 135 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.

Direct observation of the ^{2}D_{3∕2}-^{2}D_{5∕2} ground-state splitting in Xe^{9+}

We have used an electron beam ion trap to observe a visible line at 598.30(13) nm that corresponds to the 4d9 2D3/2–4d9 2D5/2 magnetic dipole transition within the ground state configuration of Xe9+. We have found no evidence to support the claim by others that a line near this position originates from Xe31+. The comparison of the measured wavelength with previous indirect experimental values, and the dependence of the line intensity on the electron beam energy, confirms the validity of the present identification. Our measured wavelength is in agreement with semiempirical Hartree-Fock calculations but shows a discrepancy with ab initio multiconfiguration Dirac-Fock calculations. We propose that the line may be useful as a diagnostic for extreme ultraviolet lithography light sources.

A comparative study on the performance of a xenon capillary Z-pinch EUV lithography light source using a pinhole camera

A pinhole camera has been employed to study the performance of a xenon capillary Z-pinch extreme ultraviolet (EUV) lithography light source driven by different dI/dt discharge current pulses. The performance of the EUV source in terms of dimension, intensity, collection efficiency and stability was specifically investigated by varying the experimental conditions such as the supplying gas pressure and dI/dt of the discharge current. Specific features, such as ring shape (annular profile) pinhole images and symmetrical and stable emission in the high dI/dt discharge current, have been observed or confirmed experimentally. Our results support the fact that the high dI/dt and short discharge currents have better EUV emission characteristics for EUV lithography compared with the low dI/dt discharge current.

Absolute photoionization cross sections forXe4+,Xe5+, andXe6+near13.5nm: Experiment and theory

Absolute photoionization cross-section measurements for a mixture of ground and metastable states of ${\mathrm{Xe}}^{4+}$, ${\mathrm{Xe}}^{5+}$, and ${\mathrm{Xe}}^{6+}$ are reported in the photon energy range of $4d\ensuremath{\rightarrow}nf$ transitions, which occur within or adjacent to the $13.5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ window for extreme ultraviolet lithography light source development. The reported values allow the quantification of opacity effects in xenon plasmas due to these $4d\ensuremath{\rightarrow}nf$ autoionizing states. The oscillator strengths for the $4d\ensuremath{\rightarrow}4f$ and $4d\ensuremath{\rightarrow}5f$ transitions in ${\mathrm{Xe}}^{q+}$ $(q=1--6)$ ions are calculated using nonrelativistic Hartree-Fock and random phase approximations. These are compared with published experimental values for ${\mathrm{Xe}}^{+}$ to ${\mathrm{Xe}}^{3+}$ and with the values obtained from the present experimental cross-section measurements for ${\mathrm{Xe}}^{4+}$ to ${\mathrm{Xe}}^{6+}$. The calculations assisted in the determination of the metastable content in the ion beams for ${\mathrm{Xe}}^{5+}$ and ${\mathrm{Xe}}^{6+}$. The experiments were performed by merging a synchrotron photon beam generated by an undulator beamline of the Advanced Light Source with an ion beam produced by an electron cyclotron resonance ion source.

Performance of gas jet type Z-pinch plasma light source for EUV lithography

A new gas jet Z-pinch extreme ultraviolet (EUV) light source having double gas jet electrodes has been developed. It has two nozzles and two diffusers. The EUV emission is collected from the side of Xe pinch plasma, which is generated in a gap between the inner nozzle and corresponding diffuser. A cylindrical shell of He gas curtain produced by the outer nozzle is specially designed for shielding the debris and suppressing the inner gas expansion. We have estimated EUV energy of 1.22 mJ/sr/pulse for a 2% bandwidth at 13.5 nm in the presence of the gas curtain. The estimated diameter and length of EUV source in FWHM are 0.07 mm and 0.34 mm, respectively, whereas the same in FW 1/ e 2 are 0.15 mm and 1.2 mm, respectively.

Candidate plasma-facing materials for extreme ultraviolet lithography source components

Material selection and lifetime issues for extreme ultraviolet (EUV) lithography are of critical importance to the success of this technology for commercial applications. This work reviews current trends in production and use of plasma-facing electrodes, insulators, and wall materials for EUV-type sources. Ideal candidate materials should be able to: withstand high thermal shock from the short pulsed plasma; withstand high thermal loads without structural failure; reduce debris generation during discharge; and be machined accurately. We reviewed the literature on current and proposed fusion plasma-facing materials as well as current experience with plasma gun and other simulation devices. Both fusion and EUV source materials involve issues of surface erosion by particle sputtering and heat-induced evaporation/melting. These materials are either bare structural materials or surface coatings. EUV materials can be divided into four categories: wall, electrode, optical, and insulator materials. For electric discharge sources, all four types are required, whereas laser-produced plasma EUV sources do not require electrode and insulator materials. Several types of candidate alloy and other materials and methods of manufacture are recommended for each component of EUV lithography light sources.

Preface to the Special Issue for Extreme Ultraviolet Lithography Light Source Development

Preface to the Special Issue for Extreme Ultraviolet Lithography Light Source Development

Laser Produced Plasma for EUV Light Source For Lithography

We describe properties of laser produced plasmas (LPP) for extreme ultra violet (EUV) light source for next generation lithography as an industrial application of LPP. We briefly present three topics related to the LPPEUV light source; laser intensity dependence of conversion efficiency from laser light to EUV light with 13.5nm wavelength with 2% bound width with tin target, present understanding of EUV emission from xenon target, and atomic processes in those targets.