Extreme Ultraviolet Power Research Articles

Development and optimization of metal silicide EUV pellicle for 400W EUV lithography

In the extreme ultraviolet lithography (EUVL) process, extreme ultraviolet (EUV) pellicles serve as thin, transparent membranes that shield the photomask (reticle) from particle contamination, thereby preserving photomask pattern integrity, reducing chip failure risks, and enhancing production yields. The production of EUV pellicles is highly challenging due to their mechanical fragility at nanometer-scale thicknesses and the need to endure the rigorous conditions of the EUVL environment, which include high temperatures and hydrogen radicals. Consequently, extensive research has been conducted on a variety of materials, such as carbon-based and silicon-based substances, for the development of EUV pellicles. This study explores the feasibility of implementing metal silicide (MeSix) pellicles for high-power EUVL applications. We successfully fabricated MeSixpellicles in two dimensions: a 10 mm × 10 mm sample and a full-size 110 mm × 144 mm pellicle. We then evaluated their optical, mechanical, thermal, and chemical properties, as well as their lifespan. The pellicles demonstrated over 90% transmittance and less than 0.04% reflectance. The films exhibited a deflection of 300μm under a 2 Pa differential pressure and an ultimate tensile strength exceeding 2 GPa. The thermal emissivity was measured at 0.3. Additionally, the durability of the pellicles was validated through exposure to 20,000 wafers using a 400 W EUV power (offline test: 20 W cm-2). The transmittance variations of the pellicles were evaluated by comparing the measurements obtained before and after exposure to 400 W EUV power.

Electron drag force in EUV induced pulsed hydrogen plasmas

Extreme ultraviolet (EUV) induced pulsed plasma is unique due to its transient characteristics: the plasma switches between non-thermal state (when EUV power is ON at the beginning of the pulse) and thermal state (end of the pulse at ∼20 μs). It is shown that although electron drag force acting on nm size particles in hydrogen plasma is negligible compared to the ion drag force at the beginning of the pulse, however it can be dominant at the end of the pulse and can play important role in particle transport leading to defectivity issues for semiconductor chip production technologies.

Cascade and cluster of correlated reactions as causes of stochastic defects in extreme ultraviolet lithography

Background: Stochastic defects are becoming major concern in the future extreme ultraviolet (EUV) lithography as their probability Pd exponentially increases with decreasing feature size and is highly sensitive to variations in process/mask conditions. Photon shot-noise and discrete/probabilistic nature of materials have been blamed as their causes. Aim: We introduce models for relating Pd to photon and resist statistics under various exposures and material conditions and analyze their impact in future EUV lithography. Approach: Three-dimensional reaction distribution is calculated by a fully coupled Monte Carlo simulation including discrete photon, photoelectron scattering, and resist stochastics. Then probability models predict Pd from statistical data extracted from Monte Carlo results. Results: Stochastic defect generation is enhanced by cascade and/or cluster of correlated reactions among nearby polymers/molecules due to secondary electrons (SE)/acid diffusion and SEs generated along scattered photoelectron trajectories. Pd decreases with increasing reaction density, suppressing effective image blur, and introducing quenchers, where reaction density is limited by SE, photoacid generator, and reaction site. Defect probability increases with decreasing target size for the same k1-factor, while strongly dependent on image slope and defocus. Conclusions: Our analyses suggest that applying EUV lithography to smaller target requires careful material choice, extremely precise process control, and further EUV power enhancement.

Characterization of radiative and kinetic properties of laser produced plasmas for efficient extreme ultraviolet nanolithography sources

Increasing extreme ultraviolet (EUV) photon power in laser-produced plasma (LPP) sources is critically important for efficient future nanolithography devices. Enhancing the lifetime of the optical collector system in these devices is another important challenge for reliable and economically feasible devices. In this work, various mechanisms affecting ion acceleration in LPP were investigated to predict the maximum ion energies and flux arriving at the collecting mirror surfaces. Plasma evolution produced by an Nd:YAG laser from Sn targets was studied in detail to predict the dynamics of EUV producing ions and their contribution to the EUV power. The multiphysics fully 3D integrated HEIGHTS computer package was used in this analysis. HEIGHTS simulations of detail plasma evolution and ion kinetic energies were compared with various worldwide experimental data. Excellent agreement was shown regarding the range of ion kinetic energies and their angular distribution as well as recombination processes and their effect on the temporal output of EUV photons. Spatial and charge distributions were predicted for EUV producing ions and ionic debris. The analysis showed that mainly two Sn ions, i.e., Sn XII and Sn XIII, determine the EUV source intensity and spatial location. It was also shown that reducing the laser spot size and increasing the pulse duration allow a significant reduction in ion kinetic energies that is important for a longer lifetime of the optical collection system.

Free-standing carbon nanotube films for extreme ultraviolet pellicle application

To enable high volume manufacturing with extreme ultraviolet (EUV) lithography, a pellicle membrane is needed to protect the reticle from particles at EUV source powers beyond 250 W. Identifying a membrane with high EUV transmission, mechanical integrity, thermal stability, and chemical resistance to the scanner environment is extremely challenging; yet, these properties are required to realize next-generation EUV pellicle solutions. Free-standing carbon nanotube (CNT) film as an alternative next-generation core pellicle material is proposed. We demonstrate that free-standing CNT films possess very high EUV transmission (up to 99%) and good transmission uniformity (∼0.4 % half range), mechanical stability (maximum deflection ∼0.08 mm at 2 Pa), thermal stability (no transmission change under greater than 250 W equivalent EUV power in vacuum), and scalability to a full pellicle size (∼15 × 12 cm2). The capability of the CNT membrane to withstand high EUV power in the presence of H2 for a limited time is demonstrated. Other CNT membrane properties are presented that are important for the pellicle application: low EUV scattering, low EUV reflectivity, and sufficient transmission to enable through-pellicle inspection with DUV light or electrons. The ability of the CNT film to stop particles is tested. The influence of hydrogen at higher EUV powers and prolonged exposures on the lifetime of the CNT pellicle remains the current research focus. Approaches for coating the free-standing CNT films for protection are discussed.

Impact of nitric oxide, solar EUV and particle precipitation on thermospheric density decrease

Recent studies have revealed that the post-storm thermospheric mass density at a fixed altitude could be lower than the pre-storm mass density. This phenomenon has been attributed to an overcooling effect caused by enhanced infrared emissions from nitric oxide (NO). Here we report that thermospheric density decrease can take place under both storm and non-storm conditions. Relevant observations are presented during two superstormes, one intense storm, and one non-storm case. Thermospheric neutral density variations observed by GOCE and CHAMP satellites are investigated along with simultaneous measurements of thermospheric nitric oxide density and emissions from TIMED/GUVI and TIMED/SABER, respectively, together with auroral hemispheric power from DMSP, Joule heating rate from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) algorithm, and solar extreme ultraviolet (EUV) flux from SOHO/SEM and TIMED/SEE. It was found that the apparent storm-time density decrease or “overcooling” is a result of combined effects: an increase in NO cooling and a decrease in both the solar EUV flux and the auroral energy input. It was also found that whether or not a density decrease exists depends on whether there are auroral activities prior to the pre-storm reference day and how the reference day is chosen. The relative contributions of the different drivers (namely, enhanced NO cooling and variations in auroral hemispheric power, Joule heating, and solar EUV at the pre-storm and post-storm days) to thermospheric density decrease remain to be determined.

S2E simulation of an ERL-based high-power EUV-FEL source for lithography

Energy recovery linac (ERL) based extreme ultraviolet (EUV) free electron lasers (FELs) are candidates of a next-generation high-power EUV source for lithography. An ERL-based EUV FEL source has been designed in order to demonstrate the feasibility of generating a 10-kW class EUV power. Start-to-End (S2E) simulation including the injection beam optimization, bunch compression, FEL lasing and bunch decompression is performed for the designed EUV source. As a result it is demonstrated that the EUV FEL can produce high power more than 10 kW at 10 mA and that the electron beam can be well transported throughout the EUV source without beam loss.

Microwave discharge plasma production with resonant cavity for EUV mask inspection tool

A microwave-discharge-produced plasma source was developed to generate 13.5 nm extreme ultraviolet (EUV) radiation for application as a mask inspection tool. The EUV radiation of a system with a high Q-factor (>3900) resonant cavity and a solid-state oscillator was studied. The gas pressure and microwave power dependences on the EUV radiation for transverse-magnetic mode TM010 and transverse-electric mode TE111 were determined. For the solid-state oscillator, the efficiency of the EUV radiation over the input power was 5.8 times higher than that for a magnetron. EUV radiation of 10 mW/(2πsr) was observed under a gas pressure of 5 Pa and microwave power of 400 W. We expect that more EUV power and a smaller plasma is generated when a magnetic field is applied to confirm the plasma and a facility is operated with an improved system to cool an entire cavity.

Extreme ultraviolet mask observations using a coherent extreme ultraviolet scatterometry microscope with a high-harmonic-generation source

In extreme ultraviolet (EUV) lithography, the three-dimensional structure of an EUV mask, which has an absorber layer and a Mo/Si multilayer on a glass substrate, strongly affects the EUV phase. We have developed a coherent EUV scatterometry microscope (CSM) to observe EUV patterns with a quantitative phase contrast based on the coherent-diffraction-imaging method, which is a simple system without an objective. A coherent stand-alone high-harmonic-generation (HHG) EUV source has been developed for practical use. Although the throughput of the relay optics in the previous study was insufficient to compensate for the fluctuation of the beam position, herein the beam position is stabilized and the relay optics are upgraded, increasing the throughput of the EUV power 130-fold. Consequently, the detection time for the same defect size is markedly reduced from 1000 to 1 s. Furthermore, a 52 × 52 nm2 absorber defect is detected in 10 s.

Multisegmented, multilayer-coated mirrors for the Solar Ultraviolet Imager

The Solar Ultraviolet Imager (SUVI) is one of the several instruments that will fly on board the next generation of Geostationary Operational Environmental Satellites R-U platforms, as part of the National Oceanic and Atmospheric Administration’s space weather monitoring fleet. SUVI is a generalized Cassegrain telescope that employs multilayer-coated optics that operate in six extreme ultraviolet (EUV) narrow bandpasses centered at 93.9, 131.2, 171.1, 195.1, 284.2 and 303.8 Å. The innovation of the design is that SUVI is the first EUV solar telescope that has six different wavelength channels accommodated on each mirror. And despite having six segmented multilayer-coatings, shadowing (due to the mask) is minimized allowing SUVI to exceed its effective area specifications. Once operational, SUVI will record full-disk, spectroheliograms every few minutes, where this data will be used to better understand the effects of solar produced EUV radiation on Earth and the near-Earth environment. The material presented discusses general aspects of the SUVI optical design, mirror fabrication, super polishing, and metrology carried out to verify optical surface quality and in-band, EUV reflectivity performance of the multilayer coatings. The power spectral density and EUV measurements are shown to exceed performance requirements and are critical for the overall calibration and monitoring of SUVI’s throughput and imaging performance, once operational.

The role of plasma evolution and photon transport in optimizing future advanced lithography sources

Laser produced plasma (LPP) sources for extreme ultraviolet (EUV) photons are currently based on using small liquid tin droplets as target that has many advantages including generation of stable continuous targets at high repetition rate, larger photons collection angle, and reduced contamination and damage to the optical mirror collection system from plasma debris and energetic particles. The ideal target is to generate a source of maximum EUV radiation output and collection in the 13.5 nm range with minimum atomic debris. Based on recent experimental results and our modeling predictions, the smallest efficient droplets are of diameters in the range of 20–30 μm in LPP devices with dual-beam technique. Such devices can produce EUV sources with conversion efficiency around 3% and with collected EUV power of 190 W or more that can satisfy current requirements for high volume manufacturing. One of the most important characteristics of these devices is in the low amount of atomic debris produced due to the small initial mass of droplets and the significant vaporization rate during the pre-pulse stage. In this study, we analyzed in detail plasma evolution processes in LPP systems using small spherical tin targets to predict the optimum droplet size yielding maximum EUV output. We identified several important processes during laser-plasma interaction that can affect conditions for optimum EUV photons generation and collection. The importance and accurate description of modeling these physical processes increase with the decrease in target size and its simulation domain.

Temperature behavior of pellicles in extreme ultraviolet lithography

We present a theoretical analysis of the temperature behavior of pellicles in extreme ultraviolet (EUV) lithography. Using modified heat transfer equations and accounting for the cooling mechanism during exposure, we calculate the temperature of the pellicle due to EUV beam absorption as a function of the incident EUV power. We find the temperature rise to be less than 620 K for a 10 ms incident EUV beam with a power of 100 W. The recovery time after EUV beam exposure is also calculated to be less than 53 ms, which is significantly smaller than the time interval between the typical EUV beam exposures (∼300 ms). Thus, we can neglect the thermal heating problem for practical EUV pellicles in mass EUV processes.

Anomalously low geomagnetic energy inputs during 2008 solar minimum

The record‐low thermospheric density during the last solar minimum has been reported and it has been mainly explained as the consequence of the anomalously low solar extreme ultraviolet (EUV) irradiance. In this study, we examined the variation of the energy budget to the Earth's upper atmosphere during last solar cycle from both solar EUV irradiance and geomagnetic energy, including Joule heating and particle precipitation. The globally integrated solar EUV power was calculated from the EUV flux model for aeronomic calculations (EUVAC) driven by the MgII index. The annal average of solar power in 2008 was 33 GW lower than that in 1996. The decrease of the globally integrated geomagnetic energy from 1996 to 2008 was close to 29 GW including 13 GW for Joule heating from Weimer (2005b) and 16 GW for particle precipitation from NOAA Polar‐Orbiting Environmental Satellites (POES) measurements. Although the estimate of the solar EUV power and geomagnetic energy vary from model to model, the reduction of the geomagnetic energy was comparable to the solar EUV power. The Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) simulations indicate that the solar irradiance and geomagnetic energy variations account for 3/4 and 1/4 of the total neutral density decrease in 2008, respectively.

Development of stable extreme-ultraviolet sources for use in lithography exposure systems

Laser-produced plasma sources offer the best option for scal- ability to support high-throughput lithography. Challenges associated with the complexity of such a source are being addressed in a pilot program where sources have been built and integrated with extreme-ultraviolet (EUV) scanners. Up to now, five pilot sources have been installed at R&D facilities of chip manufacturers. Two pilot sources are dedicated to product development at our facility, where good dose stability has been demonstrated up to levels of 32 W of average EUV power. Experi- mental tests on a separate experimental system using a laser prepulse to optimize the plasma conditions or EUV conversion show power levels equivalent to approximately 160 W within a low duty-cycle burst, before dose control is applied. The overall stability of the source relies on the generation of Sn droplet targets and large EUV collector mirrors. Stability of the Sn droplet stream is well below 1 μm root mean square during 100 þ h of testing. The lifetime of the collector is significantly enhanced with improved coatings, supporting uninterrupted operation for several weeks. © 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). (DOI: 10.1117/1.JMM.11.2.021110)

Extreme-ultraviolet source specifications: tradeoffs and requirements

Although progress has been reported, the extreme-ultraviolet (EUV) source remains one of the largest challenges for EUV lithography production to be economically viable. This article gives an update on the high-level source requirements, including the origin of these specifications. All requirements are driven by litho system cost-of-ownership considerations and the imaging capabilities. Attention will be paid to conflicting requirements and the consequent tradeoffs that have to be made in making conceptual source decisions and in designing an EUV system. Finally, we will look into the future of the top-level source requirements with the conclusions that not only EUV power requirements will keep on increasing, but that this increase has to be accompanied with a high availability and reliability of the source. Furthermore, an operation mode has to be found that is chemically, particulately, and spectrally clean so that the cost-of-ownership and imaging capabilities of the total system remain intact over its lifetime.

Compact 13.5-nm free-electron laser for extreme ultraviolet lithography

Optical lithography has been actively used over the past decades to produce more and more dense integrated circuits. To keep with the pace of the miniaturization, light of shorter and shorter wavelength was used with time. The capabilities of the present 193-nm UV photolithography were expanded time after time, but it is now believed that further progress will require deployment of extreme ultraviolet (EUV) lithography based on the use of 13.5-nm radiation. However, presently no light source exists with sufficient average power to enable high-volume manufacturing. We report here the results of a study that shows the feasibility of a free-electron laser EUV source driven by a multiturn superconducting energy-recovery linac (ERL). The proposed $40\ifmmode\times\else\texttimes\fi{}20\text{ }\text{ }{\mathrm{m}}^{2}$ facility, using MW-scale consumption from the power grid, is estimated to provide about 5 kW of average EUV power. We elaborate the self-amplified spontaneous emission (SASE) option, which is presently technically feasible. A regenerative-amplifier option is also discussed. The proposed design is based on a short-period (2--3 cm) undulator. The corresponding electron beam energy is about 0.5--1.0 GeV. The proposed accelerator consists of a photoinjector, a booster, and a multiturn ERL.

High-power EUV (13.5 nm) light source

Characteristics of a discharge-produced plasma (DPP) light source in the spectral band 13.5±0.135 nm, developed for Extreme Ultra Violet (EUV) lithography, are presented. EUV light is generated by DPP in tin vapour formed between rotating disk electrodes. The discharge is ignited by a focused laser beam. The EUV power 1000 W/(2π sr) in the spectral band 13.5±0.135 nm was achieved with input power about of ∼63 kW to the plasma at a pulse repetition rate ∼7 kHz . The results of numerical simulation are compared with the experimental data.

Laser-produced plasmas as unique x-ray souces for industry and astrophysics

Laser produced plasma is one of the brilliant x-ray source that has unique capabilities for use in a wide range of science. Here we describe two examples of laser-produced plasma x-ray source application; one is for the semiconductor device industry and the other is for the astronomy. Extreme ultraviolet (EUV) light sources for microlithography are receiving much attention as an industrial application of laser-produced x-ray source. High power and clean EUV light source, 13.5 nm of wavelength, is developed for mass-production of next generation semiconductor devices. Highest EUV conversion efficiency of 4% has been attained by using low-density and minimum-mass tin targets produced by laser-driven explosion of micro-droplet. In addition, it was recently demonstrated that laser-produced x-ray source is very useful to simulate x-ray astronomical phenomena in the laboratory. A 0.5-keV Planckian x-ray source was created with laser driven implosion for producing non-local-thermodynamical-equilibrium (non-LTE) photoionized plasmas, which is a key to understand astronomical compact objects. Laboratory experiment of non-LTE photoionized plasma offers novel test bed for validation and verification of computational codes used in x-ray astronomy.

Performance results of laser-produced plasma test and prototype light sources for EUV lithography

Improved performance and specific results are reported for several test and prototype extreme ultraviolet (EUV) light sources developed for next-generation lithography. High repetition rate and high-power CO2 laser-produced plasma sources operating on tin droplet targets are described. Details of laser architecture, source chambers and system operation are given. Stable output power, efficient light collection, and clean EUV transmission could be achieved for hours of operation. We review progress during integration of light sources with collector mirrors reaching EUV power levels at intermediate focus of 60 W and 45 W, respectively, with duty cycles of 25% and 40%. Far-field EUV images of the collected light were recorded to monitor the source output performance during extended tests of collector longevity and debris protection with system operation time exceeding 50 h. Development results on EUV spectra, out-of-band (OOB) radiation, and ion debris obtained with dedicated metrology setups are also described. Angle-resolved measurements with ion energy analyzer and Faraday cups reveal the contributions of individual ion charge states in related spectra. Our laser-produced EUV light source technology has now reached a level of maturity in full integration where prototype sources can be delivered and pilot line introduction can be prepared.

Preparation of DLC strip targets for the tabletop storage ring synchrotrons MIRRORCLE

The tabletop storage ring synchrotrons MIRRORCLE-6X and MIRRORCLE-20SX can generate powerful extreme ultraviolet (EUV) radiation. They are applicable as sources for EUV lithography and for EUV photoemission spectroscopy. EUV radiation is emitted from a strip target consisting of a vertical strip with a width of ∼3 mm mounted on a frame with an inter-arm distance of 10 mm. The highest EUV power is expected to be achieved by using a diamond-like carbon (DLC) strip with a thickness of 55–150 nm. Two technologies were developed for preparation of such DLC strip targets. In the first technology, the DLC strip is backed by a 15-nm-thick formvar layer. Such a strip is floated on a water surface, and lifted from there directly onto an open frame. Since the strip tends to curl around its vertical axis while being lifted from the water, it curls mostly around the inter-arm center, and hence has its smallest width there. In the second technology, the DLC strip is not backed. A temporarily closed frame is constructed using two extra blades, and the foil is attached easily to that frame. Subsequently, the two free strip edges are formed, via cutting with a surgical blade along the edges of the two extra blades. Lastly, the extra blades are released and left to fall. Using these two technologies, strip targets containing a 55 nm DLC+15-nm-thick formvar strip, as well as 85-nm-thick and 150-nm-thick DLC-only strips were prepared.