Gas Discharge Produced Plasma Research Articles

Xenon Discharge-Produced Plasma Radiation Source for EUV Lithography

Extreme ultraviolet (EUV) radiation with wavelengths of 11-14 nm is seen as the most promising candidate for a new lithographic technology. Compared with synchrotron radiation sources and laser-produced plasmas, gas discharge-produced plasma sources for EUV radiation are expected to offer lower cost of ownership. Using xenon, a broadband emission in the investigated wavelength range from 10 to 17 nm is observed. Very short current pulses, having a fast rise time of 85- or 140-ns duration and 23-kA amplitude, were applied across the xenon-filled Z-pinch capillary (3-mm diameter and 5-mm length) to produce EUV radiation. An EUV radiation from the Z-pinch plasma was characterized, which is based on the temporal behavior of EUV intensity and the pinhole images. Two maximum EUV radiations occur, which are sensitive to the xenon flow rate and the discharge current. The first radiation is relatively of short duration, while the second radiation lasts as long as the first period of the current flows. The EUV source size due to the first radiation is approximately 300 μm, i.e., half of the one due to the second radiation.

Dependence of Extreme Ultraviolet Emission on Xenon Flow Rate from a Z-Pinch Discharge Plasma

Extreme ultraviolet (EUV) radiation with wavelengths of 11 to 14 nm is seen as the most promising candidate for a new lithographic technology. Compared to synchrotron radiation sources and laser produced plasmas, gas discharge produced plasma (GDPP) sources for EUV radiation are expected to offer lower cost of ownership. This paper describes the dependence of EUV emission on gas flow rate. Using xenon a broadband emission in the investigated wavelength range from 10 to 18 nm is observed. Very short current pulses were applied across the xenon-filled Z-pinch capillary (3 mm diameter and 5 mm length) to produce EUV radiation. A EUV radiation from the Z-pinch plasma was characterized, which is based on the temporal behavior of EUV intensity and the pinhole images.

Tin removal from extreme ultraviolet collector optics by inductively coupled plasma reactive ion etching

Tin (Sn) has the advantage of delivering higher conversion efficiency compared to other fuel materials (e.g., Xe or Li) in an extreme ultraviolet (EUV) source, a necessary component for the leading next generation lithography. However, the use of a condensable fuel in a lithography system leads to some additional challenges for maintaining a satisfactory lifetime of the collector optics. A critical issue leading to decreased mirror lifetime is the buildup of debris on the surface of the primary mirror that comes from the use of Sn in either gas discharge produced plasma (GDPP) or laser produced plasma (LPP). This leads to a decreased reflectivity from the added material thickness and increased surface roughness that contributes to scattering. Inductively coupled plasma reactive ion etching with halide ions is one potential solution to this problem. This article presents results for etch rate and selectivity of Sn over SiO2 and Ru. The Sn etch rate in a chlorine plasma is found to be much higher (of the order of hundreds of nm/min) than the etch rate of other materials. A thermally evaporated Sn on Ru sample was prepared and cleaned using an inductively coupled plasma etching method. Cleaning was confirmed using several material characterization techniques. Furthermore, a collector mock-up shell was then constructed and etching was performed on Sn samples prepared in a Sn EUV source using an optimized etching recipe. The sample surface before and after cleaning was analyzed by atomic force microscopy, x-ray photoelectron spectroscopy, and Auger electron spectroscopy. The results show the dependence of etch rate on the location of Sn samples placed on the collector mock-up shell.

Optimizing Operational Parameters for Z-Pinch EUV Source by Artificial Neural Network

Non-equilibrium ionization plays a critical role in Z-pinch gas discharge produced plasma (GDPP) EUV source. However, the physics of the processes, plasma and surface discharges produced, magneto-hydrodynamic, photon radiation transport, and plasma-electrode interactions, which lead to EUV emission, is intrinsically complex. Many simplifying assumption are inevitable with numerical simulations, resulting in low-credibility outcomes. With the learning and generalization abilities, artificial neural networks (ANN) have been applied to model and optimize a Z-pinch plasma source, which is characterized with a experimental design at varied operational parameters including electric power input, applied voltage/current, pulse repetition, MPC parameters, electrode geometry, xenon flow rate as well as convention efficiency, EUV source size, radiation power etc.

Ion-Induced Surface Modification of EUV and VUV Plasma-Facing Collector Mirrors

AbstractGeneration of extreme ultraviolet (EUV) light for nanolithography requires the use of hot, dense plasmas. Gas discharge produced plasma (GDPP) and laser produced plasma (LPP) are the primary configurations used to generate these plasmas. Both GDPP and LPP collector mirror systems face serious issues regarding lifetime and EUV light reflectivity performance. For both configurations debris, fast ions, fast neutrals, and condensable EUV radiator fuels (Li, Sn) interact with nearby collector mirrors. Sn, in particular is used due to its high conversion efficiency in the 13.5-nm in-band spectrum. In addition to debris, collector mirrors are exposed to impurities (H,C,O,N), off-band radiation (depositing heat) and highly-charged ions leading to their degradation and consequently limiting 13.5 nm light reflection intensity.This work presents results of Ru and Rh-based collector optics irradiated by Sn ions between at 1.3 keV and exposed to Sn thermal atoms at room temperature. In-situ metrology monitors the effects of ion implantation on ion-induced erosion and EUV reflectivity changes using low-energy ion scattering spectroscopy and X-ray photoelectron spectroscopy. Results find that Sn implants at the first few monolayers leading to a mixed layer at the surface. Sn thermal atoms deposit on top of the mirror surface leading to 10-20% loss of collector mirror EUV light reflectivity.

Extreme ultraviolet light sources for use in semiconductor lithography—state of the art and future development

This paper gives an overview of the development status and plans of extreme ultraviolet (EUV) light sources at XTREME technologies, a joint venture of Lambda Physik AG, Göttingen and JENOPTIK LOS GmbH, Jena, Germany. Results for gas discharge-produced plasma (GDPP) and laser-produced plasma (LPP), the two major technologies in EUV sources, are presented.The GDPP EUV sources use the Z-pinch principle with efficient sliding-discharge pre-ionization. First prototypes of commercial gas discharge sources with an EUV power of 35 W in 2π sr have already been integrated into EUV microsteppers. These sources are equipped with a debris-filter which supports an optics lifetime exceeding 100 million pulses at 1 kHz repetition rate. The same lifetime was achieved for the components of the discharge system itself.The progress in the development of high-power discharge sources based on xenon resulted in an EUV power of 200 W into a 2π sr solid angle, in continuous operation, at 4.5 kHz repetition rate, by implementation of porous-metal cooling technology. The available intermediate focus (IF) power is 22 W taking into account experimentally verified losses in a 1.8 sr source collector module. The usable IF power depends on the etendue of the optical system of the EUV scanner. For the current size of the EUV emitting plasma the etendue acceptance factor may be below 0.5. The currently usable IF power with 1.8 sr collector mirror may therefore be about 10 W.Z-pinch discharge sources with Sn as the emitter have been developed as a more efficient alternative to xenon fuelled sources. Tin sources showed a conversion efficiency (CE) that was double that of xenon. EUV power of 400 W in 2π sr has been generated at only 4.5 kHz repetition rate. The available IF power is 44 W. Estimates evaluating the tin source performance reveal the potential for achieving high-volume manufacturing (HVM) power specification by using existing technology.Because of their small plasma size and the rather simple thermal management in the EUV generator the LPP EUV sources are investigated as alternatives to GDPP sources to achieve sufficient power for HVM with EUV lithography. These sources use xenon-jet target systems and high-power pulsed lasers as plasma excitation drivers developed at XTREME technologies. The maximum CE from laser power into EUV in-band power is 1.0% into a solid angle of 2π. Experimentally, 7 W EUV radiation is generated at 13.5 nm in a 2π sr solid angle with 0.7 kW laser power on the target. The small source volume of <0.5 mm diameter will allow large collection angles of 5 sr. The corresponding usable IF power is estimated to be 2.3 W. With the full power of the installed 1.2 kW laser driver 10 W EUV power in 2π sr is expected. LPP sources with tin targets are estimated to achieve nearly 10 W IF power with existing driver laser technology.GDPP and LPP sources still compete for the technology of HVM sources for EUV lithography. Each of these technologies has its challenges. The optimization potential of the etendue of the optical system of EUV scanners will certainly influence any decision for a HVM source technology.