In the paper we report about the progress made at XTREME technologies in the development of EUV sources based on gas discharge produced plasma (GDPP) technologies and laser produced plasma (LPP) technologies. First prototype xenon GDPP sources of the type XTS 13-35 based on the Z-pinch principle with 35 W power in 2π sr have been integrated into micro-exposure tools from Exitech, UK. Specifications of the EUV sources and experience of integration as well as data about component and optics lifetime are presented. In the source development program for Beta exposure tools and high volume manufacturing exposure tools both tin and xenon have been investigated as fuel for the EUV sources. Development progress in porous metal cooling technology as well as pulsed power circuit design has led to GDPP sources with xenon fuel continuous operating with an output power of 200 W in 2π sr at 4500 Hz repetition rate. With tin fuel an output power of 400 W in 2π sr was obtained leaving all other conditions unaltered with respect to the xenon based source. The performance of the xenon fueled sources is sufficiently good to fulfill all requirements up to the beta tool level. For both the xenon and the tin GDPP sources detailed data about source performance are reported, including component lifetime and optics lifetime. The status of the integration of the sources with grazing incidence collector optics is discussed. Theoretical estimations of collection efficiencies are compared with experimental data to determine the loss mechanisms in the beam path. Specifically contamination issues related to tin as target material as well as debris mitigation in tin sources is addressed. As driver lasers for the LPP source research diode-pumped Nd:YAG lasers have been used to generate EUV emitting plasma. As target material xenon has been employed. Conversion efficiencies have been measured and currently the maximum conversion efficiency amounts to 1 %. The laser driver power of 1.2 kW is currently achieved with a masteroscillator power-amplifier industrial Nd:YAG laser configuration. With this laser, xenon based EUV sources have achieved 10 W EUV power at 13.5 nm emitted into 2π sr solid angle. For the xenon LPP sources detailed data about the achieved source performance including component lifetime and optics lifetime are reported. The status of the integration of the sources with normal incidence collector optics is shown. The potentials and limits of Z-pinch GDPP and LPP EUV source technologies to achieve high volume manufacturing specifications are discussed in this paper.

In the paper we report about the progress made at XTREME technologies in the development of EUV sources based on Gas discharge produced plasma (GDPP) technologies as well as the integration of collector optics. Optics from different suppliers were integrated to the source and the performance of the radiation in the intermediate focus and in the far field behind the intermediate focus were determined using newly developed metrology tools.To improve the source performance in the development program for beta exposure tools and high volume manufacturing exposure tools both tin and xenon have been investigated as fuel for the EUV sources. Development progress in porous metal cooling technology as well as pulsed power circuit design has led to GDPP sources with xenon fuel continuously operating with an output power of 200 W in 2 pi sr at 4500 Hz repetition rate. With tin fuel an output power of 400 W in 2 pi sr was obtained leaving all other conditions unaltered with respect to the xenon based source. The performance of the xenon fueled sources is sufficiently good to fulfill all requirements up to the beta tool level. The required power of 1020 W in the intermediate focus region at etendue between 3 and 5 mm(2)sr was demonstrated by using a xenon based source.The status of the integration of the sources with grazing incidence collector optics is discussed in detail. Images using visible light or EUV light in the intermediate focus region or in the far field behind the intermediate focus are presented for the first time. EUV pulse to pulse energy and stability has been measured out of the source and in the intermediate focus. Data on debris reduction show that lifetime expectations for beta-tools will be met.

The availability of extreme ultraviolet (EUV) light sources, measurement tools and integrated test systems is of major importance for the development of EUV lithography for use in high volume chip manufacturing which is expected to start in 2009. The estimates of cost of an EUV exposure tool in combination with sophisticated throughput models leads to a throughput of 120 wafers per hour necessary for economic use of EUV lithography. Concluding from that light sources are necessary which deliver an EUV output power of 115 W at 13.5 nm at the entrance of the illuminator system. The power requirement in combination with the required lifetimes of source components and collector optics make the source technology the most critical issue to be solved when developing EUV lithography.The present paper gives an update of the development status of EUV light sources at XTREME technologies, a joint venture of Lambda Physik AG, Goettingen, and Jenoptik LOS GmbH, Jena, Germany. Results on both laser produced plasma (LPP) and gas discharge produced plasma (GDPP), the two major technologies in EUV sources, are given.The LPP EUV sources use xenon-jet target systems and pulsed lasers with 500 W average power at up to 10 kHz developed at XTREME technologies. The maximum conversion efficiency from laser power into EUV in-band power is 1.0% into 2pi solid angle. 2.0 W EUV radiation is generated at 13.5 nm in 2pi sr solid angle. The small source volume of < 0.3 mm diameter will allow large collection angles of 5 sr. The intermediate focus power is estimated to 1 W. Collector mirror lifetime tests showed 5 million pulses lifetime without debris mitigation. With debris mitigation in place lifetimes of more than 1 billion pulses are estimated. For the next generation of higher power EUV LPP sources a laser driver has been tested at 1.3 kW average laser power. This will lead to 5 W EUV power in intermediate focus.The GDPP EUV sources use the Z-pinch principle with efficient sliding discharge pre-ionization. Prototype commercial gas discharge sources with an EUV power of 35W in 2pi sr were already delivered for integration into EUV microsteppers. These sources are equipped with a debris-filter which results in an optics lifetime exceeding 100 million discharges at 1 kHz repetition frequency. The same lifetime was achieved for the components of the discharge system itself.The progress in the development of high-power discharge sources resulted in an EUV power of 150 W in continuous operation at 4.5 kHz repetition rate by implementation of porous metal cooling technology. The EUV plasma has a FWHM-diameter of 0.5 mm and a FWHM-length of 1.5 mm. The intermediate focus power is calculated to be in the range of 15 W - 20 W, depending somewhat on the transmission of the optical path to the intermediate focus and on the etendue specification. The typical fluctuations of the EUV energy are standard deviation sigma<5% without any active stabilization.Discharge sources with Sn as emitter were investigated as more efficient alternative to Xenon. Estimates regarding Sn sources reveal the potential of achieving 65 W intermediate focus power by using developed porous metal cooling technology. Improvement of cooling could open the path to 115 W of power for high volume manufacturing using EUV lithography. However, Sn-sources are technologically risky und much less advanced than Xe sources, since fuel-handling and debris mitigation is much more challenging in comparison to Xe-sources.GDPP and LPP sources still compete for the technology of high volume manufacturing sources for EUV lithography. Optimization potential of the etendue of the optical system of EUV scanners will certainly influence any technology decision for HVM sources.

Semiconductor chip manufacturers are expecting to use extreme ultraviolet (EUV) lithography for high volume manufacturing of DRAMS and ICs starting by the end of this decade. Among all the technologies and modules which have to be developed EUV sources at 13.5 nm are considered to be the most critical issue. Specifically the required output power of 115 W at the entrance of the illuminator system in combination with the required lifetimes of source components and collector optics make the source technology critical for EUV lithography. The present paper gives an update of the development status of EUV light sources at XTREME technologies, a joint venture of Lambda Physik AG, Goettingen, and Jenoptik LOS GmbH, Jena, Germany. Results on both laser produced plasma (LPP) and gas discharge produced plasma (GDPP), the two major technologies in EUV sources, are given. The LPP EUV sources use xenon jet target systems and pulsed lasers with 500 W average power at up to 10 kHz developed at XTREME technologies. The maximum conversion efficiency from laser power into EUV in-band power is 1.0% into 2pi solid angle. 2.0 W EUV radiation is generated at 13.5 nm in 2pi sr solid angle. The small source volume of < 0.3 mm diameter will allow large collection angles of 5 sr. The intermediate focus power is estimated to 1 W. Collector mirror lifetime tests showed 5 million pulses lifetime without debris mitigation. With debris mitigation in place lifetimes of more than 1 billion pulses are estimated. For the next generation of higher power EUV LPP sources a laser driver has been tested at 1.3 kW average laser power. This will lead to 5 W EUV power in intermediate focus. The GDPP EUV sources use the Z-pinch principle with efficient sliding discharge pre-ionization. Prototype commercial gas discharge sources with an EUV power of 35 W in 2pi sr were already delivered for integration into EUV microsteppers. These sources are equipped with a debris-filter which results in an optics lifetime exceeding 100 million discharges at 1 kHz repetition frequency. The same lifetime was achieved for the components of the discharge system itself.The progress in the development of high-power discharge sources resulted in an EUV power of 150 Win continuous operation at 4.5 kHz repetition rate by implementation of porous metal cooling technology. The EUV plasma has a FWHM-diameter of 0.5 mm and a FWHM-length of 1.5 mm. The intermediate focus power is calculated to be in the range of 15 W - 20 W, depending somewhat on the transmission of the optical path to the intermediate focus and on the etendue specification. The typical fluctuations of the EUV energy are standard deviation sigma < 5% without any active stabilization.Discharge sources with Sri as emitter were investigated as more efficient alternative to Xenon. Estimates regarding Sri sources reveal the potential of achieving 65 W intermediate focus power by using developed porous metal cooling technology. Improvement of cooling could open the path to 115 W of power for high volume manufacturing using EUV lithography. However, Sn-sources are technologically risky and much less advanced than Xe sources, since fuel-handling and debris mitigation is much more challenging in comparison to Xe-sources.GDPP and LPP sources still compete for the technology of high volume manufacturing sources for EUV lithography. Optimization potential of the etendue of the optical system of EUV scanners will certainly influence any technology decision for HVM sources.

Semiconductor chip manufacturers are expecting to use extreme UV lithography for production in 2009. EUV tools require high power, brilliant light sources at 13.5 nm with collector optics producing 120 W average power at entrance of the illuminator system. Today the power and lifetime of the EUV light source are considered as the most critical issue for EUV lithography. The present paper gives an update of the development status of EUV light sources at XTREME technologies, a joint venture of Lambda Physik AG, Goettingen, and Jenoptik LOS GmbH, Jena, Germany. Results on both laser produced plasma (LPP) and gas discharge produced plasma (GDPP), the two major technologies in EUV sources, are given. The LPP EUV sources use xenon-jet target systems and pulsed lasers with 400 W average power at 10 kHz developed at XTREME technologies. The maximum conversion efficiency form laser power into EUV in-band power is 0.75% into 2π solid angle. With 300 W laser average power at 3300 Hz repetition rate up to 1.5 W EUV radiation is generated at 13.5 nm. After a collector of 5 sr this corresponds to 0.6 W in intermediate focus without spectral purity filter and 0.5 W in intermediate focus with spectral purity filter. The direct generation of the EUV emitting plasma from electrical discharges is much simpler than LPP because the electrical energy has not to be converted into laser radiation before plasma excitation. XTREME technologies' Xenon GDPP EUV sources use the Z-pinch principle with efficient sliding discharge pre-ionization. The plasma pinch size and the available emission angle have been matched to the etendue of the optical system of 2-3 mm2 sr, i.e. no additional etendue related loss reduces the usable EUV power from the source. In continuous operation at 1000 Hz the GDPP sources emit 50W into 2π solid angle are obtained from the Z-pinch sources. Spatial and temporal emission stability of the EUV sources is in the range of a few percent. Debris shields for EUV sources have been developed which give improvement of the collector optics lifetime by several orders of magnitude.

Next generation semiconductor chip manufacturing using extreme ultraviolet (EUV) lithography requires a brilliant radiation source with output power between 50 W and 120 W in intermediate focus. This is about five to ten times higher power than that of current DUV excimer lasers used in optical lithography. Lifetime and cost of ownership however, need to be comparable to today's technology. In the present paper experimental results of both laser produced plasma and gas discharge produced plasma EUV source development at XTREME technologies - the EUV joint venture of Lambda Physik AG, Goettingen, and Jenoptik LOS GmbH, Jena, Germany - are presented. Source characterization has been performed with calibrated metrology tools for measurement of energy, power, size, spectra and stability of the EUV emission. The laser plasma investigations are performed with a 1st experimental facility comprising a commercial 40 W Nd:YAG laser coupled to a liquid xenon-jet target system, which was developed by XTREME technologies. The EUV in-band power emitted from the 0.25 mm diameter plasma into 2p solid angle is 0.2 W, the conversion efficiency amounts 0.5 percent. Estimated EUV emission parameters using a 500 W laser for plasma generation to be installed in spring 2002 are discussed. The gas discharge EUV sources described here are based on efficient Xenon Z-pinches. In the 3rd prototype generation the plasma pinch size and the available emission angle have been matched to the etendue of the optical system of 2-3 mm2. The solid angle of emission from the pinch of 1.3 mm x 1.5 mm amounts 1.8 sr. The Z-pinch EUV source can be operated continuously at 1000 Hz with an in-band output power of 10 W in 1.8 sr. This corresponds to 4.5 W in intermediate focus, if no spectral purity filter is needed. The power emitted into a solid angle of 2p sr is 35 W. Emission energy stability ranges between 1 percent and 4 percent standard deviation. Spectral, temporal as well as spatial emission characteristics of the discharge source in dependence on the gas discharge geometry have been evaluated. The potentials as well as limits for power scaling of the two technological source concepts are discussed.

In this paper we discuss new results from investigations on high power EUV sources for micro-lithography based on gas discharge produced plasmas and laser produced plasmas. The EUV development is performed at XTREME technologies GmbH, a joint venture of Lambda Physik AG, Goettingen, and Jenoptik LOS GmbH, Jena. For gas discharge EUV sources we report data based on Xenon filled Z-pinches. Prototypes of the EUV source achieve an EUV output power of 10 W in-band in continuous operation. Repetition rates of 1 kHz are possible with liquid cooling of the discharge head. The spectral distribution of the EUV radiation shows a maximum around 13.5 nm and matches the reflection characteristics of silicon/molybdenum multilayer mirrors. Conversion efficiencies between 0.25 percent and 0.7 percent into a solid angle of 2p sr were achieved with the Z-pinch source depending the discharge geometry. The total EUV average power in the spectral range between 5 nm and 50 nm is about 200 W in 1.8 sr. Pulse energy stability data show standard deviation between 1-4 percent. Spatial and temporal emission characteristics of the discharge source in dependence on the discharge geometry are discussed. The laser plasma investigations are performed with an experimental setup consisting of a diode pumped laser system coupled to a liquid jet target. Since the conversion efficiency into EUV-power depends critically on the emitter density in the interaction region, we use a Xenon-jet, which is cryogenically liquefied and injected under high pressure into the vacuum vessel. Thus the laser is impinging on a target of solid-state density, which allows the generation of EUV-radiation with high conversion efficiencies of 0.5 percent into a solid angle of 2p sr.

We report on the experimental status of the development of gas discharge produced plasma EUV sources for lithography based on the Z-pinch concept. The plasma size of similar to 1.3 mm x 1.5 mm has been matched to come close to the requirements resulting from the etendue of the optical system. The spatial stability of the plasma size as well as the plasma center is better than 15 % standard deviation. The solid angle of emission is 1.8 sr, i.e. +/- 45 deg. The sources can be operated continuously at 1000 Hz repetition frequency and provide an EUV in-band power of 10 W in 1.8 sr. Spectral measurements providing in-band and out-of-band spectral distribution of the source are discussed.

The emission of (In,Ga)N/GaN multiple quantum wells is studied by continuous-wave and time-resolved photoluminescence. The spectra are dominated by a low-energy band originating from localized states. A second, higher-energy band is shown to stem from extended states in the well. Finally, we show that a general understanding requires consideration of both potential fluctuations and electric fields.

We study, both experimentally and theoretically, the influence of polarization-induced electric fields on the optical properties of heavily doped (7 x 10(18) cm(-3)) GaN/(Al,Ga)N multiple-quantum-well structures. To investigate the impact of the strain state on the transition energy, these heterostructures are deposited on either a GaN or an (Al,Ga)N relaxed buffer layer. Furthermore, we show that the recombination dynamics in these heavily doped multiple quantum wells is still controlled by residual electric fields, contrary to the common assumption that flatband conditions are established at this doping level.

We study the influence of the strain-state and the strain and polarization-induced electric fields on the optical properties of CaN/(Al,Ga)N multiple quantum well (MQW) structures. To investigate the impact of the strain state on the transition energy, these heterostructures are deposited on either a GaN or an (Al,Ga)N buffer layer. Furthermore, we show that the recombination dynamics in heavily doped (7x10(18) cm(-3)) MQW structures is still controlled by residual electric fields, contrary to the common assumption of the flat-band state achieved by screening.

The type-II nature of the energy gap has been identified in In0.52Al0.48As/AlAs0.56Sb0.44 multiple quantum well structures through cw and time-resolved photoluminescence (PL) measurements. Direct evidence for the type-II character of the energy gap in this material system axe the energetic position of the PL, the by more than two orders of magnitude prolonged PL decay time in comparison to the substrate and the direct-gap buffer layers, as well as the increase of the decay time with increasing In0.52Al0.48As layer thickness.

The optical properties of stacked GaAs/(Al,Ga)As quantum wire arrays, with a 0.5 mu m lateral period fabricated by molecular beam epitaxy on patterned GaAs(311)A substrates, have been investigated. We observe an unexpectedly high quantum wire related contrast in the lateral distribution of the cathodoluminescence (CL) intensity, in particular at 300 K. The temperature dependence of this contrast as well as of the integrated CL intensities in the quantum wires and connecting quantum wells, reveals the loss mechanisms, which cause a reduction of the exciton transfer efficiency from the well into the wire regions. For low and intermediate temperatures, exciton localization and nonradiative recombination within the quantum well regions contribute to the decrease of the transfer efficiency. Near room temperature, the vertical escape of carriers, in particular out of the quantum well regions into the (Al,Ga)As barriers, is the limiting process. Within the framework of a detailed model, we determined the transfer time and the ratio of the radiative recombination times in the well and wire regions by combining the spatially resolved CL measurements with time-resolved photoluminescence spectroscopy. [S0163-1829(99)12539-6].

We review the linear and nonlinear optical properties of crystals transparent near and below 200 nm and suitable for up conversion of femtosecond Ti:sapphire laser sources, /spl beta/-BaB/sub 2/O/sub 4/, the crystal with the largest birefringence of all presently available materials, is investigated experimentally as a quadrupler by mixing the fundamental and the third harmonic both using a 1-kHz repetition rate Ti:sapphire regenerative amplifier and a 82-MHz mode-locked Ti:sapphire laser. Milliwatt average powers near 200 nm are achieved in both cases. The sub-200-fs pulses at the fourth harmonic are almost bandwidth limited. Sum-frequency generation as a method for upconversion of femtosecond pulses is experimentally studied by mixing the fourth harmonic generated down to 189 nm by the regenerative amplifier with a parametrically generated femtosecond pulse in the infrared. Pulse energies at the microjoule level are produced with LiB/sub 3/O/sub 5/ above 180 nm. Li/sub 2/B/sub 4/O/sub 7/ shows superior performance in the 170-180-nm range, and the shortest wavelength achieved with KB/sub 5/O/sub 8//spl middot/4H/sub 2/O is 166 nm.

Time-resolved photoluminescence spectroscopy has been applied to determine the nature of the energy gap of InAlAs/AlAsSb multiple quantum well structures. While the InAlAs buffer layer exhibits a decay time of the order of 1 ns, which is typical for direct gap semiconductors, the decay time of the InAlAs/AlAsSb multiple quantum well structures is prolonged by more than two orders of magnitude. This observation is direct evidence for the presence of an indirect energy gap. The decay time increases with increasing InAlAs layer thickness indicating the decreasing overlap of electron and hole wave functions.

We performed time-resolved and continuous wave photoluminescence on two samples of hexagonal GaN, one with free exciton emission and the other without. For the sample with free exciton emission, very different decay dynamics are observed between the front and backside emission. We find that the strain caused by the lattice mismatch between the sapphire substrate and the GaN film has a large influence on the population decay of the sample with free exciton emission and a minor influence on the decay properties of the sample dominated by bound exciton emission. A polariton picture is used to describe the observed behavior. @S0163-1829 ~98!09109-7#

Alkaline-earth fluorides are widely used in optical transmission components in the deep UV as well as for optical coatings because of their wide-band-gap, low refractive indices and hardness. One essential drawback of these materials is the formation of defects (color centers e. g.) during intense irradiation. This limits the lifetime of such optical elements for high power propagation in the UV and reduces the transmission of ultrashort laserpulses nonlinearly. Details of this process, in particular the dynamics during the early stages (formation of self-trappped excitons STE [1]) are therefor of interest.

Using time-resolved photoluminescence spectroscopy, we determine the temperature dependence of the radiative lifetime for GaN layers with doping levels from 10(16) to 10(18) cm(-3). The experimental results are analyzed by a coupled rate-equation model taking into account band-to-band, free and bound excitons, as well as donor-to-band recombination. An analytic expression for the radiative lifetime of this coupled system is derived and fit to the data. Over the entire temperature range, radiative recombination is strongly affected by the decay of either bound or free excitons. The temperature dependence and the absolute values for the radiative lifetime are governed by the coupling between the individual populations. This coupling in turn is determined by the binding energies of the respective species. Using a binding energy of 26.4 meV for the free exciton, we obtain best-fit values of 30+/-6 and 36.3+/-2 meV for the donor and the donor-bound exciton, respectively. [S0163-1829(98)50638-0].