R. Viladrosa

Discharge-based sources of XUV-X radiations: development and applications

There is an increasing use of high energy photons in many fields of research and in industry. Where large installations such as synchrotrons or dedicated laser based source facilities can provide solutions for specific needs, they are presently unable to bring convenient solutions for on-site experiments or industrial processes. Compact discharge based devices appear to be a very interesting response to the demand in many cases. They can provide high photon fluxes in a wide spectral range, from VUV to hard x-rays, covering most of the actual needs. Certainly, they still need a lot of improvement and optimization to meet the most stringent requirements. In this paper, we will present some of the recent results we obtained in that field along with new applications. Among them, we will present our report on the performance of a novel and truly compact xenon-filled fast capillary discharge system which generates radiation mostly in the EUV region (10–16 nm) developed in the framework of an EUV lithography program. We will also present results obtained in the field of hard x-ray generation with a new source capable of producing high dose pulses in quasi-continuous or burst mode at a very high frequency developed for high speed cineradiography.

Time-resolved spatial distribution of an ablative capillary discharge obtained with a pinhole camera

Time- and space-resolved measurements of an ablative polyethylene capillary discharge using a pinhole camera are presented in this paper. Measurements with and without a 0.1 µm thick polyimide filter allowed us to identify the soft x-ray production zones. The images show that the plasma, mainly composed of highly ionized carbon, was not detached from the capillary wall during the heating phase. This plasma behaviour does not favour the development of a recombination-pumped x-ray laser. For two capillary lengths, the plasma dynamics were observed at constant power density in a first run and at identical current waveform in a second run. In both cases, they were different and could induce errors on gain measurement when varying capillary lengths. To our knowledge, this is the first report of time-resolved pinhole images of ablative carbon capillary discharges used as soft x-ray sources.

Compact flash X-ray sources and their applications

Abstract Compact flash X-ray machines are opening up extended fields of applications. X-ray diodes driven by repetitive small size pulsers have been shown able to deliver high dose rates of X-rays in pulses of nanosecond to microsecond duration. Improvements have been carried out on the lifetime of the diodes and reliability of the systems to allow operation at constant emitted dose over long periods of time. After a brief review of recent developments, described here, in more details, is the progress obtained at the GREMI laboratory in the development of true table-top flash X-ray sources producing strong X-ray doses in nanosecond pulses at a high repetition rate (50 Hz). Doses up to 2 R (5.2 × 10−4 C/kg), measured at the output window, of X-rays between 5 and 200 keV can be generated from either a linear source (up to 10 cm long) or from a focal spot of less than 300 μm in diameter depending on the electrode configuration. Of the numerous applications of compact flash X-ray sources, an example is given of the use of these devices for the excitation of high pressure gas samples, realized at GREMI. Such an energetic excitation leads to important populations of highly excited ionic species.

Spectroscopic and energetic investigation of capillary discharges devoted to EUV production for new lithography generation

In this work, ablative and gas capillary discharges have been investigated as potential sources for the EUV lithography technology. Carbon and lithium ablative discharge spectroscopy and EUV energy measurements have been performed. Gas (O2, Ne, Ar, Kr and Xe) capillary discharge were powered by fast, nanosecond, high voltage Blumlein-like pulser. Detailed investigation of capillary length and diameter, gas pressure, capacitance and inductance of the electrical driver are documented. The energy density, expressed in J cm-3, appears as a monitoring factor for an efficient production of 13.5 nm radiation band. The measurement and the evaluation of measurement uncertainties lead to the conclusion that the in band, 13.5 nm +/- 0.9 nm, energy radiated by the Xe lamp developed in this work ranges from 0.5 mJ/sr/shot to 20 mJ/sr/shot for a 7 J energy input. Repetition rate investigation of the first prototype have shown operation at 50 Hz in continuous mode and up to 350 Hz in burst mode.

Compact flash x-ray source producing high average powers in nanosecond pulses

X‐ray diodes driven by repetitively pulsed Blumleins have been shown to be able to deliver high dose rates of x rays in pulses of nanosecond duration. Reported here is a study of the scaling of such devices conducted to isolate the primary factors limiting performance. Low residual gas pressure in the output diode together with the critical alignment of the electrodes were found essential for enhanced output. Optimizations served to increase the x‐ray yield by an order of magnitude and the resulting performance is reported. At the output window, dose rates exceeding 1.4 kR min−1 were obtained in nanosecond pulses from the finished device of table top size at a charging voltage of 30 kV and a pulse repetition rate of 50 Hz.

X-ray diagnostics of the near injector zone of cryogenic nitrogen jets at supercritical pressures

The German Aerospace Centre carries out since many years studies on the flow and combustion of liquid jets expanding in a high pressure chamber through a single injector. For this study, liquid nitrogen has been injected into a pressurized test chamber filled with gaseous nitrogen at different test conditions. The behavior of the flow is well known on principal but the liquid zone, near the injector, is not accessible for the analysis using classical optical diagnostics. In order to be able to study this zone of the cryogenic jet, a new compact and pulsed (50 ns FHWM typical) X-ray source has been developed and utilized. During experiments carried out on the test bench M51 of the DLR, this soft X-ray flash energy, enable us to carry out radiography of the zone close to the injector (z/d < 10) for chamber pressures from 1.0 to 6.0 MPa and temperatures of the liquid nitrogen jet ranging from 100 to 130 K. The data and their Processing result in the possibility to obtain the various density profiles corresponding to injection conditions. The obtained results are compared with those collected by other methods (experimental and numerical) already used in the DLR.

Investigations of silicon oxide UV emission in a non-thermal atmospheric plasma?comparison with synthetic spectra

UV emission of silicon oxide molecules observed from a non-thermal atmospheric pulsed dielectric barrier discharge was experimentally explored in a spectral range from 228 to 253 nm. The main vibrational bands (1, 1), (2, 2) and (0, 1) of A 1Π–X 1Σ+ electronic transition were investigated. Corresponding synthetic spectra was built up and adjusted with good agreement. Excitation temperatures (Tvib, Trot) were deduced as a function of gas composition. It is shown that the rotational temperature can represent a non-intrusive diagnostic of plasma gas temperature in process control.

CAPELLA: a kHz and low-debris capillary discharge EUV source

The development and operation of a multi watt, multi kHz and low debris EUV gas discharge source is reported. The Capillary EUV Lamp for Lithography Approach (CAPELLA) is designed and characterized for its application in the french EUV exposure tool named BEL. The burst operation at high repetition rate, up to 3 kHz, of the source during time period of a few seconds is described and shown to be relevant for the BEL application. The long time stability over hours is measured to be of 0.6 percent. Other technical BEL requirements such as energy flux, EUV output stability, spatial position stability, collection angle are briefly presented and their fulfilment is documented through the experimental data obtained on the CAPELLA prototype. An experimental characterization of debris nature and deposition rate on plasma facing silicon targets has been performed over millions of shots showing evidence of the crucial role of the discharge regime.

Capillary discharge sources of hard UV radiation

We developed and studied three different extreme ultraviolet (EUV) capillary discharge sources either dedicated to the generation of coherent or incoherent EUV radiation. The CAPELLA source has been developed especially as an EUV source for the metrology at 13.4 nm. With one of these sources, we were able to produce gain on the Balmer-Hα (18.22 nm) and Hβ (13.46 nm) spectral lines in carbon plasma. By injecting 70 GW cm−3 we measured gain-length products up to 1.62 and 3.02 for the Hα and Hβ, respectively optimization of the EUV capillary source CAPELLA led to the development of an EUV lamp which emits 2 mJ in the bandwidth of the MoSi mirror, per joule stored, per shot and in full solid angle. The wall-plug efficiency is 0.2%. Stability of this lamp is better than 4% and the lamp can operate at repetition rate of 50 Hz.

Recent progress in EUV source development at GREMI

Abstract The objective of the present paper is to provide current information on a novel and truly compact fast capillary discharge EUV source that is under investigation at GREMI. A current of a few kA having a fast rise time was applied across a xenon-filled alumina capillary to produce radiation, mostly in the EUV region (10–16 nm). The EUV radiation from the capillary was characterized by employing an EUV spectrometer and an EUV pinhole camera. Time-integrated and time-resolved spectra provided information about the radiative processes from the xenon plasma together with the wall of the capillary. A superfast pinching effect is inferred from the pinhole images. At present, this EUV source is capable of operating at a high repetition rate (350 Hz in burst mode and 100 Hz in continuous mode) without causing too much damage to the wall of the capillary. This EUV source may be a strong contender as the source of the Next Generation Lithography (NGL) assembly.