Jeroen Jonkers

An easy way to determine simultaneously the electron density and temperature in high-pressure plasmas by using Stark broadening

This paper discusses the possibility of determining, at the same time, both the electron density and temperature in a discharge produced at atmospheric pressure using the Stark broadening of lines spontaneously emitted by a plasma. This direct method allows us to obtain experimental results that are in good agreement with others previously obtained for the same type of discharge. Its advantages and disadvantages compared to other direct methods of diagnostics, namely Thomson scattering, are also discussed.

On the differences between ionizing helium and argon plasmas at atmospheric pressure

In this paper the electron density and temperature of atmospheric helium and argon plasmas operated under similar experimental conditions are compared. The conditions are chosen such that both plasmas are ionizing. It is found that a helium plasma has a higher electron temperature and a lower electron density than an equi-operational argon plasma, i.e. an argon plasma that is operated at the same external conditions. This is mainly caused by the higher excitation potential of the first excited state and the lower mass of helium, respectively. Due to these differences in electron density and temperature the densities of the helium ground state and of the excited states are much larger than their corresponding Saha equilibrium values for a wide range of conditions. The consequence of this is that the spectroscopic methods, which are used to determine the electron density and temperature, have a very limited validity region in the case of helium. For argon the deviations are much smaller so that these methods can often be applied safely.

Portable diagnostics for EUV light sources

The EUV light source is a critical factor for the success of Extreme Ultraviolet Lithography (EULV), ASML, FOM and Philips Research have developed a portable set of diagnostics for the characterization of candidate EUV sources, called Flying Circus. The set of diagnostics is used to perform the following measurements: Absolute EUV power measurements, pulse-to-pulse intensity fluctuations, plasma size and shape, size/shape/positional stability, spectral distribution of radiation and stability, timing jitter and contamination by the source. These measurements are to be performed on-site, at the laboratories of the different source developers. The design as well as the first calibration measurements performed by the Flying Circus on the FOM Xe double gas jet source and on the PLEX z-pinch source will be discussed.

Physical properties of the HCT EUV source

The paper describes the physical properties and recent technical advances of the hollow cathode triggered pinch device (HCT) for the generation of EUV radiation. In previous publications we have demonstrated continuous operation of the untriggered device at 1 kHz in pure Xe. The newer generations operate with a triggering facility which allows a wider parameter space under which stable operation is possible. Repetition frequencies of up to 4 kHz could be demonstrated. Many of the experiments are performed in repetitive bursts of variable lengths and spacing. This allows also to demonstrate that there is only little transient behavior upon switching on and off the source. Conversion efficiencies into the 2 percent frequency band around 13.5 nm are about 0.4 percent in 2p, comparable to the values reported from other groups. Another important parameter is the size of the light emitting region. Here we have studied the influence of electrode geometry and flow properties on the size, to find a best match to the requirements of the collection optics. A major problem for the design of a complete wafer illumination system is the out-of-band portion of the radiation. Especially the DUV fraction of the source spectrum is a concern because it is also reflected to some extend by the Mo-Si multilayer mirrors. We show that the source has a low overall non-EUV part of the emission. In particular, it is demonstrated that there is very little DUV coming out of the usable source volume, well below the specified level.

Multilayer reflectance during exposure to EUV radiation

Mo/S multilayer mirrors have been exposed to intense monochromatic EUV radiation in order to investigate a possible deterioration of the mirror reflectance under different vacuum conditions. Power densities up to 3 mW/mm2 were applied at the PB undulator beamline at BESSY II, applying a hydrocarbon enriched vacuum. The mirror reflectance has been monitored in situ during several hours of exposure. Vacuum pressures of 3 X 10-8 mbar (without hydrocarbons) and 10-7 mbar (with hydrocarbons) at EUV intensities of 3 mW/mm2, respectively 0.2 mW/mm2 have been applied. The reflectance of the mirrors decreased when exposed to EUV radiation in hydrocarbon enriched vacuum, while no loss in reflectance was observed when no hydrocarbons were added to the vacuum. Ozone-cleaning experiments, using UV produced ozone from air at atmospheric pressure, were performed and show that Mo/S mirrors do not suffer from prolonged exposure to ozone.

Frequency scaling in a hollow-cathode-triggered pinch plasma as radiation source in the extreme ultraviolet

The hollow-cathode triggered discharge extreme ultraviolet source is based on the same principle as pseudospark switches. The electrode geometry consists of a planar anode and cathode with central opposing holes, the one on the cathode side being connected to the hollow cathode. Radiation is generated by magnetic compression of the working gas under high-current operation. Essential for the operation is that the pressure and voltage are chosen to be on the left side of the Paschen curve to insure insulation of the gap between the electrodes. However, this insulation of the electrode system needs to be reinstalled after breakdown. Typical recovery times of a xenon-based system are down to 100 /spl mu/s, depending on the electrode geometry. It will be shown that the decay of the electron density in the hollow cathode is the limiting process. Investigation of the recovery mechanism has led to a design that allows operation above 4 kHz which is close to the required frequency for extreme ultraviolet lithography.

Sn DPP source-collector modules: status of alpha resources, beta developments, and the scalability to HVM

For industrial EUV (extreme ultra-violet) lithography applications high power extreme ultraviolet (EUV) light sources are needed at a central wavelength of 13.5 nm, targeting 32 nm node and below. Philips Extreme UV GmbH and XTREME technologies GmbH have developed DPP (Discharge Produced Plasma) Alpha tools which run in operation at several locations in the world. In this paper the status of the Alpha Sn-DPP tools as developed by Philips Extreme UV GmbH will be given. The Alpha DPP tools provide a good basis for the development and engineering of the Beta tools and in the future of the HVM tools. The first Beta source has been designed and first light has been produced. Engineering steps will folow to optimize this first generation Beta Sn-DPP source. HVM tools target EUV power levels from 200W to 500W in IF. In this paper we show that the power requried for HVM can be generated with Sn-DPP sources. Based on Alpha Sn-DPP sources we show that repetition frequency and generated EUV pulse energy is scalable up to power levels that match the HVM requirements.

EUV sources for the alpha-tools

In this paper, we report on the recent progress of the Philips Extreme UV source. The Philips source concept is based on a discharge plasma ignited in a Sn vapor plume that is ablated by a laser pulse. Using rotating electrodes covered with a regenerating tin surface, the problems of electrode erosion and power scaling are fundamentally solved. Most of the work of the past year has been dedicated to develop a lamp system which is operating very reliably and stable under full scanner remote control. Topics addressed were the development of the scanner interface, a dose control system, thermo-mechanical design, positional stability of the source, tin handling, and many more. The resulting EUV source-the Philips NovaTin(R) source-can operate at more than 10kW electrical input power and delivers 200W in-band EUV into 2π continuously. The source is very small, so nearly 100% of the EUV radiation can be collected within etendue limits. The lamp system is fully automated and can operate unattended under full scanner remote control. 500 Million shots of continuous operation without interruption have been realized, electrode lifetime is at least 2 Billion shots. Three sources are currently being prepared, two of them will be integrated into the first EUV Alpha Demonstration tools of ASML. The debris problem was reduced to a level which is well acceptable for scanner operation. First, a considerable reduction of the Sn emission of the source has been realized. The debris mitigation system is based on a two-step concept using a foil trap based stage and a chemical cleaning stage. Both steps were improved considerably. A collector lifetime of 1 Billion shots is achieved, after this operating time a cleaning would be applied. The cleaning step has been verified to work with tolerable Sn residues. From the experimental results, a total collector lifetime of more than 10 Billion shots can be expected.

Fundamental description of spectrochemical inductively coupled plasmas. Plenary lecture

For the determination of the optimum conditions for spectrochemical analysis with plasmas a simple and yet accurate description of the plasma state is essential. In this paper, which should be regarded as a review of earlier and more recent work, non-equilibrium modelling of slowly flowing atmospheric ICPs and experimental results are described. The results of modelling are in fair agreement with experimental values from the literature, in particular for lower excitation frequencies. However, for high frequencies the model plasmas tend to remain too close to the wall. It is concluded that even in argon plasmas, dissociative recombination of molecular ions gives an additional recombination route close to the wall, where the neutral ground state density is high and the temperature low. Results of experimental analysis by active and passive spectrometry are given. In addition, the possibilities inherent in time-dependent studies, such as in power interruption experiments, are indicated. The processes of droplet evaporation and analyte excitation and ionization are also summarized. The virtues of the ICP for spectrochemical analysis are briefly discussed.

Power scaling of an extreme ultraviolet light source for future lithography

For future lithography applications, high-power extreme ultraviolet (EUV) light sources are needed at a central wavelength of 13.5nm within 2% bandwidth. We have demonstrated that from a physics point of view the Philips alpha-prototype source concept is scalable up to the power levels required for high-volume manufacturing (HVM) purposes. Scalability is shown both in frequency, up to 100kHz, and pulse energy, up to 55mJ collectable EUV per pulse, which allows us to find an optimal working point for future HVM sources within a wide parameter space.