Exploring the temporally resolved electron density evolution in EUV induced plasmas

We measured for the first time the electron density in an Extreme Ultra-Violet induced plasma. This is achieved in a low-pressure argon plasma by using a method called microwave cavity resonance spectroscopy. The measured electron density just after the EUV pulse is $2.6\cdot10^{16}$ m$^{-3}$. This is in good agreement with a theoretical prediction from photo ionization, which yields a density of $4.5\cdot10^{16}$ m$^{-3}$. After the EUV pulse the density slightly increase due to electron impact ionization. The plasma (i.e. electron density) decays in tens of microseconds.Comment: 3 pages, 4 figure

Measuring the electron density in an Extreme Ultra-Violet generated plasma

In order to meet the demand of increasing computer speed and memory capacity, industries are striving to reduce the size of computer chips. This miniaturization of computer chips can be achieved by reducing the wavelength in lithography machines to Extreme Ultra-Violet (EUV, 92 eV). The low-pressure (around 1 Pa) transparent background gas (e.g. H¬2 and He) in the lithography machine is partially ionized by the absorption of EUV photons. The study of these low-density (1015 m-3) pulsed plasmas is interesting and experimentally challenging. Two different diagnostics are investigated to determine the electron density in these EUV-generated plasmas: coherent microwave scattering (CMS) and microwave cavity resonance spectroscopy (MCRS). CMS is based on the scattering of microwaves off the plasma, the scattered power has a resonance at the plasma frequency. In MCRS measurements the resonance frequency in a cavity is determined, this frequency depends on the electron density in the cavity. These two diagnostics are tested on a simulation plasma with similar dimensions and density as the EUV plasma. The results of MCRS on the simulation plasma show a detection limit of 1014 m-3 and a time-resolution of 16 ns. Currently a new setup is built to measure the electron density in the EUV plasma

Dust particle formation in argon-acetylene plasmas and interaction with (extreme) ultraviolet radiation

In extreme ultraviolet (EUV) lithography, ionic and particulate debris coming from the plasma source plays an important role. We started up a project looking more fundamentally at particulate formation in plasmas and the interaction with EUV radiation. To this end, we study a capacitively-coupled radio-frequency (13.56 MHz) argon-acetylene plasma. In low-pressure hydrocarbon plasmas dust particles spontaneously form under certain conditions. The whole process occurs in a matter of seconds to minutes after igniting the plasma and results in a cloud of particulates up to micrometer sizes levitating in the plasma. Our aluminum cylindrical discharge chamber also serves as a resonant cavity for low-power microwave (2 – 8 GHz) signals. The frequency at which resonance occurs is a measure for the free-electron density of the plasma. We present preliminary results on the temporal evolution of the electron density during dust particle formation up to several minutes after plasma ignition. Furthermore, we present an overview of approaches for future research predominantly aimed at the interactions in a more EUV-like environment

Serious bacterial infections in patients with rheumatoid arthritis under anti‐TNF‐α therapy

Objective. With rising numbers of anti‐tumour necrosis factor α (TNF‐α) treatments for rheumatoid arthritis (RA), Crohn's disease and other conditions, physicians unaware of potential pitfalls are increasingly likely to encounter associated severe infections. Our purpose was to assess the incidence and nature of severe infections in our RA patients under anti‐TNF‐α therapy. Methods. We reviewed patient charts and records of the Infectious Disease Unit for serious infections in patients with RA in the 2 yr preceding anti‐TNF‐α therapy and during therapy. Results. Serious infections affected 18.3% of patients treated with infliximab or etanercept. The incidence was 0.181 per anti‐TNF‐α treatment year vs 0.008 in the 2 yr preceding anti‐TNF‐α therapy. In several cases, only a few signs or symptoms indicated the severity of developing infections, including sepsis. Conclusions. A high level of suspicion of infection is necessary in patients under anti‐TNF‐α therapy. We suggest additional strategies for the prevention, rapid identification and pre‐emptive therapy of such infection

Conical Diffraction and Composite Lieb Bosons in Photonic Lattices

Pseudospin describes how waves are distributed between different “internal” degrees of freedom or microscopic states, such as polarizations, sublattices, or layers. Here, we experimentally demonstrate and explain wave dynamics in a photonic Lieb lattice, which hosts an integer pseudospin s=1 conical intersection. We study the most striking differences displayed by integer pseudospin states: pseudospin-dependent conical diffraction and the generation of higher charged optical vortices

Plasma accumulation effects in Extreme Ultra-Violet generated plasmas

In order to meet the demand of increasing computer speed and memory capacity, industries are striving to reduce the size of computer chips. This miniaturization can be achieved by reducing the wavelength in lithography machines to Extreme Ultra-Violet (EUV, 92 eV). The low-pressure (around 1 Pa) transparent background gas (e.g. H2 and He) in the lithography machine is partially ionized by the absorption of EUV photons. The study of these low-density 1E15 m^-3 pulsed plasmas is interesting and experimentally challenging. The electron density is measured with microwave cavity resonance spectroscopy (MCRS). In MCRS measurements the resonance frequency in a cavity is determined, this frequency depends on the electron density in the cavity. In this research the plasma accumulation is studied in an EUV-generated plasma in argon. The EUV source generates EUV pulses with a repetition frequency between 500 Hz and 10 kHz. The accumulation of plasma is clearly observed at frequencies above 1 kHz