A. Patran

Soft X-ray optimization studies on a dense plasma focus device operated in neon and argon in repetitive mode

This paper investigates the emission characteristics of a high-performance low-energy (3-kJ) repetitive dense plasma focus device, NX2, operated at up to 1-Hz repetition rate to develop it as an intense source of soft X-rays (SXR) for microlithography and micromachining. Various SXR yield optimization studies with argon and neon as filling gases were performed under different operating conditions (charging voltage, filling pressure, anode length, and insulator sleeve length). The SXR yield was computed using signals obtained from a PIN diode SXR spectrometer with appropriate filters. When operated in neon, the average optimum SXR (/spl lambda//spl sim/1 nm) yield in 4/spl pi/ steradians was found to be up to 140 J/shot, which corresponded to a wall plug efficiency of 5.6%. Operation in argon showed that optimized SXR (/spl lambda//spl sim/0.4 nm) yield was up to 1.3 J/shot. While operating with neon under optimized conditions with a water-cooled anode in repetitive mode, the NX2 device was used as a SXR source to imprint a test lithograph on a highly sensitive chemically-amplified resist SU-8. Test structures showing the effect of a stepper with aspect ratio 3:1 on 10-/spl mu/m-thick SU-8 resist film were obtained.

Optimization of the high pressure operation regime for enhanced neutron yield in a plasma focus device

The average total neutron yield is measured, using an indium foil activation detector, at various combinations of filling gas pressures (including the higher pressure operation regime) of deuterium, capacitor bank charging voltages, anode lengths and insulator sleeve lengths to optimize the neutron yield from the NX2 Plasma Focus device. A remarkable six-fold increase in the average maximum total neutron yield, to a record value of (7 ± 1) × 108 neutrons per shot, compared to the similar energy UNU-ICTP Plasma Focus device is achieved for deuterium at a relatively much higher filling gas pressure of 20 mbar. The average peak neutron energy for the axial direction (0°), radial direction (90°) and backward direction (180°) is estimated to be 2.89 ± 0.25 MeV, 2.49 ± 0.20 MeV and 2.11 ± 0.12 MeV, respectively. The average forward to radial neutron yield anisotropy is found to be 1.46 ± 0.28. The neutron energy and anisotropy measurements suggest that the neutron production mechanism may be predominantly beam target.

Effect of insulator sleeve length on soft x-ray emission from a neon-filled plasma focus device

Insulator sleeves of different lengths were used at the closed end of the coaxial electrode assembly of the 3.3 kJ United Nation University-International Centre for Theoretical Physics (UNU-ICTP) plasma focus device to investigate soft x-ray (SXR) (900–1550 eV) yield for different filling gas pressures of neon. The time and space resolved SXR emission characteristics were investigated using a multi-channel diode x-ray spectrometer and a CCD based pinhole imaging camera. At pressures below 6 mbar, the average SXR yield was also found to increase with increasing sleeve length from 19 to 22 mm. A further increase in insulator sleeve length to 25 mm, however, decreased the SXR yield. At pressures above 6 mbar, the SXR yields were almost the same for insulator sleeves of different lengths. The UNU-ICTP plasma focus device is found to be best optimized for neon SXR production with a 22 mm insulator sleeve at 4 mbar filling gas pressure, with the highest average yield of 8.2 J per shot, for which the conversion efficiency is about 0.25%. For this sleeve length, even the average yield at 2 or 6 mbar pressure was comparable with the maximum yield of a 25 mm sleeve.

An improved radiative plasma focus model calibrated for neon-filled NX2 using a tapered anode

This paper presents a 4-phase radiative plasma focus model, where the dynamics of the current sheath is represented using Lees model. The model is based on the snowplow model in the axial phase and the slug model in the radial phase, complemented with sensible estimations made for the plasma parameters. The x-ray emission characteristics are investigated using a corona plasma equilibrium model. A refinement to the code was made, firstly by taking into account the tapering of the anode in the axial phase and secondly by including the energy loss due to recombination radiation in the slow compression (radiative) phase. Our improved code was calibrated for the NX2, a 3 kJ plasma focus device, operated in neon at a pressure range of 4–7 mbar with a tapered copper anode. An additional macro was programmed to the code in order to automate the curve fitting of the simulated current traces with those obtained experimentally. The resulting theoretical x-ray yield predictions are compared against experimental data, showing good agreement in terms of pressure dependence trends. The model, however, appears to consistently underestimate the absolute x-ray yield when compared with the experimentally obtained values.

Optimization of a plasma focus device as an electron beam source for thin film deposition

Electron beam emission characteristics from neon, argon, hydrogen and helium in an NX2 dense plasma focus (DPF) device were investigated in order to optimize the plasma focus device for deposition of thin films using energetic electron beams. A Rogowski coil and CCD based magnetic spectrometer were used to obtain temporal characteristics, total electron charge and energy distributions of electron emission from the NX2 DPF device. It is found that hydrogen should be the first choice for thin film deposition as it produces the highest electron beam charge and higher energy (from 50 to 200 keV) electrons. Neon is the next best choice as it gives the next highest electron beam charge with mid-energy (from 30 to 70 keV) electrons. The operation of NX2 with helium at voltages above 12 kV produces a mid-energy (from 30 to 70 keV) electron beam with low-electron beam charge, however, argon is not a good electron beam source for our NX2 DPF device. Preliminary results of the first ever thin film deposition using plasma focus assisted pulsed electron deposition using a hydrogen operated NX2 plasma focus device are presented.

Pinching evidences in a miniature plasma focus with fast pseudospark switch

We report the observations of pinching in a miniature plasma focus (PF) (58?160?J) operated in repetitive mode using fast pseudospark switch (PSS). The size of the device, which includes the capacitor bank, PSS and the focus chamber, is of the order of 22?cm ? 22?cm ? 38?cm. Several diagnostic tools, the gated imager, streak camera, current and voltage probe, are employed simultaneously to confirm the occurrence of pinching in this fast miniature PF device. The device is optimized for operation in neon and hydrogen as the working gas. The best focus formation was obtained at pressures between 0.5 to 8.0?mbar for neon and between 7.0 to 15.0?mbar for hydrogen. When the system was operated at 100?J with hydrogen as the filling gas, the typical dip in the current derivative signal and the typical peak in the voltage signal associated with pinch compression, are observed to be most intense indicating efficient pinching in the miniature PF device.

Study of a chemically amplified resist for X-ray lithography by Fourier transform infrared spectroscopy

Future applications of microelectromechanical systems (MEMS) require lithographic performance of very high aspect ratio. Chemically amplified resists (CARs) such as the negative tone commercial SU-8 provide critical advantages in sensitivity, resolution, and process efficiency in deep ultraviolet, electron-beam, and X-ray lithographies (XRLs), which result in a very high aspect ratio. In this investigation, an SU-8 resist was characterized and optimized for X-ray lithographic applications by studying the cross-linking process of the resist under different conditions of resist thickness and X-ray exposure dose. The exposure dose of soft X-ray (SXR) irradiation at the average weighted wavelength of 1.20 nm from a plasma focus device ranges from 100 to 1600 mJ/cm2 on the resist surface. Resist thickness varies from 3.5 to 15 μm. The cross-linking process of the resist during post-exposure bake (PEB) was accurately monitored using Fourier transform infrared (FT-IR) spectroscopy. The infrared absorption peaks at 862, 914, 972, and 1128 cm−1 in the spectrum of the SU-8 resist were found to be useful indicators for the completion of cross-linking in the resist. Results of the experiments showed that the cross-linking of SU-8 was optimized at the exposure dose of 800 mJ/cm2 for resist thicknesses of 3.5, 9.5, and 15 μm. PEB temperature was set at 95 °C and time at 3 min. The resist thickness was measured using interference patterns in the FT-IR spectra of the resist. Test structures with an aspect ratio 3:1 on 10 μm thick SU-8 resist film were obtained using scanning electron microscopy (SEM).

Imaging of Fusion Protons from a 3 kJ Deuterium Plasma Focus

This paper reports a study of the proton emission from a 3 kJ, 14 kV plasma focus device operated with deuterium gas at 400 Pa. A filtered pinhole camera with a 1.8 mm diameter hole is placed axially downstream of the plasma focus, and images of the proton-emitting region are recorded using CR-39/PM-355 nuclear track detectors. The detector plates are scanned using an automated track measurement system and the spatial track density profile is acquired. The resulting density distribution is interpreted with the help of a simple pinhole imaging model that assumes the 2H(d, p)3H reaction protons are emitted from a conical region extending from the tip of the anode to a fixed distance downstream. Comparison of the experimental track density profile with the model calculations supports the view that the beam-target mechanism is the dominant fusion production mechanism in this small plasma focus device.

Fusion reactions in a plasma focus operated with 3He-D2 and 4He-D2 gas mixtures

A 3 kJ plasma focus (PF) device was operated with two different gas mixtures: 3He-D2 and 4He-D2, both having He/D atomic ratios of 1 : 1. For the 3He-D2 mixture, the fusion reactions D(3He,p)4He and D(d,p)3H were measured simultaneously using CR-39 nuclear track detectors located inside a pinhole camera positioned on the forward PF axis. A double-layer arrangement of two 1000 μm thick CR-39 detectors permitted the separate registration of protons from the D(3He,p)4He and D(d,p)3H reactions. For the 4He-D2 mixture, the D(d,p)3H protons were registered by a single CR-39 layer. Radial track density distributions were obtained for each series of experiments. For the 3He-D2 mixture, it was found that D(3He,p)4He and D(d,p)3H fusion yields were of similar magnitude, but the D(3He,p)4He fusion is concentrated close to the pinch column, whereas the D(d,p)3H fusion occurred relatively far from the pinch. The results for D(d,p)3H fusion in the 4He-D2 mixture enabled an informative comparison to bemade with the corresponding 3He-D2 data.

Studies of Fusion Protons from a 3He-D2 Plasma Focus using Nuclear Track Detectors

Protons from the fusion reactions D(3He,p)4He and D(d,p)3H have been observed in a small plasma focus device operated with a 3He‐D2 gas mixture. The partial pressures of the 3He and D2 gasses were in the ratio of 2:1, corresponding to an atomic number ratio of 1:1. Two groups of protons with energies of approximately 16MeV and 3MeV arising from the D(3He,p)4He and D(d,p)3H reactions, were recorded simultaneously using a double‐layer arrangement of CR‐39 polymer nuclear track detectors (each of thickness 1000μm). As a result of the very different ranges of 16MeV and 3MeV protons, and the particle registration properties of CR‐39, the D(d,p)3H protons were registered on the front‐most CR‐39 surface and the D(3He,p)4He protons were registered on the back‐most surface of this double‐layer configuration. A pinhole camera, containing the CR‐39 detectors, was situated on the forward plasma focus axis in order to image the emission zones of protons for both fusion reactions. It was found that the D(3He,p)4He and ...