Fast Miniature Plasma Focus Device Research Articles

X-ray lithography of SU8 photoresist using fast miniature plasma focus device and its characterization using FTIR spectroscopy

Abstract X-ray lithography (XRL) can be a potential candidate for next generation lithography. The main objective of this study is to demonstrate XRL using fast miniature plasma focus (FMPF) device as the X-ray source. The advantage of using FMPF as X-ray source is the smaller X-ray spot size due to smaller electrode dimensions leading to higher resolution micro-components. Some of the major hurdles in the realization of XRL using FMPF device have been addressed and FMPF based XRL is demonstrated for the first time. The dosage required for sufficient crosslinking in SU8 photoresist is determined using Fourier transform infrared spectroscopy analysis.

Influence of Kr doping on neon soft X-rays emission in fast miniature plasma focus device

Abstract An investigation on the possibility of enhancement of soft X-ray (SXR) (900–1600 eV) emission from a fast miniature plasma focus (FMPF) device of 235 J (at 14 kV) storage energy through doping of operating gas was performed. Neon (Ne), the operating gaseous medium, was doped with krypton (Kr) in different volumetric ratios at various operating pressures ranging from 2 to 14 mbar. The 1% Kr doping increased the average optimum SXR emission efficiency from 0.47% to 0.6% without enhancing the hard X-ray (HXR) (>1600 eV) emission. The Kr doping influenced the major pinching characteristics such as focusing efficiency and time to pinch with consequential effect on X-ray emissions. Synchronous operation of the 4 pseudo-spark gap (PSG) switches was mandatory for efficient discharge current delivery to the electrodes. A drastic improvement in the pinching efficiency was obtained with replacement of old and worn out PSG switches with the new ones. Optical imaging of current sheath dynamics was performed using gated ICCD camera to verify the normal operation of the device after the PSGs replacement. A numerical simulation analysis on the 2 cm long stainless steel tapered anode, used in this study, was done to predict the maximum SXR emission efficiency and the peak operating gas pressure. An analysis on the amount of SXR fluence generated at the source position and the proportion of it reaching the target position is also reported.

Optimization of neon soft X-ray emission from 200 J plasma focus device for application in soft X-ray lithography

The Fast Miniature Plasma Focus (FMPF) device is basically made up of coaxial electrodes with centrally placed anode and six cathode rods surrounding them concentrically. They are enclosed in a vacuum chamber, filled with low pressure operating gas. However, in our experiments, these cathode rods were removed to investigate the influence of them on neon soft X-ray (SXR) and hard X-ray (HXR) emission from the device. On removal of cathode rods, the cathode base plate serves as cathode and the plasma sheath is formed between the anode and the base plate of cathode. Neon was used as the operating gas for our experiments and the FMPF device used is of 235 J energy capacities. The experimental results showed that the FMPF device was able to focus better and the SXR emission efficiency was five times higher without cathode rods than with cathode rods. On the contrary, HXR emission did not vary with and without cathode rods. This observed phenomenon was further cross-checked through imaging of plasma dynamics, with and without cathode rods. FMPF device consists of 4 Pseudo Spark Gap (PSG) switches, which need to operate synchronously to deliver high voltage from capacitors to the anode. It was also seen that, the presence or absence of cathode rods also influence the synchronous operation of PSG switches. It also implies that this is one definite way to optimize the SXR emission from the FMPF device. This study reveals an important finding that, cathode rods play a vital role in the formation of plasma sheath with consequential influence on the radiation emission from plasma focus devices. Enhancement of the X-ray emission from this device is definitely a stepping stone in the realization of this device for industrial applications such as X-ray lithography for semiconductor industries.

Experimental study of neutron emission characteristics in a compact sub-kilojoule range miniature plasma focus device

In order to gain insight into the possible neutron production mechanism in sub-kilojoule miniature plasma foci, the anisotropy in neutron and hard x-ray emissions from a newly developed fast miniature plasma focus device (2.4 µF, 27 nH, T/4 ∼ 400 ns, 12–15 kV, 170–270 J, total mass ∼25 kg) is investigated. The system produces an average neutron yield of (1.2±0.2) × 106 neutrons/shot into 4π sr at ∼80 kA peak discharge current and 5.5 mbar deuterium operation, as measured by a 3He proportional counter. Relative measurements of radiation yields, to gauge the emission anisotropy, have been performed using a pair of fast scintillator–photomultiplier detectors placed along the axial (0°) and radial (90°) directions. The average forward to radial neutron yield anisotropy is found to be 1.3±0.2. The average peak neutron energy for the axial and radial directions is estimated to be (2.9±0.3) MeV and (2.6±0.1) MeV, respectively. The observed higher fluence along the anode axis and the coincidence between occurrence of maximum neutron yield and anisotropy at 5.5 mbar deuterium filling gas pressure, suggest that the neutron production mechanism in the sub-kilojoule range miniature plasma focus device FMPF-1 may be predominantly beam–target in nature.

Order of magnitude enhancement in neutron emission with deuterium-krypton admixture operation in miniature plasma focus device

The effect of varied concentrations of deuterium-krypton (D2–Kr) admixture on the neutron emission of a fast miniature plasma focus device was investigated. It was found that a judicious concentration of Kr in D2 can significantly enhance the neutron yield. The maximum average neutron yield of (1±0.27)×104 n/shot for pure D2 filling at 3 mbars was enhanced to (3.14±0.4)×105 n/shot with D2+2% Kr admixture operation, which represents a >30-fold increase. More than an order of magnitude enhancement in the average neutron yield was observed over the broader operating range of 1–4 mbars for D2+2% Kr and D2+5% Kr admixtures.

Order of magnitude enhancement in x-ray yield at low pressure deuterium-krypton admixture operation in miniature plasma focus device

In a 200J fast miniature plasma focus device about 17- and 10-fold increase in x-ray yield in spectral ranges of 0.9–1.6keV and 3.2–7.7keV, respectively, have been obtained with deuterium-krypton (D2–Kr) admixture at operating pressures of ⩽0.4mbar. In the pressure range of >0.4–1.4mbar, about twofold magnification in average x-ray yield along with broadening of optimum pressure range in both spectral ranges were obtained for D2–Kr admixtures. An order of magnitude enhancement in x-ray yields at low pressures for admixture operation will help in achieving high performance device efficiency for lithography and micromachining applications.

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.