Guixin Zhang

High rep rate high performance plasma focus as a powerful radiation source

Basic operational characteristics of the plasma focus are considered from design perspectives to develop powerful radiation sources. Using these ideas we have developed two compact plasma focus (CPF) devices operating in neon with high performance and high repetition rate capacity for use as an intense soft X-ray (SXR) source for microelectronics lithography. The NX1 is a four-module system with a peak current of 320 kA when the capacitor bank (7.8 /spl mu/F/spl times/4) is charged to 14 kV. It produces 100 J of SXR per shot (4% wall plug efficiency) giving at 3 Hz, 300 W of average SXR power into 4/spl pi/. The NX2 is also a four-module system. Each module uses a rail gap switching 12 capacitors each with a capacity of 0.6 /spl mu/F. The NX2 operates with peak currents of 400 kA at 11.5 kV into water-cooled electrodes at repetition rates up to 16 Hz to produce 300 W SXR in burst durations of several minutes. SXR lithographs are taken from both machines to demonstrate that sufficient SXR flux is generated for an exposure with only 300 shots. In addition, flash electron lithographs are also obtained requiring only ten shots per exposure. Such high performance compact machines may be improved to yield over 1 kW of SXR, enabling sufficient exposure throughput to be of interest to the wafer industry. In deuterium the neutron yield could be over 10/sup 10/ neutrons per second over prolonged bursts of minutes.

Characteristics and mechanisms of surface charge accumulation on a cone-type insulator under dc voltage

In order to study the phenomenon of surface charge accumulation on cone-type insulators, a surface charge measuring system is established, based on the electrostatic probe method. The surface potential distributions on a cone-type insulator are measured and the charge distributions are calculated based on the 3D field calculation by the surface charge method. The characteristics of charge distributions are compared under different voltage durations and voltage amplitudes. The results show that the charge accumulation comes to a steady state after 120 min. A threshold voltage effect is observed that charges seldom accumulate unless the applied voltage reaches a certain magnitude. The mechanisms of charge accumulation are discussed. The surface conduction and volume conduction do not seem to dominate the charge accumulation on the insulator. Partial discharges in gas may be the main sources of surface charges.

Suppression of surface charge accumulation on Al2O3-filled epoxy resin insulator under dc voltage by direct fluorination

Surface charge accumulation on insulators under high dc voltage is a major factor that may lead to the reduction of insulation levels in gas insulated devices. In this paper, disc insulators made of Al2O3-filled epoxy resin were surface fluorinated using a F2/N2 mixture (12.5% F2) at 50 °C and 0.1 MPa for different durations of 15 min, 30 min and 60 min. A dc voltage was applied to the insulator for 30 min and the charge density on its surface was measured by an electrostatic probe. The results revealed significant lower surface charge densities on the fluorinated insulators in comparison with the original one. Surface conductivity measurements indicated a higher surface conductivity by over three orders of magnitude after fluorination, which would allow the charges to transfer along the surface and thus may suppress their accumulation. Further, attenuated total reflection infrared analysis and surface morphology observations of the samples revealed that the introduction of fluoride groups altered the sur...

The Measurement Method for Corona Discharge Current Under High-Voltage Environment

Measuring corona discharge current directly on the high-voltage side is essential for the discharge mechanism research of the test object. The amplitude of the corona discharge current is in microamperes, and its frequency ranges from DC to megahertz. An optical microcurrent transducer for measurement of the current is described in this paper based on an amplitude modulation principle. A low-pass filter is used to extend the analog fiber link to recover low-frequency signals. The uncertainty of the transducer is estimated to be less than 1.3% in ratio, and its response frequency range is from DC to several megahertz.

Characteristics of Microwave Plasma Torch at Atmospheric Pressure

We studied the characteristics of a microwave argon plasma torch at atmospheric pressure. The electron temperature of the plasma was measured by optical-emission spectroscopy and increases nonlinearly from 3000 to 3800 K with the increase of the microwave power from 1.0 to 4.0 kW. The spatial distribution of the electron density was measured with a Mach-Zehnder interferometer to be on the order of 1017/cm3 and characterized by fluctuating with the time under the same experimental conditions. Based on the plasma parameters measured, it can be concluded that the plasma is in the state of local thermodynamic equilibrium.

Measurement of the electron density in a microwave plasma torch at atmospheric pressure

The electron density in a microwave plasma torch at atmospheric pressure was measured with a Mach–Zehnder interferometer. The electron density is on the order of 1017/cm3, one order higher than that deduced from the Stark broadening of spectral lines, and increases with the increase in the microwave power. The spatial distribution of the electron density was obtained. The highest electron density locates at the symmetrical axis of the plasma torch and decreases radially. It was found that the electron density fluctuates within a range of 0.3 with the time under the same experimental conditions.

A Large-Volume Open-Air Microwave Plasma Based on Parallel Multislot Rectangular Waveguides

An open-air microwave plasma is generated in the resonant cavity based on parallel multislot rectangular waveguides by using an argon pre-ionization plasma jet device. The side photos show that the plasma separates from the argon jet and gradually shifts to the locations with high electric-field strength when the microwave power increases. In the absence of the plasma jet, the early plasma structure is relatively similar to the calculated electric field distribution. As the time goes on, the plasma connects the two waveguides. Small portions of plasma always move up and down between the waveguides. At the microwave power of 5.6 kW, the plasma size is evaluated to be (110-130) mm × (407-50) mm × 87 mm, which is significantly large. As the microwave power increases from 5.6 kW to 8.0 kW, the plasma electron temperature increases from 4400 K to 7600 K. The average electron density along its length is measured by using the Mach-Zehnder interferometer. The electron density is relatively high in the center and two ends near the slots of the plasma. The electron density is as high as 1017 cm-3, and it gradually decreases from 3.03 ×1017 cm-3 in its center to zero at its edge across the width of the plasma. The open-air plasma excited at 6.5 kW is close to local thermodynamic equilibrium.

Fluorine gas treatment improves surface degradation inhibiting property of alumina-filled epoxy composite

Epoxy resins blended with micro-sized alumina show more compact surface condition and exhibit lower light emission after modified in fluorinated atmosphere. Surface morphology reflected by atomic force microscope shows that the fluorinated surface layer can overlap alumina particles inlayed in the original surface and a smoother and more compact surface condition is generated. Thermally stimulated current test exhibits that surface fluorination is able to bring more shallow traps to surface states, and the trap amount increases with the extension of fluorinating time. The photon counting technique illustrates that the fluorinated surface has lower light emission which indicates better aging inhibition properties. Therefore, we believe that the surface fluorination technique may have potential significance in modifying epoxy based insulators used in high voltage applications.

Experimental study on the emission spectra of microwave plasma at atmospheric pressure

An experimental study on microwave plasma at atmospheric pressure was conducted by employing optical emission spectroscopy. Based on a microwave plasma generation device developed for nanoparticle synthesis, we studied the influence of input microwave power and gas flow rate on the optical emission behaviors and electron temperature of plasma using Ar, He, and N2 as working gas, respectively. The physics behind these behaviors was discussed. The results are useful in characterizing microwave plasma at atmospheric pressure and can be used for improving nanoparticle synthesis system for commercial use in the future.

Visual features of microwave ignition of methane-air mixture in a constant volume cylinder

In this paper, the visual features of microwave ignition process were investigated. To realize microwave ignition under high pressure, a 2.45 GHz cylinder microwave resonator was designed. The electric field in the resonator and the quality factor were theoretically calculated. A needle-like coupling antenna was introduced to further enhance the maximum electric field to ensure the reliability of discharge. We ignited stoichiometric methane-air mixture at 10 bars by a 2 ms, 1 kW, 2.45 GHz microwave pulse. The photography images and pressure history of the ignition were obtained and analyzed. These results were compared with spark plug ignition under identical conditions.