Vacuum-UV emitter using low-pressure discharge in helium-water vapor mixture

The spectral characteristics of emission from plasma of periodic-pulsed capacitive discharge in a mixture of water vapor with helium have been studied in a spectral range of 140–315 nm. Dependences of the intensity of the characteristic emission lines of hydroxy groups in He-H₂O plasma on the partial pressure of water vapor at a helium pressure of p(He) = 2.6 kPa are presented. The results provide a basis for the creation of simple sources of vacuum-UV radiation with a cheap working medium based on water vapor.     

Radial structure of low pressure rf capacitive discharges

This paper studies the glow intensity distribution of the discharge plasma against the tube radius and reports the radial profiles of electron temperature and plasma concentration in the rf capacitive discharge registered with a Langmuir probe. An abrupt increase of electron temperature and glow intensity near the tube wall in the weak-current α-mode of the rf capacitive discharge is revealed, the radial distribution of plasma concentration and ion flow to the electrodes possessing a maximum near the radial sheath boundary. In the γ-mode of the rf capacitive discharge the electron temperature decrease in the total plasma volume leads to an electric field weakening and the peak of the glow intensity near the tube wall vanishes. The radial sheath thickness in the α-mode of the rf capacitive discharge obtained with 2D simulation experiences pulsations during the rf field period, the changing radial electric field heating electrons and increasing the plasma concentration near the boundary of the radial sheath.     

Role of transverse magnetic field in the capacitive discharge

The influence of magnetic field on the plasma which is one of the oldest problems in plasma physics and remains of great interest in plasma fusion studies, recently has been an important problem in many plasma discharge used in processing semiconductor materials, because the application of a magnetic field results in enhancement of some desirable features of specific plasma sources. In this paper, the transverse magnetic field effects on the radio frequency capacitive discharge of low and intermediate gas pressure (1.33 Pa∼40.00 Pa) are reviewed to clarify the role of the magnetic field in the capacitive discharge. Lots of physical phenomena induced by transverse magnetic field, such as power dissipation mode transition, low energy electron heating/cooling, axial variation of electron density and temperature and E × B drift are presented and analyzed. This article is expected to provide qualitative insight to understand the role of magnetic field in the capacitive discharges.     

Impedance transition and series resonance between bulk plasma and sheath in biased inductively coupled plasma

The impedance transition and electron series resonance at an RF bias substrate were observed in 13.56 MHz inductively coupled plasma (ICP). As ICP coil power increased, the impedance of the RF bias transitioned from a capacitive to an inductive load. When bias voltages and discharge impedances reached minimums, bias voltages and currents were in-phase during the transition. The transition can be understood as a series LC resonance between the sheaths (capacitor) and plasma bulks (inductance due to electron inertia). This corresponds to the electron series resonance (ESR) observed in very high-frequency capacitive discharges, and a new ESR frequency which considers sheath resistances is presented.     

脉冲调制磁化容性耦合放电中Ar+光谱特性研究

本文在平行平板脉冲调制容性耦合射频放电装置中,采用光学发射谱线诊断的方法,研究了低气压(30 Pa～65 Pa)不同磁场强度条件下氩气(Ar)放电时产生等离子体过程中电子激发温度以及Ar离子的光谱线相对强度随气压、射频功率、调制频率、占空比和磁场强度大小的变化规律.     

Stability conditions of argon and helium gas mixtures in an atmospheric pressure plasma jet

Non-equilibrium plasmas can be generated by atmospheric pressure glow discharges, amongst others by atmospheric pressure plasma jets (APPJ), which feature a capacitive radio-frequency discharge between bare metallic electrodes.We investigated the stability conditions for discharges in an APPJ operated with helium-argon mixtures. Uniform α-discharges can be sustained in mixtures ranging from pure helium to pure argon. The ignition voltage increases drastically with argon content. There is also an upper limit for the existence of the α-mode, where α-sheath breakdown occurs. Critical plasma parameters for the α-mode were determined by equivalent circuit models and discussed in respect to dependences on the different models. A critical electron density of 2.4×10¹¹ cm⁻³ was obtained for pure helium. It increases steadily with argon content and reaches a value of 1.2×10¹² cm⁻³ for pure argon. Sheath thicknesses for α-sheath breakdown were calculated in the range of 0.17-0.29 mm for helium-argon mixtures.     

Optical constants of silicone-like (Si:Ox:Cy:Hz) thin films deposited on quartz using hexamethyldisiloxane in a remote RF hollow cathode discharge plasma

Deposition of amorphous silicone-like (Si:O_x:C_y:H_z) thin films in a remote RF hollow cathode discharge plasma using hexamethyldisoloxane as monomer and Ar as feed gas has been investigated for films optical constants and plasma diagnostic as a function of RF power (100-300 W) and precursor flow rate (1-10 sccm). Plasma diagnostic has been performed using Optical Emission Spectroscopy (OES). The optical constants (refractive index, extinction coefficient and dielectric constant) have been obtained by reflection/transmission measurements in the range 300-700 nm. It is found that the refractive index increases from 1.92 to 1.97 with increasing power from 100 to 300 W, and from 1.70 to 1.92 with increasing precursor flow rate from 1 to 10 sccm. The optical energy band gap E_g and the optical-absorption tail ΔE have been estimated from optical absorption spectra, it is found that E_g decreases from 3.28 to 3.14 eV with power increase from 100 to 300 W, and from 3.54 to 3.28 eV with precursor flow rate increase from 1 to 10 sccm. ΔE is found to increase with applied RF power and precursor flow rate increase. The dependence of optical constants on deposition parameters has been correlated to plasma OES.     

容性耦合射频(CCRF)放电等离子体特性实验研究

利用自行研制的传感器和测量装置 ,通过对射频放电电压电流以及其相位角的测定 ,算出放电管的总阻抗 ,结合放电管的等效电路 ,对容性耦合射频 (CCRF)激励激光器放电特性进行研究 ,得出容性耦合射频激励激光器等离子体的伏安特性的曲线 ,以及等离子体电阻、容抗与气体压强、放电电流之间的实验曲线 ,在Godyak射频放电模型的基础上得出等离子体的电子密度 ,并同内置铜电极射频激励铜离子激光器阻抗特性进行了比较。     

Applying RF current harmonics for end-point detection during etching multi-layered substrates and cleaning discharge chambers with NF3 discharge

The present paper reports the results of studying the characteristics of the etching process of multi-layered materials (Si₃N₄/SiO₂/Si and SiO₂/Si) and of cleaning technological chambers covered with silicon nitride films (Si₃N₄) in a NF₃ RF capacitive discharge. The process of chamber cleaning was monitored with a mass spectrometer. The gas pressure, RF voltage amplitude, current-voltage phase shift, ohmic current as well as the second harmonic of the RF current were also recorded. The opportunity of using these parameters for end-point detection of etching and plasma cleaning is discussed. It is found that the second harmonic of the RF current may be successfully used for end-point detection of multi-layered materials etching and to monitor the cleaning process of technological chambers. The cleaning of chambers of complicated design may possess a double-stage pattern.     

Studies of radiofrequency plasma deposition of hexamethyldisiloxane films and their thermal stability and corrosion resistance behavior

Hexamethyldisiloxane (HMDSO) films (thickness: 282-929 nm) are prepared by the radiofrequency plasma assisted chemical vapour deposition (RF-PACVD) method using an Ar/HMDSO/O₂ gas mixture. The deposition process is carried out in an RF reactor at a working pressure of 1.2 × 10⁻¹ mbar and an RF power range of 20-100 W. From the studies on Ar/O₂ and Ar/HMDSO/O₂ discharge characteristics using a self-compensated emissive probe, it is revealed that electrons play an important role in the plasma polymerization of HMDSO monomers. Optical emission spectroscopy (OES) and Fourier transform infrared (FT-IR) spectroscopy show that the plasma deposited HMDSO films tend to be more inorganic in nature at higher RF powers. A film prepared at an RF power of 100 W exhibits more thermal stability and corrosion resistance behavior in comparison to films deposited at lower powers (20-80 W). A correlation of the results obtained from OES and FT-IR analyses with the thermal stability and corrosion resistance behavior of the films has been attempted.     

Effects of deposition parameters on SiCln (n=0-2) densities in SiCl4 glow discharge plasma

The relative densities of SiCl_n (n=0-2) in SiCl₄ radio frequency (rf) glow discharge plasma are measured by mass spectrometry. The effects of discharge parameters, including rf power, discharge pressure, substrate temperature and SiCl₄ flow rate on the relative densities of SiCl_n (n=0-2) are investigated in detail. The experimental results demonstrate that the relative densities of SiCl_n (n=0-2) in SiCl₄ plasma are dependent strongly on these discharge parameters. An optimum configuration of discharge parameters (low rf power, high discharge pressure, low substrate temperature and low flow rate), which enhanced the formation of SiCl_n (n=0-2) radicals, was searched. Further, researching of SiCl_n (n=0-2) spatial distribution for seeking a suitable deposition condition is beneficial for understanding the deposition mechanism of thin films.     

Estimation of electron parameters in the dielectric barrier discharge with a liquid electrode at atmospheric pressure

In the oxygen dielectric barrier discharge (DBD) at atmospheric pressure, the current and voltage waveforms within the range of the mean-square voltages, 3.6–10.3 kV, and currents, 0.14–0.57 mA, were measured. The discharge burns in the glow regime. From the analysis of the equivalent discharge circuit, the voltage applied to the plasma was found. On the basis of these data, the reduced strength of the electric fields, E/N, was determined. From solution of the Botzmann equation for the electrons in the O₂-H₂O mixture, the electron distribution functions over the energies (EDFE) and certain electron parameters were found; the influence of presence of the H₂O molecules on those parameters was analyzed.     

Double layer onset inside the near-electrode sheath of a RF capacitive discharge in oxygen

This paper reports the axial profiles of the electron temperature T_e in the RF capacitive discharge in oxygen recorded with a probe technique. We observed the T_e peaks near the boundaries of the sheaths as well as inside the near-electrode sheath. The T_e peak inside the sheath is, probably, due to the formation of the double layer at the anode phase of this near-electrode sheath. The assumption of a double layer formation is also supported by the photos of the sheath glow making evident the bright region inside the sheath. The results of our measurements agree with our fluid simulation satisfactorily.     

Stable pinch in the SPEED 2 plasma focus

Conditions of discharge generation in deuterium doped with heavy argon and xenon gases were investigated in experiments in the SPEED 2 plasma focus in the micropinch plasma compression mode and in the stable plasma formation regime. An extensive arsenal of diagnostic techniques, including spectral techniques in the soft-x-ray range with temporal, spatial, and energy resolution was used to achieve a controlled transition from one regime to another. The experimental data are consistent with the assumption that the discharge is stabilized by a gyromagnetic deuteron acceleration mechanism. Pis’ma Zh. Tekh. Fiz. 25, 5–12 (October 26, 1999)     

Use of plasma impedance monitoring for the determination of SF6 reactive ion etch process end points in a SiO2/Si system

It is shown here that plasma impedance monitoring can be used successfully to determine the end point of reactive ion etching of a SiO₂ layer lying on a Si substrate in SF₆ plasma. The usefulness of this technique is demonstrated using a commercial Plasma Impedance Monitoring (PIM) system. The end point conditions are tested by monitoring changes in the fundamental and the first four harmonic components of the RF current, RF voltage, phase between RF voltage and current, RF discharge power and RF impedance. The best process monitoring parameter found in this work is modeled as a polynomial equation of RF input power, chamber pressure and gas flow rate, from which the end point can be predicted with good precision and easily detected by the PIM. The end point conditions are confirmed by both Fourier Transform Infrared Spectroscopy (FTIR) measurements and via observation of plasma color changes. Received:15 June 2001 / Accepted: 18 June 2001     

The effect of ion energy on the surface morphology of platinum film under high-frequency ion plasma sputtering

The effect of ion energy (E _i = 45–220 eV) on the sputter deposition rate and surface morphology of polycrystalline platinum films processed in high-density argon plasma of low-pressure (P = 0.08 Pa) RF induction discharge has been studied. The sputtering yield of Pt has been determined as a function of the ion energy. Analysis of the data of scanning tunneling microscopy showed a large difference between the surface profiles of samples treated at minimum and maximum ion energies in the range studied. The mechanism of Pt surface morphology modification by ion plasma sputtering is discussed.     

A Vapor-Air Discharge between Electrolytic Anode and Metal Cathode at Atmospheric Pressure

An experimental investigation is performed of the structure, mechanism, and electrical and thermal characteristics of a vapor-air discharge between an electrolytic anode (EA) and a metal cathode (MC) in a wide range of parameters at pressure P = 8×10⁴ to 10⁵ Pa, current I = 0.02 to 60 A, interelectrode spacing l = 0.1 to 40 mm, and metal cathode diameter d _c = 1 to 40 mm. The main types of vapor-air discharge with EA are identified. The possibility of burning of a multichannel discharge between a metal cathode and an electrolytic anode at atmospheric pressure is demonstrated for the first time, and a vapor-air discharge with a diffuse plasma column is investigated at high currents and large interelectrode spacings. It is determined that the electrical and thermal characteristics depend significantly on current, interelectrode spacing, electrolyte composition and concentration, geometric shape, diameter, and cooling of the MC. The significant effect of the vapor-air discharge on the electrolytic anode surface is revealed. Transverse waves are observed on the electrolyte surface. Significant turbulent mixing is observed for the first time on the electrolyte-plasma interface in the case of a vapor-air discharge with electrolytic anode at atmospheric pressure and high currents.     

UV emission from capacitive discharge in inert gas-iodine vapor mixture

We have studied the optical characteristics of capacitive discharge in binary mixtures of helium, neon, argon, and krypton with iodine vapor in a spectral range of 180–300 nm. It is established that the main power of UV radiation from the discharge plasma is concentrated in the emission lines at 183.0 and 206.2 nm. The intensity of emission due the spectral lines of iodine atom was optimized with respect to the inert gas type and partial pressure. The optimum results were obtained using He-I₂ mixture with partial pressures of helium within 0.8–2.0 kPa and iodine vapor below 50–60 Pa. Being excited with a trains of nanosecond current pulses at a repetition rate of 10–100 Hz, the capacitive discharge emitted pulses with duration not exceeding 400–500 ns.     

Characteristics of capacitively coupled helium plasma driven by various frequencies under constant power conditions

The influence of excitation frequency (13.56–96 MHz) on the characteristics of capacitively coupled helium plasma is investigated by means of Langumir probe and CCD camera. Measurements are performed in helium pressure of 10.66 and 33.3 Pascal (Pa) under fixed dissipated power of 10 W. With increasing the driving frequency, the RF/HF voltage and dc-self bias markedly decrease. Meanwhile, the plasma density and electron temperature peak in the frequency range 27–56 MHz, beyond which they decrease as exciting frequency increase. A different feature of the electron energy probability function EEPF is observed with exciting frequency; Maxwellian type EEPF at low frequency of 13.56 MHz evolves into a bi-Maxwellian type with a hump/beamlike in the frequency range 27–56 and eventually comes back to Maxwellian distribution at frequency ≥76 MHz. The observed results are explained in terms of electromagnetic wave effect and capacitive to inductive heating transition induced by exciting frequency.     

Synthesis and characterization of plasma-polymerized tert-butylacrylate films

Plasma polymerized tert-butylacrylate (pp-t-BA) film was prepared using tert-butylacrylate monomer under 100 Pa of vapor pressure with varying RF power of 10-250 W and continuous wave RF power of 13.56 MHz. The deposition rates of pp-t-BA films were determined using quartz crystal microbalance (QCM) method. The chemical structure of pp-t-BA films was characterized using FT-IR, contact angle and XPS techniques. The gas sorption properties of pp-t-BA were measured using a QCM sensor array. Results showed that deposition rates of pp-t-BA film were proportional to the polymerization time at 100 Pa of monomer pressure under the same RF power. The deposition amount of pp-t-BA films increased gradually with increasing RF power of 30-150 W. Increasing the RF power on plasma polymerization decreased the amount of ester group in pp-t-BA films. Sensitivity of gas sorption on pp-t-BA films is related to the RF power of polymerization.