Electron Cyclotron Resonance Plasma Reactor Research Articles

Microstructural Analysis of Copper Foil Etched and Annealed in ECR Plasma Reactor

Microstructural analysis of commercially available cold-rolled polycrystalline copper foil, etched and annealed in an in-house developed Electron Cyclotron Resonance (ECR) Plasma Enhanced Chemical Vapour Deposition (PE-CVD) reactor, have been carried out using x-ray diffraction (XRD) studies. The annealing experiments were carried out under a vacuum environment, keeping the working pressure of the reactor at 50×10-3 mbar, for three different time spans of 30 mins, 45 mins and 1 hour at 823 K (550 °C) and 923 K (650 °C) respectively in presence of hydrogen plasma. The XRD studies reveal the significance of annealing time at two different temperatures for the determination of physical and microstructural parameters such as the average grain size and micro-strain in copper lattice by Williamson-Hall (W-H) method.

Structural and morphological tuning of iron oxide polymorphs by ECR plasma-assisted thermal oxidation.

The work presented involves the generation of oxygen plasma species at low pressure utilizing an Electron Cyclotron Resonance (ECR) plasma reactor, and their interactions with micron- and nano-sized iron films (M-Fe and N-Fe film respectively) prepared using ethyl cellulose processed at high temperature. A specially designed radiation heater (RH) was used to raise the surface temperature of the film rapidly, exactly at the film interface, where the plasma species interact with the surface. As a result of the interaction of oxygen plasma species and temperature, iron is oxidized to different polymorphs depending on the operating pressure and hence oxygen gas flow rate. The phase, as well as the morphology of the film was controlled by monitoring the oxygen flow rate using the unique Plasma-Assisted Thermal Oxidation (PATO) process. Different polymorphs, viz., Fe3O4, γ-Fe2O3, α-Fe2O3 and different morphologies, such as polygonal, compact facets, wire-like (1D) nanostructures at the surface were obtained for the films processed using PATO. The selected PATO-processed films were investigated for Field Electron Emission (FEE) properties. The 1D-grown surface of iron oxide obtained from the M-Fe film showed a turn-on field of 3 MV m−1 and emission current of 337 μA cm−2, whereas the pyramidal surface morphology obtained using N-Fe film gives a turn-on field of 3.3 MV m−1 with an emission current of 578 μA cm−2.

Designing Resonance Microwave Cavities to Optimize Plasma Generation

Methodology for designing the 2.45-GHz microwave (MW) coupling system to optimize the hydrogen plasma density in an electron cyclotron resonance (ECR) plasma reactor is presented. Two different plasma generator systems have been studied by experiments and 3-D simulations to find the criteria to reach an optimized design. The experimental work includes the detailed measurements and calculations of the electron energy distribution functions (EEDF) and ultrafast photography diagnostics to estimate the spatial distributions of plasma unbalanced charge density, potential, and electric field for both cases. It demonstrates that to simulate in 3-D, the distribution of the resonant stationary electric field along the entire MW driver system can be used to improve the design in order to reach higher plasma densities and temperatures.

Electron cyclotron resonance plasma reactor for production of carbon stripper foil

A graphite antenna for the production of carbon-containing hydrogen plasmas is being developed to prepare impurity-free charge exchange foils for high-energy synchrotrons. Microwave power at 2.45 GHz frequency drives a coaxial structure antenna with a 12-mm-diameter central graphite cylinder and a tapered surrounding cylinder serving as the ground electrode. The antenna was placed in a linear magnetic field to investigate how it performs under an electron cyclotron resonance (ECR) condition. A clear resonance phenomenon was observed in plasma luminosity, microwave power absorption, and microwave power reflection when the induction current used to produce a linear magnetic field was changed. The antenna realized the best microwave coupling to the plasma with the ECR zone formed 5 mm from the end of the center electrode. The antenna realized stable operation for more than 5 h with 100 W input microwave power and with operating hydrogen pressure from 0.5 to 50 Pa.

Interaction of Atomic Oxygen Species Generated Using Electron Cyclotron Resonance (ECR) Plasma with Thermal Protecting System (TPS) Material

Thermal Protecting System (TPS) material, consisted of silica reinforced fibres and coated with transtion metal complex was exposed to atomic oxygen produced in Electron Cyclotron Resonance (ECR) plasma reactor. The choice of atomic oxygen is based on the necessity of investigating its inteaction with transition metal complex during the re-entry of the space vehicle. The experiments were carried out at different temperature in the range of 30-500°C. The surface morphology of the tile material was investigated with and without exposure to oxygen plasma as a function of temperature using scanning electron microscopy technique, whereas structural analysis of the same samples was carried out using x-ray diffraction technique. Prior to this, ECR plasma reactor was charectorised for electron energy and plasma density using Langmuir probe so as to know the plasma parameter during the interaction.

Influence of microwave driver coupling design on plasma density at Testbench for Ion sources Plasma Studies, a 2.45 GHz Electron Cyclotron Resonance Plasma Reactor

A comparative study of two microwave driver systems (preliminary and optimized) for a 2.45 GHz hydrogen Electron Cyclotron Resonance plasma generator has been conducted. The influence on plasma behavior and parameters of stationary electric field distribution in vacuum, i.e., just before breakdown, along all the microwave excitation system is analyzed. 3D simulations of resonant stationary electric field distributions, 2D simulations of external magnetic field mapping, experimental measurements of incoming and reflected power, and electron temperature and density along the plasma chamber axis have been carried out. By using these tools, an optimized set of plasma chamber and microwave coupler has been designed paying special attention to the optimization of stationary electric field value in the center of the plasma chamber. This system shows a strong stability on plasma behavior allowing a wider range of operational parameters and even sustaining low density plasma formation without external magnetic field. In addition, the optimized system shows the capability to produce values of plasma density four times higher than the preliminary as a consequence of a deeper penetration of the magnetic resonance surface in relative high electric field zone by keeping plasma stability. The increment of the amount of resonance surface embedded in the plasma under high electric field is suggested as a key factor.

Experimental Study of Breakdown Time in a Pulsed 2.45-GHz ECR Hydrogen Plasma Reactor

An electron cyclotron resonance (ECR) plasma reactor developed at the European Spallation Source Bilbao has been operated in pulsed mode at 50 Hz to study the breakdown-process dynamics by time-resolved diagnostics. Injected power, reflected power, electrical-biased probe saturation current, and light emission were measured simultaneously for three different magnetic fields: under ECR, ECR, and asymmetric over ECR profiles. Gas pressure, power, and duty cycle have been used in a parametric study obtaining information about microwave (MW) coupling and plasma formation stages during the breakdown process. The study is relevant for designers that need to extract short beam pulses from a 2.45 ECR ion source for any application because the total breakdown time measured is defined as corresponding to reach the steady-state plasma parameters. A simple model of residual electron density evolution between pulses is proposed to describe the MW coupling as a function of incoming power and duty cycles.

Effect of ion energy on structural and electrical properties of intrinsic microcrystalline silicon layer deposited in a matrix distributed electron cyclotron resonance plasma reactor

AbstractMicrocrystalline silicon films were deposited in a matrix distributed electron cyclotron resonance (MDECR) plasma enhanced chemical vapor deposition (PECVD) system using pure silane, under varying substrate bias conditions. Microstructural characterization of the films shows a lower void fraction and a preponderance of nanograins in films deposited at negative bias, while in positive bias a thin incubation layer is seen with a higher void fraction. Plasma emission studies reveal higher electron temperature and more atomic H at positive bias, which lead to early onset of crystallization. The microstructural properties of the films are correlated with the dark and phototransport properties. Our study demonstrates the importance of substrate bias in controlling the ion energy and properties of films deposited in the MDECR reactor.

ECR plasma assisted deposition of zinc nanowires

Deposits of one dimensional nanowires of zinc with diameters of 90–120 nm have been obtained by means of dc sputtering within an electron cyclotron resonance plasma reactor. The sputtering has been made effective by using a negatively biased cylindrical target. The structure of the nanocrystalline wires deposited on glass substrates were investigated with scanning electron microscopy, transmission electron microscopy and scanning tunneling microscopy. STM revealed that the structure of the one dimensional nanowires are ensemble of nanoclusters and nanowires with diameter of 4–5 nm. The crystalline nature of the metallic nanowires was studied with X-ray and electron diffraction analysis. The native oxide present on the metallic wires was revealed by photoluminescent spectroscopy. Theoretical modeling has been used to explain the possible mechanisms operative inside the plasma which lead into deposition of zinc on the substrate starting from the precursor species.

Scanning tunneling microscopic and field emission microscopic studies of nanostructured molybdenum film synthesized by electron cyclotron resonance plasma

Cathodic sputtering is demonstrated to be effective in synthesizing thin films of molybdenum nanoparticles. An electron cyclotron resonance plasma reactor has been used as the source. The particle size distribution is found to be controllable by proper choice of the cathodic bias potential. Sizes ranging between 20 and 30 nm deposited at the optimum bias potential are found to exhibit a self assembled structure as observed by scanning tunneling microscopy. Field emission microscopic studies on these films supported on W have exhibited very stable emission current over a period of 3 h.

A comparative study on the effect of VUV radiation in plasma SiO x-coated polyimide and polypropylene films

Wettability of polyimide (PI) and polypropylene (PP) films have been improved using SiO x -like thin layers deposited from a mixture of hexamethyldisiloxane (HMDSO) and oxygen in a microwave distributed electron cyclotron resonance plasma reactor. The films wettability evolution behaviors were evaluated through the results of contact angle measurements, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The plasma depositions of SiO x thin layers in presence of VUV radiation induce a contact angle decrease to about 7° and 35° for PI and PP films, respectively. XPS data showed that such difference in wettability is attributed to the increase of hydrophilic group's proportion at the surface of coated PI films due to VUV irradiation. AFM images showed that the PI surface topography remains relatively smooth when coated in presence of VUV radiation. However, in the case of PP films, AFM images revealed the growth of irregular structure due to a substrate etching effect supported by VUV radiation. For polymers coated without VUV irradiation, the deconvolution of the C1s peaks showed a significant decrease of C O bonds for both PI and PP substrates.

Plasma etching of organic material: Combined effects of charged and neutral species

A model organic material, namely the 36-n-alkane hexatriacontane, was etched in a dissymmetrical parallel plate RF plasma reactor and a dual distributed electron cyclotron resonance (DECR) plasma reactor, in different O2-Ar mixtures. A specific attention was paid to the role of the ion bombardment, especially when its effect is combined with the chemically active species created in an oxygen discharge. The discharge was monitored by optical emission spectroscopy (OES). The modifications induced by plasma treatment on the structure of the material were analysed by Fourier transform infrared spectroscopy (FTIR), steric exclusion chromatography (SEC) and composition analysis. We found that the ion bombardment has not only a sputtering effect but also enhances the reaction rate of the chemical species on the layer surface. It appears that plasma treatment leads to cross-linking and recombination with molecules from the room atmosphere.

Thermal annealing effects on the interface state density of metal-oxide-semiconductor capacitors with electron cyclotron resonance plasma enhanced chemical vapor deposition Silicon dioxide

Silicon dioxide films (SiO 2), deposited at room temperature by electron cyclotron resonance (ECR) plasma reactor from a gas phase combination of O 2, SiH 4 and He, present excellent structural and electrical properties. However, when fabricating field effect devices it is also crucial to minimize the defect density at the semiconductor/insulator interface. We show that the interface state density, investigated in Al/SiO 2/Si MOS capacitors, can be substantially reduced performing post-deposition annealing. In particular we studied the effects of annealing temperature and time in different gas ambient: vacuum, nitrogen and forming gas (5% H 2 + N 2). We found that interface state passivation mainly occurs when thermal annealing is performed after Al-contact deposition and that it is quite insensitive to the annealing atmosphere. The present results clearly suggest that the hydrogen passivation mechanism is driven by the H-containing species present in the film and a possible mechanism to explain the results is proposed.

Effect of substrate material and bias on properties of TiN films deposited in the hybrid plasma reactor

Parameters of TiN films deposited in the hybrid hollow cathode and microwave electron cyclotron resonance (ECR) plasma reactor can be strongly affected by the substrate material. Differences have been found between films grown on Si substrates and steel substrates, as well as between steel substrates from martensite and austenite steels. Temperature measurements by simple probes made from different materials with surfaces covered by wafers from Si or from steel confirmed substantial differences depending on individual materials. These differences can be explained by material-dependent absorptions of the microwave power as well as by enhanced particle bombardment of ferromagnetic substrates connected with deformation of the magnetic field in the hybrid plasma reactor. The effect of surface bombardment has been confirmed by voltage-current measurements using electrically biased probes. The results correspond well with properties of the obtained TiN films. Observed effects could be of more general importance, e.g., for microwave ECR plasmas, magnetron sputtering, as well as for most magnetized plasma systems.

Low-temperature electron cyclotron resonance plasma-enhanced chemical-vapor deposition silicon dioxide as gate insulator for polycrystalline silicon thin-film transistors

Silicon dioxide films have been deposited at temperatures below 270°C in an electron cyclotron resonance (ECR) plasma reactor from O2, SiH4, and He gas mixture. Pinhole density analysis as a function of substrate temperature for different microwave powers was carried out. Films deposited at higher microwave power and at room temperature show defect densities (<7pinhole∕mm2), ensuring low-temperature process integration on large area. From Fourier transform infrared analysis and thermal desorption spectrometry we also evaluated very low hydrogen content if compared to conventional rf-plasma-enhanced chemical-vapor-deposited (PECVD) SiO2 deposited at 350°C. Electrical properties have been measured in metal-oxide-semiconductor (MOS) capacitors, depositing SiO2 at RT as gate dielectric; breakdown electric fields >10MV∕cm and charge trapping at fields >6MV∕cm have been evaluated. From the study of interface quality in MOS capacitors, we found that even for low annealing temperature (200°C), it is possible to considerably reduce the interface state density down to 5×1011cm−2eV−1. To fully validate the ECR-PECVD silicon dioxide we fabricated polycrystalline silicon thin-film transistors using RT-deposited SiO2 as gate insulator. Different postdeposition thermal treatments have been studied and good device characteristics were obtained even for annealing temperature as low as 200°C.

Utilization of ECR mechanism of electrons heating in multipolar magnetic systems of low-pressure plasma Reactors

In this paper, the electron-cyclotron resonance (ECR) mechanism of electrons heating by electromagnetic wave in ECR microwave low-pressure plasma reactors is considered. In such reactors, ionization is mainly provided by fast electrons trapped by multipolar magnetic system. A particle simulation is carried out for statistical ensemble of electrons in magnetic systems of different configurations with taking into account previous experimental results. The escape of fast electrons from the magnetic traps to the walls is identified as the major factor behind the loss of electrons in the limit of a collisionless plasma. A comparative evaluation of different multipolar magnetic systems is made. Basic requirements are set out concerning the optimal design of multipolar ECR plasma reactors. Several approaches for providing the efficient ECR heating of electrons are proposed.

Radioactive sputter cathodes for 32P plasma-based ion implantation

The development of clinical treatments involving the use of beta-emitting millimetric and sub-millimetric devices has been a continuing trend in nuclear medicine. Implanted a few nanometers below the surface of endovascular implants, seeds or beads, beta-emitting radioisotopes can be used in a variety of biomedical applications. Recently, new technologies have emerged to enable the rapid and efficient activation of such devices. A pulsed, coaxial electron cyclotron resonance plasma reactor was designed and tested to demonstrate the feasibility of plasma-based radioactive ion implantation (PBRII). It has been shown that such plasma reactors allow for the implantation of radioisotopes ( 32P) into biomedical devices with higher efficiencies than those obtained with conventional ion beams. Fragments containing radioactive atoms are produced in the implanter by means of a negatively biased solid sputter cathode that is inserted into an argon plasma. Dilute orthophosphoric acid solutions (H 3 32PO 4) are used for the fabrication of flat sputter targets, since they offer a high radioisotope content. However, the aggregation of the radioactive solute into highly hygroscopic ring-like deposits rather than flat, thin radioactive films is observed on certain substrates. This article describes the effect of this nonuniform distribution of the radioisotopes on the efficiency of PBRII, and presents a technique which enables a better distribution of 32P by coating the substrates with iron. The iron coating is shown to enable optimal radioisotope sputtering rates, which are essential in 32P-PBRII for the efficient activation of millimetric biomedical devices such as stents or coils.

Sustaining Mechanisms of the ECR Heating of Electrons in Low-Pressure Microwave Plasmas under Magnetic Multipole Confinement

A theoretical study is conducted on the sustaining of low-pressure electron-cyclotron-resonance (ECR) plasmas for which ionization is provided by high-energy electrons trapped by a multipolar permanent-magnet system. A particle simulation is carried out for the electron motion in magnetic systems of different configurations on assumptions suggested by previous experimental results. On this basis, the high-energy tail of the electron energy distribution function is examined. The escape of high-energy electrons (including that to the walls) is identified as the major factor behind the loss of electrons in the limit of a collisionless plasma. A comparative evaluation of different multipolar magnetic systems is made. Basic requirements are set out concerning the optimal design of ECR plasma reactors. New approaches to ECR electron heating are proposed.

Co-axial ECR plasma system for radioactive ion implantation

A pulsed, co-axial electron cyclotron resonance (ECR, 2.45 GHz) plasma reactor was designed and tested to demonstrate the feasibility of plasma-based radioactive ion implantation (32P radioisotope). The geometry of the reactor was designed to produce an efficient implantation of cylindrical implants. Therefore, the reactor is cylindrical in shape, and is equipped with a cylindrical grid in a co-axial geometry. The plasma is created between the wall and the grid; the plasma surrounds the implant, allowing for a radial implantation. A 1 ms microwave pulse creates a plasma in argon, which sputters material from a radioactive cathode. A fraction of the radioisotopes is then ionized, and the ions are implanted into negatively biased metal samples. The plasma was characterized by means of electrostatic probes, giving spatial evaluations of the electron temperature, plasma potential and electron density. Titanium samples were implanted with 32P during a study that aimed at optimizing the position of the radioactive sputter cathode in the plasma. From an analysis of the distribution of the radioactive fragments, we deduce that the plasma potential has a marked effect on the ion trajectories. In particular, it provides a more uniform implantation distribution than one would otherwise expect. For plasma densities ∼8 × 1010 cm−3, implantation efficiencies as high as 1% are measured; this is about 100 times higher than conventional beam-line ion implantation.

Silicon dioxide deposited by ECR-PECVD for low-temperature Si devices processing

Silicon dioxide films have been deposited at temperatures less than 270 °C in an electron cyclotron resonance (ECR) plasma reactor from a gas phase combination of O 2, SiH 4 and He. The physical characterization of the material was carried out through pinhole density analysis as a function of substrate temperature for different μ-wave power ( E w). Higher E w at room deposition temperature (RT) shows low defects densities (<7 pinhole/mm 2) ensuring low-temperatures process integration on large area. From FTIR analysis and Thermal Desorption Spectroscopy we also evaluated very low hydrogen content if compared to conventional rf-PECVD SiO 2 deposited at 350 °C. Electrical properties have been measured in MOS devices, depositing SiO 2 at RT. No significant charge injection up to fields 6–7 MV/cm and average breakdown electric field >10 MV/cm are observed from ramps I– V. Moreover, from high frequency and quasi-static C– V characteristics we studied interface quality as function of annealing time and annealing temperature in N 2. We found that even for low annealing temperature (200 °C) is possible to reduce considerably the interface state density down to 5 × 10 11 cm −2 eV −1. These results show that a complete low-temperatures process can be achieved for the integration of SiO 2 as gate insulator in polysilicon TFTs on plastic substrates.