Glow Discharge Plasma Immersion Ion Research Articles

A new-structured nanocarbon cushion with highly impact-resistant properties

Compared with traditional impact-resistant materials, nanocarbon materials have the advantages such as light weight, large specific volume for energy dissipation and their exceptional thermal stability for the extreme-environmental working potentials. However, based on the commonly used fabrication method, the general nanocarbon structures (e.g. carbon nanotube (CNT) array) are always constructed with the weak interaction between units. Therefore, when they are subjected to impact, the impact energy cannot be transferred throughout the whole loose and discontinuous structure efficiently, which results in the degradation of their impact-resistant capabilities. To address the above issue, we fabricated a nanocarbon “cushion” with the combination of a diamond like carbon (DLC) film and multi-wall CNT (MWCNT) array. The DLC film was deposited successfully onto the as-grown MWCNT array through enhanced glow discharge plasma immersion ion implantation and deposition (EGD-PIII&D) method to form a continuous upper layer which is vital to distribute and transfer the impact energy loading. The new nanocarbon system has high specific dissipated energy up to ∼2.22 kJ/m3, which is almost twice as much as that of the commercial polyurethane sponge. We anticipate that this study will provide new insights to develop novel nanocarbon materials for impact resistance in high-tech edge applications.

Self-enhanced plasma discharge effect in the deposition of diamond-like carbon films on the inner surface of slender tube

Enhanced glow discharge plasma immersion ion implantation and deposition (EGD-PIII&D) have been proved to be highly effective for depositing diamond-like carbon (DLC) films on the inner surface of the slender quartz tube with a deposition rate of 1.3μm/min. Such a high-efficiency DLC films deposition was explained previously as the short electrons mean free path to cause large collision frequency between electrons and neutral particles. However, in this paper, we found that the inner surface material of the tube itself play a vital role on the films deposition. To disclose the mechanism of this phenomenon, the effect of different inner surface materials on plasma discharge was experimentally and theoretically investigated. Then a self-enhancing plasma discharge is discovered. It is found that secondary electrons emitted from the inner surface material, whatever it is the tube inner surface or deposited DLC films, can dramatically enhance the plasma discharge to improve the DLC films deposition rate.

Researches on uniformity of diamond-like carbon films deposited on inner surface of long and slender quartz glass tube by enhanced glow discharge plasma immersion ion implantation and deposition

Enhanced glow discharge plasma immersion ion implantation and deposition (EGD-PIII&D) has been successfully used for depositing diamond-like carbon (DLC) on the inner surface of the quartz glass tube with an inner diameter as small as 0.9mm and aspect ratios of over 100. And the uniformity is a key problem for the DLC films deposited on the inner surface. By changing the C2H2 flow rate and negative voltage, the effects of the gas flow rate and voltage on the uniformity of the DLC films deposited on the inner surface of the quartz glass tube are experimentally examined. The electron-neutral collision frequency, νe, is used to qualitatively analyze the mechanism of uniformizing DLC films. The results reveal that uniform DLC films may be obtained by balancing both the gas flow rate and the negative voltage.

Deposition of diamond-like carbon films on interior surface of long and slender quartz glass tube by enhanced glow discharge plasma immersion ion implantation

Diamond-like carbon (DLC) films are deposited on the interior surface of 100mm long quartz glass tubes with inner diameters of 6, 4, and 0.9mm by enhanced glow discharge plasma immersion ion implantation (EGD-PIII) at 10kV. The acetylene plasma is generated inside the tube by electrons created in the plasma near the substrate and secondary electrons from ion bombardment. Acetylene gas pressure distribution obtained from finite element method shows that the pressure varies linearly from the inlet to the outlet of the tube. The electron mean free path, λe, and collision frequency, νe, are introduced to qualitatively explain the non-uniform DLC film thickness. Raman scattering indicates that the DLC films at different locations have a similar structure.

Improved ion implant fluence uniformity in hydrogen enhanced glow discharge plasma immersion ion implantation into silicon.

Enhanced glow discharge plasma immersion ion implantation does not require an external plasma source but ion focusing affects the lateral ion fluence uniformity, thereby hampering its use in high-fluence hydrogen ion implantation for thin film transfer and fabrication of silicon-on-insulator. Insertion of a metal ring between the sample stage and glass chamber improves the ion uniformity and reduces the ion fluence non-uniformity as the cathode voltage is raised. Two-dimensional multiple-grid particle-in-cell simulation confirms that the variation of electric field inside the chamber leads to mitigation of the ion focusing phenomenon and the results are corroborated experimentally by hydrogen forward scattering.

Transformation of Enhanced Glow Discharge Dynamics in Nitrogen Plasma Immersion Ion Implantation

In nitrogen enhanced glow discharge plasma immersion ion implantation, the implantation current increases sharply with the gas pressure when a threshold pressure is exceeded, indicating that the glow discharge dynamics changes with increasing diatomic gas flow rate. The voltage drop rendered by the anode glow produces noticeable N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> dissociation and electron-atom ionization in the positive column which expands to the cathode. As a result, charged particles reach the cathode more easily, and the larger plasma density and N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ratio in the positive column lead to the higher current. Our results clarify the implantation current characteristics and expedite adoption of this alternative plasma immersion technology.

Numerical simulation of enhanced glow discharge plasma immersion ion implantation using three-dimensional PIC/MC model

Enhanced glow discharge plasma immersion ion implantation is self-consistently simulated using a three-dimensional PIC/MC model. The information about ion counts, space potential, plasma density and ion incident dose is obtained. The results show that the sheath has fully expanded at 5 μs. There is a stable equilibrium of ion counts at 15 μs, which corroborates the characteristic of self-sustaining glow discharge of EGD-PIII. In the space just below anode where is found a highest plasma density, verifying the electron focusing effect. The rate of implantation is steady and the incident dose is relatively uniform except at the rim of target. A higher pulse negative bias may increase the injection rate but reduce the dose uniformity at the same time.

Improved hydrogen ionization rate in enhanced glow discharge plasma immersion ion implantation by enlarging the interaction path using an insulating tube

A small pointed hollow anode and large tabular cathode are used in enhanced glow discharge plasma immersion ion implantation (EGD-PIII). Electrons are repelled from the substrate by the electric field formed by the negative voltage pulses and concentrate in the vicinity of the anode to enhance the self-glow discharge process. To extend the application of EGD-PIII to plasma gases with low ionization rates, an insulating tube is used to increase the interaction path for electrons and neutrals in order to enhance the discharge near the anode. Results obtained from numerical simulation based on the particle-in-cell code, finite element method, and experiments show that this configuration enhances the ionization rate and subsequent ion implant fluence. The process is especially suitable for gases that have low ionization rates such as hydrogen and helium.

Influence of annular magnet on discharge characteristics in enhanced glow discharge plasma immersion ion implantation

A permanent annular magnet positioned at the grounded anode alters the discharge characteristics in enhanced glow discharge plasma immersion ion implantation (EGD-PIII). The nonuniform magnetic field increases the electron path length and confines electron motion due to the magnetic mirror effect and electron-neutral collisions thus occur more frequently. The plasma potential and ion density measured by a Langmuir probe corroborate that ionization is improved near the grounded anode. This hybrid magnetic field EGD-PIII method is suitable for implantation of gases with low ionization rates.

Ion focusing in enhanced glow discharge plasma immersion ion implantation of hydrogen and nitrogen into silicon

Ion focusing in enhanced glow discharge plasma immersion ion implantation (EGD-PIII) of hydrogen into silicon affects the lateral ion fluence uniformity. The phenomenon and its effects are investigated experimentally and theoretically under different conditions and compared to those in nitrogen EGD-PIII. Consistent results are obtained from experiments and numerical simulation disclosing that the lower the plasma density, the more severe is the ion focusing effect. The influence of the negative high voltage on the ion focusing effect is small compared to that of the plasma density.

Impact energy and retained dose uniformity in enhanced glow discharge plasma immersion ion implantation

The implantation energy and retained dose uniformity in enhanced glow discharge plasma immersion ion implantation (EGD-PIII) is investigated numerically and experimentally. Depth profiles obtained from different samples processed by EGD-PIII and traditional PIII are compared. The retained doses under different pulse widths are calculated by integrating the area under the depth profiles. Our results indicate that the improvement in the impact energy and retained dose uniformity by this technique is remarkable.

Plasma sheath physics and dose uniformity in enhanced glow discharge plasma immersion ion implantation and deposition

Based on the multiple-grid particle-in-cell code, an advanced simulation model is established to study the sheath physics and dose uniformity along the sample stage in order to provide the theoretical basis for further improvement of enhanced glow discharge plasma immersion ion implantation and deposition. At t=7.0 μs, the expansion of the sheath in the horizontal direction is hindered by the dielectric cage. The electron focusing effect is demonstrated by this model. Most of the ions at the inside wall of the cage are implanted into the edge of the sample stage and a relatively uniform ion fluence distribution with a large peak is observed at the end. Compared to the results obtained from the previous model, a higher implant fluence and larger area of uniformity are disclosed.

High-voltage glow discharge plasma immersion ion implantation assisted by magnetic field

Plasma immersion ion implantation (PIII) employing high-voltage glow discharge is an effective tool to achieve better material properties without external plasma sources. The efficacy of high-voltage glow discharge can be enhanced by the use of a magnetic field. Our experimental results disclose that the addition of permanent magnets effectively increases the plasma density and decreases the delay time to ignite the glow discharge. The discharge can also be ignited at a lower pressure in the presence of a magnetic field. This helps to improve the implantation energy due to reduced particle collisions. In addition, the process is more flexible since plasma generation depends less on the gas pressure and target bias compared to conventional high-voltage glow discharge PIII. To demonstrate the advantages of this simple, flexible and efficient technique, polyethylene terephthalate (PET) foils are treated by glow discharge PIII to improve the surface properties and smaller water contact angles are observed from the implanted samples.

Investigation of plasma potential and pulsed discharge characteristics in enhanced glow discharge plasma immersion ion implantation and deposition

Enhanced glow discharge plasma immersion ion implantation and deposition (EGD-PII&D) does not require external plasma sources. In this technique, the plasma is produced by self-glow discharge when a high negative voltage is applied to the sample. The small-area, pointed-shape hollow anode and large area tabular cathode form an electron-focused electric field. Using a special electric field design, the electrons from either the plasma or target (secondary electrons) are focused to a special hollow anode. As a result of the special electron-focusing field, the self-glow discharge process can be enhanced to achieve effective ion implantation into the substrate. In this work, the plasma potential distribution is investigated in details and the possible pulse discharge mechanism is discussed. The unique characteristics of the pulsed plasma and plasma extinction are studied.

Theoretical investigation of sheath expansion and implant fluence uniformity in enhanced glow discharge plasma immersion ion implantation

In enhanced glow discharge plasma immersion ion implantation that involves a small-pointed anode and large area tabular cathode, the high negative substrate bias acts as the plasma producer and supplies the implantation voltage. An electric field is created to focus the electrons and the electron-focusing field in turn enhances the glow discharge process. The sheath physics is theoretically investigated using numerical simulation based on the multiple-grid particle-in-cell code. Electron focusing is corroborated and the plasma sheath has enough expansion when t=40μs so that a uniform distribution of the incident ion fluence is attained.

Experimental investigation of discharge characteristics in enhanced glow discharge plasma immersion ion implantation

In enhanced glow discharge plasma immersion ion implantation (EGD-PIII) that involves a small pointed anode and large area tabular cathode, the high negative substrate bias not only acts as the plasma producer but also supplies the implantation voltage. Consequently, an electric field is created to focus the electrons and the electron focusing field in turn enhances the glow discharge process. In this work, the discharge characteristics of EGD-PIII are investigated experimentally. The discharge initiation and extinction characteristics during pulsed biasing are discussed. The duration of the post pulse-off plasma is explained from the viewpoint of particle motion and experimentally verified by employing an auxiliary disk. Our experiments show that a dual-pulse method may be utilized to determine the remnant plasma.

Investigation of plasma distribution in electron-focused electric field enhanced glow discharge plasma immersion ion implantation

In enhanced glow discharge plasma immersion ion implantation (EGDPIII) that involves a small pointed anode and large area tabular cathode, the high negative substrate bias not only acts as the plasma producer but also supplies the implantation voltage. Consequently, an electric field is created to focus the electrons and the electron-focusing field enhances the glow discharge process. In this work, the plasma distribution is measured using a Langmuir probe to obtain the plasma density. Numerical interpolation is performed to obtain the plasma density distribution throughout the entire discharge region. The effects of different distances between the anode and cathode on the glow discharge characteristics and the influence of the plasma electron density are also evaluated. Our results experimentally verify the electron-focusing phenomenon and suggest optimal processing windows for enhanced ionization rates and efficiency in EGDPIII.

Amorphous silicon nitride films of different composition deposited at room temperature by pulsed glow discharge plasma immersion ion implantation and deposition

Amorphous hydrogenated silicon nitride (a-SiNx:H) films of different compositions (0⩽x⩽1.18) were prepared by pulsed glow discharge plasma immersion ion implantation and deposition. The processing gases were silane and nitrogen at a substrate temperature ⩽50°C. The properties of the films were investigated using Rutherford backscattering, elastic recoil detection analysis, UV–visible optical absorption, Fourier transform infrared, and Raman spectroscopies, and nanoindentation. Depending on the value of x, the band gap of the films changes from 1.54to4.42eV, and hardness changes from 11.2to15.3GPa. Changes in the film properties are caused by formation of Si–N bonds and by reducing disorder in the films. It is shown that hard and transparent silicon nitride films can be obtained at room temperature.

Fluorine and boron co-doped diamond-like carbon films deposited by pulsed glow discharge plasma immersion ion processing

Fluorine (F) and boron (B) co-doped diamond-like carbon (FB-DLC) films were prepared on different substrates by the plasma immersion ion processing (PIIP) technique. A pulse glow discharge plasma was used for the PIIP deposition and was produced at a pressure of 1.33 Pa from acetylene (C2H2), diborane (B2H6), and hexafluoroethane (C2F6) gas. Films of FB-DLC were deposited with different chemical compositions by varying the flow ratios of the C2H2, B2H6, and C2F6 source gases. The incorporation of B2H6 and C2F6 into PIIP deposited DLC resulted in the formation of F–C and B–C hybridized bonding structures. The levels of the F and B concentrations effected the chemical bonding and the physical properties as was evident from the changes observed in density, hardness, stress, friction coefficient, and contact angle of water on films. Compared to B-doped or F-doped DLC films, the F and B co-doping of DLC during PIIP deposition resulted in the formation of films that possessed a reduced hydrogen concentration an...

Reciprocal space mapping of silicon implanted with nitrogen by plasma immersion ion implantation

Nitrogen was implanted in (0 0 1) silicon wafers using 12 kV pulses in a glow-discharge plasma immersion ion implantation (PIII) system and at 35 keV in an electron-cyclotron-resonance (ECR) PIII facility. An implantation depth of 80 nm and a retained dose of approximately 3×10 17 cm −2 were found, for both samples, from the nitrogen Auger profiles. Reciprocal space maps (RSMs) around the (0 0 4) and (1 1 3) Si lattice points were measured for the implanted and unimplanted Si wafers, using the high-resolution X-ray diffractometer in the triple axis configuration. An asymmetry in the reciprocal space coordinate Q z (perpendicular to the sample surface) indicates that the implanted atoms force an increase in the Si lattice parameter in this direction. A broadening in the Q x direction (parallel to the sample surface) was also observed, but with a less pronounced effect. For the sample implanted with higher energy, the shape of the map indicates a higher disorder in the crystal structure.