Sputter Type Negative Ion Source Research Articles

Insights into the effect of hollow cathode with external injection of fast ions in a sputter-type negative ion source

In sputter-type negative ion sources, the negative ion currents and ionization efficiencies are very dependent upon the creation of a sputter crater and formation of an intense plasma glow. This effect has many similarities with the well-known phenomena of hollow cathode discharges (HCDs). This paper discusses the phenomenological model related to conventional HCDs, including modes with injection of external energetic particles. We propose that HCDs play a major role in sputter-type negative ion sources. In this study, we evaluate the phenomenology of a discharge with a hollow cathode and derive an analytical formula that defines the neutral particle density inside the cathode cavity and substantiates how the classic HCD occurs in sputter-type negative ion sources. The cathode pit geometry was revealed by optical microscopy. Volt–ampere characteristics were investigated in order to compare it to typical discharges with hollow cathodes. In sputter-type negative ion sources, known as SNICS, discharge characteristics and observed light glow inside the cathode pit after its formation were very similar to data published on HCDs. The HCD phenomenon explains how the cathode current increases by orders of magnitude after creation of the cathode pit. The HCD effect in SNICS and similar sputter sources compliments existing mechanisms of negative ion production, especially ion pair production close to the cathode surface due to low energy ionization based on the collision–radiation model. The wealth of information accumulated over the last century on HCDs can be used to describe and explain the phenomenology of physics and operation of sputter negative ion sources.

Ion Implantation of Silver Nanoparticles on Electrodeposited Polycarbazole Via Plasma Sputter Type Negative Ion Sources

The discovery of conducting polymer has brought tremendous advancement in developing various polymeric materials, Carbazole pendants of poly(ethyl methacrylate) was cross-linked via an electrochemical route. The obtained film of poly( carbazole ethyl methacrylate) electrodeposited on the surface of indium tin oxide (ITO) was modified by implanting silver nanoparticles on its surface. This was done using Plasma Sputter-type Negative Ion Sources (PSTNIS) The modified and unmodified films of polycarbazole were characterized to assess its properties. Implanting silver nanoparticles on the surface of the cross-linked polymer abruptly changed its surface roughness, absorbance in the visible region and its current-voltage characteristic. A more pronounced diode-like characteristic was observed with a turn-on voltage of ∼0.4V. Investigation and tailoring the properties of electropolymerized carbazole attached to poly (ethyl methacrylate) backbone with implanted silver nanoparticles could lead to important materials with impact in optoelectronic devices.

Photo response of silver-TiO2 film

Silver and TiO2 films were deposited on glass substrates via the plasma sputter type negative ion source and a compact planar magnetron, respectively. A silver target was biased and is sputtered by argon plasma for 30 min. TiO2 was deposited by sputtering a titanium disk and introducing oxygen in a 1:13 ratio with argon plasma for 2 h. The resulting composite films (silver on TiO2 and TiO2 on silver) were analyzed by its transmissivity in the UV-VIS region showing increased optical absorbance. The synthesized films were used in the photocatalytic degradation of methylene blue showing an increase in photocatalytic degradation when only TiO2 is used. The introduction of silver with TiO2 inhibited the effective photocatalytic degradation of methylene blue.

Electrostatic energy analyzer measurements of low energy zirconium beam parameters in a plasma sputter-type negative ion source

A plasma sputter-type negative ion source is utilized to produce and detect negative Zr ions with energies between 150 and 450 eV via a retarding potential-type electrostatic energy analyzer. Traditional and modified semi-cylindrical Faraday cups (FC) inside the analyzer are employed to sample negative Zr ions and measure corresponding ion currents. The traditional FC registered indistinct ion current readings which are attributed to backscattering of ions and secondary electron emissions. The modified Faraday cup with biased repeller guard ring, cut out these signal distortions leaving only ringings as issues which are theoretically compensated by fitting a sigmoidal function into the data. The mean energy and energy spread are calculated using the ion current versus retarding potential data while the beam width values are determined from the data of the transverse measurement of ion current. The most energetic negative Zr ions yield tighter energy spread at 4.11 eV compared to the least energetic negative Zr ions at 4.79 eV. The smallest calculated beam width is 1.04 cm for the negative Zr ions with the highest mean energy indicating a more focused beam in contrast to the less energetic negative Zr ions due to space charge forces.

The luminescence and optoelectrical properties of ITO films prepared by a sputter type negative metal ion deposition

Transparent conducting indium tin oxide (ITO) thin films were prepared on glass substrates by a magnetron sputter type negative ion source which requires cesium (Cs) vapor injection for surface negative ionization on the ITO target surface. Although the film was prepared at 70°C, it attained high optical transmittance, 88% and low resistivity, 2.03×10−4Ωcm, at an optimized Cs partial pressure of PCs=1.7×10−3Pa. The as-deposited ITO films have a poly-crystalline structure with (211), (222), (400), (411) and (440) reflections.Also, ITO films prepared at PCs=1.7×10−3Pa were post-deposition vacuum annealed at 300°C for 30min. The films had a resistivity of 1.8×10−4Ωcm and a transparency of 89.2%. The post-deposition vacuum annealed ITO film was used as an anode for a transparent organic light emitting diode (TOLED). A maximum luminance of 19,000cd/m2 was obtained.

Field emission characteristics of Diamond-like Carbon (DLC) films prepared using a Magnetron Sputter-type Negative Ion Source (MSNIS)

The field emission characteristics of Diamond-like Carbon (DLC) films prepared using a MSNIS were studied. Due to Negative Electron Affinity (NEA), the high hardness, high thermal conductivity and chemical inertness, DLC films are considered as good electron emitters for Field Emission Displays. However, the very smooth DLC films showed poor field emission characteristics regardless of their sp3 contents or density. After reviewing the emitted spots using Atomic Force Microscope (AFM), a metal-diamond-vacuum triple-junction type emission model was tried. Triple-junction type patterns were fabricated using KrF excimer-laser drilling method. Without fabricating spindt type tips, stable field emission was observed with the low turn on voltages (∼2 V/μm). The FE (Field emission) characteristics such as I-V characteristic curves, turn on voltages, and emission lifetime data were obtained using a diode type FE measurement system. Overall results show significantly enhanced performance of field emission characteristics can be achieved at the laser-patterned DLC films.

Characteristics of Cu films prepared using a magnetron sputter type negative ion source (MSNIS)

Cu films have been deposited at room temperature using a magnetron sputter type negative ion source (MSNIS) at various conditions. By the principle of operation, the negative ion production probability is the function of the Cs flow rate in MSNIS. A set of films were deposited at different Cs flow rates and compared with normal-magnetron-sputtered films. The long-throw method was combined to MSNIS to increase the directionality and the negative ion arrival ratio. The film properties, such as resistivity, surface roughness, film structure, and step coverage on high aspect-ratio trench samples were obtained and analyzed using SEM, SIMS and AFM methods. The results showed that the resistivity of the film improved toward the theoretical values from 2.3 to 1.8 μΩ cm for the 100 nm thickness films. AFM scan of the film showed surface roughness was improved using MSNIS by ion bombarding effect. Depth profiling SIMS result showed Cs level resided in the film was less than 1 × 10 19 at./cm 3. As an application, Cu seed layer deposition on trench structure was investigated. Cross-sectional SEM was employed to see the step coverage of the film. The biasing effect was investigated. The different biasing conditions resulted as the clearly different coverage mode.

Characteristics of Cu films prepared using a magnetron sputter type negative ion source (MSNIS)

Cu films have been deposited at room temperature using a magnetron sputter type negative ion source (MSNIS) at various conditions. By the principle of operation, the negative ion production probability is the function of the Cs flow rate in MSNIS. A set of films were deposited at different Cs flow rates and compared with normal-magnetron-sputtered films. The long-throw method was combined to MSNIS to increase the directionality and the negative ion arrival ratio. The film properties such as resistivity, surface roughness, film structure and step coverage on high-aspect ratio trench samples were obtained and analyzed using SEM, SIMS and AFM methods. The results showed that the resistivity of the film improved toward the theoretical values from 2.3μΩcm to 1.8μΩcm for the 100nm thickness films. AFM scan of the film showed surface roughness was improved using MSNIS by ion bombarding effect. Depth profiling SIMS result showed Cs level resided in the film was less than 1×1019atom/cm3. As an application, Cu seed layer deposition on trench structure was investigated. Cross-sectional SEM was employed to see the step coverage of the film. The biasing effect was investigated. The different biasing conditions resulted as the clearly different coverage mode.

High-density DLC films prepared using a magnetron sputter type negative ion source

Diamond-like carbon (DLC) films have been deposited at room temperature using a magnetron sputter type negative ion source (MSNIS). The film characteristics such as density, surface roughness, film structure and thicknesses are obtained and analyzed using X-ray reflectivity (XRR), XPS and AFM methods. XRR results showed that the density of the film varies from 1.9 to 3.0 g/cm 3 with respect to the different deposition parameters. At average negative carbon ion energy 700 eV and Cs injector temperature 150 °C, the densest film (3.0 g/cm 3) was observed at 1 nm/s deposition rate. The surface roughness of the film was less than 1.0 nm in most cases for the 10-nm thickness film. XPS peak showed no Cs content on the film. The films prepared at different negative ion production yields and negative ion energies were compared. The result suggests that the density is the strong function of negative ion energy and the negative ion production yield. Higher cathode voltage induced denser film, while Cs flow rate had optimum temperature condition around 150 °C.

The stability of SiO 2 films prepared using a magnetron sputter type negative ion source (MSNIS)

Aging effect of SiO 2 films was investigated. SiO 2 films were prepared using a magnetron sputter type negative ion source (MSNIS) utilizing the direct ion beam deposition (DIBD) method. Thin SiO 2 films are known as suffering from aging effect after the deposition. To minimize the variation of the refractive index or thickness of the film after the long period of time, a dense film is desirable. The optical properties such as refractive index ( n), extinction coefficient ( k) and thickness were analyzed using an UV spectrometer-combined thin-film measurement system. The surface morphology and roughness were measured using an atomic force microscope (AFM). The thickness and refractive index variance after 1-month period was less than 3% for the 100 nm thickness films. The average roughness of the film on silicon substrate was less than 1 nm in most cases. The resultant films show that the film properties were strongly dependent on the ion beam energy and oxygen partial pressure of deposition. In high power density (3.2 W/cm 2), the aging effect was more noticeable. The wet-etch test of SiO 2 films with respect to Cs flow rate showed that Cs flow rate is an important parameter in operation of a MSNIS.

Raman and XPS studies of DLC films prepared by a magnetron sputter-type negative ion source

The characteristics of diamond-like carbon (DLC) films deposited on a 4-in. Si (100) substrate using a magnetron sputter-type negative ion source (MSNIS) were investigated using Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) method. In the MSNIS source, a negative ion beam is generated by a cesium-induced sputter-type secondary negative ion emission process. DLC films deposited using this MSNIS technique were compared with films prepared using a conventional magnetron sputter process under various deposition conditions. Since the final energy of the negative ion arriving at the substrate is a function of the cathode voltage, the cathode voltage dependence of the film properties was investigated. As the applied voltage is increased, the more diamond-like properties were observed. Overall results suggest that the sp 3 bonding of DLC film can be effectively controlled using a MSNIS.

Characterization of the Sn Doped In2O3 Film Prepared by DC Magnetron Sputter Type Negative Metal Ion Beam Deposition

Transparent conducting indium tin oxide (ITO) films were prepared on a glass substrate by DC magnetron sputter type negative ion source from a target of a mixture of In2O3 (90%) and SnO2 (10%). In order to investigate the influence of cesium (Cs) partial pressure (PCs) on the optoelectronic property of ITO films, the PCs was varied from 1×10-3 to 2.2×10-3 Pa. The O2/Ar flow rate, working pressure, power density, and substrate temperature were kept constant at 3.6%, 9×10-2 Pa, 2.5 Wcm-2 and 70°C, respectively. By optimizing the PCs at 1.7×10-3 Pa, transparent (transmission ∼81% at 550 nm) and conducting (resistivity ∼4.3×10-4 Ωcm) ITO films were prepared. Atomic force microscopy (AFM) images showed that the surface morphology also varied significantly with PCs and that the lowest surface rms roughness was 0.6 nm measured at PCs=1.7×10-3 Pa. XPS measurement showed that the Cs concentration in the ITO films was less than 0.2 at%.

Thin-film deposition of ZrN using a plasma sputter-type negative ion source

High grade coatings of zirconium mononitride (ZrN) are deposited on copper substrates using a multicusp plasma sputter-type negative ion source. The ion source was operated in its target/gas mode with zirconium as target metal, argon as sputtering gas and nitrogen as reactive gas. Optimum conditions for the synthesis of ZrN for a number of process parameters like volume ratio of gases, discharge conditions, substrate bias and deposition time were determined. Experimental runs conducted varied the N 2:Ar gas ratio between 20:80 to 30:70 in a total initial gas filling pressure of 0.93 Pa. The target potential ranged from 300 to 325 V with corresponding currents between 7 and 12 mA. The plasma current was between 698 mA and 1.070 A. The copper substrate was biased between −40 and 75 V while deposition time was kept constant at 1 h. No substrate heating was done. Deposited films exhibited the (1 1 1). (2 0 0) and (2 2 2) peaks of ZrN as shown from X-ray diffractograms and energy dispersive spectroscopy. Film thickness measurements from focused ion beam indicated the deposition rate between 17 to 36 nm/min.

Acceleration of cluster and molecular ions by TIARA 3 MV tandem accelerator

We succeeded in accelerating molecular and cluster ions (B 2–4, C 2–10, O 2, Al 2–4, Si 2–4, Cu 2–3, Au 2–3, LiF, and AlO) to MeV energies with high-intensity beam currents by means of a 3 MV tandem accelerator in the TIARA facility. These cluster ions were generated by a cesium sputter-type negative ion source. We tested three types of carbon sputter cathodes in which graphite powder was compressed with different pressures. The pressure difference affected the generating ratio of clusters generated to single atom ions extracted from the source and it appeared that the high-density cathode was suitable. We also investigated the optimum gas pressure for charge exchange in the tandem high-voltage terminal. Clusters of larger size tend to require lower pressure than do smaller ones. In addition, we were able to obtain doubly charged AlO molecular ions.

Applications of heavy-negative-ion sources for materials science (invited)

Applications of heavy negative ions produced by sputter-type negative-ion sources for materials science are reviewed. Submilliampere and milliampere heavy-negative-ion beams can be produced by a neutral- and ionized-alkaline–metal-bombardment-type heavy-negative-ion source and rf plasma sputter-type negative-ion sources, respectively. These negative-ion beams can be applied for materials processing such as ion implantation, ion beam etching, and ion beam deposition. In negative-ion implantation the charge-up of implanted material surfaces is greatly reduced, and thus ion implantation without target charging is possible. The etching rate due to fluorine-negative ion is mainly determined by its kinetic energy. Pure diamondlike carbon films with high sp3 structure have been prepared by C− and C2− ion beam deposition, and CN films by CN− ion beam deposition. Negative ions provide an excellent tool for materials processing applications.

Negative-ion implanter for powders and its application to nanometer-sized metal particle formation in the surface of glass beads

We have developed a negative-ion implanter for uniform implantation into each powder surface without particle scattering. It consists of a plasma sputter-type negative-ion source, a mass separator, an acceleration tube, a lens, X–Y deflectors, a 90° deflector, and a Faraday cup with an agitator. The electrostatic 90° deflector bends a horizontal beam to a vertical direction and leads it into the Faraday cup. The agitator is an electromagnetic vibrator at a frequency of 120 Hz, which mixes particles for whole surface treatment and uniform implantation. In this implanter, we obtained no scattering implantation for spherical oxide beads with diameters ranging from 5 to 1000 μm in an agitated state, and also obtained a good uniformity of implanted atoms among beads. For an application of the negative ion implantation into powders, copper ions were implanted into soda-lime glass beads and plates at conditions of 50 and 30 keV, respectively, with 1×1017 ions/cm2. In linear optical properties, both implanted samples show a clear absorption at a photon energy of 2.2 eV due to resonance absorption of copper surface plasmon. In addition, the implanted glass plate shows the large third-order nonlinear susceptibility, χ(3)=1.3×10−7 esu. These results suggest the existence of copper nanometer-sized particles in glass.

低エネルギーＣＮ分子負イオンビーム蒸着膜における窒素含有率のエネルギー依存性

CN negative-ion beam deposited films have been investigated with respect to dependencies of a nitrogen atom content and interatomic bonding state upon the incident ion energy. The CN negative ions extracted from a sputter-type negative ion source were deposited on a silicon substrate n-Si (100) at various ion energies in a range of 25-500 eV. From Rutherford backscattering spectroscopy (RBS) measurement, the maximum of N/C ratio and atomic density in films were obtained N/C = 0.60, 1.56 × 1023 atoms · cm-3 at an ion energy of 75 eV, respectively. From X-ray photoelectron spectroscopy (XPS) analysis, nitrogen atoms in the film were found to be mostly combined with carbon atoms in bonding states of C = N and C ≡ N. The maximum fraction of C-N bond reached 11% of nitrogen content at an ion energy of 500 eV. In Raman spectroscopy, CNxfilms showed similar Raman bands to those of the diamond like carbon (DLC) film.

Negative-ion sources for modification of materials (invited)

The properties of negative ions, such as charging–free ion implantation and new materials syntheses by pure kinetic bonding reaction, have been shown to be promising in terms of their interaction with material surfaces. However, high-current or high-brightness negative-ion sources are required for these purposes. Several kinds of sputter-type negative-ion sources have been developed for negative-ion implantation and deposition in order to obtain high-current heavy negative ions. Recently, a microwave discharge oxygen negative-ion source for negative-ion beam deposition and a surface plasma type hydrogen negative-ion source for projection ion-beam lithography have been investigated. In this article, these negative-ion sources for modification of materials are reviewed.

Carbon negative ion implantation into silicon

We constructed a negative ion implanter with a sputter-type negative ion source, with which negative ion implantation was available in an energy range under 50 keV. Carbon negative ions were implanted into silicon substrates for investigating fundamental phenomena, such as ion projected range and profile, and also properties of implanted layers. The experimental results indicated that the depth profile of C atoms implanted at a single energy of 50 keV was in a good agreement with the LSS theory. In a synthesis of SiC by carbon negative ion implantation into silicon with multienergies, a SiC layer whose composition almost satisfied SiC stoichiometry was obtained. Although the β-SiC bonds were weakly observed in the SiC layer as implanted which was amorphous, the polycrystal β-SiC was certainly formed after annealing over 925°C for a substrate of Si(100) and 900°C for Si(111).

Study on the mechanism of negative ion formation in cesium sputter-type negative ion sources

The mechanism of forming negative ions in cesium sputter negative ion sources is studied by means of a modified dipole layer model and quantum theory. Formulas of the change of work function on the metal surface adsorbing cesium layer and the electron transfer probability are given. The formation probabilities of the negative ions are derived using a quantum tunneling model. The negative ion yield is also calculated. The calculated results are in essential agreement with the experimental data. The philosophy described in this paper may offer a useful theoretical model for the mechanism study of cesium sputter negative ion sources.