Freeman-type Ion Source Research Articles

Characteristics of films deposited by the irradiation of GeCHx+ ions produced from hexamethyldigermane and their dependence on the injected ion energy

The characteristics of films deposited by the irradiation of GeCHx+ ions and their dependence on the injected ion energy were investigated. GeCHx+ ion beams were produced by the decomposition of hexamethyldigermane in a Freeman-type ion source. GeCHx+ ions were then mass-selected and irradiated for film deposition on Si substrates at room temperature. The GeCHx+ ion energy was set at about 100, 30, 20, and 10 eV. The Fourier transform infrared spectroscopy (FTIR) analyses of the deposited films suggested that Ge-C bonds of GeCHx+ ions were broken due to the collision between GeCHx+ ions and the substrate surface in the cases of 100 and 30 eV. In contrast, Ge-C bonds remained in the film at the ion energy of 20 or 10 eV. Subsequently, the GeCHx+ ion energy was set at 20 eV, whereas the Si substrate temperature was set at 300 °C. FTIR and X-ray diffraction analyses of the films obtained suggested that the Ge-C bonds were broken at 300 °C and the resulting Ge atoms recombined with each other to form a metallic Ge film.

Identification of fragment ions produced from hexamethyldisilazane and production of low-energy mass-selected fragment ion beam

Abstract Fragment ions produced from hexamethyldisilazane (HMDS) with a hot tungsten wire in a Freeman-type ion source were assayed using a low-energy mass-selected ion beam system. The possible candidates of chemical formulae for these ions are C+, N+, CH3+, CH4+, Si+, SiCH5+, SiC2H6+, SiC3H9+, Si2NCH4+, Si2NC2H7+, Si2NC3H10+, Si2NC4H12+, and Si2NC5H16+. The ion production strongly depended on the tungsten temperature. Among the HMDS derived fragment ions, SiCH5+ ions were mass-selected. The ion energy was 100 eV. Then, the SiCH5+ ions were irradiated to a Si substrate. It was inferred from the analysis of resulting deposited film that silicon carbide films containing a small amount of nitrogen atoms were deposited following the irradiation.

Low-energy mass-selected ion beam production of fragments from tetraethylorthosilicate for the formation of silicon dioxide film

Fragment ions produced from tetraethylorthosilicate (TEOS) in a Freeman-type ion source were investigated using a low-energy mass-selected ion beam system and then, their mass numbers were identified. Although the chemical formulae of these fragments were not completely identified yet, the possible candidates of dominant fragment ions were C2+, C+, CH2+, O+, H2O+, Si+, SiC+, SiO+, SiH(OH)2+, Si(OH)3+, SiH(OH)(OC2H5)+, SiH(OCH3)2+, Si(OH)2(OC2H5)+, SiH(OC2H5)2+, Si(OH)(OC2H5)2+, Si(OCH3)2(OC2H5)+, Si(OCH3)(OC2H5)2+, and Si(OC2H5)3+. Among these fragment ions, Si(OH)3+ ions were mass-selected. The ion energy was approximately 50 eV. Then, the Si(OH)3+ ions were irradiated to a Si substrate and resulting deposited films were analyzed. Following the completion of the ion irradiation experiment, X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy assays of the films demonstrated the occurrence of silicon dioxide deposition. We conclude that the irradiation of the mass-selected Si(OH)3+ ions, obtained from TEOS, to substrates is useful for the secure growth of silicon dioxide films.

Low-energy mass-selected ion beam production of fragments produced from hexamethyldisiloxane for the formation of silicon oxide film

Fragment ions produced from hexamethyldisiloxane (HMDSO) with a hot tungsten wire in a Freeman-type ion source were studied using a low-energy mass-selected ion beam system. The mass numbers of the fragment ions were identified. Although the chemical formulae of these fragments were not completely identified yet, the possible candidates of dominant fragment ions were H+, H2+, H3+, C+, CH3+, O+, Si+, C3H3+, SiO+, SiC2+, SiOCH2+, SiC3H9+, Si2OCH3+, Si2OC2H7+, Si2OC3H9+, Si2OC4H11+, and Si2OC5H15+. The rates of ion fragment production strongly depended on the tungsten temperature. Among those fragment ions, SiO+ ions were mass-selected. The ion energy was approximately 50eV. Then, the SiO+ ions were irradiated to substrates and resulting deposited films were analyzed. Following the completion of the ion irradiation experiment, X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy measurements of the films demonstrated the occurrence of silicon oxide deposition. We conclude that the irradiation of the mass-selected SiO+ ions, obtained from HMDSO, to substrates is useful for the secure growth of silicon oxide films.

Indium Implantation onto Zeolite for Development of Novel Catalysts with a Ion Beam System

The implantation of indium (In) onto zeolite was carried out with a low-energy mass-selected ion beam system for the possible development of novel catalysts. In ions were generated by sputtering an In2O3 target with Ar ions in a modified Freeman-type ion source. Ions generated in the ion source were extracted under high voltages to form mono-energetic 115In ion beams with the peak energy of around 500 eV. Then, the zeolite substrates were irradiated by the In ion beams. Both X-ray fluorescence and X-ray diffraction analyses revealed that the implantation of In on the zeolite surface was successful and dependent on the ion doses of In. We failed to detect the catalytic effects in the In implanted zeolite as far as at the conditions employed in the present study. However, a further study is still necessary to determine the catalytic effect of the In implanted zeolite.

Fragment ions produced from hexamethyldisilane in a Freeman-type ion source

Fragment ions produced from hexamethyldisilane (HMDS) in a Freeman-type ion source with a hot tungsten wire were studied using a low-energy mass analyzed ion beam system. Dominant fragment ions from HMDS were identified to be H+, H2+, C+, CH3+, Si+, SiCH4+, SiC2H6+, and SiC3H9+. The rates of ion fragment production strongly depended on the tungsten temperature. We conclude that the irradiation of the mass-selected SiCH4+ ions obtained from HMDS to Si substrates is useful for the secure epitaxial growth of SiC.

Low Energy Metal Ion Beam Production with a Modified Freeman-Type Ion Source for Development of Novel Catalysts

Interactions of indium (In) and silicon (Si) atoms have been found to catalyze certain organic chemical reactions with high efficiency. In a recent paper [S. Yoshimura, et al., Appl. Surf. Sci., 257, 192 (2010)], it has been demonstrated that an In injected SiO2 thin film formed under specific ion beam conditions catalyzes a reaction of benzhydrol with acetylacetone. In this study a technique to implant bismuth (Bi) ions into SiO2 thin films has been developed with highly controlled ion doses and injection energies for the formation of thin films that promote Bi(III) catalysis in organic chemistry. For this purpose, the Freeman-type ion source of our beam system was modified with a new sputtering target. In addition, sticking probabilities of Bi have been obtained with the use of a quartz crystal microbalance. Although efficiency of catalytic reactions by a Bi implanted SiO2 thin film is yet to be improved, the technique provides a Bi-Si based novel catalyst of a thin film type. [DOI: 10.1380/ejssnt.2012.139]

Computer investigation of ion beam optics for a Freeman type ion source system

The present work investigates the computer analysis of the ion beam properties produced by a Freeman type system. The extraction for such system is composed of four electrodes that permit to keep a fixed output energy by means of two accelerating gaps and one decelerating gap. The latter allows reducing the beam divergence angle. The combination of the acceleration/deceleration sections provides to keep a low beam emittance at the source outlet. The simulation of single charged argon ion trajectories for a plasma concave of curvature 4 mm was first studied with and without space charge effect using acceleration/deceleration extraction system with the aid of the SIMION computer program. The voltage applied to the accelerating electrode was optimized to accomplish the suitable ion trajectories without hitting the extraction electrode. Then, two additional studies were performed: the influence of the acceleration voltage and extraction voltage on the beam emittance and beam diameter; and the effect of the extraction gap width (distance between the plasma emission surface and the acceleration electrode) on the shape of the ion beam envelope and the position of the ion beam waist. Last, the influence of the space charge on the ion beam envelope was also investigated.

低エネルギー質量分離イオンビーム照射装置を用いたＳｉＯ２／Ｓｉ基板へのインジウムイオン注入

Implantation of In into SiO2 thin film substrates by mono-energetic In ion beams was examined with the use of a low-energy mass selected ion beam system. The goal of this study is to develop thin film based In-Si combined catalyzer for organic chemical reactions. In the experiments, In ions were generated by sputtering of an In2O3 target by Ar ions in a Freeman-type ion source and extracted to form, after mass selection, a mono-energetic beam with the peak energy of 470 eV. The ion beam was then injected into SiO2 thin films formed on Si substrates. By X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and atomic force microscopy (AFM) measurements, it was found that In nano particles were formed on the SiO2 thin film surface after the beam injections and the shapes of the particles varied depending on In ion dose.

フリーマン型イオン源におけるメチルシランのフラグメントイオンとタングステンワイヤ表面状態

Ion fragmentation of methylsilane by a hot tungsten wire in a Freeman-type ion source was investigated with low-energy mass separated ion beam apparatus for the study of catalytic chemical vapor deposition (Cat-CVD) processes. The mass analysis showed that dominant fragment ions were typically H1+, H2+, H3+, CH3+, SiH+, and SiCH4+. The ion production rates, which depended strongly on the tungsten wire temperature, decreased with time due to modification of the tungsten wire surface during the process. The x-ray diffraction and x-ray photoelectron spectroscopic measurements showed that silicon carbide, carbon, and tungsten carbide compounds were formed on the tungsten wire surface during the process.

Organosilicon ion beam for SiC heteroepitaxy

A low-energy deposition technique using a beam of organosilicon ions has been developed and successfully applied for heteroepitaxial growth of SiC on a Si substrate at temperatures of 900–1300 K. The process employs gaseous CH 3 SiH 2 CH 3 in a Freeman-type ion source to produce CH 3 Si + fragment ions that are then mass-selected and deposited at 100 eV on a Si wafer. Ion energy was precisely controlled and energy fluctuation was ±1 eV. RHEED analysis and AFM observation, respectively, showed that a thin film of SiC had been crystallized heteroepitaxially and in the form of ‘nano-tiles.’ The technique offers the potential for fabrication of self-assembled SiC nanostructures.

Organosilicon ion beam for SiC heteroepitaxy

A low-energy deposition technique using a beam of organosilicon ions has been developed and successfully applied for heteroepitaxial growth of SiC on a Si substrate at temperatures of 900–1300 K. The process employs gaseous CH 3SiH 2CH 3 in a Freeman-type ion source to produce CH 3Si + fragment ions that are then mass-selected and deposited at 100 eV on a Si wafer. Ion energy was precisely controlled and energy fluctuation was ±1 eV. RHEED analysis and AFM observation, respectively, showed that a thin film of SiC had been crystallized heteroepitaxially and in the form of ‘nano-tiles.’ The technique offers the potential for fabrication of self-assembled SiC nanostructures.

Production of Si + and Cl + ion beams from a Freeman type ion source using low toxicity and non-corrosive vapours as source gas

A method is proposed for production of Si + and Cl + ions in Freeman type ion sources using low toxicity and non-corrosive vapours of hexamethyldisilane ((CH 3) 3SiSi(CH 3) 3) and carbon tetrachloride (CCl 4), respectively. These source materials can be used without expensive and complicated safety systems required for silane and chlorine source gases. Experimental X-ray photoelectron spectroscopy results show that in the case of (CH 3) 3SiSi(CH 3) 3 vapour used as the ion source gas, the ion beam, after using standard magnetic field ion mass analysis for mass 28, contains about 62% of 28Si + ions. It is assumed that the molecular ions C 2H 4 + with the same mass 28 are the main component of the remaining 38% of this ion beam. In the case of the use of CCl 4 vapour as ion source gas and magnetic field mass analysis set for mass 35, a pure Cl + beam is observed; there are no other ions of mass 35 that can be formed from the source gas. The same system when used with water vapour as a source gas can produce pure ion beams of O + and/or H + ions without adverse effects produced in the ion source by oxygen gas (oxidation) or typical safety problems with a hydrogen gas supply (explosive).

Production of organosilicon ions for SiC epitaxy

The production of organosilicon ions in a Freeman-type ion source were studied for SiC heteroepitaxial growth on a Si wafer. One of the possibilities for SiC epitaxy is a low energy deposition of an organosilicon ion beam. The advantage of this technique is that the organosilicon ion already has a binding of Si and C. The organosilicon ion usually also has a dipole moment which is useful for atomic arrangement on a depositing surface. Methylsilane and dimethylsilane were introduced in a Freeman-type ion source and discharged for ionization. Because of fragmentation, methylsilylene ions and methylsilicenium ions were produced. The ions were accelerated and mass selected in order to create a well defined ion beam. The energy distribution, measured by a plasma monitor, was ±1 eV. By using this ion beam, heteroepitaxitial growth of 3C-SiC on Si was successfully created.

Oxygen ion source with plasma cathode

An ion source with a plasma cathode has been developed for long lifetime use in ion implanters. In this ion source, a plasma cathode replaces the conventional metallic filament used in a Freeman-type ion source. This ion source consists of two compartments, namely a plasma generator and an ion source chambers interconnected by a tapered narrow duct. The pressure difference between the two parts, maintained by differential pumping, prevents the feed gas from flowing into the plasma generator. With any combination of an argon plasma cathode and a feed gas of either fluoride (AsF 5, PF 5) or oxygen, the lifetime was found to be more than 90 h with an extraction voltage of 40 kV and a correspoding ion current density of 20 mA/cm 2, and a considerable amount of As +, P +, O +, and O 2 + ions were observed in mass spectra.

Development of Plasma Filament Ion Source for High Current Implanter.

A plasma filament ion source has been developed as a long-lived ion source for use in ion implantation. This ion source uses a primary discharge to serve as an electron source for a second discharge, which is formed into a plasma filament replacing a thermionic metallic filament used in the Freeman type ion source. The operation is relatively facile and good beam stability can be obtained. With any combination of a plasma filament of either argon or neon and a feed gas of either fluoride (AsF5, PF5, PF3, or BF3) or hydride (AsH3), the lifetime was found to be more than 90 hours with an extraction voltage of 40kV and the corresponding ion current density over 20mA/cm2. Mass spectrometry results show that this ion source has an ability of generating a considerable amount of As+ and P+ ions from AsF5 and PF5, and hence will be useful for realizing a fully cryopumped ion implanter system. This ion source is also eminently suitable for use in oxygen ion production.

Development of ion mixing equipment for R&D use and preparation of tin films by N 2 gas assisted ion beam mixing

We have developed a mass-analyzed ion mixing equipment for surface modification research use. High current ion beams of refractory metals (Cr +: 0.95 mA) were obtained by modifying a conventional Freeman type ion source. We have proposed a N 2 gas assisted ion mixing method in which a TiN film can be formed by evaporated Ti molecules and N + 2 ion beam in a N 2 gas environment. We have verified this proposal by high rate TiN deposition using our newly developed equipment and obtained the following results: (1) crystallinity of TiN film was changed from (111) preferential orientation to (200) orientation by increasing N + 2 ion beam radiation, (2) hard TiN films (Vicker's hardness > 2000) were formed by a small current of N + 2 ion beam radiation which was about one tenth of conventional dynamic mixing method, (3) hardness of TiN films and their crystallinity were closely related.

Higher charge state ion beam purity in the Eaton medium current implanter

An Eaton NV-6200 operating with the new “SKM” modified hot filament Freeman ion source technology has been characterized using multiply charged ions of phosphorus, boron, and arsenic. The improvements in ionization efficiency of the Freeman-type ion source offered by the Eaton SKM modification provide substantially increased currents of doubly charged ions and useful amounts of certain triply charged ions. We have investigated the ion beam purity of these higher charge state beams; we present quantitative data which describe the energy purity and determine whether contaminants created by charge exchange reactions during transport through the beamline are present. The process quality of high charge state implants is investigated by examining the implanted dopant concentration profile using SIMS. The energy analysis and implant profile data demonstrate that the higher charge state ions generated by the SKM ion source are transported with useful ion beam purity to the target substrate.

Production of Ion Beam Using Plasma Filament Ion Source

A plasma filament ion source has been developed as a long-lived ion source for use in ion implantation. This ion source uses a primary discharge to serve as an electron source for a second discharge, which is formed into a plasma filament replacing a thermionic metallic filament used in the Freeman-type ion source. The operation is relatively facile and a good beam stability can be obtained. With any combination of a plasma filament of either argon or neon and a feed gas of either fluoride (AsF5, PF5, PF3, or BF3) or hydride (AsH3), the lifetime was found to be more than 90 hours with an extraction voltage of 40 kV and the corresponding ion current density over 20 mA/cm2. This ion source could produce appreciable amounts of As+, B+, P+ and O+ ions, yielding analyzed currents of 10.0, 3.0, 2.6 and 3.0 mA, respectively. This device proved to be eminently suitable for oxygen ion production and also useful for ion implantation incorporated with full cryopumping. Furthermore, the role of the electron temperature of the plasma filament was shown to be of importance in the dissociation and ionization of the feed gas molecules.

Plasma filament ion source for high current implanter

A plasma filament ion source has been developed as a long lifetime ion source for use in ion implanters. In this ion source, a plasma filament replaces a conventional metallic filament used in a Freeman type ion source. This ion source consists of two compartments, i.e. a plasma generator and an ion source chamber interconnected by a tapered narrow duct. The pressure difference between the two parts made by differential pumping prevents the feed gas from flowing into the plasma generator. With any combination of a plasma filament of either argon or neon and a feed gas of either AsF 5 or PF 5, the lifetime was found to be more than 90 h with an extraction voltage of 40 kV and a corresponding ion current density of 20 mA/cm 2; a considerable amount of As + and P + ions were observed in mass spectra. This ion source is eminently suitable for oxygen ion production and useful for realizing a full cryopumping ion implanter system.