Eiji Yabe

Ion source with plasma cathode

A long lifetime ion source with plasma cathode has been developed for use in ion implantation. In this ion source, a plasma of a nonreactive working gas serves as a cathode in place of a thermionic tungsten filament used in the Freeman ion source. In an applied magnetic field, the plasma is convergent, i.e., filamentlike; in zero magnetic field, it turns divergent and spraylike. In the latter case, the plasma exhibits a remarkable ability when the working gas has an ionization potential larger than the feed gas. By any combination of a working gas of either argon or neon and a feed gas of AsF5 or PF5, the lifetime of this ion source was found to be more than 90 h with an extraction voltage of 40 kV and the corresponding ion current density 20 mA/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 suit...

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

Abstract This paper reports the use of a plasma filament instead of a heated solid filament in the Freeman ion source to make a new ion source which has a very long lifetime and especially enables the steady supply of a high intensity oxygen ion beam. The plasma filament is a highly ionized and high density plasma ( n e >10 13 cm −3 ), and composed of ions, high temperature electrons ( T e =3–9 eV ) and metastable atoms. It has been recognized that the O + ion beams are obtained using an argon or a neon plasma filament. The lifetime of this ion source is longer than that of the Freeman ion source.

An ion source with plasma generator

Abstract A small plasma generator has been developed using the same principle of plasma production as the Nagoya University TP-D machine in order to make an electron emitter with long lifetime for the ion source used in ion implantation and deposition techniques. The highly ionized and high density plasma flowing from the generator can be used instead of the tungsten filament of the Freeman type ion source. This paper reports the noteworthy ability of a flowing plasma to ionize a gas fed into the main discharge chamber whose ionization potential is lower than that of gas in the plasma generator. Also, the possibility of practical use as an ion source having a long lifetime is reported.

Ion source with plasma cathode for ion assisted deposition

Abstract An ion source with a plasma cathode has been developed to attain a long lifetime for oxygen ion production. In this ion source, a plasma of a nonreactive working gas serves as a cathode in place of a thermionic tungsten hot cathode used in the Kaufman ion source. This ion source consists of two compartments, i.e. a plasma generator provided with a metallic hot cathode and a plasma chamber interconnected by a narrow tapered duct. The pressure difference between the two parts made by differential pumping prevents the feed gas supplied to the plasma chamber from flowing into the plasma generator. Mass spectrometry results show that this ion source has the ability of generating a considerable amount of O+ ions. This ion source is also eminently suitable for oxygen ion production.

Plasma compression type hollow cathode ion source

Abstract In general, a hollow cathode ion source (HCIS) for implantation industries has the fatal demerit of low gas efficiency. This paper reports that this disadvantage of HCIS is solved by inserting insulated narrow slits between the anode and the cathode in order to compress the cross section of the discharge path. As a result, the large pressure differences between outer and inner regions of the ion source can be held and the gas efficiency is increased.

Simple hollow cathode ion source

Abstract A simple hollow cathode ion source has been developed and investigated for increasing ion source lifetime and beam current capability. The experimental results of a LaB6 cathode show that a plasma density of up to 1012/cm3 can be generated with a discharge current of 4.0 A and a pressure of 6.7 Pa, resulting in extracted ion beams that are extremely quiet and stable. The ions of non-volatile elements of cathode materials can be easily obtained by virtue of the sputtering effect of a SUS cathode. The lifetime of our ion sources can be shown to be more than 150 hours.

Production of RF Plasma Using a Magnetic Line-Cusp Field

A large-volume cylindrical rf plasma source with a magnetic line-cusp field has been developed for large-scale plasma processing. In this type of plasma source, a capacitively-coupled 13.56 MHz rf plasma is produced in the presence of a magnetic line-cusp field. Two versions of the plasma source have been designed and tested. The first version has peripheral rf electrodes placed outside the ionization chamber, and is suitable for preparing a large-volume uniform plasma. This plasma source can attain a useful area of uniform plasma over a 30-cm-diameter region within 10% nonuniformity. The second version features doughnut-shaped parallel plate electrodes which form part of the chamber wall and serve as high-current sources. The electron density in such a version is proportional to the rf power, being equal to 4×1010 cm-3 at 400 W. The measured electron-energy distribution function showed a Maxwellian distribution function due to the electron-neutral particle collisions arising from drift motion in the magnetic line-cusp field.

Production of oxygen plasmas using radio-frequency magnetron-discharge

Abstract A new type of oxygen ion source has been developed in order to substantially prolong the lifetime of a conventional oxygen ion source for various plasma processes. In this ion source, an oxygen plasma is produced by coupling a 13.56 MHz radio-frequency (rf) field to a pair of rf electrodes placed in the region of a line cusp field. Two electrodes are positioned in such a way that accelerated electrons undergo magnetron type motion around them, efficiently producing a plasma around the electrodes (rf magnetron discharge). This plasma diffuses along the magnetic field line into the center region of the cusp field where the field strength is almost nil. The above process makes it possible to produce a large volume of uniform plasma. As a result, extraction of a large area oxygen-ion-beam from the new ion source is relatively easy. The lifetime of this ion source is virtually limitless, because it does not have any corrosive parts, such as a hot filament. The new ion source can be used with any kind of reactive gases as well as oxygen.

Hollow cathode ion source for application to an implanter

Abstract A hollow cathode ion source has been studied in order to improve the life-time of an ion source for an ion implanter. Both volatile and refractory elements are shown to be ionized using two types of discharge state of the hollow cathode namely hot and cold cathode discharge. The life-time of LaB 6 as the hot cathode is more than 150 h and the ion beam currents reach more than 10 mA cm −2 at the extraction voltage of 10 kV. For the cold cathode operation, stable currents of ∼40 to 70 μA are extracted of refractory metal ions such as W and Mo.