Yoshikazu Yoshida

Generation of a Surface-Wave-Enhanced Plasma Using Coaxial-Type Open-Ended Dielectric Cavity

A high-density and uniform plasma source which utilizes surface waves is described. Microwaves propagated through a coaxial waveguide are introduced circularly into the circumferential side of the dielectric disk, which is set at the open end of the coaxial-type cavity. A surface wave is launched from the dielectric surface and generates a plasma. The plasma density and electron temperature are 8×1011 cm-3 and 4.5 eV, respectively, at Ar gas pressure of 50 mTorr and microwave power of 800 W. The ashing rate without substrate heating of photoresist is 0.6 µ m/min at the O2 gas pressure of 50 mTorr and the microwave power of 500 W.

Low‐gas‐pressure sputtering by means of microwave‐enhanced magnetron plasma excited by electron cyclotron resonance

A sputtering source utilizing both electron cyclotron resonance (ECR) microwave and dc planar magnetron plasmas is described. Microwave power is introduced into the plasma by a coaxial‐type cavity. The magnetron cathode is placed on the open end of the inner conductor. The ECR magnetic field is applied in the open end by magnetron configuration magnets. The microwave propagation from the surface of the plasma column produces additional gas ionization resulting in a denser plasma at constant voltage. The operation pressure of this source is one‐hundredth as low as that of a conventional magnetron source. The deposition rate of Cu is more than 130 nm/min for an argon gas pressure of 8×10−5 Torr, and microwave and dc powers of 500 and 200 W, respectively. Measured deposition uniformity is ±4.5% within a 10 cm diam for a 15‐cm diam target.

Formation of Ni-Zn-Ferrite Films Using Laser Ablation

Ni-Zn-ferrite thin films were formed on glass substrate by a laser ablation method employing a KrF excimer laser at wave-length 248 nm and frequency 15 Hz. Film was deposited on substrate at room temperature, 200°C and 350°C, to a thickness of 2 ¿m. Ni-Zn-ferrite films thus prepared had the spinel structure when the substrate temperature was raised to 200°C. The saturation magnetic flux densities of Ni-Zn-ferrite films annealed at 400°C were between 1300 and 2020 G. The coercive force of annealed Ni-Zn-ferrite films decreased from 534 to from 70 to 113 Oe as the N2O gas pressure was decreased from 1×10¿2 Torr to 1×10¿5 Torr.

Development of surface-wave ion source using coaxial-type cavity

A compact 2.45 GHz surface-wave ion source has been developed for the production of stable beams from gaseous feed materials. The source has been operated with two different geometries of surface wave generation, that is, a dielectric disk on ground plane structure and a dielectric disk between the parallel plate structure with a holey top plate. The designer can control the intensity of the emitted microwave simply by varying the thickness of the dielectric plate. The sources have been operated with three different thicknesses of the dielectric plate: td=10, 15, and 20 mm. td=10 mm is the optimum coupling condition. Moreover, the ion beam current of the holey-plate structure is 1.5 times as high as that of the dielectric disk structure.

DISK PLASMA GENERATION USING A HOLEY-PLATE SURFACE-WAVE STRUCTURE ON A COAXIAL WAVEGUIDE

Plasma created and sustained by a surface wave from a partial-coaxial cavity resonator have been studied. In this work, two types of plasma source geometries are compared, (1) a dielectric disk on ground plane structure (DPSW), and (2) a dielectric disk between a parallel plate structure with a holey top plate (HPSW). In both cases, an evanescent electric field is produced from the cavity resonator to a plasma production chamber of 40 mm diameter. Thus, high-density plasma is generated by the interaction of the evanescent field with particles. This work shows that the plasma density and uniformity of the holey-plate structure is higher than that of the dielectric disk structure. For the holey-plate structure, the plasma density is 7.5×1011 cm−3 with an electron temperature of 3 eV at an argon gas pressure of 13 Pa.

Microwave‐enhanced magnetron sputtering

A sputtering source utilizing both microwave and dc planar magnetron plasmas is described. Microwave power is introduced into the plasma by a coaxial‐type cavity. The magnetron target is placed on the open end of the inner conductor. The microwave propagation from the surface of the plasma column produces additional gas ionization, resulting in a denser plasma at constant voltage. The operating pressure of this source is one‐tenth as low as that of a conventional magnetron source. Measured deposition uniformity for Cu is ±4.5% within a 10‐cm diameter at dc 100 W and microwave 800‐W discharge powers for a 15‐cm‐diam magnetron at 6×10−4 Torr. The plasma impedance decreases with an increase in the inner conductor diameter and target diameter. The target‐plasma sheath potential can be controlled by microwave power.

Plasma properties in the open-ended region of a coaxial-type microwave cavity

A sputtering source utilizing both microwave and dc planar magnetron plasmas is described. Microwave power is introduced into the plasma by a coaxial‐type cavity. The magnetron target is placed on the open end of the inner conductor. This source produces a plasma which is well matched, stable, and can operate continuously at gas pressures from 3×10−4 to 2×10−2 Torr. Plasmas with densities greater than 1011 cm−3 are obtained at gas pressure of 10−4 Torr using a microwave power of 100 W. The deposition rate of Cu is more than 0.13 μm/min for an argon gas pressure of 3×10−4 Torr, and microwave and dc powers of 100 W, respectively. This new source has many potential uses such as sputtering, etching, and chemical vapor deposition.

Ion Energy Distribution of KrF Laser Ablation

The KrF laser ablation of Al, Cu, Si, and SrTiO3 targets has been studied using an electrostatic deflection energy analyzer and a quadrupole mass filter. Beam like ions appear to accompany ablation. The average kinetic energies of Si+ and metal ions are about 45 eV and 60 eV, respectively. The energies of ions are ranked in the order of Si<metal (Al, Cu)<SrTiO3. The mean ion energy of Cu+ is not affected by the laser fluence range of 2-7.5 J/cm2.

Producing multicharged fullerene ion beam extracted from the second stage of tandem-type ECRIS

We have been constructing the tandem-type electron cyclotron resonance ion source (ECRIS). Two ion sources of the tandem-type ECRIS are possible to generate plasma individually, and they also confined individual ion species by each different plasma parameter. Hence, it is considered to be suitable for new materials production. As the first step, we try to produce and extract multicharged C60 ions by supplying pure C60 vapor in the second stage plasma because our main target is producing the endohedral fullerenes. We developed a new evaporator to supply fullerene vapor, and we succeeded in observation about multicharged C60 ion beam in tandem-type ECRIS for the first time.

PIG-Type Compact Microwave Metal Ion Source

A compact microwave metal ion source using PIG (Penning lonization Gauge) geometry has been newly developed. This modified PIG ion source introduces a microwave discharge and can generate stable and high density plasma. The size of the source is 60 mm in diameter and 80 mm long. The microwave discharge power is 20~60 W at a frequency of 2.45 GHz. A tantulum ion beam current of 3.2 µA has been measured with the extraction aperture (2 mm diameter) at an extraction voltage of 13 kV.