Manabu Hamagaki

New high current low energy ion source

We have developed a new type of ion source which is excited by a low energy and high current electron beam. The source has an extractable ion current density up to 0.62 A/cm2 and a low acceleration voltage less than 60 V. This ion source will open a new way for low energy ion processing such as damageless ion etching, ion beam crystal growth, and deposition.

Layer-By-Layer Controlled Digital Etching by Means of an Electron-Beam-Excited Plasma System

Characteristics o digital etching using an electron-beam-excited plasma system in GaAs are reported. In digital etching, etchant gas pulses and Ar ions are sequentially impinged onto the substrate surface to be etched. When the energy of Ar ion is -17 eV, etch rates which correspond to the 0.5 monolayer (ML) per cycle of GaAs (0.142 nm) are obtained between 0.3 and 0.5 seconds of Cl2 feed time by using Cl radicals as etchants. With these etching parameters, a rectangular cross-sectional etch profile with smooth surface is obtained. Damages induced in digital etching was characterized by current-voltage measurement of the diode fabricated after the etching.

Induced Defects in GaAs Etched by Low Energy Ions in Electron Beam Excited Plasma (EBEP) System

Ion beam etching (IBE) of GaAs with a source gas of Cl2 or Ar was carried out at a low energy ranging from 5 to 130 eV by using an electron-beam-excited-plasma system, and residual defect centers were investigated by means of deep-level transient spectroscopy (DLTS). Foul kinds of defect centers labeled L1 L2, L3, L5 with activation energies of 0.31, 0.45, 0.58, 0.48 eV, respectively, were resolved. Three of them were associated with damages induced by IBE and it was found that they have different thresholds for their generation, i.e., 60, 40 and 20 eV for L1, L2 and L3, respectively. It is necessary to reduce ion energy to less than 20 eV for perfect damage-free IBE of GaAs.

New etching system with a large diameter using electron beam excited plasma

A new etching system using electron-beam-excited plasma (EBEP) has been developed. This EBEP system is able to steadily produce a high-density plasma with a large diameter by introducing a high-current low electron beam into the etching chamber. The nonuniformity of plasma density and floating potential in an 8-inch wafer are improved up to ±2.5% and ±2 V, respectively. Anisotropic etching of n+-poly-Si in a pure Cl2 plasma is achieved with a high etch rate of 360 nm/min. The etching selectivity is 40 for poly-Si/photoresist and 150 for poly-Si/SiO2. These experimental results show that the EBEP etching system is suitable for manufacturing advanced ULSI.

A dc high‐current low‐energy electron beam gun

A dc high‐current and low‐energy electron beam gun has been developed. The maximum electron beam current is 63 A for an accelerating energy of 140 eV. The maximum ratio of the beam current to the discharge current is 78%. The ion current, which is extracted from the helium plasma produced by the electron beam, is 12.3 A. This value corresponds to the current density of about 7 A/cm2, which is the highest value among the ion sources in steady operation. The electron density of the plasma is estimated from the ion saturation current to be about 4.6×1013 cm−3, which corresponds to the degree of ionization of 21%. This gun will open the way for many electron beam applications.

HIGH-RATE ION ETCHING OF GAAS AND SI AT LOW ION ENERGY BY USING AN ELECTRON-BEAM EXCITED PLASMA SYSTEM

By using a newly developed electron beam excited plasma (EBEP) system, etching characteristics of GaAs and Si in an ion energy range of 5 to 100 eV were investigated. Anisotropic etching profiles with high aspect ratios were obtained by both Ar ion beam etching (IBE) and Cl2 reactive ion beam etching (RIBE). Etching rates of 1.2 μm/min for GaAs and 0.5 μm/min for Si were demonstrated for the first time by Cl2 RIBE at ultralow ion acceleration voltage of 5 V. Selective ratios of etching rates for Si/SiO2 and GaAs/SiO2 are ∼33 and 80, respectively. Electrical and optical measurements on the etched samples indicated that damage degree introduced by the low‐energy ions is negligible. Therefore, the EBEP system cannot only provide high etching rate because of its high ion current but also realize damageless ion etching due to its low ion energy.

Effect of Ionization Potential of Hole Transport Layer on Device Characteristics of Organic Light Emitting Diode with Oxygen Plasma Treated Indium Tin Oxide

We have investigated the contribution of the oxygen ions and electrons, and of the kinetic energy of these species on oxygen plasma treatment of indium tin oxide (ITO) electrode. In the case of the treatment by positive oxygen ions with kinetic energy of 50 eV, the luminance increased markedly with a lowering of the operating voltage in the organic light emitting diode (OLED). The change in the device characteristics was attributed to an effective removal of organic contaminants from the ITO surface, leading to enhanced hole injection from ITO to a hole transport layer (HTL) due to an increase in work function of the ITO. Moreover, the highest luminance and luminous efficiency were obtained in the OLED having HTL with ionization potential of 5.4 eV. These results have suggested that OLEDs fabricated using the oxygen plasma treated ITO can give the best device performance by the selection of an optimum HTL.

Quasi-Steady Laser Oscillation in the Recombining Hydrogen Plasma

A quasi-steady laser oscillation at 1.88 µm has been observed in a pure hydrogen plasma. The high density plasma produced by a high power quasi-steady MPD arc-jet operating at 8.1 kA of the discharge current and 0.1 g/s of hydrogen flow is cooled by expanding itself into the vacuum chamber. Experimental results confirm that some population inversions occur as a consequence of recombination and subsequent electron thermalization.

Effect of oxygen plasma treatment of indium tin oxide for organic light-emitting devices with iodogallium phthalocyanine layer

We demonstrate the improvement of device lifetime by organic light-emitting devices with an iodogallium phthalocyanine (IGaPc) layer fabricated on indium tin oxide (ITO) treated with positive oxygen ions. The device performance improves markedly as follows: (a) long-term stability (an operational half-lifetime of 100 h at high current density of 100 mA/cm2), and (b) the driving voltage is unchanged. The change in the device characteristics is attributed to changes in IGaPc molecular configurations during the growth process, leading to enhanced hole injection from the ITO to IGaPc layer.

High Degree of Dissociation of Nitrogen Molecules in Large-Volume Electron-Beam-Excited Plasma

The degree of dissociation of nitrogen is measured in a large-volume N2-Ar mixture plasma generated by an electron-beam-excited plasma device. The device features independent control of the beam current and energy. In setting the beam current and energy at 3.4 A and 140 V, the degree of dissociation of nitrogen was 0.16. The high degree of dissociation is attributed to the characteristics of the system in which the degree depends on the beam energy fed into the plasma and not the size of the chamber, as it is in conventional plasma sources. In view of the device characteristics, high-density atomic nitrogen can be obtained with electron-beam-excited plasma in a large-volume device.